FEL2015 - Classification: Electron Beam Dynamics

Paper	Title	Page
MOP052	Linear Vlasov Solver For Microbunching Gain Estimation with Inclusion of CSR, LSC, And Linac Geometric Impedances	147
	C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA D. Douglas, R. Li, C. Tennant JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. As is known, microbunching instability (MBI) has been one of the most challenging issues in designs of magnetic chicanes for short-wavelength free-electron lasers or linear colliders, as well as those of transport lines for recirculating or energy recovery linac machines. To more accurately quantify MBI in a single-pass system, we further extend and continue to increase the capabilities of our previously developed linear Vlasov solver [1] to incorporate more relevant impedance models into the code, including transient and steady-state free-space and/or shielding CSR impedances, the LSC and linac geometric impedances with extension of the existing formulation to include beam acceleration [2]. Then, we directly solve the linearized Vlasov equation numerically for microbunching gain amplification factor. In this study we apply this code to a beamline lattice of transport arc [3] following an upstream linac section. The resultant gain functions and spectra are presented here, and some results are compared with particle tracking simulation by ELEGANT [4]. We also discuss some underlying physics with inclusion of these collective effects and the limitation of the existing formulation. It is anticipated that this more thorough analysis can further improve the understanding of MBI mechanisms and shed light on how to suppress or compensate MBI effects in lattice designs. [1] C. -Y. Tsai et al., FEL'14 (THP022), IPAC'15 (MOPMA028) and ERL2015 (TUICLH2034) [2] M. Venturini, Phys. Rev. ST Accel. Beams 10, 104401 (2007) [3] D. Douglas et al., arXiv: 1403.2318v1 [physics.acc-ph] [4] M. Borland, APS Light Source Note LS-287 (2000)
	Poster MOP052 [4.934 MB]
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MOP053	Intra-Beam Scattering in High Brightness Electron Linacs	153
	S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Intra-beam scattering (IBS) of a high brightness electron beam in a linac has been studied* analytically, and the expectations found to be in reasonable agreement with particle tracking results from the Elegant code. It comes out that, under standard conditions for a linac driving a free electron laser, IBS plays no significant role in the development of microbunching instability. A partial damping of the instability is envisaged, however, when IBS is enhanced either with dedicated magnetic insertions, or in the presence of an electron beam charge density at least 4 times larger than that produced by present photo-injectors. * S. Di Mitri, Phys. Rev. Special Topics Accel. Beams, 17, 074401 (2014).
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MOP054	Wake Field Potentials of 'Dechirpers'	157
	A. Novokhatski SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515. A corrugated structure, which is used on 'dechirpers' is usually a pipe or two plates with small corrugations (bumps) on the walls. There is a good single-mode description of the wake potentials excited by a relativistic bunch if the wave length of the mode is much longer than the distance between the bumps in the pipe. However, ultra-short bunches, which are now used in FELs, excite much higher frequency fields and the corresponding wake potentials will be very different from single-mode description. We made analyzes of these wake potentials based on a numerical solution of Maxwell's equations. The behavior of the wake fields of ultra-short bunches in corrugated structures is not much different from the fields excited usually in accelerating structures where the wake potentials are described by the exponential function. As we increase the bunch length, the wake potentials slowly transform to the form of a single mode. For a practical application we present results for a 'dechirper', which will be soon installed at LCLS. We also carried out calculations for a similar device, that was installed and measured at the Pohang Accelerator Laboratory, Korea. We find very good agreement with the experimental results.
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MOP055	The Effect of Wakefields on the FEL Performance	161
	A. Novokhatski, F.-J. Decker, Y. Nosochkov, M.K. Sullivan SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515. If a beam travels near collimator jaws or other discontinuities of the beam pipe, it gets the energy loss and the transverse kick due to the back reaction of the beam field diffracted on the collimator's jaws. The wake field effect from collimators may not only bring an additional energy jitter and change the trajectory of the beam, but may also lead to degradation of the performance of Free Electron Laser (FEL) It may be possible due to the special character of the wake fields: the response reaction depends on the longitudinal position of the particles in the bunch. We describe a model of the wake field radiation, simulation results and comparison with measurements.
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MOP056	Reversible Electron Beam Heater without Transverse Deflecting Cavities	166
	G. Stupakov, P. Emma SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy contract DE-AC03-76SF00515. Suppression of microbunching instability in modern FELs is an important issue that often limits the performance of the machine. A technique to suppress the instability with the help of a reversible electron beam heater was proposed by C. Behrens, Z. Huang, and D. Xiang []. It employs transverse deflecting cavities synchronized in a way that one of the cavities, located before a bunch compressor, generates a slice energy spread, while the other one removes it after the beam passes through the bunch compressor. Being an attractive approach, this concept unfortunately imposes extremely tight tolerances on the synchronization of the cavities. In this paper we demonstrate that a reversible heater equivalent to that of Behrens et al. can be designed using much simpler elements: bend magnets and quadrupoles in combination with the energy chirp of the beam. C. Behrens, Z. Huang, and D. Xiang, PRST-AB 15, 022802 (2012).
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MOP057	Front End Simulations and Design for the CLARA FEL Test Facility	171
	J.W. McKenzie, A.D. Brynes, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	We present the design and simulations of the Front End for CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. This is based around an S-band RF photocathode gun. Initially this will be the 2.5 cell gun, currently used on VELA facility at Daresbury, which is limited to 10 Hz repetition rate. Later, this will be up-graded to a 1.5 cell gun, currently under development, which will allow repetition rates of up to 400 Hz to be reached. The beam will be accelerated up to 50 MeV with a booster linac which will be operated in both bunching and boosting modes for different operating regimes of CLARA. Simulations are presented for a currently achieved performance of the RF system and drive laser with optimisation of the laser pulse lengths for various operational modes of CLARA.
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MOP060	RFTweak 5 - An Efficient Longitudinal Beam Dynamics Code	176
	B. Beutner, H. Dinter, M. Dohlus DESY, Hamburg, Germany
	The shaping of the longitudinal phase space in bunch compression systems is essential for efficient FEL operation. RF systems and self-field interactions contribute to the overall phase space structure. The design of the various facilities relies on extensive beam dynamics simulations to define the longitudinal dynamics. However, in everyday control room applications such techniques are often not fast enough for efficient operation, e.g. for SASE tuning. Therefore efficient longitudinal beam dynamics codes are required while still maintaining reasonable accuracy. Our approach is to pre-calculate most of the required data for self-field interactions and store them on disc to reduce required online calculation time to a minimum. In this paper we present the fast longitudinal tracking code RFTweak 5, which includes wakes, space charge, and CSR interactions. With this code the full European XFEL with a 1M particles bunch is calculated on the order of minutes on a standard laptop. Neglecting CSR effects this time reduces to seconds.
	Poster MOP060 [0.799 MB]
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MOP062	Technology Maturation for the MaRIE 1.0 X-FEL	181
	J.W. Lewellen, K. Bishofberger, B.E. Carlsten, L.D. Duffy, F.L. Krawczyk, Q.R. Marksteiner, D.C. Nguyen, S.J. Russell, R.L. Sheffield, N.A. Yampolsky LANL, Los Alamos, New Mexico, USA
	Funding: This research was funded by the Matter-Radiation Interactions in Extremes program at Los Alamos National Laboratory, under contract DE-AC52-06NA25396. Los Alamos National Laboratory is proposing a high-energy XFEL, named MaRIE, to meet its mission needs. MaRIE will be required to generate coherent 42+ keV photons, and, due to space constraints at the LANSCE accelerator complex at Los Alamos, MaRIE's design electron beam energy is 12 GeV. This combination places significant restrictions upon the MaRIE electron beam parameters, in particular the transverse emittance and energy spread at the undulator entrance. We are developing approaches to meet these requirements, but these often require solutions extending beyond the current state-of-the-art in X-FEL design. To reduce overall project risk, therefore, we have identified a number of key experimental and modeling / simulation efforts intended to address both the areas of greatest uncertainty in the preliminary MaRIE design, and the areas of largest known risk. This paper describes the general requirements for the MaRIE X-FEL, our current areas of greatest concern with the preliminary design concept, and our corresponding Technology Maturation Plan (TMP). MaRIE website: http://www.lanl.gov/science-innovation/science-facilities/marie/index.php
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MOP063	Transverse Emittance Measurement of KAERI Linac with Thick Lens Quadrupole Scan	185
	S. Setiniyaz, I.H. Baek, M.S. Chae, B.A. Gudkov, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, S.V. Miginsky, J.H. Nam, S. Park, N. Vinokurov KAERI, Daejon, Republic of Korea S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	The UED (Ultrafast Electron Diffraction) beamline of KAERI (Korea Atomic Energy Research Institute) WCI (World Class Institute) Center has been completed and successfully commissioned. Transverse emittance of the electron beam was measured at the entrance of the UED chamber with the quadrupole scan technique. In this technique, larger drift distance between the quad and screen is preferred because it gives better thin lens approximation. A space charge dominated beam however, will undergo emittance growth in the long drift caused by the space charge force. We suggest mitigating this growth by introducing quadrupole scan with short drift and without thin lens approximation. We shall discuss the measurement process and results.
	Poster MOP063 [1.287 MB]
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MOP066	Electron Bunch Length Measurement using an RF Deflecting Cavity	188
	S. Park, E.-S. Kim Kyungpook National University, Daegu, Republic of Korea S. Bae, K.H. Jang, Y.U. Jeong, H.W. Kim, J. Mun, N. Vinokurov KAERI, Daejon, Republic of Korea
	Recently, the RF photogun based-ultrafast electron diffraction (UED) system has been developed in KAERI. In the system, the emitted electron bunches are experimentally confirmed to be accelerated up to 3 MeV at 5MW of RF power. And the time duration of the each bunch is initially designed to be less than 50 fs at the sample position. To analyses the performance of the system and to measure exactly the length of the electron bunches, we developed a rectangular type of S-band deflecting cavity working on TM120 mode. The principle of electron deflecting in the cavity, design & mechanical fabrication process and test results will be present in the conference.
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MOP087	Multistage CSR Microbunching Gain Development in Transport or Recirculation Arcs	263
	C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA D. Douglas, R. Li, C. Tennant JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Coherent synchrotron radiation (CSR) induced microbunching instability has been one of the most challenging issues in the design of modern accelerators. A linear Vlasov solver has been developed [1] and applied to investigate the physical processes of microbunching gain amplification for several example lattices [2]. In this paper, by further extending the concept of stage gain as proposed by Huang and Kim [3], we develop a method to characterize the microbunching development in terms of stage orders that allow the quantitative comparison of optics impacts on microbunching gain for different lattices. We find that the microbunching instability in our demonstrated arcs has a distinguishing feature of multistage amplification (e.g, up to 6th stage amplification for our example transport arcs, in contrast to two-stage amplification for a typical 4-dipole bunch compressor chicane). We also try to connect lattice optics pattern with the obtained stage gain functions by a physical interpretation. This Vlasov analysis is validated by ELEGANT [4] tracking results with excellent agreement. [1] C. -Y. Tsai et al., MOP052, these proceedings [2] See, for example, C. -Y. Tsai et al., ERL2015 (TUICLH2034) [3] Z. Huang and K. -J. Kim, Phys. Rev. ST Accel. Beams 5, 074401 (2002) [4] M. Borland, APS Light Source Note LS-287 (2000)
	Poster MOP087 [1.962 MB]
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TUC01	The Microbunching Instability and LCLS-II Lattice Design	308
	M. Venturini LBNL, Berkeley, California, USA
	The microbunching instability is a pervasive occurrence when high brightness electron beams are accelerated and transported through dispersive sections like bunch-compression chicanes or distributions beamlines. If uncontrolled the instability can severely compromise the performance of x-ray FELs, where beam high brightness is crucial. In this talk we discuss how consideration of the microbunching instability is informing the LCLS-II design and determining the specifications for the laser heater and transport lines. We also review some of the expected and not so-expected phenomena that we have encountered while carrying out high-resolution macroparticle simulations of the instability and the analytical models we have developed to interpret the numerical results.
	Slides TUC01 [4.206 MB]
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TUC02	Ultra-Low Charge, Ultra-High Brightness Frontiers of Photoinjectors: Challenges and Perspectives
	R.K. Li SLAC, Menlo Park, California, USA
	Photoinjectors deliver high brightness electron beams that are essential to the success of FELs. Higher beam brightness can boost the performances of existing facilities and enable new capabilities of future ones. Ultralow charge (a few pC and lower) is the choice to reach higher brightness thanks to the favorable scaling, as well as longitudinally coherent, single-spike FELs. This parameter space is particularly relevant for future high rep-rate machines. Despite the ultralow total charge, the charge density is still high and collective effects need to be studied in-depth. The extreme emittance, bunch length, spot size, and charge also pose challenges on the diagnosis of these beams. In this talk, we will discuss recent progress on the generation, manipulation, and diagnosis of ultralow charge beams, including e.g. shaping the space charge dominated beams to maximize the phase space density, new techniques to characterize the nm-rad-level emittance, and new advances in photocathode physics and rf structures. Many of the above progress are motivated by the recent development of ultrafast electron diffraction and microscopy using photoinjectors. Understanding and controlling the high brightness beams in accelerators with the high stability and precision typical in the electron microscopy community, constitutes an R&D frontier on electron beams and sources for the coming decades.
	Slides TUC02 [2.858 MB]
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TUC03	Low Slice Emittance Preservation in Bunch Compressors
	S. Bettoni, M. Aiba, M. Pedrozzi, E. Prat, S. Reiche, T. Schietinger PSI, Villigen PSI, Switzerland B. Beutner DESY, Hamburg, Germany
	Minimize the dilution of the beam emittance is crucial for accelerators, and in particular for Free Electron Lasers, where the length of the machine and the finally the efficiency of the lasing process depend on it. At the SwissFEL Injector Test Facility we measured unexpected slice emittance increase after compressing the bunch also for moderate compression factors. We experimentally characterized the dependency of this phenomenon on the beam and machine parameters relevant for the compression. In order to qualitatively reproduce all the measurements outcomes it was necessary to use a 3D beam dynamic model along the bunch compressor including coherent synchrotron radiation. After excluding space charge forces, spurious dispersion and microbunching instability as possible sources for the observed emittance dilution, we identified the coherent synchrotron radiation and its interaction with the electron beam as the main responsible of the phenomenon. We also studied both experimentally and with simulations the contribution of the mismatch along the bunch to the longitudinal variations of the slice emittance. These experimental and theoretical investigations allowed a re-optimization of the injector. Typically with 150 A peak current, 200 pC charge it was possible to reach less than 200 nm.rad for the central slice with a moderate increase up to less than 300 nm.rad on the tails.
	Slides TUC03 [1.395 MB]
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TUC04	Image Charge Effect on Emittance Reduction Phenomenon in Electron Gun
	T. Nogi Kyoto Univeristy, Kyoto, Japan T. Katsurayama, T. Kii, K. Masuda, K. Morita, T. Murata, K. Nagasaki, H. Ohgaki, S. Suphakul, K. Torgasin, H. Yamashita, H. Zen Kyoto University, Kyoto, Japan
	Development of next generation light sources requires reduction of beam emittance. The emittance can be influenced in the vicinity of a cathode, where electron energy is low and the beam dynamics is dominated by space charge and image charge effect. Recently it was discovered that for ideal DC acceleration emittance rises near cathode and subsequently decreases due to self-linearization force caused by space charge effect []. This phenomenon occurs for accelerating field, which is lower than usually applied at conventional electron guns. It is an issue that this concept is feasible for electron gun configuration of real injectors. In this research we numerically investigate the transverse emittance and its dependence on parameters such as current density, accelerating field and the distance from the cathode. As a result, the position of minimal emittance was found to be correlated to perveance. This position can be varied by proper settings of parameters. In this conference, we will present these phenomena seen numerically in the SCSS thermionic gun geometry. A. Mizuno, et al., Nucl. Instr. Meth. Phys. Res. A 774 (2015) 51-59.
	Slides TUC04 [1.604 MB]
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TUP065	Beam Dynamics Simulation for the Upgraded PITZ Photo Injector Applying Various Photocathode Laser Pulses	501
	M. A. Bakr, M. Khojoyan, M. Krasilnikov, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany M. A. Bakr Assiut University, Assiut, Egypt
	The Photo Injector Test facility PITZ at DESY, Zeuthen site, characterizes and optimizes high brightness electron sources for linac-based Free Electron Laser (FELs) with a specific focus on the requirements of FLASH and the European XFEL. X-ray FELs require high brightness electron beam in terms of high peak current, small transverse emittance and energy spread. Such high quality beams are mandatory for efficient SASE generation in a single pass through long undulators with narrow gaps. Photocathode laser pulse shaping is a powerful tool to optimize the photo injector performance. Recently, a new photocathode laser system capable of producing 3D quasi-ellipsoidal pulses has been installed at PITZ. It is foreseen to operate this new system in parallel to the nominal one that generates cylindrical pulses with various temporal profiles. A set of numerical simulations was performed to study and compare the beam dynamics of electron beams produced with 3D ellipsoidal laser profile with the typical cylindrically shaped (flat-top) profile. Different bunch charges from 20 pC up to several nC are considered, in order to find an optimum PITZ machine setup which will yield the lowest transverse emittance. we present and discuss the results of this comparison in the submission.
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TUP066	Benchmark of ELEGANT and IMPACT	505
	L. Wang, P. Emma, T.O. Raubenheimer SLAC, Menlo Park, California, USA J. Qiang LBNL, Berkeley, California, USA
	The beam dynamics codes ELEGANT and IMAPCT have many users. We use these two codes for the design of LCLSII. Both codes use a 1D model for the coherent synchrotron radiation (CSR) in bend magnets. In addition, IMPACT has a 3D space-charge model, while ELEGANT uses a 1D model. To compare the two codes, especially the space-charge effects, we systematically benchmark the two codes with different physics aspects: wakefields, CSR and space-charge forces.
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TUP067	Effect of Hot Ions in LCLC-II	508
	L. Wang, T.O. Raubenheimer SLAC, Menlo Park, California, USA
	The ions in a linac, such as ERL, draw more attention recently. LCLSII has a long linac with 1MHz repetition rate. The ions, in general, are not deeply trapped due to the long bunch spacing. The effect of ion thermal energy becomes important in this regime. The beam dynamics with ions are studied numerically. There is a linear growth in amplitude, but not exponential growth as traditional fast ion instability. This instability set a maximum bunch-train length to limit the beam amplitude to fractional beam σ. Theoretical works are also done to compare the simulations. We also extend our works to different regimes where the motions of ions from stable to unstable.
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TUP068	Electron Beam Phase Space Tomographie at the European XFEL Injector	515
	M. Scholz, B. Beutner DESY, Hamburg, Germany
	Transverse emittances as well as the energy spread and the peak current of the electron bunches are important parameters for high-gain free electron lasers such as the European XFEL. Investigations of the 6D phase space characterisation would give important indications to optimise the beam quality for SASE operation. The injector of the European XFEL includes, inter alia, a laser heater, a transverse deflecting cavity, a spectrometer, a diagnostic section with four OTR screens as well as several quadrupole magnets. In this paper, we will discuss the possibilities to characterise the 6D phase space of the electron beam in the injector of the Eurpean XFEL.
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TUP069	THz Based Phase-Space Manipulation in a Guided IFEL	519
	E.J. Curry, S. Fabbri, P. Musumeci UCLA, Los Angeles, California, USA A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
	Funding: This work has been supported by DOE grant DE-FG02-92ER40693, and NSF grant PHY-1415583. We propose a guided IFEL interaction driven by a broadband THz source to compress a relativistic electron bunch and synchronize it with an external laser pulse. A high field single-cycle THz pulse is group velocity-matched to the electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. The THz pulse is generated via optical rectification from the external laser source, with peak field of up to 4.6 MV/m. We present measurements of the THz waveform before and after a parallel plate waveguide with varying aperture size and estimate the group velocity. We also present results from a preliminary 1-D multi-frequency simulation code we are developing to model the guided broadband IFEL interaction. Given a 6 MeV, 100 fs electron bunch with an initial 10^-3 energy spread, as can be readily produced at the UCLA Pegasus laboratory, the simulations predict a phase space rotation of the bunch distribution that will reduce the initial timing jitter and compress the electron bunch by nearly an order of magnitude.
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TUP070	Energy Jitter Minimization at LCLS	523
	L. Wang, A.L. Benwell, A. Brachmann, W.S. Colocho, F.-J. Decker, Z. Huang, T.J. Maxwell, T. Tao, J.L. Turner SLAC, Menlo Park, California, USA
	The energy jitters of the electron beam can affects the FEL in self-seeded modes if the jitter is large compared to the FEL parameter. We work in multiple ways to reduce the jitters, including hardware improvement, optimization linac set-up. This paper discusses the optimization of linac set-up. The solutions always suggest that we can largely reduce the energy jitter from a weak compression at BC1 and a stronger compression at BC2. Meanwhile a low beam energy at BC2 also reduce the energy jitter, which is confirmed by the experiment. The results can be explained by a simple model. Experimental results are also presented, demonstrating better than 20% and 40% relative energy jitter reduction for 13.6 and 4 GeV linac operation, respectively.
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TUP071	A FAST Particle Tracking Code	530
	L. Wang SLAC, Menlo Park, California, USA
	This paper presents a fast particle tracking (FPT) code for linac beam dynamics. It includes wake fields, coherent synchrotron radiation (CSR) and longitudinal space charge. We systematically benchmark the FPT with ELEGANT with different physics aspects: pure optics, wakefields, CSR and space-charge forces
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TUP072	Cathode Ion Bombardment in LCLS and LCLS-II RF Gun	534
	L. Wang, A. Brachmann, F.-J. Decker, Z. Li, T.O. Raubenheimer, J.F. Schmerge, F. Zhou SLAC, Menlo Park, California, USA
	This paper studies the ions bombardment on the cathode in the LCLS and LCLS-II gun. APEX gun is used here for LCLS-II, which will be operate at 1 MHz repetition rate. Therefore, It is important to estimate the ion bombardment. One specific PIC code is used track arbitrary particles (ions and electron here) in arbitrary 2D/3D electromagnetic field and solenoid field to estimate the possibility of ion bombardment. The LCLS gun has 1.6 cells while the LCLS-II gun (APEX gun) is a half-cell gun. The frequencies of the two guns are also quite different. These characters make the ion dynamics quite differently. We estimated the bombardment for various ion species and studied the effects RF pulse shape and RF phase
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WEP058	Emittance Measurements at the PAL-XFEL Injector Test Facility	690
	J. Lee POSTECH, Pohang, Kyungbuk, Republic of Korea J.H. Han, J.H. Hong, C.H. Kim, I.S. Ko, S.J. Lee, S.J. Park, H. Yang PAL, Pohang, Kyungbuk, Republic of Korea
	The PAL-XFEL Injector Test Facility (ITF) at PAL has been operating for experimental optimization of electron beam parameters and for beam test of various accelerator components. It consists of a photocathode RF gun, two S-band accelerating structures, a laser heater system, and beam diagnostics such as ICTs, BPMs, screens, beam energy spectrometers and an RF deflector. Projected and slice emittance measurements were carried out by using single quadrupole scan. In this paper, we present the emittance measurements.
	Poster WEP058 [0.646 MB]
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WEP060	Longitudinal Electron Bunch Shaping Experiments at the PAL-ITF	694
	M. Chung, J.M. Seok UNIST, Ulsan, Republic of Korea J.H. Han, J.H. Hong, H.-S. Kang, C.H. Kim PAL, Pohang, Kyungbuk, Republic of Korea J.C.T. Thangaraj Fermilab, Batavia, Illinois, USA
	Longitudinal shaping of electron beam has received much attention recently, due to its potential applications to THz generation, dielectric wakefield acceleration, improvement of FEL performance, and controlled space-charge modulation. Using a set of alpha-BBO crystals, shaping of laser pulse and electron bunch on the order of ps is tested at the Injector Test Facility (ITF) of Pohang Accelerator Laboratory (PAL). In particular, we investigate the response of the longitudinally-modulated beam to a dechirper, which is a vacuum chamber of two corrugated, metallic plates. Initial experimental results will be presented with analytical theory and numerical simulations.
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WEP061	Numerical and Experimental Studies on Electron Beam Properties from Asymmetric RF-gun	698
	S. Rimjaem, N. Chaisueb, J. Saisut, C. Thongbai, W. Thongpakdi Chiang Mai University, Chiang Mai, Thailand N. Kangrang FNRF, Chiang Mai, Thailand E. Kongmon, K. Kosaentor, P. Wichaisirimongkol IST, Chiang Mai, Thailand
	Funding: This work has been supported by the CMU Junior Research Fellowship Program, and the Department of Physics and Materials Science, Faculty of Science, Chiang Mai University. The electron linear accelerator at the Plasma and Beam Physics Research Facility (PBP-CMU Linac), Chiang Mai University, Thailand, is used to produce femtosecond electron bunches for generation of THz radiation. The main components of the PBP-CMU Linac are a thermionic RF electron gun, an alpha magnet, a travelling wave linac structure, quadrupole lens, steering magnets, and various diagnostic components. The RF-gun consists of a 1.6 S-band standing wave structure and a side-coupling cavity. The 2856 MHz RF wave is transmitted from the klystron to the gun through a rectangular waveguide input-port. Both the RF input-port and the side-coupling cavity cause an asymmetric electromagnetic field distribution inside the gun. The electron beam from the RF-gun has asymmetric transverse shape with an emittance value, which is higher than the beam from the symmetric fields. The problems are increased when the beam is transported from the gun through the whole accelerator system. Beam dynamic simulations are performed to investigate the effect of the asymmetric fields on the electron properties by using the codes PARMELA and ELEGANT. An integrated electron beam diagnostic station to measure the beam properties will be installed in the system to investigate these effects. Results from numerical and experimental studies are reported in this contribution.
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WEP062	Study on Undulator Radiation from Femtosecond Electron Bunches	702
	N. Chaisueb, S. Rimjaem Chiang Mai University, Chiang Mai, Thailand
	Funding: This work has been supported by the CMU Junior Research Fellowship Program, the Department of Physics and Material Science, Faculty of science, Chiang Mai University, and SAST Scholarship. Linac based terahertz (THz) source at the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University, consists of a thermionic RF electron gun, an alpha magnet for magnetic bunch compressor, a travelling wave S-band accelerating structure for post acceleration, and various beam diagnostic instruments. The PBP-CMU linac can produce relativistic femtosecond electron bunches, which are used to generate coherent THz radiation via transition radiation technique. To increase the radiation intensity, an electromagnetic undulator will be added in the beam transport line. The designed electromagnetic undulator has 40.5 periods with a period length of 56 mm and a pole gap of 15 mm. Numerical calculation result shows that the brightness of the undulator radiation, which is produced from electron bunches with an energy of 10 MeV, a peak current of 300 A, and an effective bunch length of 120 fs, is about 10 thousand times higher than the brightness of the transition radiation. This study investigates the dependence of the electron beam energy, electron bunch charge, and electron bunch length on the coherent undulator radiation by using the PARMELA code. The numerical simulation and procedure to generate the undulator radiation in the terahertz regime by using femtosecond electron bunches produced at the PBP research facility is reported and discussed in this contribution. The authors would like to acknowledge the financial support to participate this conference by the Department of Physics and Material Science and the Graduate School, Chiang Mai University.
	Poster WEP062 [8.172 MB]
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WEP067	Simulation of Cascaded Longitudinal-Space-Charge Amplifier at the Fermilab Accelerator Science & Technology (Fast) Facility	707
	A. Halavanau, P. Piot Northern Illinois University, DeKalb, Illinois, USA P. Piot Fermilab, Batavia, Illinois, USA
	Funding: This work was supported by the US Department of Energy under contract DE-SC0011831 with Northern Illinois University. Cascaded longitudinal space-charge amplifier (LSCA) have been proposed as a mechanism to generate density modulation over broadband.[1] The scheme was recently demonstrated in the optical regime and confirmed the production of broadband optical radiation.[2] In this paper we investigate, via numerical simulations, the performances of a cascaded LSCA beamline at the Fermilab's Advanced Superconducting Test Accelerator (ASTA) to produce broadband ultraviolet radiation. Our studies are carried using a three-dimensional space charge algorithm coupled with ELEGANT [3] and based on a tree-based space-charge algorithm (see details in Ref. [4]) [1] M. Dohlus, PRSTAB, 14 090702 (2011). [2] A. Marinelli, PRL, 110 264802 (2013). [3] M. Borland, Advanced Photon Source, LS-287, 2000. [4] A. Halavanau, Proc. IPAC15, TUPMA007 (2015).
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WEP069	Minimization of the Emittance Growth Induced by Coherent Synchrotron Radiation in Arc Compressor	711
	X.Y. Huang, X. Cui, Y. Jiao, G. Xu IHEP, Beijing, People's Republic of China
	Funding: Supported by National Natural Science Foundation of China (11475202, 11405187). Coherent synchrotron radiation (CSR) is a critical issue when electron bunches with short bunch length and high peak current transporting through a bending system in high-brightness light sources and linear colliders. For example, a high peak current of electron beam can be achieved by using magnetic bunch compressor, however, CSR induced transverse emittance growth will limit the performance of bunch compressor. In this paper, based on our 'two-dimensional point-kick analysis', an arc compressor with high compression factor is studied. Through analytical and numerical research, an easy optics design technique is introduced that could minimize the emittance dilution within this compressor. It is demonstrated that the strong compression of bunch length and the transverse emittance preservation can be achieved at the same time.
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WEP070	Start-to-End Simulation of the LCLS-II Beam Delivery System with Real Number of Electrons	714
	J. Qiang, C.E. Mitchell, C. F. Papadopoulos, M. Venturini LBNL, Berkeley, California, USA Y. Ding, P. Emma, Z. Huang, G. Marcus, Y. Nosochkov, T.O. Raubenheimer, L. Wang, M. Woodley SLAC, Menlo Park, California, USA
	The LCLS-II as a next generation high repetition rate FEL based X-ray light source will enable significant scientific discoveries. In this paper, we report on the progress in the design of the accelerator beam delivery system through start-to-end simulations. We will present simulation results for three cases, 20 pC, 100 pC and 300 pC that are transported through the hard X-ray line and the soft X-ray line for FEL radiation.
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WEP073	Dispersion of Correlated Energy Spread Electron Beams in the Free Electron Laser	718
	L.T. Campbell USTRAT/SUPA, Glasgow, United Kingdom A.R. Maier CFEL, Hamburg, Germany
	The effect of a correlated linear energy chirp in the electron beam in the FEL, and how to compensate for its effects by using an appropriate linear taper of the undulator magnetic field have previously been investigated considering relatively small chirps. In the following, it is shown that larger linear energy chirps, such as those found in beams produced by laser-plasma accelerators, exhibit dispersive effects in the undulator, and require a non-linear taper on the undulator field to properly optimise.
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Paper

Title

Page

Linear Vlasov Solver For Microbunching Gain Estimation with Inclusion of CSR, LSC, And Linac Geometric Impedances

147

C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
D. Douglas, R. Li, C. Tennant
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
As is known, microbunching instability (MBI) has been one of the most challenging issues in designs of magnetic chicanes for short-wavelength free-electron lasers or linear colliders, as well as those of transport lines for recirculating or energy recovery linac machines. To more accurately quantify MBI in a single-pass system, we further extend and continue to increase the capabilities of our previously developed linear Vlasov solver [1] to incorporate more relevant impedance models into the code, including transient and steady-state free-space and/or shielding CSR impedances, the LSC and linac geometric impedances with extension of the existing formulation to include beam acceleration [2]. Then, we directly solve the linearized Vlasov equation numerically for microbunching gain amplification factor. In this study we apply this code to a beamline lattice of transport arc [3] following an upstream linac section. The resultant gain functions and spectra are presented here, and some results are compared with particle tracking simulation by ELEGANT [4]. We also discuss some underlying physics with inclusion of these collective effects and the limitation of the existing formulation. It is anticipated that this more thorough analysis can further improve the understanding of MBI mechanisms and shed light on how to suppress or compensate MBI effects in lattice designs.
[1] C. -Y. Tsai et al., FEL'14 (THP022), IPAC'15 (MOPMA028) and ERL2015 (TUICLH2034)
[2] M. Venturini, Phys. Rev. ST Accel. Beams 10, 104401 (2007)
[3] D. Douglas et al., arXiv: 1403.2318v1 [physics.acc-ph]
[4] M. Borland, APS Light Source Note LS-287 (2000)

Poster MOP052 [4.934 MB]

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MOP053

Intra-Beam Scattering in High Brightness Electron Linacs

153

S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Intra-beam scattering (IBS) of a high brightness electron beam in a linac has been studied* analytically, and the expectations found to be in reasonable agreement with particle tracking results from the Elegant code. It comes out that, under standard conditions for a linac driving a free electron laser, IBS plays no significant role in the development of microbunching instability. A partial damping of the instability is envisaged, however, when IBS is enhanced either with dedicated magnetic insertions, or in the presence of an electron beam charge density at least 4 times larger than that produced by present photo-injectors.
* S. Di Mitri, Phys. Rev. Special Topics Accel. Beams, 17, 074401 (2014).

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MOP054

Wake Field Potentials of 'Dechirpers'

157

A. Novokhatski
SLAC, Menlo Park, California, USA

Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515.
A corrugated structure, which is used on 'dechirpers' is usually a pipe or two plates with small corrugations (bumps) on the walls. There is a good single-mode description of the wake potentials excited by a relativistic bunch if the wave length of the mode is much longer than the distance between the bumps in the pipe. However, ultra-short bunches, which are now used in FELs, excite much higher frequency fields and the corresponding wake potentials will be very different from single-mode description. We made analyzes of these wake potentials based on a numerical solution of Maxwell's equations. The behavior of the wake fields of ultra-short bunches in corrugated structures is not much different from the fields excited usually in accelerating structures where the wake potentials are described by the exponential function. As we increase the bunch length, the wake potentials slowly transform to the form of a single mode. For a practical application we present results for a 'dechirper', which will be soon installed at LCLS. We also carried out calculations for a similar device, that was installed and measured at the Pohang Accelerator Laboratory, Korea. We find very good agreement with the experimental results.

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MOP055

The Effect of Wakefields on the FEL Performance

161

A. Novokhatski, F.-J. Decker, Y. Nosochkov, M.K. Sullivan
SLAC, Menlo Park, California, USA

Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515.
If a beam travels near collimator jaws or other discontinuities of the beam pipe, it gets the energy loss and the transverse kick due to the back reaction of the beam field diffracted on the collimator's jaws. The wake field effect from collimators may not only bring an additional energy jitter and change the trajectory of the beam, but may also lead to degradation of the performance of Free Electron Laser (FEL) It may be possible due to the special character of the wake fields: the response reaction depends on the longitudinal position of the particles in the bunch. We describe a model of the wake field radiation, simulation results and comparison with measurements.

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MOP056

Reversible Electron Beam Heater without Transverse Deflecting Cavities

166

G. Stupakov, P. Emma
SLAC, Menlo Park, California, USA

Funding: This work was supported by Department of Energy contract DE-AC03-76SF00515.
Suppression of microbunching instability in modern FELs is an important issue that often limits the performance of the machine. A technique to suppress the instability with the help of a reversible electron beam heater was proposed by C. Behrens, Z. Huang, and D. Xiang [*]. It employs transverse deflecting cavities synchronized in a way that one of the cavities, located before a bunch compressor, generates a slice energy spread, while the other one removes it after the beam passes through the bunch compressor. Being an attractive approach, this concept unfortunately imposes extremely tight tolerances on the synchronization of the cavities. In this paper we demonstrate that a reversible heater equivalent to that of Behrens et al. can be designed using much simpler elements: bend magnets and quadrupoles in combination with the energy chirp of the beam.
* C. Behrens, Z. Huang, and D. Xiang, PRST-AB 15, 022802 (2012).

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MOP057

Front End Simulations and Design for the CLARA FEL Test Facility

171

J.W. McKenzie, A.D. Brynes, B.L. Militsyn
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

We present the design and simulations of the Front End for CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. This is based around an S-band RF photocathode gun. Initially this will be the 2.5 cell gun, currently used on VELA facility at Daresbury, which is limited to 10 Hz repetition rate. Later, this will be up-graded to a 1.5 cell gun, currently under development, which will allow repetition rates of up to 400 Hz to be reached. The beam will be accelerated up to 50 MeV with a booster linac which will be operated in both bunching and boosting modes for different operating regimes of CLARA. Simulations are presented for a currently achieved performance of the RF system and drive laser with optimisation of the laser pulse lengths for various operational modes of CLARA.

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MOP060

RFTweak 5 - An Efficient Longitudinal Beam Dynamics Code

176

B. Beutner, H. Dinter, M. Dohlus
DESY, Hamburg, Germany

The shaping of the longitudinal phase space in bunch compression systems is essential for efficient FEL operation. RF systems and self-field interactions contribute to the overall phase space structure. The design of the various facilities relies on extensive beam dynamics simulations to define the longitudinal dynamics. However, in everyday control room applications such techniques are often not fast enough for efficient operation, e.g. for SASE tuning. Therefore efficient longitudinal beam dynamics codes are required while still maintaining reasonable accuracy. Our approach is to pre-calculate most of the required data for self-field interactions and store them on disc to reduce required online calculation time to a minimum. In this paper we present the fast longitudinal tracking code RFTweak 5, which includes wakes, space charge, and CSR interactions. With this code the full European XFEL with a 1M particles bunch is calculated on the order of minutes on a standard laptop. Neglecting CSR effects this time reduces to seconds.

Poster MOP060 [0.799 MB]

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MOP062

Technology Maturation for the MaRIE 1.0 X-FEL

181

J.W. Lewellen, K. Bishofberger, B.E. Carlsten, L.D. Duffy, F.L. Krawczyk, Q.R. Marksteiner, D.C. Nguyen, S.J. Russell, R.L. Sheffield, N.A. Yampolsky
LANL, Los Alamos, New Mexico, USA

Funding: This research was funded by the Matter-Radiation Interactions in Extremes program at Los Alamos National Laboratory, under contract DE-AC52-06NA25396.
Los Alamos National Laboratory is proposing a high-energy XFEL, named MaRIE*, to meet its mission needs. MaRIE will be required to generate coherent 42+ keV photons, and, due to space constraints at the LANSCE accelerator complex at Los Alamos, MaRIE's design electron beam energy is 12 GeV. This combination places significant restrictions upon the MaRIE electron beam parameters, in particular the transverse emittance and energy spread at the undulator entrance. We are developing approaches to meet these requirements, but these often require solutions extending beyond the current state-of-the-art in X-FEL design. To reduce overall project risk, therefore, we have identified a number of key experimental and modeling / simulation efforts intended to address both the areas of greatest uncertainty in the preliminary MaRIE design, and the areas of largest known risk. This paper describes the general requirements for the MaRIE X-FEL, our current areas of greatest concern with the preliminary design concept, and our corresponding Technology Maturation Plan (TMP).
* MaRIE website: http://www.lanl.gov/science-innovation/science-facilities/marie/index.php

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MOP063

Transverse Emittance Measurement of KAERI Linac with Thick Lens Quadrupole Scan

185

S. Setiniyaz, I.H. Baek, M.S. Chae, B.A. Gudkov, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, S.V. Miginsky, J.H. Nam, S. Park, N. Vinokurov
KAERI, Daejon, Republic of Korea
S.V. Miginsky, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

The UED (Ultrafast Electron Diffraction) beamline of KAERI (Korea Atomic Energy Research Institute) WCI (World Class Institute) Center has been completed and successfully commissioned. Transverse emittance of the electron beam was measured at the entrance of the UED chamber with the quadrupole scan technique. In this technique, larger drift distance between the quad and screen is preferred because it gives better thin lens approximation. A space charge dominated beam however, will undergo emittance growth in the long drift caused by the space charge force. We suggest mitigating this growth by introducing quadrupole scan with short drift and without thin lens approximation. We shall discuss the measurement process and results.

Poster MOP063 [1.287 MB]

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MOP066

Electron Bunch Length Measurement using an RF Deflecting Cavity

188

S. Park, E.-S. Kim
Kyungpook National University, Daegu, Republic of Korea
S. Bae, K.H. Jang, Y.U. Jeong, H.W. Kim, J. Mun, N. Vinokurov
KAERI, Daejon, Republic of Korea

Recently, the RF photogun based-ultrafast electron diffraction (UED) system has been developed in KAERI. In the system, the emitted electron bunches are experimentally confirmed to be accelerated up to 3 MeV at 5MW of RF power. And the time duration of the each bunch is initially designed to be less than 50 fs at the sample position. To analyses the performance of the system and to measure exactly the length of the electron bunches, we developed a rectangular type of S-band deflecting cavity working on TM120 mode. The principle of electron deflecting in the cavity, design & mechanical fabrication process and test results will be present in the conference.

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MOP087

Multistage CSR Microbunching Gain Development in Transport or Recirculation Arcs

263

C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
D. Douglas, R. Li, C. Tennant
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Coherent synchrotron radiation (CSR) induced microbunching instability has been one of the most challenging issues in the design of modern accelerators. A linear Vlasov solver has been developed [1] and applied to investigate the physical processes of microbunching gain amplification for several example lattices [2]. In this paper, by further extending the concept of stage gain as proposed by Huang and Kim [3], we develop a method to characterize the microbunching development in terms of stage orders that allow the quantitative comparison of optics impacts on microbunching gain for different lattices. We find that the microbunching instability in our demonstrated arcs has a distinguishing feature of multistage amplification (e.g, up to 6th stage amplification for our example transport arcs, in contrast to two-stage amplification for a typical 4-dipole bunch compressor chicane). We also try to connect lattice optics pattern with the obtained stage gain functions by a physical interpretation. This Vlasov analysis is validated by ELEGANT [4] tracking results with excellent agreement.
[1] C. -Y. Tsai et al., MOP052, these proceedings
[2] See, for example, C. -Y. Tsai et al., ERL2015 (TUICLH2034)
[3] Z. Huang and K. -J. Kim, Phys. Rev. ST Accel. Beams 5, 074401 (2002)
[4] M. Borland, APS Light Source Note LS-287 (2000)

Poster MOP087 [1.962 MB]

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TUC01

The Microbunching Instability and LCLS-II Lattice Design

308

M. Venturini
LBNL, Berkeley, California, USA

The microbunching instability is a pervasive occurrence when high brightness electron beams are accelerated and transported through dispersive sections like bunch-compression chicanes or distributions beamlines. If uncontrolled the instability can severely compromise the performance of x-ray FELs, where beam high brightness is crucial. In this talk we discuss how consideration of the microbunching instability is informing the LCLS-II design and determining the specifications for the laser heater and transport lines. We also review some of the expected and not so-expected phenomena that we have encountered while carrying out high-resolution macroparticle simulations of the instability and the analytical models we have developed to interpret the numerical results.

Slides TUC01 [4.206 MB]

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TUC02

Ultra-Low Charge, Ultra-High Brightness Frontiers of Photoinjectors: Challenges and Perspectives

R.K. Li
SLAC, Menlo Park, California, USA

Photoinjectors deliver high brightness electron beams that are essential to the success of FELs. Higher beam brightness can boost the performances of existing facilities and enable new capabilities of future ones. Ultralow charge (a few pC and lower) is the choice to reach higher brightness thanks to the favorable scaling, as well as longitudinally coherent, single-spike FELs. This parameter space is particularly relevant for future high rep-rate machines. Despite the ultralow total charge, the charge density is still high and collective effects need to be studied in-depth. The extreme emittance, bunch length, spot size, and charge also pose challenges on the diagnosis of these beams. In this talk, we will discuss recent progress on the generation, manipulation, and diagnosis of ultralow charge beams, including e.g. shaping the space charge dominated beams to maximize the phase space density, new techniques to characterize the nm-rad-level emittance, and new advances in photocathode physics and rf structures. Many of the above progress are motivated by the recent development of ultrafast electron diffraction and microscopy using photoinjectors. Understanding and controlling the high brightness beams in accelerators with the high stability and precision typical in the electron microscopy community, constitutes an R&D frontier on electron beams and sources for the coming decades.

Slides TUC02 [2.858 MB]

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TUC03

Low Slice Emittance Preservation in Bunch Compressors

S. Bettoni, M. Aiba, M. Pedrozzi, E. Prat, S. Reiche, T. Schietinger
PSI, Villigen PSI, Switzerland
B. Beutner
DESY, Hamburg, Germany

Minimize the dilution of the beam emittance is crucial for accelerators, and in particular for Free Electron Lasers, where the length of the machine and the finally the efficiency of the lasing process depend on it. At the SwissFEL Injector Test Facility we measured unexpected slice emittance increase after compressing the bunch also for moderate compression factors. We experimentally characterized the dependency of this phenomenon on the beam and machine parameters relevant for the compression. In order to qualitatively reproduce all the measurements outcomes it was necessary to use a 3D beam dynamic model along the bunch compressor including coherent synchrotron radiation. After excluding space charge forces, spurious dispersion and microbunching instability as possible sources for the observed emittance dilution, we identified the coherent synchrotron radiation and its interaction with the electron beam as the main responsible of the phenomenon. We also studied both experimentally and with simulations the contribution of the mismatch along the bunch to the longitudinal variations of the slice emittance. These experimental and theoretical investigations allowed a re-optimization of the injector. Typically with 150 A peak current, 200 pC charge it was possible to reach less than 200 nm.rad for the central slice with a moderate increase up to less than 300 nm.rad on the tails.

Slides TUC03 [1.395 MB]

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TUC04

Image Charge Effect on Emittance Reduction Phenomenon in Electron Gun

T. Nogi
Kyoto Univeristy, Kyoto, Japan
T. Katsurayama, T. Kii, K. Masuda, K. Morita, T. Murata, K. Nagasaki, H. Ohgaki, S. Suphakul, K. Torgasin, H. Yamashita, H. Zen
Kyoto University, Kyoto, Japan

Development of next generation light sources requires reduction of beam emittance. The emittance can be influenced in the vicinity of a cathode, where electron energy is low and the beam dynamics is dominated by space charge and image charge effect. Recently it was discovered that for ideal DC acceleration emittance rises near cathode and subsequently decreases due to self-linearization force caused by space charge effect [*]. This phenomenon occurs for accelerating field, which is lower than usually applied at conventional electron guns. It is an issue that this concept is feasible for electron gun configuration of real injectors. In this research we numerically investigate the transverse emittance and its dependence on parameters such as current density, accelerating field and the distance from the cathode. As a result, the position of minimal emittance was found to be correlated to perveance. This position can be varied by proper settings of parameters. In this conference, we will present these phenomena seen numerically in the SCSS thermionic gun geometry.
* A. Mizuno, et al., Nucl. Instr. Meth. Phys. Res. A 774 (2015) 51-59.

Slides TUC04 [1.604 MB]

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TUP065

Beam Dynamics Simulation for the Upgraded PITZ Photo Injector Applying Various Photocathode Laser Pulses

501

M. A. Bakr, M. Khojoyan, M. Krasilnikov, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany
M. A. Bakr
Assiut University, Assiut, Egypt

The Photo Injector Test facility PITZ at DESY, Zeuthen site, characterizes and optimizes high brightness electron sources for linac-based Free Electron Laser (FELs) with a specific focus on the requirements of FLASH and the European XFEL. X-ray FELs require high brightness electron beam in terms of high peak current, small transverse emittance and energy spread. Such high quality beams are mandatory for efficient SASE generation in a single pass through long undulators with narrow gaps. Photocathode laser pulse shaping is a powerful tool to optimize the photo injector performance. Recently, a new photocathode laser system capable of producing 3D quasi-ellipsoidal pulses has been installed at PITZ. It is foreseen to operate this new system in parallel to the nominal one that generates cylindrical pulses with various temporal profiles. A set of numerical simulations was performed to study and compare the beam dynamics of electron beams produced with 3D ellipsoidal laser profile with the typical cylindrically shaped (flat-top) profile. Different bunch charges from 20 pC up to several nC are considered, in order to find an optimum PITZ machine setup which will yield the lowest transverse emittance. we present and discuss the results of this comparison in the submission.

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TUP066

Benchmark of ELEGANT and IMPACT

505

L. Wang, P. Emma, T.O. Raubenheimer
SLAC, Menlo Park, California, USA
J. Qiang
LBNL, Berkeley, California, USA

The beam dynamics codes ELEGANT and IMAPCT have many users. We use these two codes for the design of LCLSII. Both codes use a 1D model for the coherent synchrotron radiation (CSR) in bend magnets. In addition, IMPACT has a 3D space-charge model, while ELEGANT uses a 1D model. To compare the two codes, especially the space-charge effects, we systematically benchmark the two codes with different physics aspects: wakefields, CSR and space-charge forces.

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TUP067

Effect of Hot Ions in LCLC-II

508

L. Wang, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

The ions in a linac, such as ERL, draw more attention recently. LCLSII has a long linac with 1MHz repetition rate. The ions, in general, are not deeply trapped due to the long bunch spacing. The effect of ion thermal energy becomes important in this regime. The beam dynamics with ions are studied numerically. There is a linear growth in amplitude, but not exponential growth as traditional fast ion instability. This instability set a maximum bunch-train length to limit the beam amplitude to fractional beam σ. Theoretical works are also done to compare the simulations. We also extend our works to different regimes where the motions of ions from stable to unstable.

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TUP068

Electron Beam Phase Space Tomographie at the European XFEL Injector

515

M. Scholz, B. Beutner
DESY, Hamburg, Germany

Transverse emittances as well as the energy spread and the peak current of the electron bunches are important parameters for high-gain free electron lasers such as the European XFEL. Investigations of the 6D phase space characterisation would give important indications to optimise the beam quality for SASE operation. The injector of the European XFEL includes, inter alia, a laser heater, a transverse deflecting cavity, a spectrometer, a diagnostic section with four OTR screens as well as several quadrupole magnets. In this paper, we will discuss the possibilities to characterise the 6D phase space of the electron beam in the injector of the Eurpean XFEL.

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TUP069

THz Based Phase-Space Manipulation in a Guided IFEL

519

E.J. Curry, S. Fabbri, P. Musumeci
UCLA, Los Angeles, California, USA
A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel

Funding: This work has been supported by DOE grant DE-FG02-92ER40693, and NSF grant PHY-1415583.
We propose a guided IFEL interaction driven by a broadband THz source to compress a relativistic electron bunch and synchronize it with an external laser pulse. A high field single-cycle THz pulse is group velocity-matched to the electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. The THz pulse is generated via optical rectification from the external laser source, with peak field of up to 4.6 MV/m. We present measurements of the THz waveform before and after a parallel plate waveguide with varying aperture size and estimate the group velocity. We also present results from a preliminary 1-D multi-frequency simulation code we are developing to model the guided broadband IFEL interaction. Given a 6 MeV, 100 fs electron bunch with an initial 10^-3 energy spread, as can be readily produced at the UCLA Pegasus laboratory, the simulations predict a phase space rotation of the bunch distribution that will reduce the initial timing jitter and compress the electron bunch by nearly an order of magnitude.

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TUP070

Energy Jitter Minimization at LCLS

523

L. Wang, A.L. Benwell, A. Brachmann, W.S. Colocho, F.-J. Decker, Z. Huang, T.J. Maxwell, T. Tao, J.L. Turner
SLAC, Menlo Park, California, USA

The energy jitters of the electron beam can affects the FEL in self-seeded modes if the jitter is large compared to the FEL parameter. We work in multiple ways to reduce the jitters, including hardware improvement, optimization linac set-up. This paper discusses the optimization of linac set-up. The solutions always suggest that we can largely reduce the energy jitter from a weak compression at BC1 and a stronger compression at BC2. Meanwhile a low beam energy at BC2 also reduce the energy jitter, which is confirmed by the experiment. The results can be explained by a simple model. Experimental results are also presented, demonstrating better than 20% and 40% relative energy jitter reduction for 13.6 and 4 GeV linac operation, respectively.

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TUP071

A FAST Particle Tracking Code

530

L. Wang
SLAC, Menlo Park, California, USA

This paper presents a fast particle tracking (FPT) code for linac beam dynamics. It includes wake fields, coherent synchrotron radiation (CSR) and longitudinal space charge. We systematically benchmark the FPT with ELEGANT with different physics aspects: pure optics, wakefields, CSR and space-charge forces

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TUP072

Cathode Ion Bombardment in LCLS and LCLS-II RF Gun

534

L. Wang, A. Brachmann, F.-J. Decker, Z. Li, T.O. Raubenheimer, J.F. Schmerge, F. Zhou
SLAC, Menlo Park, California, USA

This paper studies the ions bombardment on the cathode in the LCLS and LCLS-II gun. APEX gun is used here for LCLS-II, which will be operate at 1 MHz repetition rate. Therefore, It is important to estimate the ion bombardment. One specific PIC code is used track arbitrary particles (ions and electron here) in arbitrary 2D/3D electromagnetic field and solenoid field to estimate the possibility of ion bombardment. The LCLS gun has 1.6 cells while the LCLS-II gun (APEX gun) is a half-cell gun. The frequencies of the two guns are also quite different. These characters make the ion dynamics quite differently. We estimated the bombardment for various ion species and studied the effects RF pulse shape and RF phase

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WEP058

Emittance Measurements at the PAL-XFEL Injector Test Facility

690

J. Lee
POSTECH, Pohang, Kyungbuk, Republic of Korea
J.H. Han, J.H. Hong, C.H. Kim, I.S. Ko, S.J. Lee, S.J. Park, H. Yang
PAL, Pohang, Kyungbuk, Republic of Korea

The PAL-XFEL Injector Test Facility (ITF) at PAL has been operating for experimental optimization of electron beam parameters and for beam test of various accelerator components. It consists of a photocathode RF gun, two S-band accelerating structures, a laser heater system, and beam diagnostics such as ICTs, BPMs, screens, beam energy spectrometers and an RF deflector. Projected and slice emittance measurements were carried out by using single quadrupole scan. In this paper, we present the emittance measurements.

Poster WEP058 [0.646 MB]

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WEP060

Longitudinal Electron Bunch Shaping Experiments at the PAL-ITF

694

M. Chung, J.M. Seok
UNIST, Ulsan, Republic of Korea
J.H. Han, J.H. Hong, H.-S. Kang, C.H. Kim
PAL, Pohang, Kyungbuk, Republic of Korea
J.C.T. Thangaraj
Fermilab, Batavia, Illinois, USA

Longitudinal shaping of electron beam has received much attention recently, due to its potential applications to THz generation, dielectric wakefield acceleration, improvement of FEL performance, and controlled space-charge modulation. Using a set of alpha-BBO crystals, shaping of laser pulse and electron bunch on the order of ps is tested at the Injector Test Facility (ITF) of Pohang Accelerator Laboratory (PAL). In particular, we investigate the response of the longitudinally-modulated beam to a dechirper, which is a vacuum chamber of two corrugated, metallic plates. Initial experimental results will be presented with analytical theory and numerical simulations.

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WEP061

Numerical and Experimental Studies on Electron Beam Properties from Asymmetric RF-gun

698

S. Rimjaem, N. Chaisueb, J. Saisut, C. Thongbai, W. Thongpakdi
Chiang Mai University, Chiang Mai, Thailand
N. Kangrang
FNRF, Chiang Mai, Thailand
E. Kongmon, K. Kosaentor, P. Wichaisirimongkol
IST, Chiang Mai, Thailand

Funding: This work has been supported by the CMU Junior Research Fellowship Program, and the Department of Physics and Materials Science, Faculty of Science, Chiang Mai University.
The electron linear accelerator at the Plasma and Beam Physics Research Facility (PBP-CMU Linac), Chiang Mai University, Thailand, is used to produce femtosecond electron bunches for generation of THz radiation. The main components of the PBP-CMU Linac are a thermionic RF electron gun, an alpha magnet, a travelling wave linac structure, quadrupole lens, steering magnets, and various diagnostic components. The RF-gun consists of a 1.6 S-band standing wave structure and a side-coupling cavity. The 2856 MHz RF wave is transmitted from the klystron to the gun through a rectangular waveguide input-port. Both the RF input-port and the side-coupling cavity cause an asymmetric electromagnetic field distribution inside the gun. The electron beam from the RF-gun has asymmetric transverse shape with an emittance value, which is higher than the beam from the symmetric fields. The problems are increased when the beam is transported from the gun through the whole accelerator system. Beam dynamic simulations are performed to investigate the effect of the asymmetric fields on the electron properties by using the codes PARMELA and ELEGANT. An integrated electron beam diagnostic station to measure the beam properties will be installed in the system to investigate these effects. Results from numerical and experimental studies are reported in this contribution.

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WEP062

Study on Undulator Radiation from Femtosecond Electron Bunches

702

N. Chaisueb, S. Rimjaem
Chiang Mai University, Chiang Mai, Thailand

Funding: This work has been supported by the CMU Junior Research Fellowship Program, the Department of Physics and Material Science, Faculty of science, Chiang Mai University, and SAST Scholarship.
Linac based terahertz (THz) source at the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University, consists of a thermionic RF electron gun, an alpha magnet for magnetic bunch compressor, a travelling wave S-band accelerating structure for post acceleration, and various beam diagnostic instruments. The PBP-CMU linac can produce relativistic femtosecond electron bunches, which are used to generate coherent THz radiation via transition radiation technique. To increase the radiation intensity, an electromagnetic undulator will be added in the beam transport line. The designed electromagnetic undulator has 40.5 periods with a period length of 56 mm and a pole gap of 15 mm. Numerical calculation result shows that the brightness of the undulator radiation, which is produced from electron bunches with an energy of 10 MeV, a peak current of 300 A, and an effective bunch length of 120 fs, is about 10 thousand times higher than the brightness of the transition radiation. This study investigates the dependence of the electron beam energy, electron bunch charge, and electron bunch length on the coherent undulator radiation by using the PARMELA code. The numerical simulation and procedure to generate the undulator radiation in the terahertz regime by using femtosecond electron bunches produced at the PBP research facility is reported and discussed in this contribution.
The authors would like to acknowledge the financial support to participate this conference by the Department of Physics and Material Science and the Graduate School, Chiang Mai University.

Poster WEP062 [8.172 MB]

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WEP067

Simulation of Cascaded Longitudinal-Space-Charge Amplifier at the Fermilab Accelerator Science & Technology (Fast) Facility

707

A. Halavanau, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
P. Piot
Fermilab, Batavia, Illinois, USA

Funding: This work was supported by the US Department of Energy under contract DE-SC0011831 with Northern Illinois University.
Cascaded longitudinal space-charge amplifier (LSCA) have been proposed as a mechanism to generate density modulation over broadband.[1] The scheme was recently demonstrated in the optical regime and confirmed the production of broadband optical radiation.[2] In this paper we investigate, via numerical simulations, the performances of a cascaded LSCA beamline at the Fermilab's Advanced Superconducting Test Accelerator (ASTA) to produce broadband ultraviolet radiation. Our studies are carried using a three-dimensional space charge algorithm coupled with ELEGANT [3] and based on a tree-based space-charge algorithm (see details in Ref. [4])
[1] M. Dohlus, PRSTAB, 14 090702 (2011).
[2] A. Marinelli, PRL, 110 264802 (2013).
[3] M. Borland, Advanced Photon Source, LS-287, 2000.
[4] A. Halavanau, Proc. IPAC15, TUPMA007 (2015).

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WEP069

Minimization of the Emittance Growth Induced by Coherent Synchrotron Radiation in Arc Compressor

711

X.Y. Huang, X. Cui, Y. Jiao, G. Xu
IHEP, Beijing, People's Republic of China

Funding: Supported by National Natural Science Foundation of China (11475202, 11405187).
Coherent synchrotron radiation (CSR) is a critical issue when electron bunches with short bunch length and high peak current transporting through a bending system in high-brightness light sources and linear colliders. For example, a high peak current of electron beam can be achieved by using magnetic bunch compressor, however, CSR induced transverse emittance growth will limit the performance of bunch compressor. In this paper, based on our 'two-dimensional point-kick analysis', an arc compressor with high compression factor is studied. Through analytical and numerical research, an easy optics design technique is introduced that could minimize the emittance dilution within this compressor. It is demonstrated that the strong compression of bunch length and the transverse emittance preservation can be achieved at the same time.

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WEP070

Start-to-End Simulation of the LCLS-II Beam Delivery System with Real Number of Electrons

714

J. Qiang, C.E. Mitchell, C. F. Papadopoulos, M. Venturini
LBNL, Berkeley, California, USA
Y. Ding, P. Emma, Z. Huang, G. Marcus, Y. Nosochkov, T.O. Raubenheimer, L. Wang, M. Woodley
SLAC, Menlo Park, California, USA

The LCLS-II as a next generation high repetition rate FEL based X-ray light source will enable significant scientific discoveries. In this paper, we report on the progress in the design of the accelerator beam delivery system through start-to-end simulations. We will present simulation results for three cases, 20 pC, 100 pC and 300 pC that are transported through the hard X-ray line and the soft X-ray line for FEL radiation.

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WEP073

Dispersion of Correlated Energy Spread Electron Beams in the Free Electron Laser

718

L.T. Campbell
USTRAT/SUPA, Glasgow, United Kingdom
A.R. Maier
CFEL, Hamburg, Germany

The effect of a correlated linear energy chirp in the electron beam in the FEL, and how to compensate for its effects by using an appropriate linear taper of the undulator magnetic field have previously been investigated considering relatively small chirps. In the following, it is shown that larger linear energy chirps, such as those found in beams produced by laser-plasma accelerators, exhibit dispersive effects in the undulator, and require a non-linear taper on the undulator field to properly optimise.

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