FEL2013 - List of Keywords (gun)

Paper	Title	Other Keywords	Page
MOPSO43	High Power Laser Transport System for Laser Cooling to Counteract Back-Bombardment Heating in Microwave Thermionic Electron Guns	laser, vacuum, electron, coupling	75
	J.M.D. Kowalczyk, M.R. Hadmack, J. Madey, E.B. Szarmes, M.H.E.H. Vinci University of Hawaii, Honolulu, HI, USA
	Funding: This work was funded by the Department of Homeland Security through grant #2011-DN-077-ARI055-03. Heat from a high power, short pulse laser deposited on the surface of a thermionic electron gun cathode will diffuse into the bulk producing a surface cooling effect that counteracts the electron back-bombardment (BB) heating intrinsic to the gun. The resulting constant temperature stabilizes the current allowing extension of the gun’s peak current and duty cycle. To enable this laser cooling, high power laser pulses must be transported to the high radiation zone of the electron gun, and their transverse profile must be converted from Gaussian to top-hat to uniformly cool the cathode. A fiber optic transport system is simple, inexpensive, and will convert a Gaussian to a top-hat profile. Coupling into the fiber efficiently and without damage is difficult as tight focusing is required at the input and, if coupled in air, the high fluence will breakdown the air resulting in lost energy. We have devised a vacuum fiber coupler (VFC) that allows the focus to occur in vacuum, avoiding the breakdown of air, and have successfully transported 10 ns long, 85 mJ pulses from a 1064 nm Nd:YAG laser through 20 m of 1 mm diameter fiber enabling testing of the laser cooling concept.

MOPSO44	Laser Cooling to Counteract Back-Bombardment Heating in Microwave Thermionic Electron Guns	laser, cathode, electron, simulation	79
	J.M.D. Kowalczyk, M.R. Hadmack, J. Madey University of Hawaii, Honolulu, HI, USA
	Funding: This work was funded by the Department of Homeland Security through grant #2011-DN-077-ARI055-03. A theoretical study of the use of laser cooling to counteract electron back-bombardment heating (BB) in thermionic electron guns is presented. Electron beams with short bunches, minimum energy spread, and maximum length pulse trains are required for many applications, including the inverse-Compton X-ray source being developed at UH. Currently, these three electron beam parameters are limited by BB which causes the cathode temperature and emission current to increase leading to beam loading. Beam loading elongates the bunches by shifting the electrons’ relative phases, introduces energy spread by reducing the energy of electrons emitted later in the macropulse, and forces the use of shorter macropulses to minimize energy spread. Irradiation of the electron gun cathode with a short laser pulse prior to beam acceleration allows the laser heat to diffuse into the cathode bulk effectively cooling the surface and counteracting the BB. Calculation of the the cooling produced by laser pulses of various duration and energy is presented.

MOPSO76	FEL Operation With the Superconducting RF Photo Gun at ELBE	laser, FEL, SRF, cavity	136
	J. Teichert, A. Arnold, H. Büttig, M. Justus, U. Lehnert, P.N. Lu, P. Michel, P. Murcek, R. Schurig, W. Seidel, H. Vennekate, R. Xiang HZDR, Dresden, Germany T. Kamps, J. Rudolph HZB, Berlin, Germany I. Will MBI, Berlin, Germany
	The superconducting RF photoinjector (SRF gun) operating with a 31/2-cell niobium cavity and Cs2Te photocathodes is installed at the ELBE radiation center. The gun provides beams for ELBE as well as in a separate diagnostics beam line for beam parameter measurements. Since 2012 a new UV driver laser system developed by MBI has been installed for the SRF gun . It delivers CW or bust mode pulses with 13 MHz repetition rate or with reduced rates of 500, 200, and 100 kHz at an average UV power of about 1 W. The new laser allows the gun to serve as the driver for the infrared FELs at ELBE. In the first successful experiment a 250 μA beam with 3.3 MeV from SRF gun was injected into ELBE, further accelerated in the ELBE superconducting linac modules and then guided to the U100 undulator. First lasing was achieved at the wavelength of 41 μm. The spectrum, detuning curve and further parameters were measured.

MOPSO77	Timing Jitter Measurements of the SwissFEL Test Injector	laser, electron, cathode, feedback	140
	C. Vicario, B. Beutner, M.C. Divall, C.P. Hauri, S. Hunziker, M.G. Kaiser, M. Luethi, M. Pedrozzi, T. Schietinger PSI, Villigen PSI, Switzerland C.P. Hauri EPFL, Lausanne, Switzerland
	To reach nominal bunch compression and FEL performance of SwissFEL with stable beam conditions for the users, less than 40fs relative rms jitter is required from the injector. Phase noise measurement of the gun laser oscillator shows an exceptional 30fs integrated rms jitter. We present these measurements and analyze the contribution to the timing jitter and drift from the rest of the laser chain. These studies were performed at the SwissFEL injector test facility, using the rising edge of the Schottky-scan curve and on the laser system using fast digital signal analyzer and photodiode, revealing a residual jitter of 150fs at the cathode from the pulsed laser amplifier and beam transport, measured at 10Hz. Spectrally resolved cross-correlation technique will also be reviewed here as a future solution of measuring timing jitter at 100Hz directly against the pulsed optical timing link with an expected resolution in the order of 50fs. This device will provide the signal for feedback systems compensating for long term timing drift of the laser for the gun as well as for the pulsed lasers at the experimental stations.

TUOBNO01	Beam Diagnostics for Coherent Optical Radiation Induced by the Microbunching Instability	linac, laser, diagnostics, radiation	169
	A.H. Lumpkin Fermilab, Batavia, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The generation of the ultrabright beams required by modern free-electron lasers (FELs) has generally relied on chicane-based bunch compressions that often result in the microbunching instability. Following compression, spectral enhancements can extend even into the visible wavelengths through the longitudinal space charge impedances. Optical transition radiation (OTR) screens have been extensively used for transverse electron beam size measurements for the bright beams, but the presence of longitudinal microstructures (microbunching) in the electron beam or the leading edge spikes can result in strong, localized coherent enhancements (COTR) that mask the actual beam profile. We now have evidence for the effects in both rf photocathode-gun injected linacs* and thermionic-cathode-gun injected linacs*. Since the first observations, significant efforts have been made to characterize, model, and mitigate COTR effects on beam diagnostics. An update on the state-of-the-art for diagnosing these effects will be given as illustrated by examples at APS, LCLS, SCSS, SACLA, and NLCTA. A.H. Lumpkin et al.,Phys. Rev. ST Accel. Beams 12, 040704 (2009). **H. Tanaka,"Commissioning of the Japanese XFEL at Spring8, Proceedings of IPAC2011, San Sebastián, Spain, 21-25 (2011).
	Slides TUOBNO01 [1.805 MB]

TUOBNO03	An RF Deflecting Cavity Based Spreader System for Next Generation Light Sources	FEL, cavity, dipole, electron	173
	C. Sun, L.R. Doolittle, P. Emma, J.-Y. Jung, M. Placidi, A. Ratti LBNL, Berkeley, California, USA
	Lawrence Berkeley National Laboratory (LBNL) is developing design concepts for a multi-beamline (up to 10 lines) soft x-ray FEL array powered by a superconducting linear accelerator with a high bunch repetition rate of approximately one MHz. The FEL array requires a beam spreader system which can distribute individual electron bunches from the linac to each independently configurable beamline. We propose a new spreader system using RF deflecting cavities to deflect electron bunches as an alternative design to the fast kicker scheme. This RF approach offers more stable deflection amplitude while removing the limitations on the bunch repetition rate characteristic of the kicker approach. In this work, we describes the design concept of this RF based spreader system, including technical choices, design parameters and beamline optics. [1] M. Placidi et al., Proceedings of IPAC2012, New Orleans, Louisiana, USA, pp.1765-1767
	Slides TUOBNO03 [1.391 MB]

TUICNO01	Progress in SRF Guns	SRF, electron, cavity, cathode	176
	S.A. Belomestnykh BNL, Upton, Long Island, New York, USA
	Funding: Work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE In the last couple of years great progress has been made in the commissioning and operation of SRF electron beam sources. Both elliptical cavity designs and reentrant cavities have been developed. This talk will review recent progress in SRF guns.
	Slides TUICNO01 [12.748 MB]

TUOCNO03	Progress in a Photocathode DC Gun at the Compact ERL	vacuum, cathode, acceleration, high-voltage	184
	N. Nishimori, R. Hajima, S.M. Matsuba, R. Nagai JAEA, Ibaraki-ken, Japan Y. Honda, T. Miyajima, M. Yamamoto KEK, Ibaraki, Japan H. Iijima, M. Kuriki HU/AdSM, Higashi-Hiroshima, Japan M. Kuwahara Nagoya University, Nagoya, Japan
	Photocathode DC gun to produce a train of electron bunch at high-average current and small emittance is a key component of advanced accelerators for high-power beams. However, DC guns operated at a voltage above 350 kV have suffered from field emitted electrons from a support rod since the development of Lasertron in 1980's. This critical issue has been resolved by a novel configuration, segmented insulator and guard rings, adopted in a DC gun at JAEA and stable application of high voltage at 550 kV has been demonstrated. The gun has been installed at the Compact ERL at KEK and ready for the beam generation. Similar type of DC guns are under development at KEK, Cornell, JLAB and IHEP. In this talk, we present progress in photocathode DC gun for high voltage and small emittance.
	Slides TUOCNO03 [4.946 MB]

TUOCNO06	Slice Emittance Optimization at the SwissFEL Injector Test Facility	emittance, optics, quadrupole, laser	200
	E. Prat, M. Aiba, S. Bettoni, B. Beutner, M.W. Guetg, R. Ischebeck, S. Reiche, T. Schietinger PSI, Villigen PSI, Switzerland
	Slice emittance measurements in the SwissFEL injector test facility have demonstrated emittances for the 10pC-200pC bunch charges which are well below the tight requirements of SwissFEL. Results, emittance tuning strategy and measurement methods are reported.
	Slides TUOCNO06 [0.537 MB]

TUPSO03	Dark Current Transport and Collimation Studies for SwissFEL	simulation, emittance, wakefield, cathode	209
	S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche, L. Stingelin PSI, Villigen PSI, Switzerland
	In all accelerating cavities a non negligible background of electrons can be generated by field emission (dark current), transported and further accelerated. A careful estimate of the transport of the dark current is crucial in order to minimize radiation damage to the components and activation of the machine. This paper describes the generation and the transport of dark current from the SwissFEL photo injector downstream of the accelerator. The analysis is based on numerical simulations and experimental measurements performed at the SwissFEL Injector Test Facility (SITF). In the simulations the charge distribution is generated by an emission model based on the Fowler-Nordheim equation taking into account the filling time of the cavity and then tracked through the machine. This model has been used to analyze the impact of a low energy collimation system upstream of the first travelling wave accelerating structure on the dark current transport. A slit with several apertures has been installed in the SITF to benchmark the simulations and to verify the impact of the wakefields on the nominal beam.

TUPSO07	SwissFEL Injector Design: An Automatic Procedure	emittance, laser, simulation, space-charge	219
	S. Bettoni, M. Pedrozzi, S. Reiche PSI, Villigen PSI, Switzerland
	The first section of photo-injectors are dominated by space charge effects due to the low beam energy and the high charge density. An optimization of several parameters such as the emittance and the mismatch along the bunch has to be carried out in order to optimize the final performances of the machine. We focus on the performances of the gun developed at PSI, planned to be installed in the mid of this year in the SwissFEL Injector Test Facility (SITF). Due to the number of variables and constraints we developed a code to automatically perform such an optimization. We used this code to optimize the 200 pC operating point of SwissFEL and to fine tune other charges configurations from 10 pC, obtaining considerably reduction of the slice emittance as compared to the CTF gun, presently installed in the SITF and on which the old lattice optimization was based. The same code with minor modifications has been successfully applied to the facility.

TUPSO21	SwissFEL Cathode Load-lock System	cathode, vacuum, laser, extraction	259
	R. Ganter, M. Bopp, N. Gaiffi, T. Le Quang, M. Pedrozzi, M. Schaer, T. Schietinger, L. Schulz, L. Stingelin, A. Trisorio PSI, Villigen PSI, Switzerland
	The SwissFEL electron source is an RF photo-injector in which the photo-cathode plug can be exchanged. Without load-lock, the cathode exchange takes about one week and cathode surface gets contaminated in the atmosphere during installation, leading to unpredictable quantum efficiency (QE) fluctuations. This motivated the construction of a load lock system to prepare and insert cathodes in the photo-injector. This load lock system consists of three parts: the preparation chamber, the transportable vacuum suitcase and the gun load lock chamber. This three parts system gives the possibility to prepare the cathode surface with methods like vacuum firing and plasma cleaning. The QE can be checked and the plug can be inserted in the gun without breaking vacuum. This will allow establishing an optimized a reproducible cathode preparation procedure. Since several cathodes can be loaded in advance, the exchange procedure reduces the machine shutdown to a few hours (shorter RF conditioning). The system is described and first experience with its use is reported.

TUPSO28	Development of Photocathode RF-gun at PAL	laser, emittance, coupling, electron	279
	J.H. Hong, J.H. Han, H.-S. Kang, Y.W. Parc, S.J. Park, Y.J. Park PAL, Pohang, Kyungbuk, Republic of Korea I.S. Ko POSTECH, Pohang, Kyungbuk, Republic of Korea
	We are developing two types of S-band photocathode RF-guns for the X-ray free electron laser (XFEL) at Pohang Accelerator Laboratory (PAL). One is a 1.6-cell RF-gun with a dual side coupler and two pumping ports. This RF-gun is similar to the earlier guns developed at PAL. The other one is a 1.5-cell RF-gun with a coaxial coupler and a cathode preparation system. This RF-gun is similar to the DESY-type L-band RF-gun. We have designed and fabricated two types of RF-guns. In this paper we introduce and compare two different RF-guns.

TUPSO30	Conditioning Status of the First XFEL Gun at PITZ	vacuum, solenoid, cathode, cavity	282
	I.I. Isaev, J.D. Good, M. Groß, L. Hakobyan, L. Jachmann, M. Khojoyan, W. Köhler, G. Kourkafas, M. Krasilnikov, D. Malyutin, B. Marchetti, R. Martin, A. Oppelt, M. Otevřel, B. Petrosyan, D. Richter, A. Shapovalov, F. Stephan, G. Vashchenko, R.W. Wenndorff DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria P. Boonpornprasert, S. Rimjaem Chiang Mai University, Chiang Mai, Thailand M.A. Nozdrin JINR, Dubna, Moscow Region, Russia G. Pathak Uni HH, Hamburg, Germany
	The paper describes the recent results of conditioning and dark current measurements for the photocathode RF gun at the photoinjector test facility at DESY, Zeuthen site (PITZ). The aim of PITZ is to develop and operate an optimized photo injector for free electron lasers and linear accelerators which require high quality beams. In order to get high gradients in the RF gun extensive conditioning is required. A data analysis of the conditioning process is based on data saved by a Data Acquisition system (DAQ). Conditioning results of the first gun cavity for the XFEL is presented. The events which occurred during the conditioning are briefly described.

TUPSO32	Project of the Short Pulse Facility at KAERI	electron, quadrupole, kicker, bunching	287
	N. Vinokurov, S.V. Miginsky BINP SB RAS, Novosibirsk, Russia S. Bae, B.A. Gudkov, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S.V. Miginsky, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov KAERI, Daejon, Republic of Korea N. Vinokurov NSU, Novosibirsk, Russia
	Funding: This work is supported by the WCI Program of the National Research Foundation of Korea funded by the Ministry of Education, Science, and Technology of Korea (NRF Grant No. WCI 2011-001). The low-energy electron accelerator with subpicosecond electron bunches is under construction at Korea Atomic Energy Research Institute (KAERI). It will serve as the user facility for high-energy ultrafast electron difraction and synchronized high-power terahertz pulse and short x-ray pulse generation. The accelerator consists of RF gun with photocathode and 20-MeV linac. The bunching of accelerated beam is achieved in the ninety-degree achromatic bend. After that fast kicker deflects some of bunches to the target for x-ray generation, other bunches come to terahertz radiator (undulator or multifoil). Bunches from the RF gun are also planned to use for ultrafast electron difraction. Some detailes of the design, current status of the project and future plans are described.

TUPSO41	The Ultrashort Beam Linac System and Proposed Coherent THz Radiation Sources at NSRRC	electron, radiation, linac, undulator	309
	W.K. Lau, A.P. Lee NSRRC, Hsinchu, Taiwan N.Y. Huang, Z.Y. Wei NTHU, Hsinchu, Taiwan
	The NSRRC ultrashort beam facility is a low energy linac system which is being built to produce femtosecond electron beam for novel light source development. Experiments on prebunched THz FEL and inverse Compton scattering x-ray source are under study. The electron source is a 2998 MHz, 1.5-cell thermionic rf gun with uneven full-cell to half-cell field ratio that is optimized to produce a energy-chirped electron beam. With movable slits in its vacuum vessel, the alpha magnet system is served also as a beam selector. Further bunch compression is done by velocity bunching in the rf linac. Recent progress of the construction of this facility as well as the design study of a prebunched THz FEL with this ultrashort electron beam will be reported.

TUPSO47	First Results of a Longitudinal Phase Space Tomography at PITZ	electron, booster, laser, emittance	334
	D. Malyutin, M. Groß, I.I. Isaev, M. Khojoyan, G. Kourkafas, M. Krasilnikov, B. Marchetti, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany
	The Photo Injector Test facility at DESY, Zeuthen Site (PITZ), was established as a test stand of the electron source for FLASH and the European X-ray Free Electron Laser (XFEL). One of the tasks at PITZ is the detailed characterization of longitudinal properties of the produced electron bunches. The measurements of the electron bunch longitudinal phase space can be done by tomographic methods using measurements of the momentum spectra by varying the electron bunch energy chirp. At PITZ the energy chirp of the electron bunch can be changed by varying the RF phase of the accelerating structure downstream the gun. The resulting momentum distribution can be measured in a dispersive section installed downstream the accelerating structure. The idea of the measurement and the tomographic reconstruction technique is described in this paper. The setup and first measurement results of the bunch longitudinal phase space measurements using the tomographic technique for several electron bunch charges, including 20 pC, 100 pC and 1 nC, are presented as well.

TUPSO50	Numerical Study on Electron Beam Properties in Triode Type Thermionic RF Gun	cavity, cathode, electron, FEL	344
	M. Mishima, M. Inukai, T. Kii, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, K. Torgasin, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	The KU-FEL(Kyoto University- Free Electron Laser) facility uses a thermionic 4.5 cell S-band RF gun for electron beam generation because of such advantages over photocathode rf guns as lower cost, higher average current, longer cathode lifetime, and less vacuum requirement. The main disadvantage of using a thermionic RF gun is the back bombardment effect, which causes energy drop in macro pulse of FEL. A triode structure for RF gun was designed in order to minimize the inherent back-bombardment effect. The 2D-simulation has shown significant reduction of back-bombardment power, longitudinal emittance, and an increase of peak current. A coaxial RF cavity was fabricated based on the design for modification of the existing RF gun to a triode type one. The coaxial RF cavity is equipped with gasket tuning system in order to adjust the cavity resonance frequency. However the frequency adjustment by variation of gasket thickness changes the coaxial cavity geometry and might affect the predicted beam optics. Another parameter influencing beam optics is the position of thermionic cathode to be installed in the coaxial cavity, which might vary due to misalignment. K. Masuda, et al., Proceedings of FEL 2009, Liverpool, Pages 281-284 (2009). **K. Torgasin, et al., Proceedings of FEL 2012, Nara(2012).

TUPSO57	Generation of Ultrafast, High-brightness Electron Beams	cathode, electron, cavity, brightness	355
	J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd AES, Princeton, New Jersey, USA
	Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-SC0009556. The production and preservation of ultrafast, high-brightness electron beams is a major R&D challenge for free electron laser (FEL) and ultrafast electron diffraction (UED) because transverse and longitudinal space charge forces drive emittance dilution and bunch lengthening in such beams. Several approaches, such as velocity bunching and magnetic compression, have been considered to solve this problem but each has drawbacks. We present a concept that uses radial bunch compression in an X-band photocathode radio frequency electron gun. By compensating for the path length differential with a curved cathode in an extremely high acceleration gradient cavity, we have demonstrated numerically the possibility of achieving more than an order of magnitude increase in beam brightness over existing electron guns. The initial thermo-structural analysis and mechanical conceptual design of this electron source are presented.

TUPSO58	Developments of a High-average-current Thermionic RF Gun for ERLs and FELs	cavity, cathode, electron, FEL	359
	J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd AES, Princeton, New Jersey, USA
	Funding: Supported by ONR under Contract No. N00014-10-C-0191. The development of a high-average-current thermionic RF gun with the required beam performance for lasing would provide significant cost of ownership and reliability gains for high-average-power energy recovery linac (ERL) and free electron laser (FEL) devices. The beam for these applications requires high quality and high performance, specifically: low transverse emittance, short pulse duration and high average current. We are developing a gridded thermionic cathode embedded in a copper one-and-half cell UHF cavity to generate the electron beam. The fundamental RF and higher harmonics are combined on the grid and a gated DC voltage controls the beam emission from the cathode. Simulations indicate that short pulse ~ 10 psec, < 1 MeV electron beams with low-emittance ~ 15 mm-mrad at currents ≥ 100 mA can be generated. The elimination of sensitive photocathodes and their drive laser systems would provide significant capital cost saving, improved reliability and uptime due to increased robustness and hence operating and lifecycle cost savings as well. We will present the gun design and performance simulations and the progress achieved to date in optimizing the device.

TUPSO63	High Average Brightness Photocathode Development for FEL Applications	cathode, laser, SRF, electron	376
	T. Rao, I. Ben-Zvi, J. Skaritka, E. Wang BNL, Upton, Long Island, New York, USA
	Next generation, high average flux, light sources call for electron beams with high average current as well as high peak brightness. Alkali antimonide cathodes, especially K2CsSb show great promise in delivering electron beams to meet these requirements. In the past few years, there have been a number of experiments geared towards understanding the stoichiometry, crystalline structure, surface properties and sensitivity of these cathodes. At BNL, we have used the x-ray beams from NSLS, CFN and CHESS for in-situ characterization of K-Cs-Sb cathode growth. We have also designed and built several load-lock systems for ex-situ cathode fabrication and quick cathode exchange, to be used with a number of guns. One load-lock system/cathode combination has been tested with a DC gun and the others will be tested with SRF guns operating at 112 and 704 MHz. In this paper we will present the results on improving the QE with excimer laser and the performance of the load-lock/cathode combination in the guns.

TUPSO67	Design Optimization of 100 Kv DC Gun Wehnelt Electrode for FEL Linac at LEBRA	electron, cathode, simulation, extraction	387
	T. Sakai, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Tanaka LEBRA, Funabashi, Japan
	The 125-MeV electron linac at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University has been used for generation of the near infrared FEL and the Parametric X-ray Radiation. In addition, the THz beam generated in a bending magnet became available in the FEL experimental rooms in 2012 by transporting in the FEL optical beam line. The electron gun system for the LEBRA linac can extract the electron beam in three modes, the full bunch, the superimposed and the burst modes. However, the shape of the electron gun wehnelt electrode has not been optimized for the operation with the superimposed or the burst modes; the wehnelt was designed for use in the full bunch operation. The beam trace simulation suggested that the beam extracted from the cathode in the superimposed and the burst modes was slightly lost at the anode due to the strong space charge effect resulted from a high peak extraction current. Therefore, simulation of the beam trace was carried out to optimize the wehnelt shape for the maximum beam extraction efficiency for all the beam operation modes. The present paper reports the result of the simulation on the optimized electron gun design.

TUPSO69	Injector Design Studies for NGLS	emittance, simulation, electron, cathode	391
	C. F. Papadopoulos, P. Emma, D. Filippetto, H.J. Qian, F. Sannibale, M. Venturini, R.P. Wells LBNL, Berkeley, California, USA
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 The APEX project at LBNL is developing an electron injector to operate a high repetition rate x-ray FEL. The injector is based on the VHF gun, a high-brightness, high-repetition-rate photocathode electron gun presently under test at LBNL. The design of the injector is particularly critical because it has to take the relatively low energy beam from the VHF gun, accelerate it at more relativistic energies while simultaneously preserving high-brightness and performing longitudinal compression. The present status of the APEX injector design studies is presented.

TUPSO78	Design of a Collimation System for the Next Generation Light Source at LBNL	collimation, kicker, linac, undulator	410
	C. Steier, P. Emma, H. Nishimura, C. F. Papadopoulos, H.J. Qian, F. Sannibale, C. Sun LBNL, Berkeley, California, USA
	Funding: This work is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The planned Next Generation Light Source at LBNL is designed to deliver MHz repetition rate electron beams to an array of free electron lasers. Because of the high beam power approaching one MW in such a facility, effective beam collimation is extremely important to minimize radiation damage, prevent quenches of superconducting cavities, limit dose rates outside of the accelerator tunnel and prevent equipment damage. We describe the conceptual design of a collimation system, including detailed simulations to verify its effectiveness.

TUPSO82	Spectroscopy System for LCLS Photocathodes	electron, vacuum, cathode, emittance	421
	P. Stefan, A. Brachmann, T. Vecchione SLAC, Menlo Park, California, USA
	Funding: Work supported by US DOE contract DE-AC02-76SF00515. Photocathode reliability is important from an operational standpoint. Unfortunately LCLS copper photocathodes have not always been reliable. Some have operated well for long periods of time while others have required continual maintenance. It is believed that the observed variations in quantum efficiency, emittance and lifetimes are inherently surface related, corresponding to changes in composition or morphology. The RF Electron-gun Cathode, Electron Surface Spectrometer, or RECESS, system has been commissioned to study this by making essential measurements that could not be obtained otherwise. These involve photocathode surface chemical characterization. The system is designed to use a combination of angle-resolved ultraviolet and x-ray photoelectron spectroscopy and is capable of either stand-alone operation or interoperability with a beam line at SSRL. Here we report on the first commissioning spectra and the direction of the project going forward.

TUPSO84	SLAC RF Gun Photocathode Test Facility	laser, emittance, diagnostics, vacuum	427
	T. Vecchione, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, H. Loos, J. Sheppard, S.P. Weathersby, F. Zhou SLAC, Menlo Park, California, USA
	Funding: Work supported by US DOE contract DE-AC02-76SF00515. A RF gun photocathode test facility has been commissioned at SLAC. The facility consists of a S-band gun, high power RF, a UV drive laser and beam diagnostics. Here we report on the capabilities of the facility demonstrated during commissioning. Currently the facility is being used to study in-situ laser processing of copper photocathodes. In the future the facility will be used to study fundamental gun and photocathode performance limitations and enhancement strategies. Eventually it is envisioned to integrate a load lock and plug into the gun enabling the evaluation of high performance surface sensitive semiconductor photocathodes and the incorporation of ex-situ surface science analytical techniques.

TUPSO88	New Concept for the SwissFEL Gun Laser	laser, cathode, FEL, electron	442
	A. Trisorio, M.C. Divall, C.P. Hauri, C. Vicario PSI, Villigen PSI, Switzerland A. Courjaud Amplitude Systemes, Pessac, France
	The operation of Swiss FEL put very stringent constrains on the gun laser system. First the parameters, such as energy stability, timing jitter, double pulse operation, temporal and spatial pulse shape of the ultra-violet laser pulses used to generate the photo-electrons are challenging even for the state of the art laser technologies. Second, the laser system must be extremely stable, reliable and its maintenance cost as low as possible. In this perspective, we prospected for alternative technologies to the well known, commonly used but costly Ti:sapphire laser systems. We show that a hybrid Yb fiber and solid state Yb:CaF2 amplifier system can be a very interesting approach. This gain medium allows the production of sub-500 fs, high fidelity, high stability, high energy pulses in the ultra-violet with low timing jitter. The system profits of the mature, stable direct diode pumping technology and optimized design. It delivers the two high-energy, shaped UV pulses separated by 28 ns to produce the photo-electrons, a short IR probe (<100 fs FWHM) to temporally characterize those pulses and the two stretched IR pulses ( 50 ps FWHM) necessary for the laser heater.

TUPSO92	Dark Current Measurements at the Rossendorf SRF Gun	cavity, cathode, SRF, electron	455
	R. Xiang, A. Arnold, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate HZDR, Dresden, Germany R. Barday, T. Kamps HZB, Berlin, Germany V. Volkov BINP SB RAS, Novosibirsk, Russia
	Funding: the European Community-Research Infrastructure Activity (EuCARD, contract number 227579) and the German Federal Ministry of Education and Research grant 05 ES4BR1/8 In high gradient photo injectors electron field emission creates so-called dark current. The dark current produces beam loss that increases the radiation level, causes damages to the accelerator components, and produces additional background for the users. Field emitted electrons which stay inside the gun, increases RF power consumption and heat load for the superconducting cavities. It is also believed that dark current is the source of local outgassing and plasma formation which can damage sensitive photocathodes. Thus, to understand and control the dark current has become increasingly important for accelerators. In this presentation, we report on dark current measurement at the ELBE SRF Gun at HZDR. The measurements were carried out with the 3.5 cell-cavity SRF gun and Cs2Te photocathodes. We discuss the dark current behavior for different cavity gradients and various solenoid fields. Simulations have been done to understand the experimental results.

WEPSO31	THz Radiation Source Potential of the R&D ERL at BNL	electron, SRF, linac, emittance	566
	D. Kayran, I. Ben-Zvi, Y.C. Jing, B. Sheehy BNL, Upton, Long Island, New York, USA
	Funding: Work supported by BSA DOE, Contract No. DE-AC02-98CH10886 An ampere class 20 MeV superconducting Energy Recovery Linac (ERL) is under commissioning at Brookhaven National Laboratory (BNL) for testing concepts for high-energy electron cooling and electron-ion colliders. This ERL will be used as a test bed to study issues relevant for very high current ERLs. High repetition rate (9.5 MHz), CW operation and high performance of electron beam with some additional components make this ERL an excellent driver for high power coherent THz radiation source. We discuss potential use of BNL ERL as a source of THz radiation and results of the beam dynamics simulation. We present the status and commissioning progress of the ERL. Ilan Ben-Zvi. et al. Coherent harmonic generation of THz radiation using wakefield bunching (presented at this conference)

WEPSO44	Design Studies for FLUTE, A Linac-based Source of Terahertz Radiation	radiation, laser, simulation, linac	598
	S. Naknaimueang, V. Judin, S. Marsching, A.-S. Müller, M.J. Nasse, R. Rossmanith, R. Ruprecht, M. Schreck, M. Schuh, M. Schwarz, M. Weber, P. Wesolowski KIT, Karlsruhe, Germany W. Hillert, M. Schedler ELSA, Bonn, Germany
	FLUTE is a linac-based THz source with nominal beam energy of 40-50 MeV which is presently under construction at KIT. It will be operated in a wide bunch charge range and will use different electron bunch compression schemes. The source will also study different mechanisms of radiation generation and serve as a test facility for related accelerator technology. This contribution presents the results of an overall optimization of the accelerator and a bunch compressor. A usage of a dispersive compressor and a velocity buncher, as well as combination of both are discussed. It is shown that bunch lengths in the range of a few femtoseconds can be achieved at very low bunch charges, while nC-bunches can be compressed down to approximately 200 fs. The utilization of both schemes results in high THz radiation fields at the experimental port.

WEPSO46	Study on the fluctuation of electron beam position in KU-FEL	FEL, electron, cavity, feedback	602
	K. Okumura, M. Inukai, T. Kii, T. Konstantin, K. Masuda, K. Mishima, H. Negm, H. Ohgaki, M. Omer, Y. Tsugamura, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	Stability of electron beam is important for stable FEL operation. In Kyoto University MIR-FEL facility (KU-FEL), a BPM (Beam Position Monitor) system consisting of six 4-button electrode type BPMs was installed for monitoring of the electron beam position. The fluctuation of the electron beam position has been observed in horizontal and vertical directions. The origin of the beam position fluctuation is not clarified. In horizontal direction, the main fluctuation source is expected to be the energy fluctuation. As the one of candidate of the energy fluctuation, the cavity temperature of the RF gun has been suspected because the gun is operated in detuned condition [1] which enhances beam energy dependence on the cavity temperature. Another candidate is considered to be the fluctuation of the RF power fed to the gun. Therefore, we start to study the effect of the cavity temperature and the RF power on the position of electron beam. In this conference, we will present the measured result and numerical evaluation of the beam position dependence on temperature and RF power. [1] H. Zen, et al, “Beam Energy Compensation in a Thermionic RF Gun by Cavity Detuning,” IEEE transaction on nuclear science, Vol.56, No. 3, Pages 1487-1491 (2009)

Paper

Title

Other Keywords

Page

High Power Laser Transport System for Laser Cooling to Counteract Back-Bombardment Heating in Microwave Thermionic Electron Guns

laser, vacuum, electron, coupling

75

J.M.D. Kowalczyk, M.R. Hadmack, J. Madey, E.B. Szarmes, M.H.E.H. Vinci
University of Hawaii, Honolulu, HI, USA

Funding: This work was funded by the Department of Homeland Security through grant #2011-DN-077-ARI055-03.
Heat from a high power, short pulse laser deposited on the surface of a thermionic electron gun cathode will diffuse into the bulk producing a surface cooling effect that counteracts the electron back-bombardment (BB) heating intrinsic to the gun. The resulting constant temperature stabilizes the current allowing extension of the gun’s peak current and duty cycle. To enable this laser cooling, high power laser pulses must be transported to the high radiation zone of the electron gun, and their transverse profile must be converted from Gaussian to top-hat to uniformly cool the cathode. A fiber optic transport system is simple, inexpensive, and will convert a Gaussian to a top-hat profile. Coupling into the fiber efficiently and without damage is difficult as tight focusing is required at the input and, if coupled in air, the high fluence will breakdown the air resulting in lost energy. We have devised a vacuum fiber coupler (VFC) that allows the focus to occur in vacuum, avoiding the breakdown of air, and have successfully transported 10 ns long, 85 mJ pulses from a 1064 nm Nd:YAG laser through 20 m of 1 mm diameter fiber enabling testing of the laser cooling concept.

MOPSO44

Laser Cooling to Counteract Back-Bombardment Heating in Microwave Thermionic Electron Guns

laser, cathode, electron, simulation

79

J.M.D. Kowalczyk, M.R. Hadmack, J. Madey
University of Hawaii, Honolulu, HI, USA

Funding: This work was funded by the Department of Homeland Security through grant #2011-DN-077-ARI055-03.
A theoretical study of the use of laser cooling to counteract electron back-bombardment heating (BB) in thermionic electron guns is presented. Electron beams with short bunches, minimum energy spread, and maximum length pulse trains are required for many applications, including the inverse-Compton X-ray source being developed at UH. Currently, these three electron beam parameters are limited by BB which causes the cathode temperature and emission current to increase leading to beam loading. Beam loading elongates the bunches by shifting the electrons’ relative phases, introduces energy spread by reducing the energy of electrons emitted later in the macropulse, and forces the use of shorter macropulses to minimize energy spread. Irradiation of the electron gun cathode with a short laser pulse prior to beam acceleration allows the laser heat to diffuse into the cathode bulk effectively cooling the surface and counteracting the BB. Calculation of the the cooling produced by laser pulses of various duration and energy is presented.

MOPSO76

FEL Operation With the Superconducting RF Photo Gun at ELBE

laser, FEL, SRF, cavity

136

J. Teichert, A. Arnold, H. Büttig, M. Justus, U. Lehnert, P.N. Lu, P. Michel, P. Murcek, R. Schurig, W. Seidel, H. Vennekate, R. Xiang
HZDR, Dresden, Germany
T. Kamps, J. Rudolph
HZB, Berlin, Germany
I. Will
MBI, Berlin, Germany

The superconducting RF photoinjector (SRF gun) operating with a 31/2-cell niobium cavity and Cs2Te photocathodes is installed at the ELBE radiation center. The gun provides beams for ELBE as well as in a separate diagnostics beam line for beam parameter measurements. Since 2012 a new UV driver laser system developed by MBI has been installed for the SRF gun . It delivers CW or bust mode pulses with 13 MHz repetition rate or with reduced rates of 500, 200, and 100 kHz at an average UV power of about 1 W. The new laser allows the gun to serve as the driver for the infrared FELs at ELBE. In the first successful experiment a 250 μA beam with 3.3 MeV from SRF gun was injected into ELBE, further accelerated in the ELBE superconducting linac modules and then guided to the U100 undulator. First lasing was achieved at the wavelength of 41 μm. The spectrum, detuning curve and further parameters were measured.

MOPSO77

Timing Jitter Measurements of the SwissFEL Test Injector

laser, electron, cathode, feedback

140

C. Vicario, B. Beutner, M.C. Divall, C.P. Hauri, S. Hunziker, M.G. Kaiser, M. Luethi, M. Pedrozzi, T. Schietinger
PSI, Villigen PSI, Switzerland
C.P. Hauri
EPFL, Lausanne, Switzerland

To reach nominal bunch compression and FEL performance of SwissFEL with stable beam conditions for the users, less than 40fs relative rms jitter is required from the injector. Phase noise measurement of the gun laser oscillator shows an exceptional 30fs integrated rms jitter. We present these measurements and analyze the contribution to the timing jitter and drift from the rest of the laser chain. These studies were performed at the SwissFEL injector test facility, using the rising edge of the Schottky-scan curve and on the laser system using fast digital signal analyzer and photodiode, revealing a residual jitter of 150fs at the cathode from the pulsed laser amplifier and beam transport, measured at 10Hz. Spectrally resolved cross-correlation technique will also be reviewed here as a future solution of measuring timing jitter at 100Hz directly against the pulsed optical timing link with an expected resolution in the order of 50fs. This device will provide the signal for feedback systems compensating for long term timing drift of the laser for the gun as well as for the pulsed lasers at the experimental stations.

TUOBNO01

Beam Diagnostics for Coherent Optical Radiation Induced by the Microbunching Instability

linac, laser, diagnostics, radiation

169

A.H. Lumpkin
Fermilab, Batavia, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The generation of the ultrabright beams required by modern free-electron lasers (FELs) has generally relied on chicane-based bunch compressions that often result in the microbunching instability. Following compression, spectral enhancements can extend even into the visible wavelengths through the longitudinal space charge impedances. Optical transition radiation (OTR) screens have been extensively used for transverse electron beam size measurements for the bright beams, but the presence of longitudinal microstructures (microbunching) in the electron beam or the leading edge spikes can result in strong, localized coherent enhancements (COTR) that mask the actual beam profile. We now have evidence for the effects in both rf photocathode-gun injected linacs* and thermionic-cathode-gun injected linacs**. Since the first observations, significant efforts have been made to characterize, model, and mitigate COTR effects on beam diagnostics. An update on the state-of-the-art for diagnosing these effects will be given as illustrated by examples at APS, LCLS, SCSS, SACLA, and NLCTA.
*A.H. Lumpkin et al.,Phys. Rev. ST Accel. Beams 12, 040704 (2009).
**H. Tanaka,"Commissioning of the Japanese XFEL at Spring8, Proceedings of IPAC2011, San Sebastián, Spain, 21-25 (2011).

Slides TUOBNO01 [1.805 MB]

TUOBNO03

An RF Deflecting Cavity Based Spreader System for Next Generation Light Sources

FEL, cavity, dipole, electron

173

C. Sun, L.R. Doolittle, P. Emma, J.-Y. Jung, M. Placidi, A. Ratti
LBNL, Berkeley, California, USA

Lawrence Berkeley National Laboratory (LBNL) is developing design concepts for a multi-beamline (up to 10 lines) soft x-ray FEL array powered by a superconducting linear accelerator with a high bunch repetition rate of approximately one MHz. The FEL array requires a beam spreader system which can distribute individual electron bunches from the linac to each independently configurable beamline. We propose a new spreader system using RF deflecting cavities to deflect electron bunches as an alternative design to the fast kicker scheme. This RF approach offers more stable deflection amplitude while removing the limitations on the bunch repetition rate characteristic of the kicker approach. In this work, we describes the design concept of this RF based spreader system, including technical choices, design parameters and beamline optics.
[1] M. Placidi et al., Proceedings of IPAC2012, New Orleans, Louisiana, USA, pp.1765-1767

Slides TUOBNO03 [1.391 MB]

TUICNO01

Progress in SRF Guns

SRF, electron, cavity, cathode

176

S.A. Belomestnykh
BNL, Upton, Long Island, New York, USA

Funding: Work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE
In the last couple of years great progress has been made in the commissioning and operation of SRF electron beam sources. Both elliptical cavity designs and reentrant cavities have been developed. This talk will review recent progress in SRF guns.

Slides TUICNO01 [12.748 MB]

TUOCNO03

Progress in a Photocathode DC Gun at the Compact ERL

vacuum, cathode, acceleration, high-voltage

184

N. Nishimori, R. Hajima, S.M. Matsuba, R. Nagai
JAEA, Ibaraki-ken, Japan
Y. Honda, T. Miyajima, M. Yamamoto
KEK, Ibaraki, Japan
H. Iijima, M. Kuriki
HU/AdSM, Higashi-Hiroshima, Japan
M. Kuwahara
Nagoya University, Nagoya, Japan

Photocathode DC gun to produce a train of electron bunch at high-average current and small emittance is a key component of advanced accelerators for high-power beams. However, DC guns operated at a voltage above 350 kV have suffered from field emitted electrons from a support rod since the development of Lasertron in 1980's. This critical issue has been resolved by a novel configuration, segmented insulator and guard rings, adopted in a DC gun at JAEA and stable application of high voltage at 550 kV has been demonstrated. The gun has been installed at the Compact ERL at KEK and ready for the beam generation. Similar type of DC guns are under development at KEK, Cornell, JLAB and IHEP. In this talk, we present progress in photocathode DC gun for high voltage and small emittance.

Slides TUOCNO03 [4.946 MB]

TUOCNO06

Slice Emittance Optimization at the SwissFEL Injector Test Facility

emittance, optics, quadrupole, laser

200

E. Prat, M. Aiba, S. Bettoni, B. Beutner, M.W. Guetg, R. Ischebeck, S. Reiche, T. Schietinger
PSI, Villigen PSI, Switzerland

Slice emittance measurements in the SwissFEL injector test facility have demonstrated emittances for the 10pC-200pC bunch charges which are well below the tight requirements of SwissFEL. Results, emittance tuning strategy and measurement methods are reported.

Slides TUOCNO06 [0.537 MB]

TUPSO03

Dark Current Transport and Collimation Studies for SwissFEL

simulation, emittance, wakefield, cathode

209

S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche, L. Stingelin
PSI, Villigen PSI, Switzerland

In all accelerating cavities a non negligible background of electrons can be generated by field emission (dark current), transported and further accelerated. A careful estimate of the transport of the dark current is crucial in order to minimize radiation damage to the components and activation of the machine. This paper describes the generation and the transport of dark current from the SwissFEL photo injector downstream of the accelerator. The analysis is based on numerical simulations and experimental measurements performed at the SwissFEL Injector Test Facility (SITF). In the simulations the charge distribution is generated by an emission model based on the Fowler-Nordheim equation taking into account the filling time of the cavity and then tracked through the machine. This model has been used to analyze the impact of a low energy collimation system upstream of the first travelling wave accelerating structure on the dark current transport. A slit with several apertures has been installed in the SITF to benchmark the simulations and to verify the impact of the wakefields on the nominal beam.

TUPSO07

SwissFEL Injector Design: An Automatic Procedure

emittance, laser, simulation, space-charge

219

S. Bettoni, M. Pedrozzi, S. Reiche
PSI, Villigen PSI, Switzerland

The first section of photo-injectors are dominated by space charge effects due to the low beam energy and the high charge density. An optimization of several parameters such as the emittance and the mismatch along the bunch has to be carried out in order to optimize the final performances of the machine. We focus on the performances of the gun developed at PSI, planned to be installed in the mid of this year in the SwissFEL Injector Test Facility (SITF). Due to the number of variables and constraints we developed a code to automatically perform such an optimization. We used this code to optimize the 200 pC operating point of SwissFEL and to fine tune other charges configurations from 10 pC, obtaining considerably reduction of the slice emittance as compared to the CTF gun, presently installed in the SITF and on which the old lattice optimization was based. The same code with minor modifications has been successfully applied to the facility.

TUPSO21

SwissFEL Cathode Load-lock System

cathode, vacuum, laser, extraction

259

R. Ganter, M. Bopp, N. Gaiffi, T. Le Quang, M. Pedrozzi, M. Schaer, T. Schietinger, L. Schulz, L. Stingelin, A. Trisorio
PSI, Villigen PSI, Switzerland

The SwissFEL electron source is an RF photo-injector in which the photo-cathode plug can be exchanged. Without load-lock, the cathode exchange takes about one week and cathode surface gets contaminated in the atmosphere during installation, leading to unpredictable quantum efficiency (QE) fluctuations. This motivated the construction of a load lock system to prepare and insert cathodes in the photo-injector. This load lock system consists of three parts: the preparation chamber, the transportable vacuum suitcase and the gun load lock chamber. This three parts system gives the possibility to prepare the cathode surface with methods like vacuum firing and plasma cleaning. The QE can be checked and the plug can be inserted in the gun without breaking vacuum. This will allow establishing an optimized a reproducible cathode preparation procedure. Since several cathodes can be loaded in advance, the exchange procedure reduces the machine shutdown to a few hours (shorter RF conditioning). The system is described and first experience with its use is reported.

TUPSO28

Development of Photocathode RF-gun at PAL

laser, emittance, coupling, electron

279

J.H. Hong, J.H. Han, H.-S. Kang, Y.W. Parc, S.J. Park, Y.J. Park
PAL, Pohang, Kyungbuk, Republic of Korea
I.S. Ko
POSTECH, Pohang, Kyungbuk, Republic of Korea

We are developing two types of S-band photocathode RF-guns for the X-ray free electron laser (XFEL) at Pohang Accelerator Laboratory (PAL). One is a 1.6-cell RF-gun with a dual side coupler and two pumping ports. This RF-gun is similar to the earlier guns developed at PAL. The other one is a 1.5-cell RF-gun with a coaxial coupler and a cathode preparation system. This RF-gun is similar to the DESY-type L-band RF-gun. We have designed and fabricated two types of RF-guns. In this paper we introduce and compare two different RF-guns.

TUPSO30

Conditioning Status of the First XFEL Gun at PITZ

vacuum, solenoid, cathode, cavity

282

I.I. Isaev, J.D. Good, M. Groß, L. Hakobyan, L. Jachmann, M. Khojoyan, W. Köhler, G. Kourkafas, M. Krasilnikov, D. Malyutin, B. Marchetti, R. Martin, A. Oppelt, M. Otevřel, B. Petrosyan, D. Richter, A. Shapovalov, F. Stephan, G. Vashchenko, R.W. Wenndorff
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
P. Boonpornprasert, S. Rimjaem
Chiang Mai University, Chiang Mai, Thailand
M.A. Nozdrin
JINR, Dubna, Moscow Region, Russia
G. Pathak
Uni HH, Hamburg, Germany

The paper describes the recent results of conditioning and dark current measurements for the photocathode RF gun at the photoinjector test facility at DESY, Zeuthen site (PITZ). The aim of PITZ is to develop and operate an optimized photo injector for free electron lasers and linear accelerators which require high quality beams. In order to get high gradients in the RF gun extensive conditioning is required. A data analysis of the conditioning process is based on data saved by a Data Acquisition system (DAQ). Conditioning results of the first gun cavity for the XFEL is presented. The events which occurred during the conditioning are briefly described.

TUPSO32

Project of the Short Pulse Facility at KAERI

electron, quadrupole, kicker, bunching

287

N. Vinokurov, S.V. Miginsky
BINP SB RAS, Novosibirsk, Russia
S. Bae, B.A. Gudkov, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S.V. Miginsky, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov
KAERI, Daejon, Republic of Korea
N. Vinokurov
NSU, Novosibirsk, Russia

Funding: This work is supported by the WCI Program of the National Research Foundation of Korea funded by the Ministry of Education, Science, and Technology of Korea (NRF Grant No. WCI 2011-001).
The low-energy electron accelerator with subpicosecond electron bunches is under construction at Korea Atomic Energy Research Institute (KAERI). It will serve as the user facility for high-energy ultrafast electron difraction and synchronized high-power terahertz pulse and short x-ray pulse generation. The accelerator consists of RF gun with photocathode and 20-MeV linac. The bunching of accelerated beam is achieved in the ninety-degree achromatic bend. After that fast kicker deflects some of bunches to the target for x-ray generation, other bunches come to terahertz radiator (undulator or multifoil). Bunches from the RF gun are also planned to use for ultrafast electron difraction. Some detailes of the design, current status of the project and future plans are described.

TUPSO41

The Ultrashort Beam Linac System and Proposed Coherent THz Radiation Sources at NSRRC

electron, radiation, linac, undulator

309

W.K. Lau, A.P. Lee
NSRRC, Hsinchu, Taiwan
N.Y. Huang, Z.Y. Wei
NTHU, Hsinchu, Taiwan

The NSRRC ultrashort beam facility is a low energy linac system which is being built to produce femtosecond electron beam for novel light source development. Experiments on prebunched THz FEL and inverse Compton scattering x-ray source are under study. The electron source is a 2998 MHz, 1.5-cell thermionic rf gun with uneven full-cell to half-cell field ratio that is optimized to produce a energy-chirped electron beam. With movable slits in its vacuum vessel, the alpha magnet system is served also as a beam selector. Further bunch compression is done by velocity bunching in the rf linac. Recent progress of the construction of this facility as well as the design study of a prebunched THz FEL with this ultrashort electron beam will be reported.

TUPSO47

First Results of a Longitudinal Phase Space Tomography at PITZ

electron, booster, laser, emittance

334

D. Malyutin, M. Groß, I.I. Isaev, M. Khojoyan, G. Kourkafas, M. Krasilnikov, B. Marchetti, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany

The Photo Injector Test facility at DESY, Zeuthen Site (PITZ), was established as a test stand of the electron source for FLASH and the European X-ray Free Electron Laser (XFEL). One of the tasks at PITZ is the detailed characterization of longitudinal properties of the produced electron bunches. The measurements of the electron bunch longitudinal phase space can be done by tomographic methods using measurements of the momentum spectra by varying the electron bunch energy chirp. At PITZ the energy chirp of the electron bunch can be changed by varying the RF phase of the accelerating structure downstream the gun. The resulting momentum distribution can be measured in a dispersive section installed downstream the accelerating structure. The idea of the measurement and the tomographic reconstruction technique is described in this paper. The setup and first measurement results of the bunch longitudinal phase space measurements using the tomographic technique for several electron bunch charges, including 20 pC, 100 pC and 1 nC, are presented as well.

TUPSO50

Numerical Study on Electron Beam Properties in Triode Type Thermionic RF Gun

cavity, cathode, electron, FEL

344

M. Mishima, M. Inukai, T. Kii, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, K. Torgasin, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

The KU-FEL(Kyoto University- Free Electron Laser) facility uses a thermionic 4.5 cell S-band RF gun for electron beam generation because of such advantages over photocathode rf guns as lower cost, higher average current, longer cathode lifetime, and less vacuum requirement. The main disadvantage of using a thermionic RF gun is the back bombardment effect, which causes energy drop in macro pulse of FEL. A triode structure for RF gun was designed in order to minimize the inherent back-bombardment effect. The 2D-simulation has shown significant reduction of back-bombardment power, longitudinal emittance, and an increase of peak current*. A coaxial RF cavity was fabricated based on the design for modification of the existing RF gun to a triode type one. The coaxial RF cavity is equipped with gasket tuning system in order to adjust the cavity resonance frequency**. However the frequency adjustment by variation of gasket thickness changes the coaxial cavity geometry and might affect the predicted beam optics. Another parameter influencing beam optics is the position of thermionic cathode to be installed in the coaxial cavity, which might vary due to misalignment.
*K. Masuda, et al., Proceedings of FEL 2009, Liverpool, Pages 281-284 (2009).
**K. Torgasin, et al., Proceedings of FEL 2012, Nara(2012).

TUPSO57

Generation of Ultrafast, High-brightness Electron Beams

cathode, electron, cavity, brightness

355

J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd
AES, Princeton, New Jersey, USA

Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-SC0009556.
The production and preservation of ultrafast, high-brightness electron beams is a major R&D challenge for free electron laser (FEL) and ultrafast electron diffraction (UED) because transverse and longitudinal space charge forces drive emittance dilution and bunch lengthening in such beams. Several approaches, such as velocity bunching and magnetic compression, have been considered to solve this problem but each has drawbacks. We present a concept that uses radial bunch compression in an X-band photocathode radio frequency electron gun. By compensating for the path length differential with a curved cathode in an extremely high acceleration gradient cavity, we have demonstrated numerically the possibility of achieving more than an order of magnitude increase in beam brightness over existing electron guns. The initial thermo-structural analysis and mechanical conceptual design of this electron source are presented.

TUPSO58

Developments of a High-average-current Thermionic RF Gun for ERLs and FELs

cavity, cathode, electron, FEL

359

J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd
AES, Princeton, New Jersey, USA

Funding: Supported by ONR under Contract No. N00014-10-C-0191.
The development of a high-average-current thermionic RF gun with the required beam performance for lasing would provide significant cost of ownership and reliability gains for high-average-power energy recovery linac (ERL) and free electron laser (FEL) devices. The beam for these applications requires high quality and high performance, specifically: low transverse emittance, short pulse duration and high average current. We are developing a gridded thermionic cathode embedded in a copper one-and-half cell UHF cavity to generate the electron beam. The fundamental RF and higher harmonics are combined on the grid and a gated DC voltage controls the beam emission from the cathode. Simulations indicate that short pulse ~ 10 psec, < 1 MeV electron beams with low-emittance ~ 15 mm-mrad at currents ≥ 100 mA can be generated. The elimination of sensitive photocathodes and their drive laser systems would provide significant capital cost saving, improved reliability and uptime due to increased robustness and hence operating and lifecycle cost savings as well. We will present the gun design and performance simulations and the progress achieved to date in optimizing the device.

TUPSO63

High Average Brightness Photocathode Development for FEL Applications

cathode, laser, SRF, electron

376

T. Rao, I. Ben-Zvi, J. Skaritka, E. Wang
BNL, Upton, Long Island, New York, USA

Next generation, high average flux, light sources call for electron beams with high average current as well as high peak brightness. Alkali antimonide cathodes, especially K2CsSb show great promise in delivering electron beams to meet these requirements. In the past few years, there have been a number of experiments geared towards understanding the stoichiometry, crystalline structure, surface properties and sensitivity of these cathodes. At BNL, we have used the x-ray beams from NSLS, CFN and CHESS for in-situ characterization of K-Cs-Sb cathode growth. We have also designed and built several load-lock systems for ex-situ cathode fabrication and quick cathode exchange, to be used with a number of guns. One load-lock system/cathode combination has been tested with a DC gun and the others will be tested with SRF guns operating at 112 and 704 MHz. In this paper we will present the results on improving the QE with excimer laser and the performance of the load-lock/cathode combination in the guns.

TUPSO67

Design Optimization of 100 Kv DC Gun Wehnelt Electrode for FEL Linac at LEBRA

electron, cathode, simulation, extraction

387

T. Sakai, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Tanaka
LEBRA, Funabashi, Japan

The 125-MeV electron linac at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University has been used for generation of the near infrared FEL and the Parametric X-ray Radiation. In addition, the THz beam generated in a bending magnet became available in the FEL experimental rooms in 2012 by transporting in the FEL optical beam line. The electron gun system for the LEBRA linac can extract the electron beam in three modes, the full bunch, the superimposed and the burst modes. However, the shape of the electron gun wehnelt electrode has not been optimized for the operation with the superimposed or the burst modes; the wehnelt was designed for use in the full bunch operation. The beam trace simulation suggested that the beam extracted from the cathode in the superimposed and the burst modes was slightly lost at the anode due to the strong space charge effect resulted from a high peak extraction current. Therefore, simulation of the beam trace was carried out to optimize the wehnelt shape for the maximum beam extraction efficiency for all the beam operation modes. The present paper reports the result of the simulation on the optimized electron gun design.

TUPSO69

Injector Design Studies for NGLS

emittance, simulation, electron, cathode

391

C. F. Papadopoulos, P. Emma, D. Filippetto, H.J. Qian, F. Sannibale, M. Venturini, R.P. Wells
LBNL, Berkeley, California, USA

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The APEX project at LBNL is developing an electron injector to operate a high repetition rate x-ray FEL. The injector is based on the VHF gun, a high-brightness, high-repetition-rate photocathode electron gun presently under test at LBNL. The design of the injector is particularly critical because it has to take the relatively low energy beam from the VHF gun, accelerate it at more relativistic energies while simultaneously preserving high-brightness and performing longitudinal compression. The present status of the APEX injector design studies is presented.

TUPSO78

Design of a Collimation System for the Next Generation Light Source at LBNL

collimation, kicker, linac, undulator

410

C. Steier, P. Emma, H. Nishimura, C. F. Papadopoulos, H.J. Qian, F. Sannibale, C. Sun
LBNL, Berkeley, California, USA

Funding: This work is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
The planned Next Generation Light Source at LBNL is designed to deliver MHz repetition rate electron beams to an array of free electron lasers. Because of the high beam power approaching one MW in such a facility, effective beam collimation is extremely important to minimize radiation damage, prevent quenches of superconducting cavities, limit dose rates outside of the accelerator tunnel and prevent equipment damage. We describe the conceptual design of a collimation system, including detailed simulations to verify its effectiveness.

TUPSO82

Spectroscopy System for LCLS Photocathodes

electron, vacuum, cathode, emittance

421

P. Stefan, A. Brachmann, T. Vecchione
SLAC, Menlo Park, California, USA

Funding: Work supported by US DOE contract DE-AC02-76SF00515.
Photocathode reliability is important from an operational standpoint. Unfortunately LCLS copper photocathodes have not always been reliable. Some have operated well for long periods of time while others have required continual maintenance. It is believed that the observed variations in quantum efficiency, emittance and lifetimes are inherently surface related, corresponding to changes in composition or morphology. The RF Electron-gun Cathode, Electron Surface Spectrometer, or RECESS, system has been commissioned to study this by making essential measurements that could not be obtained otherwise. These involve photocathode surface chemical characterization. The system is designed to use a combination of angle-resolved ultraviolet and x-ray photoelectron spectroscopy and is capable of either stand-alone operation or interoperability with a beam line at SSRL. Here we report on the first commissioning spectra and the direction of the project going forward.

TUPSO84

SLAC RF Gun Photocathode Test Facility

laser, emittance, diagnostics, vacuum

427

T. Vecchione, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, H. Loos, J. Sheppard, S.P. Weathersby, F. Zhou
SLAC, Menlo Park, California, USA

Funding: Work supported by US DOE contract DE-AC02-76SF00515.
A RF gun photocathode test facility has been commissioned at SLAC. The facility consists of a S-band gun, high power RF, a UV drive laser and beam diagnostics. Here we report on the capabilities of the facility demonstrated during commissioning. Currently the facility is being used to study in-situ laser processing of copper photocathodes. In the future the facility will be used to study fundamental gun and photocathode performance limitations and enhancement strategies. Eventually it is envisioned to integrate a load lock and plug into the gun enabling the evaluation of high performance surface sensitive semiconductor photocathodes and the incorporation of ex-situ surface science analytical techniques.

TUPSO88

New Concept for the SwissFEL Gun Laser

laser, cathode, FEL, electron

442

A. Trisorio, M.C. Divall, C.P. Hauri, C. Vicario
PSI, Villigen PSI, Switzerland
A. Courjaud
Amplitude Systemes, Pessac, France

The operation of Swiss FEL put very stringent constrains on the gun laser system. First the parameters, such as energy stability, timing jitter, double pulse operation, temporal and spatial pulse shape of the ultra-violet laser pulses used to generate the photo-electrons are challenging even for the state of the art laser technologies. Second, the laser system must be extremely stable, reliable and its maintenance cost as low as possible. In this perspective, we prospected for alternative technologies to the well known, commonly used but costly Ti:sapphire laser systems. We show that a hybrid Yb fiber and solid state Yb:CaF2 amplifier system can be a very interesting approach. This gain medium allows the production of sub-500 fs, high fidelity, high stability, high energy pulses in the ultra-violet with low timing jitter. The system profits of the mature, stable direct diode pumping technology and optimized design. It delivers the two high-energy, shaped UV pulses separated by 28 ns to produce the photo-electrons, a short IR probe (<100 fs FWHM) to temporally characterize those pulses and the two stretched IR pulses ( 50 ps FWHM) necessary for the laser heater.

TUPSO92

Dark Current Measurements at the Rossendorf SRF Gun

cavity, cathode, SRF, electron

455

R. Xiang, A. Arnold, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate
HZDR, Dresden, Germany
R. Barday, T. Kamps
HZB, Berlin, Germany
V. Volkov
BINP SB RAS, Novosibirsk, Russia

Funding: the European Community-Research Infrastructure Activity (EuCARD, contract number 227579) and the German Federal Ministry of Education and Research grant 05 ES4BR1/8
In high gradient photo injectors electron field emission creates so-called dark current. The dark current produces beam loss that increases the radiation level, causes damages to the accelerator components, and produces additional background for the users. Field emitted electrons which stay inside the gun, increases RF power consumption and heat load for the superconducting cavities. It is also believed that dark current is the source of local outgassing and plasma formation which can damage sensitive photocathodes. Thus, to understand and control the dark current has become increasingly important for accelerators. In this presentation, we report on dark current measurement at the ELBE SRF Gun at HZDR. The measurements were carried out with the 3.5 cell-cavity SRF gun and Cs2Te photocathodes. We discuss the dark current behavior for different cavity gradients and various solenoid fields. Simulations have been done to understand the experimental results.

WEPSO31

THz Radiation Source Potential of the R&D ERL at BNL

electron, SRF, linac, emittance

566

D. Kayran, I. Ben-Zvi, Y.C. Jing, B. Sheehy
BNL, Upton, Long Island, New York, USA

Funding: Work supported by BSA DOE, Contract No. DE-AC02-98CH10886
An ampere class 20 MeV superconducting Energy Recovery Linac (ERL) is under commissioning at Brookhaven National Laboratory (BNL) for testing concepts for high-energy electron cooling and electron-ion colliders. This ERL will be used as a test bed to study issues relevant for very high current ERLs. High repetition rate (9.5 MHz), CW operation and high performance of electron beam with some additional components make this ERL an excellent driver for high power coherent THz radiation source*. We discuss potential use of BNL ERL as a source of THz radiation and results of the beam dynamics simulation. We present the status and commissioning progress of the ERL.
*Ilan Ben-Zvi. et al. Coherent harmonic generation of THz radiation using wakefield bunching (presented at this conference)

WEPSO44

Design Studies for FLUTE, A Linac-based Source of Terahertz Radiation

radiation, laser, simulation, linac

598

S. Naknaimueang, V. Judin, S. Marsching, A.-S. Müller, M.J. Nasse, R. Rossmanith, R. Ruprecht, M. Schreck, M. Schuh, M. Schwarz, M. Weber, P. Wesolowski
KIT, Karlsruhe, Germany
W. Hillert, M. Schedler
ELSA, Bonn, Germany

FLUTE is a linac-based THz source with nominal beam energy of 40-50 MeV which is presently under construction at KIT. It will be operated in a wide bunch charge range and will use different electron bunch compression schemes. The source will also study different mechanisms of radiation generation and serve as a test facility for related accelerator technology. This contribution presents the results of an overall optimization of the accelerator and a bunch compressor. A usage of a dispersive compressor and a velocity buncher, as well as combination of both are discussed. It is shown that bunch lengths in the range of a few femtoseconds can be achieved at very low bunch charges, while nC-bunches can be compressed down to approximately 200 fs. The utilization of both schemes results in high THz radiation fields at the experimental port.

WEPSO46

Study on the fluctuation of electron beam position in KU-FEL

FEL, electron, cavity, feedback

602

K. Okumura, M. Inukai, T. Kii, T. Konstantin, K. Masuda, K. Mishima, H. Negm, H. Ohgaki, M. Omer, Y. Tsugamura, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

Stability of electron beam is important for stable FEL operation. In Kyoto University MIR-FEL facility (KU-FEL), a BPM (Beam Position Monitor) system consisting of six 4-button electrode type BPMs was installed for monitoring of the electron beam position. The fluctuation of the electron beam position has been observed in horizontal and vertical directions. The origin of the beam position fluctuation is not clarified. In horizontal direction, the main fluctuation source is expected to be the energy fluctuation. As the one of candidate of the energy fluctuation, the cavity temperature of the RF gun has been suspected because the gun is operated in detuned condition [1] which enhances beam energy dependence on the cavity temperature. Another candidate is considered to be the fluctuation of the RF power fed to the gun. Therefore, we start to study the effect of the cavity temperature and the RF power on the position of electron beam. In this conference, we will present the measured result and numerical evaluation of the beam position dependence on temperature and RF power.
[1] H. Zen, et al, “Beam Energy Compensation in a Thermionic RF Gun by Cavity Detuning,” IEEE transaction on nuclear science, Vol.56, No. 3, Pages 1487-1491 (2009)