MPI, Muenchen, Germany
Existing relativistic proton (p+) bunches carry large amounts of energy (kJ) and are therefore attractive as drivers for plasma-based particle accelerators, such as the plasma wakefield accelerator or PWFA. However, short (~ps) p+ bunches capable of driving large amplitude (~GV/m) wakefields are not available today. It was recently proposed to use long (~300ps) p+ bunches self-modulated at the plasma wavelength by a transverse two-stream instability in a high-density (~1014-1015/cc) plasma to resonantly drive wakefields*. Based on this idea and on the long term prospect for short p+ bunches a p+-driven PWFA experimental program was proposed to study the acceleration of electrons to the TeV energy range. Initial experiments will use the 450GeV, 1-3·1011 p+ bunches from the CERN SPS and plasmas 5-10m in length. The wakefields will be sampled by an externally injected, low energy (10-20MeV) electron bunch that will gain energy in the GeV range. The experimental plan, as well as the expected results will be presented.
*N. Kumar et al., Phys. Rev. Lett. 104, 255003 (2010).
University of Oslo, Oslo, Norway
UCLA, Los Angeles, California, USA
SLAC, Menlo Park, California, USA
TUB, Beijing, People's Republic of China
MPI, Muenchen, Germany
We present the first results from experimental studies of the electron hose instability in the plasma-wakefield acceleration experiments at FACET. Theory and PIC simulations of an electron beam as it travels through a plasma indicate that hosing may lead to a significant distortion of the transverse phase space. The FACET dump line is equipped with a Cherenkov light based spectrometer which can resolve transverse motion as a function of beam energy. We compare the predictions from simulations and theory to the experimental results obtained.
Paul Scherrer Institut, Villigen, Switzerland
ELETTRA, Basovizza, Italy
JINR, Dubna, Moscow Region, Russia
CERN, Geneva, Switzerland
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
The geometry of an accelerator cavity determines its eigenmodes and thereby its performance characteristics. Therefore, accelerating performance and wakefield characteristics may be improved by an intentional modification of the geometry. However, undesired geometry perturbations due to manufacturing tolerances and operational demands can likewise impair it. To analyze the effects of geometry variations on the eigenmodes, parameter studies are to be undertaken. Using common eigenmode solvers it usually is necessary to perform a full eigenmode computation for each variation step, even if the geometry is only slightly altered. Parameter studies for cavity perturbations thus tend to be computationally extensive and inefficient. In this paper, we present the fundamentals of an efficient eigenmode computation method for varying cavity geometries. Knowing a set of initial eigenmodes of an unperturbed geometry, the method allows expanding the eigenmodes of any geometry that is part of the unperturbed one as a series of the initial eigenmodes. Thereby the computation effort may be significantly reduced. The method is demonstrated by means of analytically evaluable cavity geometries.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
A PIC simulation of the interaction of a positive charged bunch with an e-cloud yields the wake kick from the electrons on the tail particles of the bunch. The wake is induced from a certain offset in the transverse position of the head parts of the bunch which perturb the electron distribution. Such a pre-computed wake functions of each offset part of the bunch are forming a matrix which could be used for investigating single bunch stability under several assumptions. In this paper we investigate the linear scalability of the kick with the offset value. Furthermore we investigate the wake values for different realistic electron densities. Another important parameter for realizing the single bunch stability simulation is the optimal number of bunch slices in longitudinal direction. Here we study the thickness of the slices in conjunction with the mobility of the electrons around the beam axis.
CERN, Geneva, Switzerland
ISIR, Osaka, Japan
Euclid TechLabs, LLC, Solon, Ohio, USA
BNL, Upton, Long Island, New York, USA
ANL, Argonne, USA
SINAP, Shanghai, People's Republic of China
We report observation of a strong wakefield induced energy modulation in an energy-chirped electron bunch passing through a terahertz dielectric-lined waveguide. This modulation can be effectively converted into a spatial modulation by means of a chicane, forming micro-bunches (density modulation) with a periodicity of 0.5 - 1 picosecond, hence capable of driving coherent THz radiation. The experimental results agree well with theoretical predictions.
Euclid TechLabs, LLC, Solon, Ohio, USA
BNL, Upton, Long Island, New York, USA
ANL, Argonne, USA
We report an observation of de-chirping of a linearly chirped (in energy) electron bunch by its passage through a 5 cm long dielectric loaded waveguide structure. The experiment was conducted at the ATF facility at BNL according to a concept dubbed a wakefield silencer originally developed at the ANL AATF*, which involves defining the electron bunch peak current distribution and selecting the optimal waveguide structure suitable for chirp cancellation using self-induced wakefields of the electron bunch. Our experiment has been carried out with a 247 micron triangular beam with a 200 keV energy spread, which was reduced by a factor of three to approximately 70 keV by passing it through a 0.95 THz dielectric-lined structure. Theoretical analysis supports the experimental results. Further exploration and applications of this technique will be discussed as well.
* M. Rosing, J. Simpson, Argonne Wakefield Accelerator Note, WF -144 (1990).
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
In next generation high repetition rate FELs, beam energy loss due to resistive wall wakefields will produce significant amount of heat. The heat load for a superconducting undulator (operating at low temperature), must be removed and will be expensive to remove. In this paper, we study this effect in an undulator proposed for a Next Generation Light Source (NGLS) at LBNL. We benchmark our calculations with measurements at the LCLS and carry out detailed parameter studies using beam from a start-to-end simulation. Our preliminary results suggest that the heat load in the undulator is about 2 W/m with an aperture size of 6 mm for nominal NGLS design parameters.
SSRF, Shanghai, People's Republic of China
SINAP, Shanghai, People's Republic of China
ANL, Argonne, USA
We report on the development of the diagnostic system for the ongoing upgrade to the Argonne Wakefield Accelerator (AWA) facility where the electron drive beam energy will be increased from 15 to 75 MeV. The facility will produce a wide dynamic range of drive bunch train formats ranging from a single microbunch of 100 pC to bunch trains of up to 32 bunches spaced by 769 ps with up to 100 nC per bunch. In addition to standard diagnostics, this drive bunch train format poses two challenges for the diagnostic system: (i) the close spacing of the drive bunches, 769 ps, makes resolving the individual pulses difficult and (ii) the dynamic range of the bunch charge varies by x1000. A critical parameter of the drive bunch train for the wakefield accelerator is the charge along the train. To measure this, we are planning to use a 15 GHz digital oscilloscope to read either a BPM or Bergoz FCT. To handle the large dynamic range of charge, the imaging system will make use of GigE Vision cameras and a distributed system of motorized lenses, with remote control of focus, zoom, and aperture, which are operated through terminal servers and RS232 controllers.
Far-Tech, Inc., San Diego, California, USA
A cavity BPM for 1300 MHz cryomodules is under development by FAR-TECH, Inc. The BPM is capacitively loaded to fit in a small area, and uses a novel coupling scheme which further cuts down space requirements. We discuss status of the fabrication, and eventual plan to test the diagnostic at the ANL Wakefield Accelerator facility.
JLAB, Newport News, Virginia, USA
Muons, Inc, Batavia, USA
Illinois Institute of Technology, Chicago, Illinois, USA
LBNL, Berkeley, California, USA
Start-to-end simulation plays an important role in designing next generation light sources. In this paper, we present recent progress in further development and application of the parallel beam dynamics code, IMPACT, towards the fully start-to-end, multi-physics simulation of a next generation X-ray FEL light source. We will discuss numerical methods and physical models used in the simulation. We will also present some preliminary simulation results of a beam transporting through photoinjector, beam delivery system, and FEL beamlines.
KEK, Ibaraki, Japan
SLAC, Menlo Park, California, USA
The Facility for Advanced Accelerator and Experimental Tests (FACET) at the SLAC National Accelerator Laboratory is designed to deliver a beam with a transverse spot size on the order of 10 μm x 10 μm in a new beamline constructed at the two kilometer point of the SLAC linac. Commissioning the beamline requires mitigating alignment errors and their effects, which can be significant and result in spot sizes orders of magnitude larger. Sextupole and quadrupole alignment errors in particular can introduce errors in focusing, steering, and dispersion which can result in spot size growth, beta mismatch, and waist movement. Alignment errors due to static misalignments, mechanical jitter, energy jitter, and other physical processes can be analyzed to determine the level of accuracy and precision that the beamline requires. It is important to recognize these effects and their tolerances in order to deliver a beam as designed.
SLAC, Menlo Park, California, USA
KEK, Ibaraki, Japan
ANL, Argonne, USA
Illinois Institute of Technology, Chicago, Illinois, USA
ANL, Argonne, USA
Illinois Institute of Technology, Chicago, Illinois, USA
Cesium telluride photocathodes have been fabricated for the Argonne Wakefield Accelerator (AWA) upgrade. The as-deposited photocathodes have consistently produced quantum efficiency values better than 10% with 254 nm light source and with variation of less than 5% over a circular area of 1.2 inches in diameter. We present various characterizations of the photocathode that have performed, including rejuvenation, lifetime, and performance in the L-band AWA photoinjector.
Diamond, Oxfordshire, United Kingdom
JAI, Oxford, United Kingdom
BNL, Upton, Long Island, New York, USA
In new 3rd generation synchrotron light sources with small transverse emittance, higher harmonic cavities (Landau cavities) are installed for bunch lengthening to increase the Touschek lifetime, and to provide Landau damping for beam stability. In this contribution we study the effects of passive Landau cavities in the NSLS-II storage ring for arbitrary fill-patterns with the OASIS tracking code.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
Cockcroft Institute, Warrington, Cheshire, United Kingdom
Paul Scherrer Institut, Villigen, Switzerland
TUB, Beijing, People's Republic of China
CERN, Geneva, Switzerland
IFIC, Valencia, Spain
CERN, Geneva, Switzerland
CIEMAT, Madrid, Spain
The CLIC design relies on the presence of Pre-Damping Rings (PDR) and Damping Rings (DR) to achieve, through synchrotron radiation, the very low emittance needed to fulfill the luminosity requirements. Kicker systems are required to inject and extract the beam from the Pre-Damping and Damping Rings. In order to achieve low beam coupling impedance and reasonable broadband impedance matching to the electrical circuit, striplines have been chosen for the kicker elements. In this paper the final design for the DR kicker is presented, including an optimization of the geometric parameters to achieve the requirements for both characteristic impedance and field homogeneity. In addition, a sensitivity analysis of characteristic impedance and field homogeneity to geometric parameters is reported.
UMAN, Manchester, United Kingdom
CERN, Geneva, Switzerland
Euclid TechLabs, LLC, Solon, Ohio, USA
ANL, Argonne, USA
In general, a high gradient is desirable for future linear collider designs because it can reduce the total linac length. More importantly, the efficiency and the cost to sustain the high gradient should also be considered in the optimization process of an overall design. In this article, we explore a parametric territory of short rf pulse, high group velocity, high frequency, and high gradient, etc., that may lead to an affordable high energy linear collider in the future.
MIT/PSFC, Cambridge, Massachusetts, USA
MIT/PSFC, Cambridge, Massachusetts, USA
SLAC, Menlo Park, California, USA
LLNL, Livermore, California, USA
SLAC, Menlo Park, California, USA
End Station A Test Beam (ESTB) is a test beam line at SLAC in the large End Station A (ESA) experimental hall. It uses a fraction of the bunches of the 14.7 GeV electron beam from the Linac Coherent Light Source (LCLS). ESTB provides a unique test beam for particle and particle astrophysics detector research, accelerator instrumentation and accelerator R&D, development of radiation-hard detectors, and material damage studies. It has exceptionally clean and well-defined secondary electron beams, a huge experimental area and good existing conventional facilities. Recently, a new kicker magnet has been installed to divert 5 Hz of the LCLS low energy beam into the A-line. The full installation will include 4 kicker magnets to allow diversion of high energy beams. A new beam dump and a new Personnel Protection System (PPS) have been built in ESA. In stage II, a secondary hadron target will be able to produce pions up to about 12 GeV/c at 1 particle/pulse. This paper reports the progress on ESTB construction and commissioning.
LANL, Los Alamos, New Mexico, USA
Niowave, Inc., Lansing, Michigan, USA
We present an update on the 2.1 GHz superconducting rf (SRF) photonic band gap (PBG) resonator experiment in Los Alamos. The SRF PBG cell was designed to operate at 2.1 GHz. PBG cells have great potential for outcoupling long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. Using PBG structures in superconducting particle accelerators will allow operation at higher frequencies and moving forward to significantly higher beam luminosities thus leading towards a completely new generation of colliders for high energy physics. However, the technology of fabrication of PBG accelerator cells from niobium has not been well developed to date. Here we report the results of our efforts to fabricate a 2.1 GHz PBG cell and to test it at high gradients in a liquid helium bath at the temperature of 2 Kelvin. The high gradient performance of the cell will be evaluated and the results will be compared to simulations with the CST Microwave Studio.
Northern Illinois University, DeKalb, Illinois, USA
MPQ, Garching, Munich, Germany
DESY, Hamburg, Germany
Tech-X, Boulder, Colorado, USA
Dielectric wakefield accelerators offer many advantages over conventional RF accelerators such as higher acceleration gradients and cost effectiveness. In this paper we describe our experimental plans to demonstrate enhanced transformer ratios with drive and witness bunches. The experiment, will be performed at the Free-electron LASer in Hamburg (FLASH) and utilizes unique pulse shaping capabilities using the dual-frequency superconducting linac to produce high transformer ratios (>2). The beam-driven acceleration mechanism will be based on a cylindrical-symmetric dielectric-lined waveguide (DLW). The experimental setup is described, and start-to-end numerical simulations of the experiment will be presented.
ANL, Argonne, USA
JLAB, Newport News, Virginia, USA
POSTECH, Pohang, Kyungbuk, Republic of Korea
In particle accelerators, bellows are commonly used to connect beamline components. Such bellows are traditionally shielded to lower the beam impedance. Excessive beam impedance can cause overheating in the bellows, especially in high beam current operation. For an SRF-based accelerator, the bellows must also be particulate free. Many designs of shielded bellows incorporate rf slides or fingers that prevent convolutions from being exposed to wakefields. Unfortunately these mechanical structures tend to generate particulates that, if left in the SRF accelerator, can migrate into superconducting cavities, the accelerator's critical components. In this paper, we describe a prototype unshielded bellows that has low beam impedance and no risk of particulate generation.
IHEP, Beijing, People's Republic of China
ANL, Argonne, USA
Euclid TechLabs, LLC, Solon, Ohio, USA
An experimental program to demonstrate staging in a dielectric two-beam wakefield accelerator (dielectric TBA) is being planned at the Argonne Wakefield Accelerator (AWA) facility. We are planning an experiment that both fits in the AWA tunnel and mimics conditions similar to the recently presented conceptual design of a linear collider based on the dielectric TBA. This conceptual design is based on a new parameter space of the TBA scheme utilizing an ultra-short (~20ns) rf pulse in a dielectric TBA. The decelerating structures are driven by a series of drive microbunch trains that are 20 ns in duration and separated by 100 ns. This means that the fast kicker must have an extremely quick risetime as well as become stable within about 50 ns. In this paper, we consider designs for a fast kicker based on RF deflecting cavities and stripline kickers.
Fermilab, Batavia, USA
ANL, Argonne, USA
Northern Illinois University, DeKalb, Illinois, USA
We demonstrate the generation of a train of electron bunches with variable spacing at the Argonne Wakefield Accelerator. The photocathode ultraviolet laser pulse consists of a train of four pulses produced via polarization splitting using two alpha-BBO crystals. The photoemitted electron bunches are then manipulated in a horizontally-bending dogleg with variable longitudinal dispersion. A downstream vertically-deflecting cavity is then used to diagnose the temporal profile of the electron beam. The generation of a train composed of four bunches with tunable spacing is demonstrated. Such train of bunch could have application to, e.g., the resonant excitation of wakefield in dielectric-lined waveguides.
NSC/KIPT, Kharkov, Ukraine
One of wakefield acceleration methods as a slowing medium uses the plasma of a capillary discharge*. The capillary tube is a slowing medium, therefore at propagation in it of a laser pulse or relativistic electron bunches (REB) along with plasma wakefields will be excited an eigen waves of dielectric structure. So far influence of electrodynamic properties of capillary tube material on plasma wakefields is not investigated. On an example of a cylindrical waveguide of gigahertz operation frequency range, we investigate excitation of wakefields by REB in a dielectric waveguide (DW) with the accelerating channel filled with isotropic plasma. The excited field consists of Langmuir wave fields (LW) and fields of eigen waves of DW. At certain plasma density a longitudinal electric field of LW it is significantly less than the similar of DW waves , and transverse components of the LW field are significantly higher than transverse component of DW waves. The periods of these two types of waves generally do not coincide. The range of plasma densities which provides a simultaneous acceleration and focusing of test bunch by LW is found.
* Steinhauer L.C., Kimura W.D. Phys. Rev. STAB. V.9, 081301 (2006).
NSC/KIPT, Kharkov, Ukraine
Omega-P, Inc., New Haven, USA
Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA
The reciprocity principle* is often used in applications of classical electromagnetism. We have employed this principle for testing wakefields set up by an electron bunch in a two-channel coaxial dielectric structure (CDWA)**. For numerical studies we take a ~1-THz fused silica structure which we plan to test at FACET/SLAC; it has dimensions: outer shell, OD=800 μm, ID=500 μm; inner shell OD=181 μm, ID=50 μm. The structure is energized by a 23-GeV, 3-nC bunch having axial RMS size=25 μm. FACET has no drive bunch of annular shape as required for a CDWA; nevertheless, our analytical studies and simulations prove that for the axial wakefield, an annular drive bunch can be replaced by a pencil-like bunch of the same charge traveling in the annular vacuum channel. The longitudinal electric field along the accelerator channel axis (as recorded by a witness bunch) set up by this pencil-like bunch is the same as in the conventional structure of the CDWA. Moreover, if we interchange the drive bunch and the witness bunch, the witness bunch will register the same axial wakefield. However, the stability of the annular bunch is far superior to that of the pencil bunch.
*L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media (Addison-Wesley: Reading, MA, 1960).
**G. Sotnikov et al., PRST-AB, 061302 (2009).
SLAC, Menlo Park, California, USA
FACET (Facility for Advanced Accelerator Experimental Tests) is a new User Facility at SLAC National Accelerator Laboratory. The first User Run started in spring 2012 with 20 GeV, 3 nC electron beams. The facility is designed to provide short (20 um) bunches and small (20 um wide) spot sizes, producing uniquely high power beams. FACET supports studies from many fields but in particular those of Plasma Wakefield Acceleration and Dielectric Wakefield Acceleration. The creation of drive and witness bunches and shaped bunch profiles is possible with "Notch" Collimation. FACET is also a source of THz radiation for material studies. Positrons will be available at FACET in future user runs. We present the User Facility and the available tools and opportunities for future experiments.
Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA
Omega-P, Inc., New Haven, USA
NSC/KIPT, Kharkov, Ukraine
A mm-scale THz Coaxial Dielectric Wakefield Accelerator structure is currently under study by Yale University Beam Physics Lab and collaborators for its performance with annular drive bunches. With our recent successful experiments with the cm-scale GHz rectangular module at AWA/Argonne (USA) and planned activity there with yet another cm-scale GHz coaxial structure, the program of new research has two objectives. The first is to design a structure to produce acceleration gradients approaching 0.35 GeV/m per each nC of drive charge when excited by an annular-like bunch; has an attractive feature that the drive and accelerated bunches both have good focusing and stability properties; and also exhibits a large transformer ratio. The second goal is to build and test the structure at FACET/SLAC (USA). At FACET the structure can be excited only with the available pencil-like drive bunch, but the reciprocity principle allows one to observe some of the properties that would be seen if the excitation were to be by an annular drive bunch. This presentation shows our latest findings, discusses related issues, and discusses our plans for experiments.
LETI, Saint-Petersburg, Russia
Euclid TechLabs, LLC, Solon, Ohio, USA
Analysis of Cherenkov radiation generated by high current relativistic electron bunch passing through a rectangular waveguide with anisotropic dielectric loading has been carried out. Some of the materials used for the waveguide loading of accelerating structures (sapphire) possess significant anisotropic properties. In turn, it can influence excitation parameters of the wakefields generated by an electron beam. Using orthogonal eigenmodes decomposition for the rectangular dielectric waveguide, the analytical expressions for the wakefields have been obtained. Numerical modeling of the longitudinal and transverse (deflecting) wakefields has been carried out as well. It is shown that the dielectric anisotropy causes frequency shift in comparison to the dielectric-lined waveguide with the isotropic dielectric loading.
Saint-Petersburg State University, Saint-Petersburg, Russia
Analysis of a field of a particle bunch in a waveguide loaded with a dielectric is important for the wakefield acceleration technique and for other problems in accelerator physics. We investigate the field of the bunch crossing a boundary between two dielectrics in a circular waveguide. We take into account the finite length of the bunch and analyze both the field structure and the energy loss. Special attention is paid to two cases: the bunch flies from vacuum into dielectric and from dielectric into vacuum. In the first case, investigation of formation of stationary wakefield is of interest (this is important for the wakefield acceleration technique). In the second case, quasi monochromatic wave is generated in the vacuum region. This effect can be used for elaboration of a quasi-monochromatic radiation generator of new type. In both cases we also study dynamics of the energy loss of the bunch.
* T.Yu. Alekhina, A.V. Tyukhtin. Proc. of IPAC2011, San Sebastian, Spain, WEPZ012, p. 2793 (2011).
Saint-Petersburg State University, Saint-Petersburg, Russia
Investigation of the bunch radiation in plasma is important for the plasma wakefield acceleration (PWFA) technique and other applications in accelerator physics. We study the electromagnetic field of small relativistic bunch moving in a magnetized cold plasma along the magnetic field. The energy loss of the bunch was investigated earlier, however the structure of electromagnetic field was not analyzed. We perform analytical and numerical investigation of total field. Different equivalent representations for the field components are obtained. One of them allows separating quasistatic field and radiation one. Method of computation is developed as well. Some interesting physical effects are described. One of them is strong increase of some components of radiation field near the charge motion line (in the case of point charge). The case of a charged disc is considered as well. Prospects of use of obtained results for PWFA are discussed.
ANL, Argonne, USA
Euclid TechLabs, LLC, Solon, Ohio, USA
Illinois Institute of Technology, Chicago, Illinois, USA
Research at the AWA Facility has been focused on the development of electron beam driven wakefield structures. Accelerating gradients of up to 100 MV/m have been excited in dielectric loaded cylindrical structures operating in the microwave range of frequencies. Several upgrades, presently underway, will enable the facility to explore higher accelerating gradients, and also be able to generate longer RF pulses of higher intensity. The upgraded 75 MeV drive beam will consist of bunch trains of up to 32 bunches spaced by 0.77 ns with up to 100 nC per bunch. The RF pulses generated by the drive bunches are expected to reach GW power levels, establishing accelerating gradients of hundreds of MV/m.
Fermilab, Batavia, USA
LANL, Los Alamos, New Mexico, USA
We designed an experiment to conduct a thorough investigation of higher order mode spectrum in a room-temperature traveling-wave photonic band gap (PBG) accelerating structure at 11.7 GHz. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in room-temperature PBG structures was conducted at MIT in 2005. Since then, the importance of that device has been recognized by many research institutions. However, the full experimental characterization of the wakefield spectrum in a beam test has not been performed to date. The Argonne Wakefield Accelerator (AWA) test facility at the Argonne National Laboratory represents a perfect site where this evaluation could be conducted with a single high charge electron bunch and with a train of bunches. We present the design of the accelerating structure that will be tested at AWA in the near future. The structure will consist of sixteen 2pi/3 PBG cells, including two coupler cells. We will also present the results of the initial cold-testing of the few sample cells and a plan for the beam test.
LANL, Los Alamos, New Mexico, USA
We present a design of a superconducting photonic band gap (PBG) accelerator cell operating at 2.1 GHz. The cell is designed with the PBG rods that are specially shaped to reduce the peak magnetic fields and at the same time to preserve its effectiveness for suppression of the higher order modes (HOMs). It has been long recognized that PBG structures have great potential in reducing and even completely eliminating HOMs in accelerators. This is especially beneficial for superconducting electron accelerators for high power free-electron lasers (FELs), which are intended to provide high current continuous duty electron beams. Using PBG structures to reduce the prominent beam-breakup phenomena due to HOMs will allow significantly increased beam-breakup thresholds, and consequently will allow the increase of the frequency of SRF accelerators and the development of novel compact high-current accelerator modules for FELs. High gradient limitations of PBG resonators and the optimal arrangement of the wakefield couplers will be discussed in details in this presentation.
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
UCLA, Los Angeles, California, USA
MPI, Muenchen, Germany
Instituto Superior Tecnico, Lisbon, Portugal
We demonstrate experimentally for the first time the self-modulation of a relativistic electron bunch in a plasma. This demonstration serves as a proof-of-principle test for the mechanisms of transverse self-modulation of particle bunches in plasmas. It indicates the possibility of using long electron or proton bunches as drivers for plasma based accelerators. The long (~5ps) bunch available at BNL-ATF is used in this experiment and in the particle-in-cell OSIRIS. We use the 2D version for cylindrically symmetric geometries. The energy of the beam particles is measured after the plasma exit in the experiment. The obvious energy gain and loss by electrons indicates the excitation of longitudinal wakefields, and hence of transverse focusing fields. Both simulations and experiments show that the electron beamlets are formed at the scale of the plasma wavelength, and the number of beamlets changes as the plasma density is varied. We also measured the variation in beam transverse size downstream from the plasma as well as the variations in coherent transition radiation energy to demonstrate the effect of transverse self–modulation.
RadiaBeam, Santa Monica, USA
Penn State University, University Park, Pennsylvania, USA
Euclid TechLabs, LLC, Solon, Ohio, USA
ANL, Argonne, USA
Diamond has been proposed as a dielectric material for dielectric loaded accelerating (DLA) structures. It has a very low microwave loss tangent, the highest available thermoconductive coefficient and high RF breakdown field. In this paper we report results from a wakefield breakdown test of diamond-loaded rectangular accelerating structure. The high charge beam from the AWA linac (~70 nC, σz = 2.5mm) will be passed through a rectangular diamond - loaded resonator and induce an intense wakefield. A groove is cut on the diamond to enhance the field. Electric fields up to 0.5 GV/m will be present on the diamond surface to attempt to initiate breakdown. A surface analysis of the diamond is be performed before and after the beam test.
Euclid TechLabs, LLC, Solon, Ohio, USA
BNL, Upton, Long Island, New York, USA
ANL, Argonne, USA
We have directly measured the mm-wave wake fields induced by subpicosecond, intense relativistic electron bunches in a diamond loaded accelerating structure via the dielectric wake-field acceleration mechanism. Fields produced by a first, drive, beam were used to accelerate a second, witness, electron bunch which followed the driving bunch at an adjustable distance. The energy gain of the witness bunch as a function of its separation from the drive bunch is a direct measurement of the wake potential. We also present wakefield mapping results for THz quartz structures. In this case decelerating wake inside the bunch is inferred from the drive beam energy modulation.
Euclid TechLabs, LLC, Solon, Ohio, USA
Diamond is being evaluated as a dielectric material for dielectric loaded accelerating structures. It has a very low microwave loss tangent, high thermal conductivity, and supports high RF breakdown fields. We report on progress in fabricating chemical vapor deposited (CVD) diamond materials for cylindrical dielectric structures for use in wakefield particle accelerators. Tubes with inner diameters of 3 and 5 mm have been grown from polycrystalline CVD diamond on mandrels using microwave plasma assisted CVD. The material has been laser trimmed to the desired thicknesses and lengths. In addition, structures with smaller inner diameters (ca. 0.3 mm) have been laser machined from blocks of single crystal diamond grown by CVD. Rectangular (planar) dielectric structures have been constructed from plates of polished CVD diamond. Wakefields in these structures have been studied at the Brookhaven ATF.
Euclid TechLabs, LLC, Solon, Ohio, USA
LETI, Saint-Petersburg, Russia
A complete analytical solution for Cherenkov wakefields generated by an azimuthally asymmetric annular beam propagating in a coaxial two-channel dielectric structure is presented. The transformer ratio of the annular beam Cherenkov wakefield accelerator initially proposed by R. Keinigs, M. Jones* is dramatically increased in comparison to a collinear cylindrical wakefield accelerating structure. A particle-Green's function beam dynamics code BBU-3000** to study beam breakup effects has been upgraded to incorporate annular drive beams and coaxial dielectric wakefield accelerating structures*. Beam dynamics simulations of the annular drive beam with asymmetric charge distributions have been carried out to determine the sensitivity of this method to beam imperfections in GHz and THz frequency ranges.
*R. Keinigs, M. Jones, Proc. 7th Int. Conf. High-Power Part. Beams, Beams’88, Karlsruhe, Germany, 864 (1988).
**P. Schoessow et al., AIP Conference Proceedings 1299, 262 (2010).
Euclid TechLabs, LLC, Solon, Ohio, USA
LETI, Saint-Petersburg, Russia
Recent advances in ferroelectric ceramics have resulted in new possibilities for nonlinear devices for particle accelerator and rf applications. The new FACET (Facility for Advanced Accelerator Experimental Tests) at SLAC provides an opportunity to use the GV/m fields from its intense short pulse electron beams to perform experiments using the nonlinear properties of ferroelectrics. Simulations of Cherenkov radiation in the THz planar and cylindrical nonlinear structures to be used in FACET experiments will be presented. Signatures of nonlinearity are clearly present in the simulations: superlinear scaling of field strength with beam intensity, frequency upshift, and development of higher frequency spectral components.
MPI, Muenchen, Germany
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
Plasma can sustain multi-GV/m longitudinal electric fields that can be used for particle acceleration. In the plasma wakefield accelerator, or PWFA, the wakefields are driven by a single or a train of electron bunches with length comparable to the plasma wavelength. A train of bunches resonantly driving the wakefields can lead to energy gain by trailing particles many times the energy of the incoming drive train particles (large transformer ratio). In proof-of-principle experiments at the Brookhaven National Laboratory Accelerator Test Facility, we demonstrate by varying the plasma density over four orders of magnitude, and therefore the accelerator frequency over two orders of magnitude (~100GHz to a few THz), that trains with ~ps period resonantly drive wakefields in ~1016/cc density plasmas. We also demonstrate energy gain by a trailing witness electron bunch that follows the drive train with a variable delay. Detailed experimental results will be presented.
MPI, Muenchen, Germany
USC, Los Angeles, California, USA
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
IPFN, Lisbon, Portugal
* N. Kumar et al., Phys. Rev. Lett. 104, 255003 (2010).
** J. Vieira et al., submitted (2011).
BNL, Upton, Long Island, New York, USA
An Energy Recovery Linac (ERL) with a high peak electron bunch current is proposed for the Electron-Ion collider (eRHIC) project at the Brookhaven National Laboratory. The present design is based on the multi-pass electron beam transport in existing tunnel of the Relativistic Heavy Ion Collider (RHIC). As a result of a high peak current and a very long beam transport, consideration of various collective beam dynamics effects becomes important. Here we summarize effects of the coherent synchrotron radiation, resistive wall, accelerating cavities and wall roughness on the resulting energy spread and energy loss for several scenarios of the eRHIC project, including results for different electron distributions. A possible correction scheme of accumulated correlated energy spread is also presented.
CLASSE, Ithaca, New York, USA
Minimization of surface fields for a given accelerating rate is the subject of cavity optimization because high electric and magnetic fields lead to field emission or thermal breakdown, respectively. The ratio between peak electric and magnetic fields is a function of geometry and the desired ratio depends on application. For each application the optimal geometry may be different. The elliptic shape of the cavity have been found evolutionarily: starting from a pill-box with beam-pipes having rounded corners. No attempts up to now are known for a search of non-elliptical optimal shapes. Here we describe the search for a cavity shape that has the lowest surface fields, not restricting to the conventional elliptical cavity shapes.
SLAC, Menlo Park, California, USA
The beam for FACET (Facility for Advanced aCcelerator Experimental Tests) at SLAC requires an energy-time correlation ("chirp") along the linac, so it can be compressed in two chicanes, one at the mid point in sector 10 and one W-shaped chicane just before the FACET experimental area. The induced correlation has the opposite sign to the typical used for BNS damping, and therefore any orbit variations away from the center kick the tail of the beam more than the head, causing a shear in the beam and emittance growth. Any dispersion created along the linac has similar effects due to the high (>1.2% rms) energy spread necessary for compression. The initial huge emittances could be reduced by a factor of 10, but were still bigger than expected by a factor of 2-3. Normalized emittance of 2 um-rad in Sector 2 blew up to 150 um-rad in Sector 11 but could be reduced to about 6-12 um-rad for the vertical plane although the results were not very stable. Investigating possible root causes for this, we found locations where up to 10 mm dispersion was created along the linac, which were finally verified with strong steering and up to 7 mm settling of the linac accelerator at these locations.
MPI-P, München, Germany
MPI, Muenchen, Germany
* A. Caldwell, K. Lotov, Plasma wakefield acceleration with a modulated proton bunch, arXiv: 1105.1292 (2011).
URLS, Rome, Italy
INFN/LNF, Frascati (Roma), Italy
MAX-lab, Lund, Sweden
ELETTRA, Basovizza, Italy
CERN, Geneva, Switzerland
CERN, Geneva, Switzerland
CERN, Geneva, Switzerland
IHEP, Beijing, People's Republic of China
CERN, Geneva, Switzerland
EPFL, Lausanne, Switzerland
Paul Scherrer Institut, Villigen, Switzerland
EPFL, Lausanne, Switzerland
CERN, Geneva, Switzerland
CLASSE, Ithaca, New York, USA
Wake fields arise from the discontinuities in a smooth vacuum chamber and will cause energy spread in the passing bunch. In an energy recovery linac (ERL), the spent bunches are decelerated before they are dumped to reuse the beam’s energy for the acceleration of new bunches. While the energy spread accumulated from wakes before deceleration is small compared to the beam’s energy after full acceleration, it becomes more important relatively as the beam’s energy decreases.* Thus, in an ERL wake fields can produce very significant energy spread in the beam as it is decelerated to the energy of the beam dump. We report on calculations of wake fields due to the roughness of the surface of the vacuum chamber walls as it affects the Cornell ERL design. These calculations include the effects from the measured roughness for real vacuum chamber wall surfaces.
* M. Billing, “Effect of Wake Fields in an Energy Recovery Linac”, PAC’09, Vancouver, BC, Canada, 4-8 May 2009.
JLAB, Newport News, Virginia, USA
In applying mode expansion to solve the CSR impedance for a section of toroidal vacuum chamber with rectangular cross section, we identify the eigenvalue problem for the radial eigenmodes which is different from that for cylindrical structures. In this paper, we present the general expressions of the radial eigenmodes, and discuss the properties of the eigenvalues on the basis of the Sturm-Liouville theory.
BNL, Upton, Long Island, New York, USA
* V. Balbekov, PRSTAB, 14, 094401 (2011).
** M. Blaskiewicz, PRSTAB 1, 044201 (1998).
BNL, Upton, Long Island, New York, USA
JLAB, Newport News, Virginia, USA
Muons, Inc, Batavia, USA
Illinois Institute of Technology, Chicago, Illinois, USA
University of Oslo, Oslo, Norway
CERN, Geneva, Switzerland
An optimized design of the main linac accelerating structure for a 500 GeV first stage of CLIC is presented. A similar long-range wakefield suppression scheme as for 3 TeV CLIC based on heavy waveguide damping is adopted. The accelerating gradient for the lower energy machine is 80 MV/m. The 500 GeV design has larger aperture radius in order to increase the maximum bunch charge and length which is limited by the short-range wakefields. The cell geometries have been optimized using a new parametric optimizer for Ace3P and details of the RF cell design are described. Parameters of the full structure are calculated and optimized using a power flow equation.
CERN, Geneva, Switzerland
KEK, Ibaraki, Japan
UMAN, Manchester, United Kingdom
Fermilab, Batavia, USA
ANL, Argonne, USA
Northern Illinois University, DeKalb, Illinois, USA
A 1/2-1-1/2 cell normal-conducting 1.3-GHz deflecting cavity was recently installed at the Argonne Wakefield Accelerator. The cavity will soon be included in a transverse-to-longitudinal phase space exchanger that will eventually be used to shaped the current profile of AWA electron bunches in support of dielectric wakefield experimentS with enhanced transformer ratio. In this paper we report on the initial commissioning of the deflecting cavity including rf-conditioning and beam-based measurement of the deflecting strength.
Euclid TechLabs, LLC, Solon, Ohio, USA
TUB, Beijing, People's Republic of China
ANL, Argonne, USA
CERN, Geneva, Switzerland