HU/AdSM, Higashi-Hiroshima, Japan
Hiroshima University, Higashi-Hiroshima, Japan
PPPL, Princeton, New Jersey, USA
A recently developed novel perturbative Hamiltonian transformation method which allows the determination of approximate matched kinetic quasi-equilibrium solutions for an intense charged particle beam propagating through a periodic focusing quadrupole lattice is presented.* Using this method we have identified numerically the class of self-consistent periodic kinetic 'equilibria' for intense beam propagation in alternating-gradient focusing systems, and extended the nonlinear perturbative particle simulation method to intense beam propagation in such systems. The new method has been implemented in the nonlinear perturbative particle-in-cell code BEST which is used to study properties of the newly constructed beam 'equilibria'. The results of these studies are presented and analyzed in detail.
* E.A. Startsev, R.C. Davidson and M. Dorf, Phys. Rev. ST Accel. Beams 13, 064402 (2010).
LBNL, Berkeley, California, USA
The Neutralized Drift Compression Experiment (NDCX-I) generates high intensity ion beams to explore Warm Dense Matter physics. A ~150 kV, ~500 ns ramped voltage pulse is applied to a ~300 keV, 5-10 μs, 25 mA K+ ion beam across a single induction gap. The velocity modulated beam compresses longitudinally during ballistic transport along a space-charge-neutralizing plasma transport line, resulting in ~3A peak current with ~2-3 ns pulse durations (FWHM) at the target plane. Transverse final focusing is accomplished with a ~8 T, 10 cm long pulsed solenoid magnet. Time-dependent focusing in the induction gap, and chromatic aberrations in the final focus optics limit the peak fluence at the target plane for the compressed beam pulse. We report on time-dependent phase space measurements of the compressed pulse in the ballistic transport beamline, and measurement of the time-dependent radial impulses derived from the interaction of the beam and the induction gap voltage. We present results of start-to-end simulations to benchmark the experiments. Fast correction strategies are discussed with application to both NDCX-I and to the new NDCX-II accelerator.
Korea Basic Science Institute, Busan, Republic of Korea
Pusan National University, Pusan, Republic of Korea
RIKEN Nishina Center, Wako, Japan
The establishment of a compact linear accelerator is in progress by Korea Basic Science Institute. The main capability of this facility is the production of multiply ionized metal clusters and the generation of intense beams of highly charged ions for material, medical and nuclear physical research. To generate the intense beam of highly charged ions, we will develop an Electron Cyclotron Resonance Ion Source (ECRIS) using 28GHz microwaves. For this ECRIS, the designing of a superconducting magnet, microwave inlet, beam extraction, and plasma chamber were in progress. A superconducting magnet system have also being developed. In this presentation, I report the current status of our compact linear accelerator development and future plan.
UCLA, Los Angeles, California, USA
SLAC, Menlo Park, California, USA
LANL, Los Alamos, New Mexico, USA
Recent experiments on former facility FFTB at SLAC has demonstrated that a single electron beam driven Plasma Wakefield Accelerator (PWFA) can be produced with an accelerating gradient of 52 GeV/m over a meter-long scale*. If another electron bunch is properly loaded into such a wakefield, it will obtain a high energy gain in a short distance as well as a small energy spread. Such PWFA experiment with two bunches will be performed in FACET, which is a new facility at SLAC**. Simulation results show that with possible beam parameters in FACET the first electron bunch (with less current than that in the FFTB experiment) can still produce a meter-long plasma column with a density of 5x1016 cm-3 via field ionization when we use a gas with a lower ionization energy. The second electron bunch can have a 10 GeV energy gain with a very narrow energy spread. If a pre-ionized plasma is used instead of the neutral gas, the energy gain of the second bunch can be enhanced to 30 GeV.
* I. Blumenfeld et al., Nature 445, 741 (2007).
** M. J.Hogan, et al.,NewJ. Phys.12, 055030(2010).
Muons, Inc, Batavia, USA
Old Dominion University, Norfolk, Virginia, USA
LBNL, Berkeley, California, USA
ANL, Argonne, USA
Fermilab, Batavia, USA
Voss Scientific, Albuquerque, New Mexico, USA
Many present and future particle accelerators are limited by the maximum electric gradient and peak surface fields that can be realized in RF cavities. Despite considerable effort, a comprehensive theory of RF breakdown has not been achieved, and mitigation techniques to improve practical maximum accelerating gradients have had only limited success. Recent studies have shown that high gradients can be achieved quickly in 805 MHz RF cavities pressurized with dense hydrogen gas without the need for long conditioning times, because the dense gas can dramatically reduce dark currents and multipacting. In this project we use this high pressure technique to suppress effects of residual gas and geometry found in evacuated cavities to isolate and study the role of the metallic surfaces in RF cavity breakdown as a function of radiofrequency and surface preparation. A 1.3-GHz RF test cell with replaceable electrodes (e.g. Mo, Cu, Be, W, and Nb) has been built, and a series of detailed experiments is planned at the Argonne Wakefield Accelerator. These experiments will be followed by additional experiments using a second test cell operating at 402.5 MHz.
BINP SB RAS, Novosibirsk, Russia
University of Chicago, Chicago, Illinois, USA
Tech-X, Boulder, Colorado, USA
BNL, Upton, Long Island, New York, USA
Next generation ion colliders will require effective cooling of high-energy hadron beams. Coherent electron cooling (CEC) can in principle cool relativistic hadron beams on orders-of-magnitude shorter time scales than other techniques. We present Vlasov-Poisson and delta-f particle-in-cell (PIC) simulations of a CEC modulator section. These simulations correctly capture the subtle time and space evolution of the density and velocity wake imprinted on the electron distribution via anisotropic Debye shielding of a drifting ion. We consider 1D and 2D reduced versions of the problem, and compare the exact solutions of Wang and Blaskiewicz with Vlasov-Poisson and delta-f PIC simulations. We also consider interactions under non-ideal conditions where there is a density gradient in the electron distribution, and present simulations of the ion wake.
* V.N. Litvinenko and Y.S. Derbenev, Phys. Rev. Lett. 102, 114801 (2009).
Duke ECE, Durham, North Carolina, USA
UCLA, Los Angeles, California, USA
LBNL, Berkeley, California, USA
The numerical modeling code INF&RNO (INtegrated Fluid & paRticle simulatioN cOde, pronounced "inferno") is an efficient 2D cylindrical code to model the interaction of a short laser pulse with an underdense plasma. The code is based on an envelope model for the laser while either a particle-in-cell (PIC) or a fluid description can be used for the plasma. The effect of the laser pulse on the plasma is modeled with the time-averaged ponderomotive force. These and other features allow for a significant speedup compared to standard full PIC simulations while still retaining physical fidelity. A boosted Lorentz frame (BLF) modeling capability has been introduced within the fluid framework enhancing the performance of the code. An example of a 10 GeV laser-plasma accelerator modeled using INF&RNO in the BLF is presented.
LBNL, Berkeley, California, USA
Plasma accelerators may be driven by the ponderomotive force of an intense laser or the space-charge force of a charged particle beam. Plasma wake excitation driven by lasers or particle beams is examined, and the implications of the different physical excitation mechanisms for accelerator design are discussed.
LBNL, Berkeley, California, USA
In order to build a compact, staged laser plasma accelerator the in-coupling of the laser beam to the different stages represents one of the key issues. To limit the spatial foot print and thus to realize a high overall acceleration gradient, a concept has to be found which realizes this in-coupling within a few centimeters. We present experiments on a tape-drive based plasma mirror which could be used to reflect the focused laser beam into the acceleration stage.
References:
* W. Leemans et. al, Phys. Today, 62, 44 (2009)
** G. Doumy et. al, Phys. Rev. E 69, 026402 (2004)
*** B. Dromey et. al,, Rev. Sci. Instrum. 75, 645 (2004)
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
USC, Los Angeles, California, USA
The ideal drive beam current profile for the plasma wakefield accelerator (PWFA) has been predicted by 1D and 2D simulations to be characterized by a triangular ramp that rises linearly from head to tail, followed by a sharp drop. A technique for generating such bunches experimentally was recently demonstrated. We present here an adaptation of this scheme to generate ramped bunches using the 23 GeV electron beam produced in the first two-thirds of the SLAC linac, and discuss plans to implement this scheme for high transformer ratio demonstration experiments at the FACET plasma wakefield accelerator facility.
SLAC, Menlo Park, California, USA
FACET is a new facility under construction at the SLAC National Accelerator Laboratory. The FACET beam line is designed to provide 23 GeV tightly focused and compressed electron and positron bunches for beam driven plasma wakefield acceleration research and other experiments. Achieving optimal beam parameters for various experimental conditions requires the optics capability for tuning in a sufficiently wide range. This will be achieved by using optics tuning systems (knobs). Design of such systems for FACET is discussed.
The Pennsylvania State University, University Park, Pennsylvania, USA
Penn State University, University Park, Pennsylvania, USA
Sensing of shielded fissile materials at long range is critically dependent on the development of compact particle accelerators. Direct laser acceleration (DLA) of electrons has the potential to meet this requirement. In DLA, the axial component of the electric field of a focused radially polarized laser pulse accelerates particles. The acceleration gradient could be estimated as 77 MeV/mm for 800 nm laser with power of 0.5 TW and 8.5 μm guided mode radius. The implementation of long guided propagation of laser pulses and the phase matching between electrons and laser pulses may limit the DLA in reality. A preformed corrugated plasma waveguide could be applied to extend the laser beam propagation distance and for quasi-phase matching between laser and electron pulses for net acceleration. We perform numerical calculations to estimate the phase matching conditions for a radially polarized laser pulse propagating in a corrugated plasma waveguide. Further, the electric field distribution of a radially polarized laser pulse propagating in this waveguide is also analyzed via particle-in-cell simulations, and will be used to guide future experiments.
* P. Serafim, et al., IEEE Trans. Plasma Sci. 28, 1155 (2000).
** A.G. York, et al., Phys. Rev. Lett. 100, 195001 (2008).
UCLA, Los Angeles, California, USA
In plasma based accelerators (LWFA and PWFA), the methods of injecting high quality electron bunches into the accelerating wakefield is of utmost importance for various applications. Understanding how injection occurs in both self and controlled scenarios is therefore important. To simplify this understanding, we start from single particle motion in an arbitrary traveling wave wakefields, an electromagnetic structure with a fixed phase velocity(e.g., wakefields driven by non-evolving drivers), and obtain the general conditions for trapping to occur. We then compare this condition with high fidelity 3D PIC simulations through advanced particle and field tracking diagnostics. Numerous numerical convergence tests were performed to ensure the correctness of the simulations. The agreement between theory and simulations helps to clarify the role played by driver evolution on injection, and a physical picture of injection first proposed in * is confirmed through simulations. Several ideas, including ionization assisted injection, for achieving high quality controlled injection were also explored and some simulation results relevant to current and future experiments will be presented.
*W. Lu et al., PRSTAB 10, 061301, 2007
USC, Los Angeles, California, USA
UCLA, Los Angeles, California, USA
We show that a positron bunch with parameters accessible at FACET can excite a stable plasma wakefield over a few meters and a witness electron bunch experiences an accelerating gradient on the order of 10 GeV/m. Initial simulations show that the positron drive bunch is strongly affected by the transverse components of the wakefield: the positron bunch evolves significantly, which affects both the wakefield and witness bunch dynamics. Various solutions are presented, of which the positron-electron train shceme generates a desirable wakefield.
MPI-P, München, Germany
LANL, Los Alamos, New Mexico, USA
UCLA, Los Angeles, California, USA
University of Dundee, Nethergate, Dundee, Scotland, United Kingdom
USTRAT/SUPA, Glasgow, United Kingdom
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
UAD, Dundee, United Kingdom
The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme is developing laser-plasma accelerators for the production of ultra-short electron beams as drivers of incoherent and coherent radiation sources from plasma and magnetic undulators. Here we report on the latest laser wakefield accelerator experiments on the University of Strathclyde ALPHA-X accelerator beam line looking at narrow energy spread electron beams. ALPHA-X uses a 26 TW Ti:sapphire laser (energy 900 mJ, duration 35 fs) focused into a helium gas jet (nozzle length 2 mm) to generate high quality monoenergetic electron beams with central energy in the range 80-180 MeV. The beam is fully characterised in terms of the charge, transverse emittance, energy spread and bunch length. In particular, the energy spectrum (with less than 1% measured energy spread) is obtained using a high resolution magnetic dipole imaging spectrometer.
Euclid TechLabs, LLC, Solon, Ohio, USA
ANL, Argonne, USA
We report here on the development of THz diamond wakefield structures produced using Chemical Vapor Deposition (CVD) technology*. The diamond structures would be used in a THz generation experiment at the new FACET facility at SLAC. We consider a dielectric based accelerating structure to study of the physical limitations encountered driving >GV/m wakefields in the cylindrical and planar geometries of a dielectric wakefield accelerator (DWA). In a DWA, an ultrashort drive bunch traverses the evacuated central region of the structure, creating Cherenkov wakefields in the dielectric to accelerate a witness bunch. A diamond-based DWA structure will allow a sustained accelerating gradient exceeding breakdown threshold demonstrated with the FFTB experiments**. The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric rf structures: high breakdown voltage, extremely low dielectric losses and the highest thermoconductive coefficient available for removing waste heat from the device.
*R. J. Barker et al., Modern Microwave and Millimeter-Wave Power Electronics, IEEE Press/Wiley-Interscience, Piscataway NJ 2005, Chapter 7
**M.C. Thompson et al. Phys. Rev.Lett.100:214801, 2008.
LBNL, Berkeley, California, USA
Tech-X, Boulder, Colorado, USA
Control of injection into a high gradient laser-plasma accelerator is presented using the beat between two ’colliding’ laser pulses to kick electrons into the plasma wake accelerating phase. Stable intersection and performance over hours of operation were obtained using active pointing control. Dependence of injector performance on laser and plasma parameters were characterized in coordination with simulations. By scanning the intersection point of the lasers, the injection position was controlled, mapping the acceleration length. Laser modifications to extend acceleration length are discussed towards production of tunable stable electron bunches as needed for applications including Thomson gamma sources and high energy colliders.
LBNL, Berkeley, California, USA
University of Nevada, Reno, Reno, Nevada, USA
UCB, Berkeley, California, USA
A technique has been developed to accurately align a laser beam through a plasma channel by minimizing the shift in laser centroid and angle at the channel outptut. If only the shift in centroid or angle is measured, then accurate alignment is provided by minimizing laser centroid motion at the channel exit as the channel properties are scanned. The improvement in alignment accuracy pro- vided by this technique is important for minimizing electron beam pointing errors in laser plasma accelerators.
NRL, Washington, DC, USA
ANL, Argonne, USA
Euclid TechLabs, LLC, Solon, Ohio, USA
Icarus Research, Inc., Bethesda, Maryland, USA
A joint program is under way to study externally driven X-band dielectric-loaded accelerating (DLA) structures and CLIC-type power extraction structures. The structures are designed and fabricated by Argonne National Laboratory and Euclid Techlabs and tested at up to 20 MW drive power using the X-band Magnicon Facility at the Naval Research Laboratory, with additional tests carried out at SLAC. Thus far, tests have been carried out on a large variety of structures fabricated from quartz, alumina, and MCT-20, and the principal problems have been multipactor loading and rf breakdown.* Multipactor loading occurs on the inner surface of the dielectric in a region of strong normal and tangential rf electric fields; rf breakdown occurs principally at discontinuities in the dielectric. Gap-free DLA structures have been tested at 15 MV/m without breakdown. New tests are being prepared to address these two issues. New gap-free structures will make use of a metallic coating on the outer surface of the dielectric in order to permit tapering both the inner and outer diameters for rf matching, while new multipactor studies will examine the use of grooved surfaces to suppress multipactor.
* C. Jing, W. Gai, J.G. Power, R. Konecny, W. Liu, S.H. Gold, A.K. Kinkead, S.G. Tantawi, V. Dolgashev, and A. Kanareykin, IEEE Trans. Plasma Sci., vol. 38, pp. 1354–1360, June 2010.
Tech-X, Boulder, Colorado, USA
LBNL, Berkeley, California, USA
The use of colliding laser pulses to control the injection of plasma electrons into the plasma wake of a laser-plasma accelerator is a promising approach to obtain reproducible and tunable electron bunches with low energy spread and emittance. We present recent particle-in-cell simulations of colliding pulse injection for parameters relevant to ongoing experiments at LBNL. We perform parameter scans in order to determine the best conditions for the production of high quality electron bunches, and compare the results with experimental data. We also evaluate the effect of laser focusing in the plasma channel and of higher order laser mode components on the bunch properties.
UCLA, Los Angeles, California, USA
Laser-Driven Ion Acceleration in thin foils has demonstrated high-charge, low-emittance MeV ion beams with a picosecond duration. Such high-brightness beams are very attractive for a compact ion source or an injector for RF accelerators. However in the case of foils scaling of the pulse repetition rate and improving shot-to-shot reproducibility is a serious challenge. CO2 laser-plasma interactions provide a possibility for using a debris free gas jet for target normal sheath acceleration of ions. Gas jets have the advantage of precise density control around the critical plasma density for 10 um pulses (1019 cm-3) and can be run at 1-10 Hz. The master oscillator–power amplifier CO2 laser system at the UCLA Neptune Laboratory is being upgraded to generate 1 J, 3 ps pulses at 1Hz. For this purpose, a new 8 atm CO2 module is used to amplify a 3 ps pulse to ~10 GW level. Final amplification is realized in a 1-m long TEA CO2 amplifier, for which the bandwidth necessary for 3 ps pulses is provided by the field broadening mechanism. Modeling of the pulse amplification shows that ~0.3 TW power is achievable that should be sufficient for producing 1-3 MeV H+ protons from the gas plasma.
UCLA, Los Angeles, California, USA
CO2 laser-plasma interactions provide a unique parameter space for using a gas jet for Target Normal Sheath Acceleration (TNSA) of ions instead of a thin foil target. The generation of 1-5 MeV protons from the interaction of a 3 ps TW CO2 laser pulse with a gas target with a peak density around the critical plasma density (1019 cm-3) has been studied by 2D particle-in-cell simulations. The proton acceleration in the preformed plasma, having similar to the gas jet symmetric, linearly ramped density distribution, occurs via formation of a sheath of hot electrons on the back surface of the target. The maximum energy of the hot electrons and, hence net acceleration of protons is mainly defined by Forward Raman scattering instability in the underdense part of the plasma. This mechanism of an additional heating of electrons is strongly affected by nonlinear laser-plasma interactions and results in the proton energy enhancement by more than an order of magnitude in comparison with the regular ponderomotive force scaling of TNSA. Forward directed ion beams from a gaseous target can find an application as a high-brightness ion source-injector.
CELIA, Talence, France
BNL, Upton, Long Island, New York, USA
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
Laser acceleration of ion beams is normally realized via irradiating thin-foil targets with near-IR solid-state lasers with up to petawatt (PW) peak power. Despite demonstration of significant achievements, further progress towards practical application of such beam sources is hindered by the challenges inherent in constructing still more intense and higher-contrast lasers. Our recent studies of the radiation pressure acceleration indicate that the combination of a 10-μm CO2 laser with a gas jet target offers a unique opportunity for a breakthrough in the field. Strong power scaling of this regime holds the promise of achieving the hundreds of MeV proton beams with just sub-PW CO2 laser pulses. Generation of such pulses is a challenging task. We discuss a strategy of the CO2 laser upgrade aimed to providing a more compact and economical hadron source for cancer therapy. This include optimization of the method of the 10μm short-pulse generation, higher amplification in the CO2 gas under combined isotopic and power broadening effects, and the pulse shortening to a few laser cycles (150-200 fs) via self-chirping in the laser-produced plasma and the consecutive dispersive compression.
USC, Los Angeles, California, USA
LANL, Los Alamos, New Mexico, USA
UCLA, Los Angeles, California, USA
We study numerically the excitation of plasma wakefields by a train of electron bunches using the UCLA particle-in-cell code Quickpic*. We aim to find an optimal regime that combines both the advantages of linear and non-linear plasma wakefield accelerator. On one hand, the longitudinal electric field excited by individual bunches add as in the linear region, and the transformer ratio can be maximized (i.e. much larger than 2) by adjusting the number of particles in the bunches as well as their distance. On the other hand, the bunches create large wakefield independent of transverse sizes evolution while propagating through the plasma as in the non-linear region. In principle, such a scheme can multiply the energy of the witness bunch following the drive bunch train in a single plasma wakefield accelerating stage. The parameters for electron bunches are chosen based on the current experiment at the Brookhaven National Laboratory Accelerator Test Facility (ATF), where this scheme can be tested. Detailed simulation results will be presented.
* C. Huang, J. Comp. Phys.
USC, Los Angeles, California, USA
UCLA, Los Angeles, California, USA
In the non-linear or blow-out regime of a plasma wakefield, the electrons of the accelerated bunch oscillate in a pure ion column. It was demonstrated that a single bunch can emit betatron radiation in the keV to MeV range*. In a drive/witness bunch system, the witness bunch can be injected into the ion column with a transverse momentum or initial radial offset, so that the whole bunch oscillates about the column axis as one marcro-electron. This results in a larger emitted power and higher photon energy. The energy loss due to radiation can be compensated for by the energy gain from the wakefield so that the emission process can be sustained over long distance. Detailed results will be presented about the characteristics of the witness bunch oscillations and radiation through numerical simulations** and calculations.
* S.Q. Wang, et al., Phys. Rev.Let., 88(13), 135004,(2002), D. K. Johnson et al., Phys. Rev. Lett. 97(17), 175003, (2006)
** C.H. Huang, et al., J. Comp. Phys., 217(2), 658, (2006)
LBNL, Berkeley, California, USA
CLASSE, Ithaca, New York, USA
Harvard University, Cambridge, Massachusetts, USA
The TE wave propagation method has become a widely used technique for measuring electron cloud density in an accelerator beampipe. In most instances the wave very low power is not capable of affecting the low-energy electrons distribution. During experiments in the CESR Damping Ring Test Accelerator (Cesr-TA), we have observed a particular situation where a resonance between the wave and a dipole magnetic field produces a large modification in the electron cloud distribution that can be measured by other detectors. We believe this resonance is strongly dependent on the geometry of standing waves pattern that discontinuities in the beampipe generate. We present measurements in Cesr-TA, which describe the effect and are in support of our hypothesis.
LBNL, Berkeley, California, USA
A new single-shot diagnostic is presented for mapping THz spatiotemporal waveforms with high temporal resolu- tion for use in diagnostics of electron bunch temporal pro- files. The THz waveform is encoded using electro-optic sampling onto either the phase or amplitude of a broadband chirped probe pulse, and is recovered using linear spectral interferometry with a temporally-short reader pulse. The technique was used to measure waveforms of coherent, ultrashort THz pulses emitted by electron bunches from a laser-plasma accelerator with sub-50 fs resolution. The presence of strong spatiotemporal coupling in the THz waveforms and of complex temporal electron bunch structure was determined.
LBNL, Berkeley, California, USA
UCB, Berkeley, California, USA
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
Cross-calibrations of charge diagnostics are conducted to verify their validity for measuring electron beams produced by laser plasma accelerators (LPAs). Employed diagnostics are a scintillating screen, activation based mea- surement, and integrating current transformer. The diagnostics agreed within ±8 %, showing that they can provide accurate charge measurements for LPAs provided they are used properly.
SLAC, Menlo Park, California, USA
FACET, the Facility for Advanced Accelerator and Experimental Tests, is a new facility being constructed in sector 20 of the SLAC linac primarily to study beam driven plasma wakefield acceleration beginning in summer 2011. The nominal FACET parameters are 23 GeV, 3 nC electron bunches compressed to ~20 μm long and focussed to ~10 μm wide. Characterization of the beam- plasma interaction requires complete knowledge of the incoming beam parameters on a pulse-to- pulse basis. FACET diagnostics include Beam Position Monitors, Toroidal current monitors, X-ray and Cerenkov based energy spectrometers, optical transition radiation (OTR) profile monitors and coherent transition radiation (CTR) bunch length measurement systems. The compliment of beam diagnostics and their expected performance are reviewed.
SLAC, Menlo Park, California, USA
Three temporal diagnostic techniques are considered for use in the FACET facility at SLAC, which will incorporate a unique two-bunch beam for plasma wakefield acceleration experiments. The results of these experiments will depend strongly on the the inter-bunch spacing as well as the longitudinal profiles of the two bunches. A reliable, single-shot, high resolution measurement of the beam’s temporal profile is necessary to fully quantify the physical mechanisms underlying the beam driven plasma wakefield acceleration. In this study we show that a transverse deflecting cavity is the diagnostic which best meets our criteria.
CEA, Arpajon, France
UCLA, Los Angeles, California, USA
LLNL, Livermore, California, USA
Instituto Superior Tecnico, Lisbon, Portugal
IPFN, Lisbon, Portugal
A series of laser wakefield accelerator experiments leading to electron energy exceeding 1 GeV are described. Theoretical concepts and experimental methods developed while conducting experiments using the 10 TW Ti:Sapphire laser at UCLA were implemented and transferred successfully to the 100 TW Calisto Laser System at the Jupiter Laser Facility at LLNL. To reach electron energies greater than 1 GeV with current laser systems, it is necessary to inject and trap electrons into the wake and to guide the laser for more than 1 cm of plasma. Using the 10 TW laser, the physics of self-guiding and the limitations in regards to pump depletion over cm-scale plasmas were demonstrated. Furthermore, a novel injection mechanism was explored which allows injection by ionization at conditions necessary for generating electron energies greater than a GeV. The 10 TW results were followed by self-guiding at the 100 TW scale over cm plasma lengths. The energy of the self-injected electrons, at 3x1018 cm-3 plasma density, was limited by dephasing to 720 MeV. Implementation of ionization injection allowed extending the acceleration well beyond a centimeter and 1.4 GeV electrons were measured.
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
We present initial experimental results showing the excitation of plasma wakefields by a train of two drive bunches. These wakefields are experienced by a trailing witness bunch that gains energy while retaining a finite energy spread. These well controlled plasma wakefield accelerator (PWFA) experiments are important to test the theory of the PWFA and serve as a testbed for techniques that will be used in high energy experiments.
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
USC, Los Angeles, California, USA
FACET, the Facility for Advanced Accelerator and Experimental Tests, is a new facility being constructed in sector 20 of the SLAC linac primarily to study beam driven plasma wakefield acceleration beginning in summer 2011. The nominal FACET parameters are 23GeV, 3nC electron bunches compressed to ~20μm long and focused to ~10μm wide. The intense fields of the FACET bunches will be used to field ionize neutral lithium or cesium vapor produced in a heat pipe oven. Previous experiments at SLAC demonstrated 50GeV/m gradients in an 85cm field ionized lithium plasma where the interaction distance was limited by head erosion. Simulations indicate the lower ionization potential of cesium will decrease the rate of head erosion and increase single stage performance. The initial experimental program will compare the performance of lithium and cesium plasma sources with single and double bunches. Later experiments will investigate improved performance with a pre-ionized cesium plasma. The status of the experiments and expected performance are reviewed.
MPI-P, München, Germany
UCLA, Los Angeles, California, USA
CERN, Geneva, Switzerland
Instituto Superior Tecnico, Lisbon, Portugal
LANL, Los Alamos, New Mexico, USA
BINP SB RAS, Novosibirsk, Russia
USC, Los Angeles, California, USA
HHUD, Dusseldorf, Germany
IPFN, Lisbon, Portugal
UCLA, Los Angeles, California, USA
At the Neptune Laboratory at UCLA, we have developed a high-power CO2 MOPA laser system which produces world record multi-terawatt 10um pulses. The CO2 laser pulses consist of a train of 3ps pulses separated by 18ps, each with a peak power of up to 4TW and a total pulse train energy of ~100J. These relativistic laser pulses are applied for Laser Driven Ion Acceleration in an H2 gas jet operated around the critical density of 1019 cm-3 for 10um light using the Target Normal Sheath Acceleration mechanism. The laser is focused into the gas jet reaching a normalized field strength of a0~2 in vacuum. For these conditions, protons with a maximum energy of 25MeV and a narrow energy spread of ΔE/E < 1% are recorded. Initial analysis of these experimental results shows a stronger scaling of the proton energy than that predicted from the ponderomotive force, and highlights the importance of an accumulated effect of multiple CO2 laser pulses lasting over 100ps. The temporal dynamics of the overdense plasma slab are probed with a picosecond 532nm pulse and the results will be discussed.
PPPL, Princeton, New Jersey, USA
LLNL, Livermore, California, USA
Handong Global University, Pohang, Republic of Korea
LANL, Los Alamos, New Mexico, USA
The effect of a weakly coupled periodic lattice in terms of achieving emittance exchange between the transverse and longitudinal directions is investigated using the generalized Courant-Snyder theory for coupled lattices.
* H. Qin, M. Chung, and R. C. Davidson, PRL. 103, 224802 (2009).
** H. Qin and R. C. Davidson, PRST-AB 12, 064001 (2009).
Fermilab, Batavia, USA
UMD, College Park, Maryland, USA
In this paper the authors present results of threedimensional analysis of multipactor in dielectric-loaded accelerator structures. The studies are aimed at checking some assumptions that were used in previous two-dimensional theory. In particular, it is demonstrated that the spatial distribution of charged particles can be azimuthally non-uniform which suggests using a more complex space charge model in some cases. Also, it is shown that the particle axial velocity components can be making a substantial contribution to particle energy and should not be ignored in future studies.
ANL, Argonne, USA
Fermilab, Batavia, USA
We have been extending and refining our model of vacuum breakdown and gradient limits and will describe recent developments. The model considers a large number of mechanisms but finds that vacuum arcs can be described fairly simply and self consistently, however simulations of individual mechanisms can be, in some cases, involved. Although based on accelerator rf data, we believe our model of vacuum arcs should have general applicability.
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
LLNL, Livermore, California, USA
LBNL, Berkeley, California, USA
PPPL, Princeton, New Jersey, USA
UMD, College Park, Maryland, USA
Intense heavy-ion beams have long been considered a promising driver option for inertial-fusion energy production. This paper briefly compares inertial confinement fusion (ICF) to the more-familiar magnetic- confinement approach and presents some advantages of using beams of heavy ions to drive ICF instead of lasers. Key design choices in heavy-ion fusion (HIF) facilities are discussed, particularly the type of accelerator. We then review experiments carried out at Lawrence Berkeley National Laboratory (LBNL) over the past thirty years to understand various aspects of HIF driver physics. A brief review follows of present HIF research in the US and abroad, focusing on a new facility, NDCX-II, being built at LBNL to study the physics of warm dense matter heated by ions, as well as aspects of HIF target physics. Future research directions are briefly summarized.
LBNL, Berkeley, California, USA
Tech-X, Boulder, Colorado, USA
JLAB, Newport News, Virginia, USA
Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.
SLAC, Menlo Park, California, USA
FACET, the Facility for Advanced Accelerator and Experimental Tests, is a new facility being constructed in sector 20 of the SLAC linac primarily to study beam driven plasma wakefield acceleration. The FACET beamline consists of a chicane and final focus system to compress the 23 GeV, 3 nC electron bunches to ~20μm long and ~10μm wide. Simulations of the FACET beamline indicate the short-duration and large, 1.5% rms energy spread beams may suffer a factor of four emittance growth from a combination of chromaticity, incoherent synchrotron radiation (ISR), and coherent synchrotron radiation (CSR). Emittance growth is directly correlated to head erosion in plasma wakefield acceleration and is a limiting factor in single stage performance. Studies of the geometric, CSR, and ISR components are presented. Numerical calculation of the rms emittance can be overwhelmed by long tails in the simulated phase space distributions; more useful definitions of emittance are given. A complete simulation of the beamline is presented as well, which agrees with design specifications.
MIT, Cambridge, Massachusetts, USA
Charged-particle motion is studied in the self-electric and self-magnetic fields of a well-matched, intense charged-particle beam and an applied periodic solenoidal magnetic focusing field. The beam is assumed to be in a state of adiabatic thermal equilibrium. The phase space is analyzed and compared with that of the well-known Kapchinskij-Vladimirskij (KV)-type beam equilibrium. It is found that the widths of nonlinear resonances in the adiabatic thermal beam equilibrium are narrower than those in the KV-type beam equilibrium. Numerical evidence is presented, indicating almost complete elimination of chaotic particle motion in the adiabatic thermal beam equilibrium.
MIT, Cambridge, Massachusetts, USA
Adiabatic thermal equilibrium is an important state of a charged-particle beam. The rigid-rotor thermal beam equilibrium in a uniform magnetic focusing field is established. The equivalent kinetic and warm-fluid theories of adiabatic thermal beam equilibrium in a periodic solenoidal magnetic focusing field are discussed. Good agreement between theories and experiment is found. The warm-fluid theory of adiabatic thermal beam equilibrium in an alternating-gradient quadrupole magnetic focusing field is discussed. For the periodic solenoidal magnetic focusing field, charged-particle dynamics in the adiabatic thermal beam equilibrium are studied numerically and compared with those in the Kapchinskij-Vladimirskij (KV) type beam equilibrium. Numerical evidence is presented, indicating almost complete elimination of chaotic particle motion in the adiabatic thermal beam equilibrium.
PPPL, Princeton, New Jersey, USA
LLNL, Livermore, California, USA
A variety of masks were installed on the Paul Trap Simulator Experiment (PTSX) cesium ion source in order to perform experiments with modified transverse distribution functions. Masks were used to block injection of ions into the PTSX chamber, thereby creating injected transverse beam distributions that were either hollow, apertured and centered, apertured and off-center, or comprising five beamlets. Experiments were performed using either trapped plasmas or the single-pass, streaming, mode of PTSX. The transverse streaming current profiles clearly demonstrated centroid oscillations. Further analysis of these profiles also shows the presence of certain collective beam modes, such as azimuthally symmetric radial modes. When these plasmas are trapped for thousands of lattice periods, the plasma quickly relaxes to a state with an elevated effective transverse temperature and is subsequently stable. Both sinusoidal and periodic step function waveforms were used and the resulting difference in the measured transverse profiles will be discussed.
LLNL, Livermore, California, USA
LBNL, Berkeley, California, USA
A one-dimensional Vlasov-Poisson model for sheet beams is presented to provide a simple framework for analysis of space-charge effects. Centroid and rms envelope equations including image charge effects are derived and reasonable parameter equivalences with commonly employed 2D transverse models of unbunched beams are established. This sheet beam model is applied to analyze several problems of fundamental interest. First, a sheet beam thermal equilibrium distribution in a continuous focusing channel is constructed and shown to have analogous properties to two- and three-dimensional thermal equilibrium models in terms of the equilibrium structure and Deybe screening properties. Second, the simpler formulation for sheet beams is exploited to explicitly calculate the distribution of particle oscillation frequencies within a thermal equilibrium beam. It is shown that as space-charge intensity increases, the frequency distribution becomes broad which suggesting robust stability properties for beams with strong space-charge.
PPPL, Princeton, New Jersey, USA
Tech-X, Boulder, Colorado, USA
Low-frequency oscillations (LFOs) have been observed in a high average power gyrotron and the trapped electron population contributing to the oscillation has been measured. As high average power gyrotrons are the most promising millimeter wave source for thermonuclear fusion research, it is important to get a better understanding of this parasitic phenomenon to avoid any deterioration of the electron beam quality thus reducing the gyrotron efficiency. 2D Particle-in-cell (PIC) simulations quasi-statically model the development of oscillations of the space charge in the adiabatic trap, but the physics of the electron dynamics in the adiabatic trap is only partially understood. Therefore, understanding of the LFOs remains incomplete and a full picture of this parasitic phenomenon has not been seen yet. In this work, we use a 3D conformal finite-difference time-domain (CFDTD) PIC method to accurately and efficiently study the LFOs in a high average power gyrotron. Complicated structures, such as a magnetron injection gun, can be well described. Employing a highly parallelized computation, the model can be simulated in time domain more realistically.
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
LANL, Los Alamos, New Mexico, USA
IPFN, Lisbon, Portugal
UCLA, Los Angeles, California, USA
Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI could play an important role in the generation of magnetic fields and radiation in the after-glow of gamma ray bursts and also in energy transport for the fast-igniter inertial confinement fusion concept. Simulations were conducted with the particle-in-cell code QuickPIC* for e- beam and plasma parameters at the Brookhaven National Laboratory – Accelerator Test Facility, BNL-ATF. Results show that for a 2cm plasma the instability reaches near saturation. An experimental program was proposed and accepted at the BNL-ATF and an experiment is currently underway. There are three components to the experimental program: 1) imaging of the beam density/filaments at the exit from the plasma, 2) measurement and imaging of the transverse plasma density gradient and measurement of the magnetic field and 3) identifying the radiation spectrum of the instability. Preliminary results from phase one will be presented along with the progress and diagnostic design for the following phases of the experiment.
* C. Huang et. al. Journal of Computational Physics 217, 2(2006)
ANL, Argonne, USA
Far-Tech, Inc., San Diego, California, USA
FAR-TECH, Inc is developing a hybrid, quasi-3D model to model charge breeding of an ion beam in an electron cyclotron resonance ion source. The model is a combination of 3D mapping of the plasma background calculated by GEM1D* and 3D tracking of the ion trajectories with MCBC**. The 3D electron distribution function and electric field of the background plasma are calculated self-consistently. The test beam ions are then tracked in it using MCBC which includes Coulomb, ionization and charge exchange collisions. The exact ion trajectories in the plasma and steady state 3D ion distribution at the extraction aperture are predicted and compared with previous simulations and experiments.
* D. H. Edgell et al., Rev. Sci. Instrum. 73, 641, 2002.
** J. S. Kim et al., Rev. Sci. Instrum. 79, 02B906, 2008.
Tech-X, Boulder, Colorado, USA
Numerical simulations of electron cloud buildup and in particular rf microwave diagnostics provide important insights into the dynamics of particle accelerators and the potential for mitigation of destabilizing effects of electron clouds on particle beams. Typical Particle-In-Cell (PIC) simulations may accurately model cloud dynamics; however, due to the large range of temporal scales needed to model side band production due to ecloud modulation, typical PIC models may not be the best choice. We present here preliminary results for advance numerical modeling of rf electron cloud diagnostics, where we replace kinetic particles with an equivalent plasma dielectric model. This model provides significant speedup and increased numerical stability, while still providing accurate models of rf phase shifts induced by electron cloud plasmas over long time scales.
Tech-X, Boulder, Colorado, USA
ORNL RAD, Oak Ridge, Tennessee, USA
ORNL, Oak Ridge, Tennessee, USA
The H- linac for the Spallation Neutron Source (SNS) includes an electrostatic low-energy beam transport (LEBT) subsystem. The ion source group at SNS is developing a solenoid-based LEBT, which will include MHz frequency chopping of the partly-neutralized, 65~keV, 60~mA H- beam. Particle-in-cell (PIC) simulations using the parallel VORPAL framework are being used to explore the possibility of beam instabilities caused by the cloud of neutralizing ions generated from the background gas, or by other dynamical processes that could increase the emittance of the H- beam before it enters the radio-frequency quadrupole (RFQ) accelerator.
Institute for Plasma Research, Bhat, Gandhinagar, India
Pandit Deendayal Petroleum University, Gandhinagar, India
sbanerje@ipr.res.in
sudhir@ipr.res.in
Institute for Plasma Research
BNL, Upton, Long Island, New York, USA
Kyushu University, Department of Applied Quantum Physics and Nuclear Engineering, Fukuoka, Japan
The Electron Beam Ion Source (EBIS) at Brookhaven National Laboratory is a new heavy ion-projector for RHIC and NASA Space Radiation Laboratory. Laser Ion Source (LIS) with solenoid can supply many kinds of ion from solid targets and is suitable for long pulse length with low current as ion provider for RHIC-EBIS. In order to understand a plasma behavior for fringe field of solenoid, we measure current, pulse width and total ion charges by a new ion probe. The experimental result indicates that the solenoid confines the laser ablation plasma transversely.
LBNL, Berkeley, California, USA
A microwave ion source has been designed and constructed for use with a sealed-tube, high-yield neutron generator. When operated with a tritium-deuterium gas mixture the generator will be capable of producing 5 · 1011 n/s in non-proliferation applications. Microwave ion sources are well suited for such a device because they can produce high extracted beam currents with a high atomic fraction at low gas pressures of 0.2 − 0.3 Pa required for sealed tube operation. The magnetic field strength for achieving electron cyclotron resonance (ECR) condition, 87.5 mT at 2.45 GHz microwave frequency, was generated and shaped with permanent magnets surrounding the plasma chamber and a ferromagnetic plasma electrode. This approach resulted in a compact ion source that matches the neutron generator requirements. The needed proton-equivalent extracted beam current density of 40 mA/cm2 was obtained at moderate microwave power levels of ∼ 400W. Results on magnetic field design, pressure dependency and atomic fraction measured for different wall materials are presented.
Muons, Inc, Batavia, USA
ORNL, Oak Ridge, Tennessee, USA
In this project we are developing an RF H− surface plasma source (SPS) with saddle (SA) RF antenna which will provide better power efficiency for high pulsed and average current, higher brightness with longer lifetime and higher reliability. Several versions of new plasma generators with a small AlN test chamber and different antennasandmagneticfieldconfigurationsweretestedin the SNS ion source Test Stand. A prototype SA SPS was installed in the Test Stand with a larger, normal-sized SNS AlN chamber that achieved unanalyzed peak currents of up to 67 mA with an apparent efficiency of 1.6 mA/kW. Control experiments with H− beam produced by SNS SPS with internal and external antennas were conducted. A new version of the RF triggering plasma source (TPS) has been designed. A Saddle antenna SPS with water cooling is being fabricated for high duty factor testing.
ORNL RAD, Oak Ridge, Tennessee, USA
University of Tennessee, Knoxville, Tennessee, USA
ORNL, Oak Ridge, Tennessee, USA
The RF ion source at Spallation Neutron Source has been upgraded to meet higher beam power requirement. One important subsystem for efficient operation of the ion source is the 2MHz RF impedance matching network. The real part of the antenna impedance is very small and is affected by plasma density for 2MHz operating frequency. Previous impedance matching network for the antenna has limited tuning capability to cover this potential variation of the antenna impedance since it employed a single tuning element and an impedance transformer. A new matching network with two tunable capacitors has been built and tested. This network can allow precision matching and increase the tunable range without using a transformer. A 5-element broadband matching network also has been designed, built and tested. The 5-element network allows wide band matching up to 50 kHz bandwidth from the resonance center of 2 MHz. The design procedure, simulation and test results are presented.
ORNL, Oak Ridge, Tennessee, USA
ORNL RAD, Oak Ridge, Tennessee, USA
Running routinely with ~40-mA, 1-MW beams, the SNS linac is fed from the ion source with ~1ms long, ~50-mA H− beam pulses at 60 Hz. This requires the daily extraction of ~230 C of H− ions, which exceeds the routine daily production of other H− accelerator sources by almost an order of magnitude. The source service cycle has been extended from 2, to 3, to 4, and up to 5.6 weeks without age-related failures. The 7-9 kC of H− ions delivered in single service cycles exceed the service cycle yields of other accelerator sources. The paper discusses the findings as well as the issues and their mitigations, which enabled the simultaneous increase of the beam current, the duty factor, the availability, and the service cycle.
PPPL, Princeton, New Jersey, USA
CERN, Geneva, Switzerland
ORNL, Oak Ridge, Tennessee, USA
NSCL, East Lansing, Michigan, USA
JLAB, Newport News, Virginia, USA
ORNL RAD, Oak Ridge, Tennessee, USA
The SNS SCL is reliably operating at 0.93 GeV output energy with an energy reserve of 10MeV with high availability. Most of the cavities exhibit field emission, which directly or indirectly (through heating of end groups) limits the gradients achievable in the high beta cavities in normal operation with the beam. One of the field emission sources would be surface contaminations during surface processing for which mild surface cleaning, if any, will help in reducing field emission. An R&D effort is in progress to develop in-situ surface processing for the cryomodules in the tunnel without disassembly. As the first attempt, in-situ plasma processing has been applied to the CM12 in the SNS SRF facility after the repair work with a promising result. This paper will report the R&D status of plasma processing in the SNS.
BNL, Upton, Long Island, New York, USA
Kyushu University, Department of Applied Quantum Physics and Nuclear Engineering, Fukuoka, Japan
Warm Dense Matter (WDM) is a growing rapidly science field, which is related to planetary science and inertial fusion. It is difficult to expect the behavior because the state with high density and low temperature is completely different from ideal condition. The well-defined WDM generation is required to understand it. Moderate energy ion beam (~ 0.3 MeV/u) slightly above Bragg peak is an advantageous method for WDM because of the uniform energy deposition. Direct Plasma Injection Scheme (DPIS) with a linear accelerator has a potential for the beam parameter. The design of linear accelerator for WDM is presented.