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.
Fermilab, Batavia, USA
Handong Global University, Pohang, Republic of Korea
Politecnico di Torino, Torino, Italy
Muons, Inc, Batavia, USA
IIT, Chicago, Illinois, USA
Breakdown plasma in a high-pressure hydrogen gas filled RF cavity has been studied from a time domain spectroscopic light analysis. The observed breakdown plasma temperature and density reached 21,000 K and 1020 cm-3, respectively. The electron recombination rate has been evaluated from the decay of plasma density in various gas pressures. The recombination mechanism in dense plasma will be discussed. Finally, the similarity and difference of the breakdown processes between the high-pressure hydrogen gas filled RF cavity and a vacuum RF one will be discussed.
IIT, Chicago, Illinois, USA
Handong Global University, Pohang, Republic of Korea
Politecnico di Torino, Torino, Italy
Fermilab, Batavia, USA
Muons, Inc, Batavia, USA
A high pressure hydrogen gas filled RF cavity was subjected to an intense proton beam to study the evolution of the beam induced plasma inside the cavity. The electron recombination rate with the dense ionized hydrogen plasma has been measured under varying conditions. Recombination rates as high as 10-7 cm3/s have been recorded. This technique shows promise in the R&D program for a muon accelerator. The use of hydrogen, both as a way to prevent breakdown in an RF cavity and as a mechanism for cooling a beam of muons, will be discussed.
Fermilab, Batavia, USA
Handong Global University, Pohang, Republic of Korea
Politecnico di Torino, Torino, Italy
IIT, Chicago, Illinois, USA
Muons, Inc, Batavia, USA
Muon Colliders and Neutrino Factories call for R&D for a high-gradient RF system capable of operating in a high magnetic field. Adding a high pressure gas inside an RF cavity (HPRF) prevents cavity breakdown, allowing higher gradients in a magnetic field. A high-energy beam passing through an HPRF cavity ionizes the gas, producing plasma. Plasma electrons absorb cavity’s energy, reducing the energy available for beam acceleration. Doping cavity gas with electronegative gas (gas that tends to attract and bond electrons) reduces the number of plasma electrons. The experiments were carried out at the MuCool Test Area (MTA) facility at Fermilab. Different concentrations of an electronegative gas SF6 were added to hydrogen gas. The results of room-temperature tests showing a great reduction in power drop in the cavity will be presented. However, a realistic cavity would operate at liquid nitrogen temperature, where SF6 freezes. Thus, a search for a better electronegative gas candidate is underway; we plan to test oxygen-doping next.
CEA/DSM/IRFU, France
Muons, Inc, Batavia, USA
Fermilab, Batavia, USA
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
Factors limiting operating lifetime of Compact Surface Plasma Sources (CSPS) are analyzed and possible treatments for lifetime enhancement are considered. CSPSs have high plasma density (up to 1014 cm-3), high emission current density of negative ions (up to 8 A/cm2), small (1–5 mm) gap between cathode emitter, and a small extraction aperture in the anode. They are very simple, have high energy efficiency up to 100 mA/kW of discharge (~100 times higher then modern large Volume RF SPS) and have a high gas efficiency (up to 30%) using pulsed valves. CSPSs are very good for pulsed operation but electrode power density is often too high for dc operation. However, CSPSs were successfully adopted for DC operation with emission current density ~300 mA/cm2 in Hollow cathode Penning Discharge and up to 1 A/cm2 in Spherical focusing semiplanotron. Flakes from electrodes sputtering and blistering induced by back accelerated positive ions are the main reasons of ion source failure. Suppression of back accelerated positive ions, flakes explosion by pulsed discharges, and flakes gasification by discharge in NF3 (or XeF2) can be used for significant increase of operating lifetime of CSPSs.
Muons, Inc, Batavia, USA
ORNL, Oak Ridge, Tennessee, USA
Progress in development of 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 will be considered. Several versions of new plasma generators with a small Al2O3chamber and different antennas and magnetic field configurations were tested in the SNS small 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 in the similar conditions were conducted. A new version of the RF triggering plasma source (TPS) has been designed and fabricated. A Saddle antenna SPS with water cooling is being fabricated for high duty factor testing
ISIR, Osaka, Japan
Fermilab, Batavia, USA
PKU/IHIP, Beijing, People's Republic of China
IHEP, Beijing, People's Republic of China
Tech-X, Boulder, Colorado, USA
CLASSE, Ithaca, New York, USA
Electron clouds have the potential to pose serious limitations on accelerator performance in both hadron and lepton beams. Experiments using rf diagnostics are being performed to measure electron cloud densities at a number of accelerator facilities. However, it is difficult to calibrate plasma density with signal strength in these experiments, and modeling involves a number of technical and numerical challenges. Typically 2-Dimensional electrostatic methods have been used to model cloud buildup under beam crossing conditions. However, since traveling-wave rf experiments typically occur over many meters of beam pipe where magnetic fields are changing, one needs to develop 3-Dimensional electromagnetic models in order to accurately simulate rf diagnostics. We have developed accurate models of electron cloud-induced phase shifts in rf in a system with spatially varying magnetic field configurations using the plasma simulation code VORPAL. We present here results for measuring phase shifts in the CESR wiggler with realistic, spatially non-uniform magnetic field configurations.
JLAB, Newport News, Virginia, USA
Muons, Inc, Batavia, USA
Illinois Institute of Technology, Chicago, Illinois, USA
IAP, Frankfurt am Main, Germany
ESS Bilbao, Bilbao, Spain
University of the Basque Country, Faculty of Science and Technology, Bilbao, Spain
ESS-Bilbao, Zamudio, Spain
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.
ORNL, Oak Ridge, Tennessee, USA
Fermilab, Batavia, USA
Many quantum integrable systems are obtained using an accelerator physics technique known as Ermakov (or normalized variables) transformation. This technique was used to create classical nonlinear integrable lattices for accelerators and nonlinear integrable plasma traps. Now, all classical results are carried over to a nonrelativistic quantum case.
RISE, Tokyo, Japan
BNL, Upton, Long Island, New York, USA
High intensity, high charge state, various ion species and small emittance heavy ion beam is required for particle physics, medical uses, inertial fusion, and a simulator of space radiation. Direct Plasma Injection Scheme (DPIS), the way to make laser abrasion plasma developed in the past several years, is used for Heavy Ion beam Accerelation. High density plasma with an initial drift velocity will fly to the entrance of the Radio Frequency Quadropole (RFQ) LINAC; ions will be separated from plasma via high voltage and injected it to RFQ LINAC directly. After RFQ LINAC, ions accepted to the RF buckets are accelerated to a current of over 10mA. Until now, we tried a carbon target using the partial modulation rod of the RFQ LINAC, and succeeded in accelerating carbon4+, carbon5+, and carbon6+ non-bunched beam.* In this instance, we succeeded in commissioning of new full modulation RFQ rod designed for the charge mass ratio(q/A) 1/6. We tested the acceleration of carbon4+, and it could be catched by the RF bucket and accelerated. After this, we'll try accelerating carbon2+ (q/A=1/6) for demonstrating the feasibility of the Ag15+ ion accelerating.
* T. Kanesue, M. Okamura, K. Kondo, J. Tamura, H. Kashiwagi, Z. Zhang, Drift distance survey in direct plasma injection scheme for high current beam production, Rev Sci Instrum. 2010 Feb;81(2):02B723
TEMF, TU Darmstadt, Darmstadt, Germany
GSI, Darmstadt, Germany
Japan Atomic Energy Agency (JAEA), International Fusion Energy Research Center (IFERC), Rokkasho, Kamikita, Aomori, Japan
JAEA, Ibaraki-ken, Japan
Korea Basic Science Institute, Busan, Republic of Korea
Muons, Inc, Batavia, USA
ORNL RAD, Oak Ridge, Tennessee, USA
ORNL, Oak Ridge, Tennessee, USA
CERN, Geneva, Switzerland
Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
KIT, Karlsruhe, Germany
Istituto Nazionale di Fisica Nucleare, Milano, Italy
INFN/LNF, Frascati (Roma), Italy
Università di Roma II Tor Vergata, Roma, Italy
Universita' degli Studi di Milano, Milano, Italy
URLS, Rome, Italy
Università degli Studi di Milano, Milano, Italy
LBNL, Berkeley, California, USA
Tech-X, Boulder, Colorado, USA
LLNL, Livermore, California, USA
Modeling of laser-plasma wakefield accelerators in an optimal frame of reference [J.-L. Vay, Phys. Rev. Lett. 98 130405 (2007)] allows direct and efficient full-scale modeling of deeply depleted and beam loaded laser-plasma stages of 10 GeV-1 TeV (parameters not computationally accessible otherwise). This verifies the scaling of plasma accelerators to very high energies and accurately models the laser evolution and the accelerated electron beam transverse dynamics and energy spread. Over 4, 5 and 6 orders of magnitude speedup is achieved for the modeling of 10 GeV, 100 GeV and 1 TeV class stages, respectively. Agreement at the percentage level is demonstrated between simulations using different frames of reference for a 0.1 GeV class stage. Obtaining these speedups and levels of accuracy was permitted by solutions for handling data input (in particular particle and laser beams injection) and output in a relativistically boosted frame of reference, as well as mitigation of a high-frequency instability that otherwise limits effectiveness.
Used resources of NERSC, supported by US-DOE Contract DE-AC02-05CH11231.
JLAB, Newport News, Virginia, USA
The College of William and Mary, Williamsburg, USA
Avenues for the production of thin films tailored for Superconducting RF (SRF) applications are showing promise with recent developments in vacuum deposition techniques using energetic ions. JLab is using energetic condensation via Electron Cyclotron Resonance and High Power Impulse Magnetron Sputtering (HiPIMS) for the development of Nb films and multilayer SIS (superconductor-insulator-superconductor) structures to reach bulk Nb performance and beyond. Nb films with RRR comparable to bulk values are readily produced. The influence of the deposition energy on the material and RF properties of the Nb thin film is investigated with the characterization of their surface, structure, superconducting properties and RF response. Nucleation studies are investigating the best conditions to create a favorable template for growing the final SRF surface. This paper presents results on surface impedance measurements correlated with surface and material characterization for Nb and multilayered SIS films produced on a variety of substrates.
ODU, Norfolk, Virginia, USA
Old Dominion University, Norfolk, USA
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
Duke ECE, Durham, North Carolina, USA
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
UCLA, Los Angeles, California, USA
We analyze the use of a relativistic laser pulse with a controlled frequency chirp incident on a rising plasma density gradient to drive an acceleration structure for proton and light ion acceleration. The Chirp Induced Transparency Acceleration (ChITA) scheme is described with an analytical model of the velocity of the snowplow at critical density on a pre-formed rising plasma density gradient that is driven by positive chirp in the frequency of a relativistic laser pulse. The velocity of the ChITA-snowplow is shown to depend upon rate of rise of the frequency of the relativistic laser pulse, the normalized magnetic vector potential of the laser pulse and the plasma density gradient scale-length. We observe using 1-D OSIRIS simulations the formation and forward propagation of ChITA-snowplow, being continuously pushed by the chirping laser at a velocity in accordance with the analytical results. The trace protons reflect off of this propagating snowplow structure and accelerate monoenergetically. The control over ChITA-snowplow velocity allows the tuning of accelerated proton energies.
ESS Bilbao, LEIOA, Spain
University of the Basque Country, Faculty of Science and Technology, Bilbao, Spain
EPFL, Lausanne, Switzerland
The operation of the waveguide automatic tuner unit (ATU) for optimizing the impedance matching and the RF power coupling in the ESS-Bilbao H+ Ion Source (ISHP) is presented. Since the plasma chamber can be considered as a time varying load impedance for the pulsed RF 2.7 GHz high power generator, several approaches have been studied for accurately measuring the load impedance. In the later case, a set of power detectors connected to electric field probes, IQ demodulators and gain/phase detectors connected to dual directional couplers have been integrated. An experimental comparison of these approaches is presented, showing their accuracy, limitations and error-correction methods. Finally, the control system developed for the automatic operation of the triple capacitive post tuner is described, as well as illustrative results.
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).
The Pennsylvania State University, University Park, Pennsylvania, USA
Penn State University, University Park, Pennsylvania, USA
Direct laser acceleration (DLA) of charged particles using the axial electric field of a radially polarized intense laser pulse has the potential to realize a compact accelerator required in security and medical applications. The implementation of guided propagation of laser pulses over long distances and the phase matching between electrons and laser pulses may limit the performance of DLA in reality*. A 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. To accelerate electrons from a low initial energy (for example, ~5 MeV from a photoinjector gun) up to hundreds of MeV, an aperiodic corrugated plasma waveguide with successive increase of on-axis density modulation period is needed**. We conducted particle-in-cell simulations to design the appropriate aperiodic plasma structure for DLA. For each section of the corrugated waveguide, the dependence of density modulation period on the initial electron energy and laser pulse intensity is investigated. The simulation results are guiding the design of proof-of-principle experiments for compact, tabletop DLA.
* P. Serafim, et al., IEEE Trans. Plasma Sci. 28, 1155 (2000).
** J. P. Palastro, et al., Phys. Rev. E. 77, 036405 (2008).
INFN/LNF, Frascati (Roma), Italy
Istituto Nazionale di Fisica Nucleare, Milano, Italy
Università di Roma II Tor Vergata, Roma, Italy
ENEA C.R. Frascati, Frascati (Roma), Italy
INFN-Roma II, Roma, Italy
INFN, Roma, Italy
INFN-Roma, Roma, Italy
Naples University Federico II, Mathematical, Physical and Natural Sciences Faculty, Napoli, Italy
INFN-Ferrara, Ferrara, Italy
UNIPI, Pisa, Italy
CNR/IPP, Pisa, Italy
INFN-Bologna, Bologna, Italy
Università di Roma I La Sapienza, Roma, Italy
Rome University La Sapienza, Roma, Italy
INFN-FI, Sesto Fiorentino, Italy
Universita' degli Studi di Milano, Milano, Italy
ISM-CNR, Rome, Italy
Bologna University, Bologna, Italy
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.
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.
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.
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).
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
When a positron beam enters a plasma, plasma electrons are drawn in toward the beam axis, creating a region of extremely large charge density with complicated, nonlinear fields. Few analytic solutions exist to describe these fields, and this necessitates the use of simulations to model positron beam and plasma interactions. This presentation should cover recent work on positron PWFA simulations using the QuickPIC* particle-in-cell code. I will discuss the computational challenges associated with positron PWFA and specific applications of the simulations for future experimental tests at the FACET user facility at SLAC.
* C. Huang et al., "QuickPIC: A highly efficient particle-in-cell code for modeling wakefield acceleration in plasmas," J. Comp. Phys. 217, 658 (2006).
ITEP, Moscow, Russia
MIT, Cambridge, Massachusetts, USA
Self-consistent simulations are performed to verify the theoretical predictions of adiabatic thermal beams in periodic solenoidal magnetic focusing fields*,**. In particular, results are obtained for adiabatic thermal beams that do not rotate in the Larmor frame. For such beams, the theoretical predictions of the rms beam envelope, the conservation of the rms thermal emittance, the adiabatic equation of state, and the Debye length are verified in the self-consistent simulations.
*K.R. Samokhvalova, J. Zhou and C. Chen, Phys. Plasma 14, 103102 (2007).
**J. Zhou, K.R. Samokhvalova and C. Chen, Phys. Plasma 15, 023102 (2008).
Northern Illinois University, DeKalb, Illinois, USA
In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (>2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration. We also explore practical techniques capable of tailoring current profiles into these optimal shapes.
MPI-P, München, Germany
MPI, Muenchen, Germany
* A. Caldwell, K. Lotov, Plasma wakefield acceleration with a modulated proton bunch, arXiv: 1105.1292 (2011).
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 has potential relevance to astrophysics, magnetic field and radiation generation in the afterglow of gamma ray bursts, and inertial confinement fusion, energy transport in the fast-igniter concept. An experimental study of this instability is underway at the Accelerator Test Facility, ATF, at Brookhaven National Laboratory with the 60MeV electron beam and centimeter length capillary discharge plasma. The experimental program includes the systematic study and characterization of the instability as a function of beam (charge, transverse and longitudinal profile) and plasma (plasma density) parameters. Specifically, the transverse beam profile is measured directly at the plasma exit using optical transition radiation from a thin gold-coated silicon window. Experimental results show the reduction of the beam transverse size and the appearance of multiple (1-4) filaments and are a function of the plasma density. We will present simulation and experimental results, provide discussion of these results and outline next steps in the experiment.
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
We report preliminary results on plasma generation in a 5-cell CEBAF SRF cavity for the application of cavity interior surface cleaning. CEBAF currently has ~300 of these five cell cavities installed in the JLab accelerator which are mostly limited by cavity surface contamination. The development of an in-situ cavity surface cleaning method utilizing a resonant microwave discharge could lead to significant performance improvement. This microwave discharge is currently being used for set of plasma cleaning procedures targeted to the removal of various organic, metal and metal oxide impurities. These contaminants are responsible for the increase of surface resistance and the reduction of RF performance in installed cavities. CEBAF five cell cavity volume is ~ 0.5 m2, which places the discharge in the category of large-volume plasmas. Our preliminary study includes microwave breakdown and optical spectroscopy, which was used to define the operating pressure range and the rate of removal of organic impurities.
BNL, Upton, Long Island, New York, USA
The thorough study of coherent electron cooling, the modern cooling technique capable to deal with accelerators operating in the range of few TeVs*, rises many interesting questions. One of them is a shielding dynamics of a hadron in an electron beam. Now this effect is computed analytically in an infinite beam approximation**. Many effects are drastically different in finite and infinite plasmas. Here we propose a method to compute the dynamical shielding effect in a finite cylindrical plasma - the realistic model of an electron beam in accelerators.
* V. N. Litvinenko, Y. S. Derbenev, Phys. Rev. Lett. 102, 114801 (2009).
** G. Wang, M. Blaskiewicz, Phys. Rev. E 78, 026413 (2008).
JLAB, Newport News, Virginia, USA
Muons, Inc, Batavia, USA
Illinois Institute of Technology, Chicago, Illinois, USA
Tech-X, Boulder, Colorado, USA
BNL, Upton, Long Island, New York, USA
Next generation electron-hadron colliders will require effective cooling of high-energy, high-intensity hadron beams. Coherent electron cooling (CeC) can in principle cool relativistic hadron beams on orders-of-magnitude shorter time scales than other techniques*. The parallel VORPAL framework is used for 3D delta-f PIC simulations of anisotropic Debye shielding in a full longitudinal slice of the co-propagating electron beam, choosing parameters relevant to the proof-of-principle experiment under development at BNL. The transverse density conforms to an exponential Vlasov equilibrium for Gaussian velocities, with no longitudinal density variation. Comparison with 1D1V Vlasov/Poisson simulations shows good agreement in 1D. Parallel 3D simulations at NERSC show 3D effects for ions moving longitudinally and transversely. Simulation results are compared with the constant-density theory of Wang and Blaskiewicz**.
* V.N. Litvinenko and Y.S. Derbenev, Phys. Rev. Lett. 102, 114801 (2009).
** Wang and Blaskiewicz, Phys Rev E 78, 026413 (2008).
PKU/IHIP, Beijing, People's Republic of China
ANL, Argonne, USA
Tech-X, Boulder, Colorado, USA
Fermilab, Batavia, USA
JIHT RAS, Moscow, Russia
We are continuing to extend and simplify our understanding of vacuum arcs. We believe that all the breakdown phenomena we see (with and without B fields) can be explained by: 1) fracture due to electrostatic forces at surface crack junctions, 2) the development of a unipolar arc driven by the cavity electric field, and 3) cooling, and cracking of the surface after the event is finished. Recent progress includes the evaluation of non-Debye sheaths using Molecular Dynamics, studies of sheath driven instabilities, a model of degradation of gradient limits in strong B fields, analysis of the variety of arcs that can occur in cavities and their damage and further studies of breakdown triggers.
Voss Scientific, Albuquerque, New Mexico, USA
LBNL, Berkeley, California, USA
Muons, Inc, Batavia, USA
Fermilab, Batavia, USA
Recent studies have shown that high gradients can be achieved quickly in high-pressure gas-filled cavities 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 vacuum 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 series of experiments at 805 MHz using hydrogen fill pressures up to 0.01 g/cm3 of H2 have demonstrated high electric field gradients and scaling with the DC Paschen law limit, up to ~30 MV/m, depending on the choice of electrode material. For higher field stresses, the breakdown characteristics deviate from the Paschen law scaling. Fully-kinetic 0D collisional particle-in-cell (PIC) simulations give breakdown characteristics in H2 and H2/SF6 mixtures in good agreement with the 805 MHz experimental results below this field stress threshold. The impact of these results on gas-filled RF accelerating cavity design will be discussed.
LBNL, Berkeley, California, USA
LLNL, Livermore, California, USA
The Particle-In-Cell Framework Warp is being developed by the Heavy Ion Fusion US program to guide the development of accelerators for high energy density experiments and ultimately for inertial fusion energy. Accurate predictions of the beam phase space are important for understanding the limits to the pulse compression, in particular for NDCX-II now under construction at LBNL. We will present a new numerical method that correct for the effects of linear correlations, offering accurate mapping of energy spread and temperature. The interaction of the beam with the neutralizing plasma can affect non linearly the phase space of the beam. We will present fully kinetic simulation of the beam/plasma interaction aimed toward a better understanding of these effects and possibilities for mitigating or exploiting them. We will also present an application of the original warped coordinate algorithm to the modeling of charge separation in the transition of a 50 MeV singly charged Uranium beam to higher charge state upon passing through a stripping foil, with the goal of decreasing the cost of a Heavy Ion Fusion driver. We also describe studies of beams in plasmas and of injector optimization.
Used resources of NERSC.