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plasma

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MOPC038 Ultra-high Brightness Electron Beams by All-optical Plasma-based Injectors laser, electron, undulator, emittance 157
 
  • V. Petrillo
    Universita' degli Studi di Milano, Milano
  • L. Serafini, P. Tomassini
    INFN-Milano, Milano
  We study the generation of low emittance high current mono-energetic beams from plasma waves driven by ultra-short laser pulses, in view of achieving beam brightness of interest for FEL applications. The aim is to show the feasibility of generating nC charged beams carrying peak currents much higher than those attainable with photoinjectors, together with comparable emittances and energy spread, compatibly with typical FEL requirements. We identified a particularly suitable regime which is based on a LWFA plasma driving scheme on a gas jet modulated in areas of different densities with sharp density gradients. Simulations show that in the first regime, using a properly density modulated gas jet, it is possible to generate beams at energies of about 30 MeV with peak currents of 20 kA, slice transverse emittances as low as 0.3 mm.mrad and energy spread around 0.4%. This beams break the barrier of 1018 A/(mm.mrad)2 in brightness, a value definitely above the ultimate performances of photo-injectors, therefore opening a new range of opportunities for FEL applications. A few examples of FELs driven by such kind of beams injected into laser undulators are finally shown.  
 
MOPC084 A Laser-driven Acceleration Method ion, laser, target, acceleration 253
 
  • L. Torrisi, S. Gammino, D. Margarone
    INFN/LNS, Catania
  • A. Borrielli, F. Caridi
    INFN & Messina University, S. Agata, Messina
  A laser ion source (LIS) has been obtained with a repetitive pulsed laser at power density of the order of 1010 W/cm2 or higher, with pulse duration of the order of ns and repetition rate of the order of tens Hz. Any solid target can be ablated producing plasma with equivalent temperatures higher than 100 eV, densities higher than 1017/cm3 and charge states higher than 10+. Extracted current densities can be higher than 10 mA/cm2. The study of the electric fields generated inside the non equilibrium plasmas is a by-product of the research in ion generation. Ions are emitted from the plasma in the direction of the electric field with energies of the order of 50 eV/nucleon or higher, depending on the laser intensity. Emitted ions have a Boltzmann ion energy distribution depending on the ion charge state. Previous papers show that the electric field is as high as 10 MV/cm in our case. Magnetic trapping of electrons has been used to increase the ion acceleration, focusing and current. This new ion acceleration method based on LIS seems to be very interesting because it may permit to build accelerators with small dimensions and relatively low cost.  
 
MOPC139 Refractory Ovens for ECR Ion Sources and Their Scaling ion, ion-source, resonance, electron 397
 
  • M. Cavenago, A. Galatà, M. Sattin
    INFN/LNL, Legnaro, Padova
  • T. Kulevoy, S. Petrenko
    ITEP, Moscow
  The radiofrequency (rf) oven can be used as a metal vapour injector for Electron Cyclotron Resonance ion source; the application to high temperature boiling metals (like Cr, Ti and V) was recently demonstrated. Duration and reusability of oven parts were excellent, since crucible only need to be maintained at a temperature Ts larger than other parts; for vanadium case, achieved Ts was up to 2300 K with about 280 W of rf power, with the present design and size, tailored to our 14.4 GHz ECRIS. Optimization for different sources is discussed, and modern design tools are reviewed. Materials, more than rf power coupling, emerge as ultimate limits. Comparisons of results with resistive oven and sputter probes and with different metals are briefly reported.  
 
MOPC140 Status of the Multipurpose Fully Superconducting ECR Ion Source ion, injection, diagnostics, extraction 400
 
  • G. Ciavola, L. Celona, S. Gammino, F. Maimone, D. Mascali
    INFN/LNS, Catania
  • H. A. Koivisto
    JYFL, Jyvaskyla
  • R. Lang, J. Maeder, J. Rossbach, P. Spaedtke, K. Tinschert
    GSI, Darmstadt
  The MSECRIS source has been designed with the aim to exceed the highest currents of highly charged heavy ions available up to now. It is based on a minimum B trap made of a hexapole and three solenoids. The design magnetic field is 2.7 T for the hexapole and 4.5 T for the mirror field, in order to permit to operate not only at 28 GHz but also at higher frequency, thus increasing the plasma density and finally the beam current. Such high level of magnetic field is a challenge because of the forces arising on the superconducting coils and it largely exceeds the highest magnetic field available for existing ECRIS. A description of the source and of its preliminary results will be given. The source has been built in the frame of the European collaboration EURONS/JRA07-ISIBHI and it is now installed at the EIS testbench of GSI.  
 
MOPC143 Multi-beamlet Study of Beam Transport in the ISIS H- Ion Source Analysing Magnet extraction, ion-source, ion, acceleration 409
 
  • D. C. Faircloth, S. R. Lawrie, A. P. Letchford, M. E. Westall, M. Whitehead, T. Wood
    STFC/RAL/ISIS, Chilton, Didcot, Oxon
  The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). The existing 90° analysing magnet on the ISIS H- Penning ion source does not perfectly transport the beam after extraction. The present ion source has a 10 mm x 0.6 mm slit extraction aperture. To understand how the beam is transported in the analysing magnet, new ion source aperture plates are manufactured with 5 individual holes instead of a slit. These holes produce separate beamlets that are used to study transport in the sector magnet. This paper details the experiments with the modified aperture plates on the Ion Source Development Rig (ISDR) at ISIS.  
 
MOPC145 Commissioning of the ECR Ion Sources at CNAO Facility ion, ion-source, emittance, extraction 415
 
  • G. Ciavola, L. Celona, S. Gammino, F. Maimone
    INFN/LNS, Catania
  • C. Bieth, W. Bougy, G. Gaubert, O. Tasset, A. C.C. Villari
    PANTECHNIK, BAYEUX
  • A. Galatà
    INFN/LNL, Legnaro, Padova
  • R. Monferrato, M. Pullia
    CNAO Foundation, Milan
  The Centro Nazionale di Adroterapia Oncologica (National Center for Oncological Hadrontherapy, CNAO) is the Italian center for deep hadrontherapy. It will deliver treatments with active scanning both with proton and carbon ion beams. At CNAO two ECR sources of the Supernanogan type (built by the Pantechnik company according to specifications set by INFN) are installed and run continuously and in parallel, to allow the fast change of the particle species. The two sources are identical and can provide both particle species after a simple switch from one gas to the other, which allows as well to run the facility, in emergency, with only one source. Each source is equipped with a dedicated beam line including a spectrometer and beam diagnostics. Optimisation of beam emittance and intensity is of primary importance to obtain the necessary current at the RFQ-LINAC and then at injection. The preliminary tests have shown the complete fulfillment of the specifications in terms of beam current and emittance and the final tests are ongoing. A description of the source design and performance will be presented.  
 
MOPC146 Development of Piezoelectric Pulse Gas Valve for Small ECR Ion Source ion, ion-source, extraction, vacuum 418
 
  • M. Ichikawa, H. Fujisawa, Y. Iwashita, Y. Tajima, H. Tongu, M. Yamada
    Kyoto ICR, Uji, Kyoto
  In a conventional ion source, the source gas is continuously fed even in its pulse operation. This requires a high load to a vacuum pumping system. The situation is prominent when the gas load is relatively higher in such a high current ion source. In order to improve this situation, we try to supply gas only when it is needed by synchronizing the gas feed with the extraction of the ion beam. We have developed a small pulse-gas-valve using a commercially available disc-shape piezoelectric element. This valve is small enough to be mounted in our ECR ion source and is capable of very fast open-and-close operation of an order of kHz repetition. A small ECR ion source with this valve will be presented.  
 
MOPC147 Measurement of Ion Beam from Laser Ion Source for RHIC EBIS ion, laser, target, ion-source 421
 
  • T. Kanesue
    Kyushu University, Department of Applied Quantum Physics and Nuclear Engineering, Fukuoka
  • M. Okamura
    BNL, Upton, Long Island, New York
  • J. Tamura
    Department of Energy Sciences, Tokyo Institute of Technology, Yokohama
  Laser ion source (LIS) is a candidate of the primary ion source for the RHIC EBIS. LIS will provide intense charge state 1+ ions to EBIS for further ionization. We measured plasma properties of a variety of atomic species such as Si, Fe and Au using the second harmonics of Nd:YAG laser (532 nm wave length, up to 0.82 J / 6 ns). Since a suitable laser power density for production of charge state 1+ ions is different from different species, laser power density was optimized to obtain a maximum beam intensity in each species. Also the results of emittance measurement using pepper pot after ion extraction with about 20 kV extraction voltage will be shown. Based on the obtained results, performance of the LIS as the primary ion source for EBIS will be discussed in this paper.  
 
MOPC151 Status of the Versatile Ion Source VIS extraction, ion, proton, controls 430
 
  • F. Maimone, L. Celona, F. Chines, G. Ciavola, G. Gallo, N. Gambino, S. Gammino, D. Mascali, R. Miracoli, S. Passarello, E. Zappalà
    INFN/LNS, Catania
  The characteristics of the ideal injector for high power proton accelerators has been studied in the past with the TRIPS ion source built at INFN-LNS, Catania and now in operation at INFN-LNL, Legnaro. The beam production must obey to the request of high brightness, stability and reliability. The new Versatile Ion Source (VIS) is a permanent magnet version of the TRIPS source with a simplified and robust extraction system. It operates up to 80 kV without a bulky high voltage platform, producing multi-mA beams of protons and H2+. The description of the source design and the preliminary performance will be presented. An outline of the forthcoming developments is given, with particular care to the use of a low loss dc break and to the use of a travelling wave tube amplifier to get an optimum matching between the microwave generator and the plasma.  
 
MOPC154 Method for Efficiency and Time Response Measurement on Diverse Target Ion Sources with Stable Alkali ion, ion-source, target, gun 436
 
  • A. Pichard, J. A. Alcantara Nunez, R. Alves Conde, M. Dubois, R. Frigot, P. Jardin, P. Lecomte, J. Y. Pacquet, M. G. Saint-Laurent
    GANIL, Caen
  Developments of new setups for radioactive ion beam production by the isotope-separator-on-line (ISOL) method are underway at GANIL in the frame of the SPIRAL (Système de Production d’Ions Radioactifs Accélérés en Ligne) and SPIRAL-II projects. The measurement of total efficiency and time behaviour of these new target/ion-source systems (TISSs) is a crucial step for these devices which aims to produce short-lived isotopes with high intensity. The overall atom-to-ion transformation efficiency depends on several processes: diffusion of the atoms out of the production target, effusion towards the ion source and ionization. The efficiency can be extracted using the ratio between the emerging yield and implanted flux in the TISS. Several methods have already been developed to achieve these measurements: the use of stable or radioactive beams, gas injection, or the introduction of solid material into the TISS. This paper focuses primarily on a method that uses stable alkali. A pulsed/CW alkali ion gun has been built and will be used to optimise diverse TISSs.

[1] C. Eléon et al., Proceedings of the XVe International Conference EMIS, 24-29th June 2007, Deauville, France, to be published.

 
 
MOPC156 ECR Ion Source for the KEK All-ion Accelerator ion, extraction, vacuum, simulation 442
 
  • H. Suzuki, Y. Arakida, T. Iwashita, M. Kawai, T. Kono, K. Takayama
    KEK, Ibaraki
  • S. I. Inagaki
    Kyushu University
  • K. Okazaki
    Nippon Advanced Technology Co. Ltd., Ibaraki-prefecture
  R&D works to realize an all-ion accelerator (AIA)* -capable of accelerating all ions of any possible charge state, based on the induction synchrotron concept, which was demonstrated using the KEK 12 GeV-PS**, are going on. As an ion source for the KEK-AIA, an electron cyclotron resonance (ECR) ion source has been developed. Permanent magnets made of NdFeB to generate a cusp field and 9.4 GHz microwave to energize plasma electrons have been employed. The microwave power of 750 W generated in a traveling wave tube is focused into the interaction region with a horn antenna. Regarding the cut off density for 9.4 GHz, the vacuum and the gas feeding system has been designed. The base pressure of 1·10-5 Pa is reached with a single turbo molecular pump of 300 l/min, and the gas flow rate less than 1 cc/min is maintained with a mass flow controller. The plasma chamber is water-cooled against Joule heating. The geometry of the extraction electrodes and the downstream transport line have been optimized by IGUN simulations. The whole system will be embedded in the high voltage terminal box of 200 kV. Details of the design and the preliminary test will be described at this conference.

*K. Takayama, Y. Arakida, T. Iwashita, Y. Shimosaki, T. Dixit, and K. Torikai, J. of Appl. Phys. 101, 063304 (2007).
**K. Takayama et al., Phys. Rev. Lett. 98, 054801 (2007).

 
 
MOPD023 Parametric Study of a Novel Coaxial Bunched Beam Space-charge Limit space-charge, electron, focusing, klystron 493
 
  • M. Hess
    IUCF, Bloomington, Indiana
  Recently, a non-trivial space-charge limit for off-axis bunched electron beams in a coaxial conducting structure was derived theoretically*. The space-charge limit describes the minimum strength of an external solenoidal focusing field which is needed to stabilize the beam’s center-of-mass motion in the presence of induced surface charges on the coaxial structure. In this paper, we perform a parametric study of the space-charge limit to numerically determine its dependency on the conducting structure geometry, i.e., the ratio of the inner and outer conductor radii, as well as its’ dependency on the transverse and longitudinal bunch distributions. As an application, we show how this parametric study can be important for the design of high-power microwave sources, such as the UC-Davis/SLAC 2.8 GHz coaxial ubitron oscillator**.

*M. Hess, accepted for publication in IEEE Trans. Plasma Sci. (2008).
**A. J. Balkcum et al. IEEE Trans. Plasma Sci., vol. 26, pp. 548-555, 1998.

 
 
MOPP065 Microwave Transmission Measurement of the Electron Cloud Density in the Positron Ring of PEP-II electron, dipole, vacuum, simulation 694
 
  • M. T.F. Pivi, A. Krasnykh
    SLAC, Menlo Park, California
  • J. M. Byrd, S. De Santis, K. G. Sonnad
    LBNL, Berkeley, California
  • F. Caspers, T. Kroyer, F. Roncarolo
    CERN, Geneva
  Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a section of the accelerator. We infer the absolute phase shift with relatively high accuracy from the phase modulation of the transmission due to the modulation of the electron cloud density from a gap in the positively charged beam. We have used this technique for the first time to measure the average electron cloud density over a 50 m straight section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center. We have also measured the variation of the density by using low field solenoid magnets to control the electrons.  
 
MOPP073 Plasma Lens for Muon and Neutrino Beams target, proton, focusing, simulation 718
 
  • S. A. Kahn, S. Korenev
    Muons, Inc, Batavia
  • M. B. Bishai, M. Diwan, J. C. Gallardo, A. Hershcovitch, B. M. Johnson
    BNL, Upton, Long Island, New York
  The plasma lens is examined as an alternate to focusing horns and solenoids for use in a neutrino or muon beam facility. The plasma lens concept is based on a combined high current lens/target configuration. The current is fed at electrodes located upstream and downstream form the target where pion capturing is needed. The current flows primarily in the plasma, which has a lower resistivity than the target. A second plasma lens section, with an additional current feed, follows the target to provide shaping of the plasma for optimum focusing. The plasma lens is immersed in an additional solenoidal magnetic field to facilitate the plasma stability. The geometry of the plasma is shaped to provide optimal pion capture. Simulations of this plasma lens system have shown a 25% higher neutrino production than the horn system. Plasma lenses have additional advantages: larger axial currents than horns, minimal neutrino contamination during antineutrino running, and negligible pion absorption or scattering. Results from particle simulations using plasma lens will be presented.  
 
MOPP095 Advanced Experimental Techniques for RF and DC Breakdown Research electron, vacuum, simulation, ion 775
 
  • J. W. Kovermann
    RWTH, Aachen
  • S. Calatroni, A. Descoeudres, T. Lefevre, W. Wuensch
    CERN, Geneva
  Advanced experimental techniques are being developed to do in-situ analysis of DC and RF breakdowns. First measurements with a specially built spectrometer have been made with a DC spark setup at CERN and with CLIC accelerating structures in the 30GHz power test facility. This spectrometer measures the light intensity development during a breakdown for narrow wavelength intervals in the visible and near infrared range which will give information about the involved elements, temperature and plasma parameters and eventually precursors of a breakdown. Planned experiments for X-ray spectroscopy and imaging, measurements of RF-signals and ion and electron energy distribution and infrared imaging of breakdown sites are presented.  
 
MOPP161 Plasma Etching Rates and Surface Composition of Bulk Nb Treated in Ar/Cl2 Microwave Discharge electron, survey, ion, monitoring 928
 
  • M. Raskovic, S. Popovic, J. Upadhyay, L. Vuskovic
    ODU, Norfolk, Virginia
  • H. L. Phillips, A-M. Valente-Feliciano
    Jefferson Lab, Newport News, Virginia
  To achieve theoretically predicted values of the accelerating fields in superconducting radiofrequency (SRF) cavities, their inside surface should be fairly smooth and free of impurities. Thus, surface preparation is the critical step in production of SRF cavities. Plasma etching process is a dry chemistry technique that can be used to achieve these requirements. It is based on interaction between reactive halogen species produced in the glow discharge and the surface. During this process, volatile Nb halides are evaporated from the surface of Nb, removing the mechanically damaged and contaminated layer. We present treatment of bulk Nb samples in the Ar/Cl2 microwave discharge. We achieved etching rates comparable to the rates obtained with the electropolishing method without introducing impurities in Nb. The rate dependence on various discharge parameters and reactive gas composition is presented. Surface composition and topology measurements were carried out before and after plasma treatment to determine level of impurities. Optimal experimental conditions determined on samples will applied be on single cell cavities, pursuing improvement of their RF performance.  
 
TUZG01 IFMIF: Status and Developments target, beam-transport, rfq, radio-frequency 974
 
  • P. Garin
    CEA, Gif-sur-Yvette
  On the way to the fusion demonstrator (DEMO), ITER is designed to tackle the physics properties of thermonuclear plasmas in relevant conditions, as well as the key technologies. But because of its experimental character, the amount of neutrons produced by ITER all along its life will be about two orders of magnitude below what is expected in a fusion Power Plant. A dedicated facility, called IFMIF (International Fusion Materials Irradiation Facility), is thus mandatory to study and analyse the behaviour of materials under a high flux of energetic neutrons (14 MeV). The Engineering Validation and Engineering Design Activities (EVEDA), launched in the framework of a bilateral agreement between Euratom and the Government of Japan in 2007, with a duration of 6 years, aims at producing the detailed design file enabling the construction of IFMIF. The key systems will be also tested during this phase. One of the most important one is the accelerator, bringing a deuteron beam of 125 mA to an output energy of 40 MeV. The whole facility will be described, including the detail of the accelerator, as well as the organisational framework of the project.  
slides icon Slides  
 
TUPC104 On Application of Cherenkov Radiation in Presence of Dispersive Anisotropic Materials to Diagnostics of Ultrarelativistic Beams radiation, diagnostics, vacuum 1302
 
  • A. V. Tyukhtin
    Saint-Petersburg State University, Saint-Petersburg
  One of the main methods of diagnostics of charge particles and beams is based on application of Cherenkov radiation. The attractive idea is application of modern metamaterials for these goals. It has been noted that anisotropic dispersive materials can give some important preferences*. However imperfection of Cherenkov diagnostics is low sensibility with respect to energies of ultra-relativistic particles having large Lorentz factor. In this work, it will be shown that this limitation can be overcome with help of using special anisotropic dispersive media (they can be produced in the form of artificial metamaterials). Properties of Cherenkov radiation in the presence of such material will be analyzed. The case of unbounded material and the case of waveguide loaded with such material will be considered. It will be shown that the convenient method of determination of Lorentz factor can be based on measurement of frequencies of harmonics generated in the waveguide. This technique allows obtaining good sensibility for very large magnitudes of Lorentz factor. Other possibilities of application of anisotropic and left-handed metamaterials to beam diagnostics will be discussed as well.

*A. V. Tyukhtin, S. P. Antipov, A. Kanareykin, P. Schoessow. Proc. of PAC07, Albuquerque, NM, USA, p.4156 (2007).

 
 
TUPP141 Electron Accelerators for Cleaning Flue Gases and for Oil Liquefaction electron, radiation, cathode, vacuum 1848
 
  • S. Korenev, R. P. Johnson
    Muons, Inc, Batavia
  High-power electron beams can be used to reduce the environmental impact of coal and oil-fired power generating plants by removing harmful materials from flue gases. This technology has been tested in the laboratory and at smaller industrial levels, but to make it economically attractive, the accelerator costs must be reduced and the efficiency must be increased for removing toxic components in low concentrations. We propose a simple electron accelerator with a wide beam to reduce costs. To remove toxic materials we propose a plasma reactor for desulfurization and selective catalytic reduction. The designs of 0.5 to 1.0 MeV accelerators with 20 to 100 kW average power are considered, along with the design of a plasma reactor for flue gas treatment. The design of a pilot facility for the oil industry is also presented.  
 
TUPP143 Collective Ionization by Attosecond Electron Bunches electron, target, ion, collective-effects 1851
 
  • A. Ogata, T. Kondoh, K. Norizawa, J. Yang, Y. Yoshida
    ISIR, Osaka
  Present accelerator technology has realized linac bunch length on the order of femtosecond. If the bunch length becomes onto the order of attosecond, its inverse is comparable to the ionization frequency; ionization potential divided by Plank's constant. The stopping power then becomes proportional to square of the number of bunch electrons. Such a bunch ionizes the target collectively. This collective, or coherent ionization will provide us plenty of applications including unknown ones at the present. This phenomenon has historically been expected in cluster beams, which can be regarded as ultra-short bunches. The present paper adapts formalism of stopping power of a medium characterized by a dielectric function against cluster beams to that against electron bunches. It then describes some numerical calculations on the collective ionization by the attosecond electron bunches.  
 
TUPP148 Multigrid Negative Ion Source Test and Modeling ion, electron, ion-source, simulation 1857
 
  • M. Cavenago
    INFN/LNL, Legnaro, Padova
  • V. Antoni, G. Serianni, P. Veltri
    Consorzio RFX, Euratom ENEA Association, Padova
  Negative ion sources are a fundamental ingredient of neutral ion beam injectors for tokamak, like the ITER project and beyond. While detail of formation of negative ions and meniscus of the plasma beam interface at source extraction at source extraction is still debated, reasonable modelling of the beam extraction is well possible. A project of a small source (up to 9 beamlet of 15 mA each of H-, 60 kV acceleration voltage) is here described, and relevant modeling tools are reviewed. Power load deposition on the extraction grid (about 1.5 kW total) and on the source walls (comparable) need accurate cooling design. The extracted beam is direclty useful for wall damage studies.  
 
WEOBG02 Experimental Results of a Plasma Wakefield Accelerator Using Multiple Electron Bunches electron, resonance, simulation, diagnostics 1912
 
  • E. Kallos, T. C. Katsouleas, P. Muggli
    USC, Los Angeles, California
  • W. D. Kimura
    STI, Washington
  • K. Kusche, J. H. Park, I. Pogorelsky, D. Stolyarov, V. Yakimenko
    BNL, Upton, Long Island, New York
  We present some preliminary experimental results of a plasma wakefield accelerator technique which utilizes multiple electron bunches in order to drive a plasma wave. The experiments were performed at the Accelerator Test Facility of Brookhaven National Laboratory where 5-8 equidistant bunches with a spacing which was varied between 100-250 m were fed into a 6mm-long capillary discharge plasma. By varying the time delay of the bunches with respect to the discharge different plasma densities could be tuned, and the effects of the plasma on the bunches were recorded. Such multiple bunch schemes are of great interest because they can provide increased efficiencies and high transformer ratios for advanced accelerators.  
slides icon Slides  
 
WEPC146 Plasma Lens of the ITEP Heavy Ion Accelerator ion, focusing, heavy-ion, simulation 2353
 
  • A. A. Drozdovsky, V. Abramenko, M. M. Basko, A. Golubev, D. D. Iosseliany, A. V. Kantsyrev, A. P. Kuznetsov, Yu. B. Novozhilov, O. V. Pronin, P. V. Sasorov, S. M. Savin, B. Y. Sharkov, V. V. Yanenko
    ITEP, Moscow
  At ITEP, on the bases of the TWAC-ITEP (Terawatt Accumulator) complex, a new facility is being built to conduct research at high energy densities in matter*. Application of a plasma lens to this area of research has a number of essential advantages in comparison with the traditional system based on quadruple lenses**. In accordance with the principal goals of this project, a pulse-power generator has been developed, with which a stable discharge current of up to 250 kA and duration of 4 μs has been achieved and which was used for experimental and theoretical investigation of the plasma lens performance. The plasma lens was installed into the exit channel of the TWAC accelerator complex, and its testing began by focusing of a C+6 beam with the ion energy of 200 MeV/a.u.m. As one of the first results, a minimum focal spot diameter of 350 μm FWHM has been measured at a target distance of 50 mm from the end of the discharge tube. The lens parameters were as follows: capacitance – 24 μF, charging voltage – 13 kV, discharge current – 220 kA, current half-wave – 4 μs, argon pressure – 3 mbar.

*Sharkov B. Yu. et al. Nucl. Instr. Meth. A464 (2001), p. 1.
** D. H.H. Hoffmann et al. Nucl. Instr. Methods Phys. Res., Sect. B 161-163, (2000), p. 9.

 
 
WEPP111 Modeling Breakdown in RF Cavities Using Particle-in-cell (PIC) codes simulation, electron, background, ion 2767
 
  • S. Mahalingam, J. R. Cary, P. Stoltz, S. A. Veitzer
    Tech-X, Boulder, Colorado
  A main limitation on future accelerator projects is breakdown of metallic structures. We have developed computer models of the process of breakdown using Particle-In-Cell (PIC) codes which include: Fowler-Nordheim field emission due to large surface electric fields, impact ionization of neutral gas, ion-induced secondary electron emission, ion-induced sputtering of neutrals, the effects of applied magnetic fields, plasma radiation effects, and surface heating. Two computational tools have been used to self-consistently model the breakdown. These are
  1. OOPIC Pro, a 2-Dimensional serial electromagnetic code with cylindrical coordinates, and
  2. VORPAL, a 3-Dimensional massively parallel electromagnetic code with cartesian grids.
We describe here the results of our numerical experiments including the effects of applied magnetic field strength and direction on the breakdown process, sensitivity of breakdown triggers on field emission parameters, and the potential to measure the onset of breakdown by examining impurity radiation. We show comparison with breakdown experiments performed at Fermilab and Argonne for copper structures being considered for a future muon collider project.
 
 
WEPP127 ALaDyn: a High Accuracy Code for the Laser-plasma Interaction simulation, laser, electron, acceleration 2794
 
  • C. Benedetti, A. Sgattoni
    Bologna University, Bologna
  • P. Tomassini
    INFN-Milano, Milano
  ALaDyn (Acceleration by LAser and DYNamics of charged particles) is a relativistic fully parallelized PIC code to investigate the interaction of a laser pulse with a plasma and/or an externally injected beam. The code is based on compact high order finite differences schemes ensuring higher spectral accuracy compared to standard Yee schemes. We present the main features and the performances of the code together with a set of validation tests obtained comparing the results with well-established analytical/numerical results. A preliminary benchmarking with the PIC code VORPAL is also presented. An application to a physically relevant case concerning the externally-injected configuration proposed for the CNR-INFN experiment PLASMONX will be analyzed.  
 
WEPP132 Efficiency Enhancement of Active High-Power Pulse Compressors coupling, extraction, controls 2803
 
  • S. V. Kuzikov, Yu. Danilov, A. A. Vikharev
    IAP/RAS, Nizhny Novgorod
  High power microwaves needed to accelerate particles in multi-TeV colliders can be produced using active pulse compressors. An active compressor has a storage cavity whose Q-factor is modulated by means of RF switch. An efficiency of such compressor is limited due to diffraction losses at power accumulation regime and in conventional case does not exceed 81.4%. A new microwave pulse compressor operated with a superposition of quasi-degenerated modes is suggested. A proper choice of eigen frequencies and Q-factors of these modes allows essential enhancement of efficiency (asymptotically up to 100%). A 30 GHz project of multi-megawatt compressor based on dual-mode circular cross-section cavity is considered.  
 
WEPP134 Ultra-short x-ray Radiation coming from a Laser Wakefield Accelerator electron, laser, radiation, betatron 2809
 
  • V. Leurent, L. Divol, T. Doeppner, D. H. Froula, S. H. Glenzer, P. Michel, J. Palastro
    LLNL, Livermore, California
  • C. E. Clayton, C. Joshi, K. A. Marsh, A. E. Pak, J. E. Ralph, T.-L. Wang
    UCLA, Los Angeles, California
  • B. B. Pollock, G. R. Tynan
    UCSD, La Jolla, California
  A Laser Wakefield Accelerator (LWFA) is under development at LLNL Jupiter Laser Facility to produce multi-GeV electron bunches promising to provide a bright and compact source of x-ray radiation for high energy density studies. The interaction of a high power (200 TW), short laser (50 fs) pulse with neutral He gas can accelerate monoenergetic electrons up to 1 GeV in a stable self-guiding regime*, over a dephasing length of 1 cm (for a plasma density of 1.5x1018 cm-3), overcoming the limitation of vacuum diffraction and allowing long interaction lengths for LWFA. The waveguide can be extended over several centimeters by using a novel scheme, which employs an external magnetic field (up to 5 T uniform along 12 cm) to control the radial heat flux** resulting from the interaction of a high energy (100 J), long pulse (1 ns) laser with a gas tube. The acceleration of electrons over several centimeters can produce multi-GeV bunches and thus a powerful x-ray source. Analysis will be presented on femtosecond x-ray radiation produced by wiggling an electron bunch with energy above 1 GeV in this new LWFA scheme.

* W. Lu et al., Phys. Rev. Spec. Top-ac 10, 061301 (2007)
** D. H. Froula et al., Phys. Rev. Lett. 98, 135001 (2007)

 
 
WEPP138 Experimental Demonstration of Ultrashort μJ-Class Pulses in the Terahertz Regime from a Laser Wakefield Accelerator laser, radiation, electron, controls 2818
 
  • G. R.D. Plateau, C. G.R. Geddes, N. H. Matlis, C. B. Schroeder, C. Toth, J. van Tilborg
    LBNL, Berkeley, California
  • O. Albert
    LOA, Palaiseau
  • E. Esarey, W. Leemans
    University of Nevada, Reno, Reno, Nevada
  Ultrashort terahertz pulses with energies in the μJ range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV* and energy spreads of a few-percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because they are only tens of femtoseconds long, electron bunches can radiate coherently (CTR) in a wide bandwidth (~ 1 - 10 THz) yielding terahertz pulses of high intensity**,***. In addition to providing a non-invasive bunch-length diagnostic**** and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Here we present energy-based measurements using a Golay cell and a single-shot electro-optic technique which were used to characterize the full waveform of these μJ-class THz pulses, including phase and amplitude information.

*W. P. Leemans et al. N. P. 2/696 (2006).
**W. P. Leemans et al. P. R.L. 91/074802 (2003).
***C. B. Schroeder et al. P. R.E 69/016501 (2004).
****J. van Tilborg et al. P. R.L. 96/014801 (2006).

 
 
WEPP146 Generation of Electron Microbunches Trains with Adjustable Sub-picosecond Spacing for PWFA and FEL applications electron, laser, quadrupole, emittance 2830
 
  • P. Muggli, E. Kallos
    USC, Los Angeles, California
  • M. Babzien, K. Kusche, V. Yakimenko
    BNL, Upton, Long Island, New York
  We demonstrate that trains of subpicosecond electron microbunches, with subpicosecond spacing, can be produced by placing a mask in a large dispersion region of the beam line where the beam transverse size is dominated by the correlated energy spread. The particles are selected based on the scattering of their emittance at the mask. The electrons that hit the solid arts of the mask are subsequently lost. The mask spatial pattern is converted into a time pattern in the dispersion-free region of the beam line. The experiment was performed with the Brookhaven National Laboratory Accelerator Test Facility 60 MeV beam. We show that the number, length, and spacing of the microbunches can be controlled through the parameters of the beam and the mask. Trains with one to eight equidistant microbunches are produced. The microbunches spacing is adjusted in the 100 to 300 microns or 300 fs to 1 ps range and comparable microbunch length. The train structure is measured using CTR interferometry, and is stable in time and energy. Such microbunch trains can be further compressed and accelerated, and have applications to free electron lasers (FELs) and plasma wakefield accelerators (PWFAs).  
 
WEPP155 Laser Driven Linear Collider laser, acceleration, collider, damping 2850
 
  • A. A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  We continue detailed description of scheme allowing long term acceleration with >10 GeV/m in multi-cell microstructures side-illuminated by laser radiation. The basis of the scheme is a fast sweeping device for the laser bunch. After sweeping the laser bunch has a slope ~45° with respect to the direction of propagation. So the every cell of microstructure becomes excited locally only for the moments, when the particles are there. Self consistent parameters of collider based on this idea allow consideration this type of collider as a candidate for the near-future accelerator era.  
 
THPC085 VORPAL Simulations Relevant to Coherent Electron Cooling electron, ion, simulation, hadron 3185
 
  • G. I. Bell, D. L. Bruhwiler, A. V. Sobol
    Tech-X, Boulder, Colorado
  • I. Ben-Zvi, V. Litvinenko
    BNL, Upton, Long Island, New York
  • Y. S. Derbenev
    Jefferson Lab, Newport News, Virginia
  Coherent electron cooling (CEC)* combines the best features of electron cooling and stochastic cooling, via free-electron laser technology**, to offer the possibility of cooling high-energy hadron beams with order-of-magnitude shorter cooling times. Many technical difficulties must be resolved via full-scale 3D simulations, before the CEC concept can be validated experimentally. VORPAL is the ideal code for simulating the “modulator” and “kicker” regions, where the electron and hadron beams will co-propagate as in a conventional electron cooling section. Unlike previous VORPAL simulations*** of electron cooling physics, where dynamical friction on the ions was the key metric, it is the details of the electron density wake driven by each ion in the modulator section that must be understood, followed by strong amplification in the FEL. We present some initial simulation results. In particular, we compare the semi-analytic binary collision model with electrostatic particle-in-cell (PIC).

*Ya. S. Derbenev, COOL ’07 Proc. (2007).
**V. N. Litvinenko and Ya. S. Derbenev, FEL ’07 Proc. (2007).
***A. V. Fedotov et al. Phys. Rev. ST/AB 9, 074401 (2006).

 
 
THPC098 Halo characterization of initially mismatched beams through phase-space modeling emittance, simulation, focusing, coupling 3206
 
  • R. P. Nunes, F. B. Rizzato
    IF-UFRGS, Porto Alegre
  This work discusses a method of characterizing the beam particles with just some assumptions about the entire beam phase-space topology. At equilibrium, the beam phase-space can be recognized as composed by almost two distinct regions: a thin horizontal branch over the r axis that is populated by the core particles and a curve branch in the dr/ds x r plane, which is populated by the halo particles. Since these regions have a regular shape, then it is readily possible to convert them to an analytical expression. Two distinct shapes have been employed (circular and elliptical) to model the beam halo branch. With this, all usual initial beam mismatch values are covered with accuracy to determine the beam envelope and emittance at equilibrium. Full self-consistent N-particle beam simulations have been carried out and its results compared with the ones obtained with the model. Results agreed nice for all analyzed mismatch cases.  
 
THPC100 Collisionless Relaxation in the Transport of Space Charge Dominated Beams simulation, focusing, space-charge, resonance 3209
 
  • R. Pakter, Y. Levin, T. N. Teles
    IF-UFRGS, Porto Alegre
  Relaxation to a final stationary state of particles interacting through long-range forces, such as Coulomb, is intrinsically different than that of systems with short-range interactions. While in the latter case it is known that the interparticle collisions drive the system to an equilibrium Maxwell-Boltzmann distribution, in the former case, the collision duration time diverges and the state of thermodynamic equilibrium is never reached. In this paper, a theory is presented which allows to quantitatively predict the final stationary state achieved by a transported space-charge dominated beam during a process of collisionless relaxation*. It is shown that a fully matched beam relaxes to a Fermi-Dirac distribution. However, when a mismatch is present and the beam oscillates, halo formation leads to a phase separation. The theory developed allows to quantitatively predict both the density and the velocity distributions in the final stationary state, including the halo.

* Y. Levin, R. Pakter, and T. N. Teles, Phys. Rev. Lett., 100, 040604 (2008).

 
 
THPC103 Wave Breaking and Test Particle Dynamics in Inhomogeneous Beams emittance, simulation, focusing, space-charge 3218
 
  • F. B. Rizzato, Y. Levin, R. P. Nunes, R. Pakter, E. G. Souza
    IF-UFRGS, Porto Alegre
  This work analyzes the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation. Wave breaking is shown to relax the mismatched beam and we make use of Lynden-Bell's theory of violent relaxation to estimate characteristics of the relaxed state.  
 
THPC104 Optical Diagnostic on Gabor Plasma Lenses electron, ion, emittance, simulation 3221
 
  • K. Schulte, M. Droba, O. Meusel, U. Ratzinger
    IAP, Frankfurt am Main
  Gabor lenses have been built and successfully been used for the focussing of particle beams. In the case of a positive ion beam the space charge of the confined electron cloud may cause an over compensation of the ion beam space charge force and consequently focus the beam. The nonneutral plasma (NNP) is influenced by the external fields and its current state can be determined by the beam emittance growth. Experiments using a high field Gabor lens have shown a correlation between the thermalization of the enclosed electron cloud and the focussing quality. A three segmented Gabor lens was constructed recently for a more detailed investigation of the plasma parameters as a function of the external fields. The commissioning of the lens has been finished successfully and the light emitted by the interaction between the electron cloud and the residual gas has been observed. In a next step the experiments will concentrate on the spectral analyses of the emitted light to evaluate the temperature and density distribution of the confined NNP. Experimental results will be presented in comparison with numerical simulation.  
 
THPP052 Electron Cooling Force Calculations for HESR electron, ion, antiproton, beam-transport 3482
 
  • K. Rathsman, B. Gålnander, D. Reistad
    TSL, Uppsala
  • H. Danared
    MSL, Stockholm
  The High energy storage ring HESR at FAIR is being realized by a consortium consisting of Forschungszentrum Jülich, GSI Darmstadt and Uppsala University. An important feature of this new facility is the combination of phase-space cooled beams and dense internal targets. Charmonium spectroscopy, which is one of the main items in the experimental program, requires antiproton momentum up to 8.9 GeV/c with a resolution of dp/p=0.00001. This can only be achived with electron cooling. The electron cooler proposed for HESR allows beam cooling between 1.5 GeV/c and 8.9 GeV/c. Along the 24 m interaction section beween electrons and antiprotons, the electrons are guided by a solenoid field of 0.2 T with a field straightness of 0.00001 radians rms. To predict the final momentum resolution of the antiproton beam in HESR, electron cooling force calculations, simulations of electron cooling and comparison to experimental data are needed. This paper focuses on the force calculations. The method is based on the theory by Derbenev and Skrinsky, (i.e. the Vlasov techique) and the electron cooling force is numerically calulated using adaptive Monte Carlo integration methods.  
 
THPP086 Diamond Stripper Foil Experience at SNS and PSR target, beam-losses, injection, electron 3563
 
  • R. W. Shaw, Y.-J. Chen, R. L. Coleman, D. M. Gardner, C. Luck, A. G. McDermott, M. A. Plum, L. L. Wilson
    ORNL, Oak Ridge, Tennessee
  • M. J. Borden, T. Spickermann
    LANL, Los Alamos, New Mexico
  • C. S. Feigerle
    University of Tennessee, Knoxville, Tennessee
  The SNS is currently operating at about 15% of the 1.4 MW design power, and the diamond stripper foils developed at ORNL continue to perform well. Several corrugated, nanocrystalline diamond stripping foils have been tested at SNS. Beyond about 300 C of injected charge, significant distortion and darkening of the foils is observed. These foils are currently limited in freestanding area to about 17x25 mm due to stress-induced tears in larger foils; this limit positions the residual silicon wafer mounting handle close enough to the circulating beam that additional losses have been observed. The PSR experience with these diamond foils has been promising, with the interesting observation that both the foil current due to secondary emission of electrons and the thermionic foil current are reduced for diamond foils relative to LANL/KEK foils. For comparable thickness foils, losses due to the Ho yield also appear to be higher for diamond. A recent development in our foil preparation has been a change to nano-seeded nucleation from the earlier microcrystal slurry ultrasonic abrasion technique. This has led to a more reproducible and uniform foil morphology with smaller crystallites.  
 
FRXCGM01 High Quality GeV Electron Beams from Plasma-Laser Accelerators electron, laser, synchrotron, free-electron-laser 3733
 
  • W. Leemans
    LBNL, Berkeley, California
  Accelerators are essential tools of discovery and have many practical uses. At the forefront of accelerator technology are the machines that deliver beams for particle physics, for synchrotron and free electron based radiation sources. The technology that drives these accelerators is extremely sophisticated but is limited by the maximum sustainable accelerating field. This impacts the size and cost of the device. More than two decades ago, lasers were proposed as power source for driving novel accelerators based on plasmas as the accelerating medium. An overview will be presented of what these devices can produce to date, including the 2004 demonstration of high quality electron beams* and the 2006 demonstration of GeV class beams from a 3 cm long accelerating structure**. We then discuss the key challenges for broad applicability of the technology and our goal of making a laser accelerator driven a VUV/soft x-ray free electron laser.

* C. G.R. Geddes et al., Nature 431, 538-541 (2004); S. P.D. Mangles et al., ibidem, p.535-538; J. Faure et al., ibidem, p. 541-544.
** W. P. Leemans et al., Nature Physics 2, 696-699 (2006).

 
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