Bulletin of the American Physical Society
49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007; Orlando, Florida
Session GO7: Laser Driven Electron and Ion Acceleration |
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Chair: Karl Krushelnick, University of Michigan Room: Rosen Centre Hotel Salon 7/8 |
Tuesday, November 13, 2007 9:30AM - 9:42AM |
GO7.00001: Experimental Demonstration of 1 GeV Energy Gain and Stable Self Trapping in a Laser Wakefield Accelerator D. Panasenko, A.J. Gonsalves, K. Nakamura, C. Toth, C.G.R. Geddes, E. Cormier-Michel, C.B. Schroeder, E. Esarey, W.P. Leemans, S.M. Hooker, J. Cary, D. Bruhwiler GeV-class electron accelerators have broad applications, including synchrotron facilities, free electron lasers, and high-energy physics (HEP). Laser-wakefield accelerators (LWFAs) may reduce cost and size of such accelerators (and push the HEP energy frontier), since LWFAs sustain electric fields of hundreds of GV/m, thousands of times those achievable in RF accelerators. Results will be presented on production of GeV-class beams using LWFAs$^*$. Laser pulses with peak power ranging from 10-40TW were guided in gas-filled capillary discharge waveguides of length 15mm and 33mm, allowing the production of high-quality electron beams with energy up to 1 GeV. Stable self trapping and acceleration of beams to 500 MeV with few percent energy spread was also demonstrated. Electron beam characteristics and laser guiding, and their dependence on laser and plasma parameters will be discussed and compared to simulations. $^*$Leemans et al., Nature Physics, 2006 [Preview Abstract] |
Tuesday, November 13, 2007 9:42AM - 9:54AM |
GO7.00002: Stable electron bunches with low absolute momentum spread using plasma down ramp injection in a laser wakefield accelerator C.G.R. Geddes, K. Nakamura, C. Toth, E. Esarey, C.B. Schroeder, W.P. Leemans, E. Cormier-Michel, J. Cary, D. Bruhwiler Control of particle trapping in a laser wakefield accelerator using plasma density gradients produced stable electron bunches at momenta near 1 MeV/c and with 170 keV/c FWHM momentum spread, 20 keV/c RMS central momentum variation, and repeatable charge and pointing. A 10 TW laser pulse was focused near the downstream edge of a mm-long hydrogen gas jet so that plasma density near focus decreased in the laser propagation direction. Particle simulations indicate the gradient slowed wake phase velocity resulting in stable trapping. Simulations and transition radiation experiments indicate the bunches are ultrafast. Simulations further show that the bunches can be post accelerated in plasma wakes, potentially producing stable multi-GeV beams with greatly reduced momentum spread. [Preview Abstract] |
Tuesday, November 13, 2007 9:54AM - 10:06AM |
GO7.00003: Observation of large-angle quasi-monoenergetic electrons from a laser wakefield Dmitri Kaganovich, Daniel Gordon, Antonio Ting, Natalie Milioutina, Phillip Sprangle A relativistically intense laser pulse is focused into a gas jet and quasi-monoenergetic electrons emitted at a 37 degree angle with respect to the laser axis are observed. The average energy of the electrons was between 1 and 2 MeV and the total accelerated charge was about 1 nC emitted into a 10 degree cone angle. The electron characteristics were sensitive to plasma density. The results are compared with three dimensional particle-in-cell simulations. This electron acceleration mechanism might be useful as a source of injection electrons in a laser wakefield accelerator. [Preview Abstract] |
Tuesday, November 13, 2007 10:06AM - 10:18AM |
GO7.00004: Electron Acceleration in Guiding and Non-Guiding Structures C. Kamperidis, S.P.D. Mangles, S. Kneip, K. Krushelnick, Z. Najmudin, T.P. Rowlands-Rees, A.J. Gonzalves, S.M. Hooker, E. Brunetti, J. Gallacher, D.A. Jaroszynksi, C.D.M. Murphy, P.A. Norreys, F. Budde We make a direct comparison of recent experimental results on laser wakefield acceleration, when the electrons are produced and accelerated in optically guiding and non-guiding plasma structures. In these experiments, $\sim$10TW laser pulses were guided through plasma channels of up to 50mm long, created either by external means (capillary channel formation) or by relativistic self-focusing of the laser pulse itself. Quasimonoenergetic electron beams were generated with energies up to 200MeV and energy spreads of a few \%. High resolution, large scale 2D PIC simulations suggest that although the laser pulse evolution and injection process is similar, the final acceleration results differ from one case to the other, depending on background plasma density and whether or not a preformed guiding channel is used. [Preview Abstract] |
Tuesday, November 13, 2007 10:18AM - 10:30AM |
GO7.00005: Direct Acceleration of Electrons in a Corrugated Plasma Waveguide John Palastro, Andrew York, Thomas Antonsen, Howard Milchberg Direct laser acceleration of electrons provides a low power tabletop alternative to laser wakefield accelerators. Until recently, however, direct acceleration has been limited by diffraction, phase matching, and material damage thresholds. The development of the corrugated plasma channel has simultaneously removed all of these limiting factors and promises to allow direct acceleration of electrons over many centimeters at high gradients using femtosecond lasers. We present a simple analytic model of laser propagation in a corrugated plasma channel and examine the laser-electron beam interaction. Simulations show accelerating gradients of several hundred MeV/cm for laser powers much lower than required by standard laser wakefield schemes. [Preview Abstract] |
Tuesday, November 13, 2007 10:30AM - 10:42AM |
GO7.00006: Evolution of Relativistic Plasma-Wave front in LWFA Fang Fang, Christopher Clayton, Kenneth Marsh, Joseph Ralph, Arthur Pak, Nelson Lopes, Chandrashekhar Joshi In a laser wake field accelerator experiment where the length of the pump laser pulse is several plasma period long, the leading edge of the laser pulse undergoes frequency downshifting as the laser energy is transferred to the wake. Therefore, after some propagation distance, the group velocity of the leading edge of the pump pulse, and therefore of the driven electron plasma wave, will slow down. This can have implications for the dephasing length of the accelerated electrons and therefore needs to be understood experimentally. We have carried out an experimental investigation where we have measured the velocity v$_{f}$ of the `wave-front' of the plasma wave driven by a nominally 50fs (FWHM), intense (a0 $\sim $ 1), 0.8$\mu $m laser pulse. To determine the speed of the wave front, time- and space-resolved reflectometry, interferometry, and Thomson scattering were used. Although low density data (n$_{e} \sim $ 1.3 * 10$^{19}$cm$^{-3})$ showed no significant changes in v$_{f}$ over 1.5mm (and no accelerated electrons), high-density data (n$_{e} \sim $ 5*10$^{19}$cm$^{-3})$ shows accelerated electrons and an approximately 5{\%} drop in v$_{f}$ after a propagation distance of about 800$\mu $m. [Preview Abstract] |
Tuesday, November 13, 2007 10:42AM - 10:54AM |
GO7.00007: Laser acceleration with imploding plastic cylinder shell Kiminori Kondo, Nobuhiko Nakanii, Yoshitaka Mori, Eisuke Miura, Kazuki Tsuji, Kazuya Kimura, Kazuo Takeda, Syuji Fukumochi, Mamoru Kashihara, Tsuyoshi Tanimotoi, Hirotaka Nakamura, Takahiko Ishikura, Motonobu Tampo, Ryosuke Kodama, Yoneyoshi Kitagawa, Kunioki Mima, Kazuo Tanaka High energy electrons over 500 MeV were generated with Gekko XII laase system and PW laser system in ILE (Institute of Laser Engineering, Osaka University). For making a hollow plasma tube to take a long propagation distance, a plastic cylinder shell was imploded by 6 beams of Gekko XII laser system. The relativistic optical pulse yielded from PW laser system propagated through 3 mm long plasma tube with making a self-modulated laser wakefield. Thermal electrons were self-injected to this acceleration field formed by the electron plasma wave, and were accelerated to the relativistic speed. The kinetic energy distribution of these electrons was measured by the calibrated electron spectrometer (ESM). The observed accelerated electrons are over 500 MeV with a broad spectrum and reach up to800 MeV. [Preview Abstract] |
Tuesday, November 13, 2007 10:54AM - 11:06AM |
GO7.00008: Photon acceleration and modulational instability during wakefield excitation using long laser pulses Raoul Trines, Christopher Murphy, Robert Bingham, Kathryn Lancaster, Oleg Chekhlov, Peter Norreys, Jose Tito Mendonca, Luis Silva, Stuart Mangles, Christos Kamperidis, Alexander Thomas, Karl Krushelnick, Zulfikar Najmudin Recent laser-wakefield experiments on the Astra laser at RAL using laser pulses that are several times longer than the wakefield period have yielded transmission spectra that exhibit a series of secondary peaks flanking the main laser peak. It has been found that these peaks are too closely spaced to be the result of Raman instabilities; instead, photon acceleration of the laser's photons in the wakefield has been proposed as the likely origin of the secondary peaks. In this paper, we present the results of recent Astra experiments in which a laser pulse of 50-200 fs containing 300-600 mJ was focused on a helium gas jet on a 25 micron focal spot. The observed transmission spectra have been modelled using a dedicated photon-kinetic numerical code. The origin of various spectral characteristics will be explained in terms of photon acceleration, and the feasibility of using this effect as a wakefield diagnostic will be discussed. [Preview Abstract] |
Tuesday, November 13, 2007 11:06AM - 11:18AM |
GO7.00009: Control of laser-accelerated ions: Recent advances and preliminary results from the new Trident 250-TW laser B. Manuel Hegelich, Brian J. Albright, Lin Yin, Kirk A. Flippo, D. Cort Gautier, Samuel Letzring, Roland Schulze, Mark Schmitt, Juan C. Fernandez Advanced target design, treatment and characterization enable progress in laser-driven ion acceleration. We demonstrate spectral shaping and mono-energetic features from in-situ formed source layers on different substrate materials. Advanced targets and experimental techniques allow control of the properties of laser accelerated ion beams, which is of importance to future applications like Ion Fast Ignition (IFI), WDM research and others. We will also present preliminary results from the new 250-TW Trident laser system that will allow the extrapolation of scaling laws similar to those derived for proton acceleration. [Preview Abstract] |
Tuesday, November 13, 2007 11:18AM - 11:30AM |
GO7.00010: Proton acceleration: new developments for focusing and energy selection, and applications in plasma physics P. Audebert In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. These sources have exceptional properties, i.e. high brightness and high spectral cut-off, high directionality and laminarity, short burst duration. We have shown that for proton energies $>$10 MeV, the transverse and longitudinal emittance are respectively $<$0.004 mm-mrad and $<$10$^{-4}$ eV-s, i.e. at least 100-fold and may be as much as 10$^{4}$-fold better than conventional accelerators beams. Thanks to these properties, these sources allow for example point-projection radiography with unprecedented resolution. We will show example of such time and space-resolved radiography of fast evolving fields, either of associated with the expansion of a plasma in vacuum [*] or with the propagation of a ICF-relevant laser beam in an underdense plasma. These proton sources also open new opportunities for ion beam generation and control, and could stimulate development of compact ion accelerators for many applications. [Preview Abstract] |
Tuesday, November 13, 2007 11:30AM - 11:42AM |
GO7.00011: In-situ target preparation and characterization for mono-energetic laser driven ion sources Cort Gautier, Kirk Flippo, Roland Schulze, Brian Albright, Lin Yin, Juan Fernandez, Manuel Hegelich Recent advances in laser-driven ion acceleration demonstrated the direct production of mono-energetic ion pulses from ultrahigh intensity lasers. A key component responsible for this mechanism is a highly ordered, 10A source layer on a high-Z substrate. Due to the typical vacuum conditions in ultrahigh power laser target chambers, in-situ formation and characterization is a prerequisite to control and manipulate those ion pulses and achieve lower shot-to-shot fluctuations. We present results of an experimental investigation of the in-situ formation and characterization of this ion source layer. Using X-ray photoelectron spectroscopy (XPS) we observed a temperature dependence of the formation of a thin carbon layer on Pd and Pt substrates in a controlled hydrocarbon environment. These results validate our hypothesis for the mechanisms responsible for laser driven mono-energetic ion production and will be compared to PIC simulation and measurements of mono-energetic ions from Pd and Pt targets shot at intensities of I$\sim $10$^{19}$ W/cm$^{2}$ at the Trident short pulse laser facility. [Preview Abstract] |
Tuesday, November 13, 2007 11:42AM - 11:54AM |
GO7.00012: Generation of Monoenergetic proton beams from double-layer foils by flat-top laser pulses.. Stepan Bulanov, Vladimir Chvykov, Andrei Brantov, Valery Bychenkov, Galina Kalinchenko, Takeshi Matsuoka, Pascal Rousseau, Stephen Reed, Viktor Yanovsky, Dale Litzenberg, Karl Krushelnick, Anatoly Maksimchuk The effect of laser pulse shaping on the proton acceleration by a tightly focused pulse from ultra-thin double layer solid targets in the regime of Directed Coulomb Explosion (DCE) is discussed. The theoretical model and the results of PIC simulations of this regime are presented. In DCE regime the foil is first accelerated by the radiation pressure and then experiences a Coulomb explosion thus generating a moving charge separation longitudinal field that effectively accelerates second layer protons. The utilization of the pulse shaping, namely the use of flat-top pulses, leads to a significant enhancement of the efficiency of proton acceleration due to the increase of the longitudinal field. [Preview Abstract] |
Tuesday, November 13, 2007 11:54AM - 12:06PM |
GO7.00013: ABSTRACT HAS BEEN MOVED TO SESSION YP8.00079 |
Tuesday, November 13, 2007 12:06PM - 12:18PM |
GO7.00014: Collimated High-Quality Proton Beam Generation in Laser Tailored-Target Interaction S. Kawata, M. Nakamura, R. Sonobe, N. Onuma, Y. Nodera, S. Miyazaki, T. Kikuchi, Q. Kong A high-quality collimated proton beam generation is demonstrated by using a tailored thin foil target. A robustness of a thin-foil tailored hole target is demonstrated by particle simulations in laser-produced proton generation. The tailored target has holes at the target rear surface. When an intense short pulse laser illuminates the thin foil target with the hole, transverse edge fields of an accelerated electron cloud and an ion cloud are shielded by a protuberant part of the hole so that the proton beam divergence is suppressed [1, 2]. This paper presents the robustness of the hole target against laser parameter changes in a laser spot size and in a laser pulse length, against a contaminated proton source layer and against a laser alignment error. The 2.5-dimensional PIC (particle-in-cell) simulations also present that a multiple-hole target is robust against a laser alignment error and a target positioning error. The multi-hole target may serve a robust target for practical uses to produce a collimated proton beam. [1]~R. Sonobe, et al., Phys. Plasmas, 12 (2005) 073104. [2] M. Nakamura, et al., J. Appl. Phys., 101 (2007) 113305. [Preview Abstract] |
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