03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques
A20 Plasma Wakefield Acceleration

Paper	Title	Page
WEOAB03	The Production of High Quality Electron Beams in the ALPHA-X Laser Wakefield Accelerator	1956
	S.M. Wiggins, M.P. Anania, C. Aniculaesei, E. Brunetti, S. Cipiccia, B. Ersfeld, M.R. Islam, R.C. Issac, D.A. Jaroszynski, G.G. Manahan, R.P. Shanks, G.H. Welsh USTRAT/SUPA, Glasgow, United Kingdom W.A. Gillespie University of Dundee, Nethergate, Dundee, Scotland, United Kingdom A. MacLeod UAD, Dundee, United Kingdom
	Funding: The U.K. EPSRC, the EC's Seventh Framework Programme (LASERLAB-EUROPE / LAPTECH, grant agreement no. 228334) and the Extreme Light Infrastructure (ELI) project. The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme is developing laser-plasma accelerators for the production of ultra-short electron beams as drivers of incoherent and coherent radiation sources from plasma and magnetic undulators. Here we report on the latest laser wakefield accelerator experiments on the University of Strathclyde ALPHA-X accelerator beam line looking at high quality electron beams. ALPHA-X uses a 26 TW Ti:sapphire laser (energy 900 mJ, duration 35 fs) focused into a helium gas jet (nozzle length 2 mm) to generate high quality monoenergetic electron beams with central energy in the range 80-180 MeV. The beam is fully characterized in terms of the charge, bunch length, energy spread and transverse emittance. The energy spectrum (with less than 1% measured energy spread) is obtained using a high resolution magnetic dipole imaging spectrometer while pepper-pot mask measurements show that the normalized transverse emittance is as low as 1.1 pi mm mrad (resolution limited). The conditions needed to obtain this high quality are discussed.
	Slides WEOAB03 [2.904 MB]
WEPZ021	Self-Consistent Dynamics of Electromagnetic Pulses and Wakefields in Laser-Plasma Interactions	2811
	A. Bonatto, R. Pakter, F.B. Rizzato IF-UFRGS, Porto Alegre, Brazil
	In the present work we study the stability of laser pulses propagating in a cold relativistic plasma, which can be of interest for particle acceleration schemes. After obtaining a Lagrangian density from the one-dimensional equations for the laser pulse envelope and the plasma electron density, we define a trial function and apply the variational approach in order to obtain an analytical model which allows us to calculate an effective potential for the pulse width. Using this procedure, we analyze the stability of narrow and large laser pulses and then compare its results with numerical solutions for the envelope and density equations.
WEPZ023	Results from Plasma Wakefield Acceleration Experiments at FACET	2814
	S.Z. Li, C.I. Clarke, R.J. England, J.T. Frederico, S.J. Gessner, M.J. Hogan, R.K. Jobe, M.D. Litos, D.R. Walz SLAC, Menlo Park, California, USA E. Adli University of Oslo, Oslo, Norway W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, S. Tochitsky UCLA, Los Angeles, California, USA P. Muggli USC, Los Angeles, California, USA
	Funding: Work supported by the U.S. Department of Energy under contract number DE- AC02-76SF00515. We report initial results of the Plasma Wakefield Acceleration (PWFA) Experiments performed at FACET - Facility for Advanced aCcelertor Experimental Tests at SLAC National Accelerator Laboratory. At FACET a 23 GeV electron beam with 1.8x1010 electrons is compressed to 20 microns longitudinally and focused down to 10 microns x 10 microns transverse spot size for user driven experiments. Construction of the FACET facility completed in May 2011 with a first run of user assisted commissioning throughout the summer. The first PWFA experiments will use single electron bunches combined with a high density lithium plasma to produce accelerating gradients >10GeV/m benchmarking the FACET beam and the newly installed experimental hardware. Future plans for further study of plasma wakefield acceleration will be reviewed.
WEPZ024	Some Considerations in Realizing a TeV Linear Collider Based on the PDPWA Scheme	2817
	G.X. Xia, A. Caldwell MPI-P, München, Germany P. Muggli MPI, Muenchen, Germany
	Proton-driven plasma wakefield acceleration (PDPWA) has recently been proposed as an approach to bring the electron beam to the energy frontier in a single passage of acceleration. Particle-in-Cell (PIC) simulation shows that a TeV proton bunch, with a bunch intensity of 1011, and a bunch length as short as 100 microns can resonantly excite a large amplitude plasma wakefield and accelerate an externally injected electron bunch to 600 GeV in a single stage of 500 m long plasma. This novel PDPWA scheme may open a new path for designing a TeV linear lepton collider by using the currently available proton drivers. In this paper, we investigate some key issues, e.g. bunch length, centre-of-mass (CoM) energy, luminosity and dephasing in realizing a TeV linear collider based on the PDPWA scheme.
WEPZ025	Study of Self-injection of an Electron Beam in a Laser-driven Plasma Cavity	2820
	S. Krishnagopal, S.A. Samant, D. Sarkar BARC, Mumbai, India P. Jha Lucknow University, Lucknow, India A.K. Upadhyay CBS, Mumbai, India
	Over the last few years, remarkable advances in laser wakefield acceleration of electrons have been achieved, including quasi-monoenergetic beams and GeV energy in a few centimeters. However, it is necessary to achieve good beam quality (large current, low energy-spread and low emittance) for applications such as free-electron lasers. We study self-injection in two regimes of the laser-plasma interaction: the moderate intensity, self-guiding regime, and the low intensity, near-injection-threshold regime, both in a homogeneous plasma that completely fills the simulation volume. We find good beam quality with injection of on-axis electrons, especially at lower intensity. We also study the case when the laser has to travel through vacuum before entering the plasma. We find that injection here is completely different, from off-axis electrons, and the beam quality is poorer.
WEPZ027	Stabilization of the LWFA and its Application to the Single-shot K-edge Densitometry	2823
	K. Koyama, H. Madokoro, Y. Matsumura University of Tokyo, Tokyo, Japan R. Kuroda, K. Yamada AIST, Tsukuba, Ibaraki, Japan H. Masuda, M. Uesaka The University of Tokyo, Nuclear Professional School, Ibaraki-ken, Japan S. Masuda Osaka University, Suita, Osaka, Japan
	Funding: This work was supported in part by Global COE Program “Nuclear Education and Research Initiative,” MEXT, Japan Injection of electrons into a laser wakefield accelerator (LWFA) via a wavebreaking process was investigated in order to obtain stable output of electron bunches. A density down ramp for occurring the wavebreaking was formed by an oblique shockwave, which was excited by setting a little flow-deflector on an edge of the supersonic nozzle of high-Mach number (M=5). Parameters of the jet were examined by using PIC code and evaluated by using an interferometer, the density was 1019cm-3, density ratio was 2, and the characteristic length was 70 microns. Injection experiments using 7-TW laser pulses suggested that electrons were injected in the density ramp. Since the all-optical Compton X-ray is attractive source for an accurate densitometry, a preliminary experiment of a single-shot K-edge densitometry was performed by using X-ray pulses generated by the laser-Compton scattering (LCS) device based on a compact S-band 40 MeV linac at AIST. The single-shot K-edge densitometry was also applicable to evaluate the transverse emittance of electron bunches.
WEPZ028	Status of Plasma Electron Hose Instability Studies in FACET	2826
	E. Adli University of Oslo, Oslo, Norway W. An, W.B. Mori UCLA, Los Angeles, California, USA R.J. England, J.T. Frederico, M.J. Hogan, S.Z. Li, M.D. Litos, Y. Nosochkov SLAC, Menlo Park, California, USA
	Funding: This work is supported by the Research Council of Norway, the Fulbright Visiting Scholar Program and US DOE contract DE-AC02-76SF00515. In the FACET plasma-wakefield acceleration experiments a dense 23 GeV electron beam will interact with lithium and cesium plasmas, leading to plasma ion-channel formation. The interaction between the electron beam and the plasma sheath-electrons may lead to a fast growing electron hose instability. By using optics dispersion knobs to induce a controlled z-x tilt along the beam entering the plasma, we investigate the transverse behavior of the beam in the plasma as function of the tilt. We seek to quantify limits on the instability in order to further explore potential limitations on future plasma wakefield accelerators due to the electron hose instability.
WEPZ030	Study on a Gas-filled Capillary Waveguide for Laser Wakefield Acceleration	2829
	M.S. Kim, D. Jang, D. Jang, H. Suk APRI-GIST, Gwangju, Republic of Korea
	In gas-filled capillary waveguide for lase wakefield accelerators the gas flows through the two gas feed lines used to sustain constant pressure. Compared to the supersonic gas-jet system operated under high pressure, the gas at low pressure (<1atm) is injected inside capillary waveguide, so that this waveguide has experimental limit to the measurement of the neutral density. In order to investigate the gas pressure in capillary system we used computational fluid dynamics (CFD) simulation. In this paper, we presented the gas pressure changed by a variety of parameters, such as length and sizes of gas feed lines, and the method to decrease the turbulence effect at the ends of capillary.
WEPZ031	Accelerator Studies on a Possible Experiment on Proton-driven Plasma Wakefields at CERN	2832
	R.W. Assmann, I. Efthymiopoulos, S.D. Fartoukh, G. Geschonke, B. Goddard, C. Heßler, S. Hillenbrand, M. Meddahi, S. Roesler, F. Zimmermann CERN, Geneva, Switzerland A. Caldwell, G.X. Xia MPI-P, München, Germany P. Muggli MPI, Muenchen, Germany
	There has been a proposal by Caldwell et al to use proton beams as drivers for high energy linear colliders. An experimental test with CERN's proton beams is being studied. Such a test requires a transfer line for transporting the beam to the experiment, a focusing section for beam delivery into the plasma, the plasma cell and a downstream beam section for measuring the effects from the plasma and safe disposal of the beam. The work done at CERN towards the conceptual layout and design of such a test area is presented. A possible development of such a test area into a CERN test facility for high-gradient acceleration experiments is discussed.
WEPZ032	Energy Spectrometer Studies for Proton-driven Plasma Acceleration	2835
	S. Hillenbrand, R.W. Assmann, F. Zimmermann CERN, Geneva, Switzerland S. Hillenbrand, A.-S. Müller KIT, Karlsruhe, Germany T. Tückmantel HHUD, Dusseldorf, Germany
	Plasma-based acceleration methods have seen important progress over the last years. Recently, it has been proposed to experimentally study plasma acceleration driven by proton beams, in addition to the established research directions of electron and laser driven plasmas. Here, we present the planned experiment with a focus on the energy spectrometer studies carried out.
WEPZ034	Double Resosnant Plasma Wakefields	2838
	B.D. O'Shea, A. Fukasawa, B. Hidding, J.B. Rosenzweig, S. Tochitsky UCLA, Los Angeles, California, USA D.L. Bruhwiler Tech-X, Boulder, Colorado, USA
	Present work in Laser Plasma Accelerators focuses on a single laser pulse driving a non-linear wake in a plasma. Such single pulse regimes require ever increasing laser power in order to excite ever increasing wake amplitudes. Such high intensity pulses can be limited by instabilities as well engineering restrictions and experimental constraints on optics. Alternatively we present a look at resonantly driving plasmas using a laser pulse train. In particular we compare analytic, numerical and VORPAL simulation results to characterize a proposed experiment to measure the wake resonantly driven by four Gaussian laser pulses. The current progress depicts the interaction of 4 CO2 laser pulses, λlaser = 10.6μm, of 3 ps full width at half max- imum (FWHM) length separated peak-to-peak by 18 ps, each of normalized vector potential a0 ≃ 0.7. Results con- firm previous discourse (*,**) and show, for a given laser pro- file, an accelerating field on the order of 900 MV/m, for a plasma satisfying the resonant condition, ωp=π/tfwhm. * Umstadter, D., et al, Phys. Rev. Lett. 72, 1224 ** Umstadter, D., et al, Phys. Rev. E 51, 3484
WEPZ036	A Multi-Parameter Optimization of Plasma Density for an Advanced Linear Collider	2841
	P. Muggli USC, Los Angeles, California, USA R.W. Assmann CERN, Geneva, Switzerland S. Hillenbrand KIT, Karlsruhe, Germany P. Muggli MPI, Muenchen, Germany
	Funding: Work supported by US DoE Recent plasma wakefield accelerator (PWFA) experiments showed that an accelerating gradient as high as 50GV/m can be driven and sustained over a meter-long plasma*. Based on this result, a strawman design for a future, multi-stage, PWFA-based electron/positron collider with an energy gain of ~25GeV/stage has been generated**. However, the choice of plasma density remains open. On one hand, high density means large accelerating gradients and possibly a shorter collider. On the other it means that the accelerating structure dimensions become very small, on the order of the plasma wavelength (<100 microns in each dimension?). Operating at high gradient and with such small structure imposes very strong constraints on the particle bunches: small dimensions and spacing, large current or limited charge, etc. These constraints result in challenges in producing bunches (compression, shaping for optimum loading, etc.) and could limit the achievable collider luminosity (beam-beam effects, etc.). We explore the global implications of operating at a lower accelerating gradient with the goal of relaxing the beam and plasma parameters while meeting the requirements of the collider. * P. Muggli and M.J. Hogan, Comptes Rendus Physique, 10(2-3), 116 (2009). ** A. Seryi, M.J. Hogan, T. Raubenheimer, private communication.