Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session U5: Plasma-Based Accelerators and Beams |
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Sponsoring Units: DPB DPP Chair: Bob Siemann, Stanford Linear Accelerator Center Room: Marriott Tampa Waterside Grand Salon G/H |
Monday, April 18, 2005 3:30PM - 4:06PM |
U5.00001: Recent Advances in Plasma Accelerators Invited Speaker: |
Monday, April 18, 2005 4:06PM - 4:42PM |
U5.00002: High Quality Electron Beams from Laser Accelerators Invited Speaker: Twenty five years ago, laser driven accelerators were proposed as an alternative to conventional accelerator systems.[1] The appeal was and is the large accelerating gradients (up to hundreds of GV/m) that can allow the development of compact devices capable of producing multi-GeV electron beams. Until recently, all experiments produced large gradients but beams with 100 {\%} energy spread and only a small amount of electrons at high energy. This has recently changed. At the multi-beam L'OASIS facility at LBNL we have produced beams with narrow energy spread using a channel guided laser accelerator.[2] At Rutherford Appleton Laboratories (UK)[3] and at the Ecole Polytechnique (France),[4] beams with narrow energy spread were produced by using laser beams with relatively large focal spots. These results demonstrate that laser-plasma based accelerator can produce high quality electron beams. A review of the L'OASIS experiments will be presented as well as our plans and activities for producing a GeV-class electron beam. \newline \newline [1] T. Tajima and J.M. Dawson, Phys. Rev. Lett. \textbf{43}, 267-270 (1979). \newline [2] C.G.R. Geddes et al., Nature \textbf{431}, 538- 541(2004). \newline [3] S.P.D. Mangles et al., Nature \textbf{431}, 535 --538 (2004). \newline [4] J. Faure et al., Nature \textbf{431, }541-544 (2004). [Preview Abstract] |
Monday, April 18, 2005 4:42PM - 5:18PM |
U5.00003: Laser-Produced and Accelerated High Energy Protons Invited Speaker: Ultra-low emittance, multi-MeV proton beams have recently been produced by the interaction of high-intensity short-pulse lasers with thin metallic foils [1]. The acceleration process proceeds in two steps. First the laser ponderomotively accelerates huge, MA currents of $\sim $MeV electrons which propagate through the foil and form a dense relativistic electron sheath on the non-irradiated rear surface. This sheath produces an electrostatic field $>$10$^{12}$ V/m that ionizes the surface atoms almost instantaneously, forming a $\sim $1 nm thick ion layer which, together with the electron sheath, resembles a virtual cathode. The ions are accelerated initially normal to the foil surface, followed by a diverging plasma expansion phase driven by the electron plasma pressure. By structuring the rear surface of the foil, we have succeeded to produce modulations in the transverse phase space of the ions, which resemble fiducial ``beamlets'' within the envelope of the expanding plasma. This allows one to image the initial accelerating sheath, and map the plasma expansion of the beam envelope, to fully reconstruct the transverse phase space. We find that for protons of 10 MeV, the normalized transverse rms emittance is less than 0.004 $\pi $ mm.mrad [1], i.e. 100-fold better than typical RF accelerators and at substantially higher ion currents exceeding 10 kA. Recent results will be reported on stripping the electrons while maintaining the low emittance from experiments at the LULI 100 TW laser, and theoretical estimates of the lowest emittance which can be expected based on ion heating mechanisms during the initial sheath formation and ion acceleration processes, will be presented. [1] T.E. Cowan, J. Fuchs, H. Ruhl \textit{et al}., \textit{Phys. Rev. L}ett. \underline {92}, 204801 (2004). [Preview Abstract] |
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