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内容記述 |
The laser-plasma acceleration of electrons is studied by using one of the world's most intense lasers, with a power of 200 TW and an ultra-short pulse duration of 30 fs, aiming at the production of high-energy mono-energetic electron beams. <br /> The present experiment has been performed using the Ti:sapphire laser system at Laser Fusion Research Center, China Academy of Engineering Physics. The laser light with central wave length of 795 nm was focused onto a spot of 14 μm in radius on the helium gas jet. The path length through the jet is varied from 4 to 10 mm. By tuning the laser focal positions and the gas densities, electron beams with energies up to about 100 MeV, approxtmately following the Maxwell's distribution, were observed under the conditions of the laser peak intensities of 1.6-3.1×10<sup>19</sup> W/cm<sup>2</sup> and the plasma densities of 0.7-3.0×10<sup>19</sup>cm<sup>-3</sup>. In three laser shots out of many trials, electron beams containing mono-energetic components at 40-80 MeV were observed. The most outstanding peak was at 46 MeV with a spread of 5 MeV in full width at half maximum (FWHM), and a vertical angular spread of 0.33° in FWHM. <br /> The observed peak energy was, contrary to our expectation, much lower than the world's record at the time of experiment, 170 MeV achieved by using a 30-TW laser. <br />For qualitative understanding of the present experiment, a two-dimensional particle-in-cell (PIC) simulation has been performed. In the simulation, various parameters were tuned around experimental values and did not show any mono-energetic peak, which observed in the experiment. Mono-energetic peaks, however, grow at early stages in the time-propagation and eventually decelerated in later phase. <br /> Encouraged by this simulation, optimal parameters for producing mono-energetic electron beams using the same laser power are discussed. |
要旨・審査要旨 (202.7 kB)
