Enhancement of X-ray pulse production from betatron oscillation of the electron bunch in a plasma-waveguide-based laser wakefield accelerator by modification of the waveguide structure

• Main Authors: Jun-Guan Jhou, 周君冠
• Other Authors: Szu-Yuan Chen
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/55104410896317492265

碩士 === 國立臺灣大學 === 物理研究所 === 101 === Here we demonstrate the use of laser-driven plasma accelerators, which accelerate high-charge electron beams to high energy in short distances. The particles being accelerated in the plasma accelerator also undergo transverse (betatron) oscillations to intrinsically ultrafast beams of hard X-rays. The experiment was performed at National Central University, Taiwan, using a 100-TW-class Ti:sapphire laser system with 10-Hz pulse repetition rate. Five laser beams from this system were used for the experiment. The axicon ignitor and heater pulses were used to fabricate a ∼ 1-cm length in full width at half maximum (FWHM) uniform plasma waveguide in a gas jet. The 1.1-J, 40-fs pump pulse was coupled into the plasma waveguide at a delay of 1.9 ns with respect to the axicon heater pulse to excite a plasma wave (plasma bubble) which can accelerate electrons. The focal spot size was 10 μm in FWHM. By adding a transverse heater 1 pulse into the axicon ignitor-heater scheme for producing a plasma waveguide, a variable three-dimensionally structured plasma waveguide can be fabricated. With this technique, electron injection in a plasma-waveguide-based laser wakefield accelerator was achieved and resulted in production of electron beam energy large than 200 MeV. Then a 116-mJ, 210-ps transverse heater 2 pulse was used to introduce lower density spatial gaps between uniform plasma density sections that behind the fabricated plasma waveguide. When accelerated electrons that enter the depression at the proper phase in their betatron oscillation will increase their transverse displacement, thus exiting the depression with larger betatron amplitude. This technique opens a route to a compact hard-X-ray pulse source. We could produce x-ray with photon energies in the range of 1–10 keV by using lower density spatial gaps between uniform plasma density sections. If we compare laser- driven betatron-radiation x-ray source with conventional particle accelerator facilities, we find the size is significantly smaller and the cost is much cheaper. This reduces the size of the synchrotron source from the tens of meters to the centimeter scale, simultaneously accelerating and wiggling the electron beam. Then the betatron radiation has intrinsically striking features for ultra-fast imaging. Therefore laser- driven betatron-radiation x-ray source has the potential to be a table top hard-X-ray pulse source.