利用強場電磁波產生高能質子束的數值模擬研究; Simulation Study of Generation of the Energetic Proton Beam Induced by High-Field Electromagnetic Waves in overdense plasmas

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题名:	利用強場電磁波產生高能質子束的數值模擬研究;Simulation Study of Generation of the Energetic Proton Beam Induced by High-Field Electromagnetic Waves in overdense plasmas
作者:	黃俊翰;ChunHan Haung
贡献者:	太空科學研究所
关键词:	雙層靶材;滲漏光帆;強場;加速;質子;proton;acceleration;two-layers;Leaky-Light-Sail
日期:	2011-07-28
上传时间:	2012-01-05 14:11:30 (UTC+8)
摘要:	「太陽高能粒子 (Solar energetic particles, SEPs)」是經由太陽閃焰獲得能量的正離子與電子。這些高能粒子能量範圍相當地廣，可由幾萬電子伏特到十億電子伏特。其中，能量大於約四千萬電子伏特的高能粒子，會對衛星的電子儀器、探測船、以及太空人的生命造成危害。本論文透過一維「粒子模擬碼(Particle-in-Cell)」模擬研究「輻射壓力加速 (radiation pressure acceleration, RPA)」機制中的「滲漏光帆 (Leaky Light-Sail)」加速正離子。當波長為800奈米、脈衝長度為267飛秒(femtosecond)、強度為5.34×1019 W/cm2的同調性圓極化電磁波照射在薄靶材上時，將能得到高能的單能質子束。在此研究中，我們選用了鋁、壓克力做為單層靶材，次為由鋁和壓克力所組成的雙層靶材，以及加上真空層形成的三層靶材。我們的研究結果指出，使用雷射脈衝分別照射在這三種靶材上時，當使用三層靶材時，有較好的質子能量加速梯度為3.8 MeV/μm，約為100 MeV的單能質子束；使用單層壓克力靶材時，能得到較好的質子能量約為160 MeV。高能且單能質子束在癌症治療上具更相當的應用價值。此論文中的結果也能當作為未來研究在太陽閃焰事件中，非同調性高頻、高強度電磁波加速正離子的參考。 Solar energetic particles (SEPs) are energetic ions and electrons produced during the solar flare events. The energy of particles observed during the SEP events ranges from keV to GeV. The electronic instruments of the satellites, spacecrafts, and astronauts could be damaged by the SEPs if the energy of SEPs is greater than 40 MeV. In this thesis, we study the Leaky-Light-Sail radiation-pressure acceleration (LLS RPA) of ions by means of one-dimensional Particle-in-Cell (PIC) simulation. Mono energetic protons are produced when we injected an intense laser pulse on an ultra thin target. The laser pulse is a coherent circularly polarized electromagnetic wave with a wavelength 800 nm, pulse duration 267 fs, and intensity 5.34×1019 W/cm2. Three types of thin target were used in this study. One of them is a single-layer thin target made by aluminum or Poly(methyl methacrylate). Another one is a two-layer thin target made by aluminum and Poly(methyl methacrylate). The other of them is a three-layer thin target made by aluminum, vacuum, and Poly(methyl methacrylate). Our simulation results indicate that irradiating the laser pulse on the three-layer target can produce the much better accelerating gradient of proton’s energy about 3.8 MeV/μm, and the energy of the energetic proton beam is larger than 100 MeV. The highest proton energy (about 160 MeV) can be achieved by irradiating the laser pulse on the single Poly(methyl methacrylate) target. The generation of mono energetic proton beam has valuable applications on the cancer treatments. The results obtained in this thesis can also serve as a guideline for future study on ion accelerations by incoherent high-frequency high-intensity electromagnetic waves in the solar flare events.
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