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레이저 유도 플라즈마 가속 양성자 빔의 타깃 구조에 따른 가속 원리 연구 원문보기

  • 저자

    김경남

  • 학위수여기관

    공주대학교 대학원

  • 학위구분

    국내박사

  • 학과

    물리학과

  • 지도교수

    김용기

  • 발행년도

    2014

  • 총페이지

    viii, 142 p.

  • 키워드

    고출력 레이저 플라즈마 가속 양성자 빔;

  • 언어

    kor

  • 원문 URL

    http://www.riss.kr/link?id=T13534458&outLink=K  

  • 초록

    The generation of an energetic proton beam by irradiating a thin foil with an ultra-intense laser pulse has attracted much interest not only by its fundamental physics but also by its potential applications in medical therapy, nuclear physics, and fundamental physics. Much efforts have been devoted to understand the underlying physics in the interaction of an ultra-intense laser pulse and a relativistic plasma, which led to a lot of progresses in experiments and theories. Such progresses have made it possible to investigate possible applications of ion beams generated by the laser-induced plasma acceleration. Among the possible applications, a hadron cancer therapy is considered to be the most prominent one. However, they failed to achieve the proton energy required in the therapy machine yet. Even more, no possible route to the energy could be found with well-known acceleration mechanisms such as TNSA and RPA. This situation encouraged scientists to investigate new acceleration mechanism. This thesis is one of such efforts to find new acceleration mechanism. For the stable generation of proton beam, pulse to pulse stabilization of a laser energy is important. The KAERI 30 TW Ti:sapphire laser system has been stabilized based on the Frantz-Nodvik model. With 18% single-pass loss in the pre-amplifier, the highest stability could be obtained. The laser energy of 1 J with pulse width of 300 ps before compression has been stabilized with 0.42% fluctuation. New target structures, Vacuum Sandwiched Double Layer (VSDL) and Ion Layer Embedded multi Foil (ILEF) were proposed for the generation of a high quality proton beam. The acceleration mechanisms in the proposed targets were analyzed by a two-dimensional particle-in-cell simulation as well as a one-dimensional hydrodynamic simulation. Such analysis showed that ions in the proposed targets are accelerated by a bulk electrostatic field, which is prominently different from the sheath field acceleration in a single layer foil target. In addition to this, those targets are composed of foils with thickness of a few μm, which makes it easier to treat and more insensitive to a laser prepulse compared with a foil, tens of nm in thickness. The computer simulation showed that those targets generate proton beams with higher energy and narrower energy spread than the single foil target. An 18 MeV proton beam with energy spread of 35% was generated when a laser pulse of 27 fs in pulse width and 2×1019W/cm2 in intensity is irradiated on a VSDL target. The peak energy is higher than that of single foil by a factor of 3. The advantage of ILEF mechanism is that it can control the proton energy spectra by adjusting target thickness. For the same laser parameters as above, a 22 MeV proton energy with 8% of energy spread was obtained when ion layer was located between 2 μm of Layer I and 0.4 μm of layer 2. When the layer I thickness was similar to that of the Layer II, proton energy spectra showed plateau region from 15 to 35MeV. Preliminary experiments have been performed for the proposed targets. However, due to the difficulty in fabricating the target by a simple method, it failed to obtained consistent results. Even though, some results showed meaningful energy spectra, which could be interpreted by the proposed acceleration mechanism. Based on such results, it is expected to realize the new acceleration mechanism with a well-defined target. These efforts eventually make it possible to bring a huge accelerator into a laboratory, which might innovate daily life style in many areas.


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