Helium Retention and Release Characteristics of Multi-layer Pebbles for Pebble Drop Devertor

卵石滴偏滤器系统的显著特点之一是抽运氢同位素和氦的性能。为了开发最佳的燃料泵送和回收系统，对多层鹅卵石对氢和氦的滞留和释放特性、鹅卵石通过细缝落下形成鹅卵石帷幕和等离子体屏蔽效果评价、等离子体流动中鹅卵石对等离子体的屏蔽机理进行了研究。通过氦保留实验，在辐照温度和解吸温度相同的情况下，石墨样品的瞬时氦释放量随着辐照温度的升高而减少。在700K以上，即使考虑高通量离子束辐照下氦的瞬时释放，也几乎没有观察到氦的滞留。根据实验结果估计了球滴偏滤器系统的氦抽运性能，并与ARIES-AT…的氦产生率进行了比较更多托卡马克反应堆的概念。研究发现，即使在673K的温度下，偏滤器仍具有足够的泵浦性能，略低于保留极限(700K)。为了开发落石系统，在偏滤器入射等离子体遮盖率大于90%的情况下，确定了用于卵石放电的狭缝宽度为3 cm以上。为了研究鹅卵石对等离子体的屏蔽机理，利用ECR等离子体源进行了模拟实验。在实验中，ECR放电产生的氢等离子体沿磁力线扩散到恒定场区(100~500G)。然后在恒定场区插入直径为2 cm和5 cm的圆盘(偏滤器卵石模拟器)，研究卵石对等离子体参数的影响。用朗缪尔探头测量了等离子体密度、温度和电势等参数的径向和轴向二维分布。该测量清楚地显示了圆板周围等离子体预铺层的二维结构。在10m托尔的放电气压下，模拟结果与实验结果基本吻合。较少

One of the notable characteristics of a pebble drop divertor system is pumping performance of hydrogen isotopes and helium. In order to develop optimum fuel pumping and recycling system, the following subjects were studied : retention and release characteristics of hydrogen and helium by multi-layer pebbles, forming pebble curtain by pebble dropping through thin slits and evaluation of plasma shielding effects, plasma shielding mechanism by pebbles in plasma flow.According to helium retention experiments, transient helium release from graphite samples decrease with increasing irradiation temperature in the case that irradiation temperature and desorption temperature was the same. Almost no helium retention was observed over 700 K even if transient release of He under high flux ion beam irradiation was taken into consideration. Helium pumping performance of the pebble drop divertor system was estimated from the experimental results and compared with a helium generation rate of ARIES-AT … More tokamak reactor concept. It was found that the pebble drop divertor system has enough pumping performance even at the pebble temperature of 673 K, which is slightly less than the retention limit ( 700K).For the development of pebble falling system, the width of the slit for pebble discharge is determined to more than 3 cm in the case that the shading rate of incoming divertor plasma is more than 90%. This slit size does not cause any problem for the installation of the pebble falling system in actual fusion reactors.For the study of plasma shielding mechanism by pebbles, simulation experiments by using an ECR plasma source was performed. In the experiments, hydrogen plasma produced by ECR discharge was diffused along magnetic field lines to a constant field region (100〜500 G). Then circular plates with the diameter of 2 cm and 5 cm (simulator for divertor pebbles) were inserted in the constant field plasma region to investigate the effects of pebbles on plasma parameters. Two dimensional distributions (radial and axial) of plasma parameters such as density, temperature, and potential were measured by a Langmuir probe. This measurement clearly showed two dimensional structure of the plasma presheath around the circular plates. Simulation results roughly agree with experimental results in the discharge gas pressure of 10 m Torr. Less