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

卵石滴偏转器多层卵石的氦气保留和释放特性

基本信息

批准号：
13308024
负责人：
NISHIKAWA Masahiro
金额：
$ 31.37万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2004
项目状态：
已结题

项目摘要

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

小球分流器系统的一个显著特征是氢同位素和氦的泵送性能。为了开发最优的燃料泵送和回收系统，研究了多层鹅卵石对氢和氦的保留和释放特性，鹅卵石通过细缝滴入形成卵石幕，等离子体屏蔽效果评价，等离子体流中鹅卵石对等离子体的屏蔽机理。氦保留实验表明，在辐照温度与解吸温度相同的情况下，石墨样品的瞬态氦释放量随着辐照温度的升高而降低。在700k以上，即使考虑高通量束流辐照下氦的瞬态释放，也几乎没有观察到氦的滞留。根据实验结果估计了球滴分流器系统的氦气泵送性能，并与ARIES-AT…More托卡马克反应器概念的氦气生成速率进行了比较。研究发现，即使在卵石温度为673 K时，卵石滴分流器系统仍具有足够的泵送性能，略低于保留极限（700K）。为研制落石系统，确定了在入流导流器等离子体遮光率大于90%的情况下，卵石放电缝隙宽度大于3cm。在实际的核聚变反应堆中，这种狭缝的大小不会对落石系统的安装造成任何问题。为了研究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。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 ~ 500 G）。然后在恒定场等离子体区分别插入直径为2 cm和5 cm的圆形板（分流器卵石模拟器），研究卵石对等离子体参数的影响。用Langmuir探针测量了等离子体密度、温度和电势等参数的二维（径向和轴向）分布。这一测量清晰地显示了围绕圆形板的等离子体预鞘的二维结构。在排气压力为10 m Torr时，模拟结果与实验结果基本一致。少