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arXiv 2211.04791physics.plasm-ph
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无铯条件下离子源SPIDER中的负离子密度

Negative ion density in the ion source SPIDER in Cs free conditions

M. Barbisan, R. Agnello, G. Casati, R. Pasqualotto, C. Poggi, E. Sartori, M. Spolaore, G. Serianni

AI总结:

本研究针对ITER中性束注入器原型离子源SPIDER,在无铯氢/氘运行条件下,探究磁过滤场、偏置电流及加速系统电场对可引出负离子密度的影响,给出了优化运行参数区间。

摘要:

SPIDER实验装置运行于意大利帕多瓦市Consorzio RFX的中性束测试平台,是ITER(国际热核聚变实验堆)中性束注入器所用H-/D-离子源的原型装置。实现从离子源引出的离子电流最大化,以及减少共引出电子的数量,是该装置需要达成的核心目标之一。光腔衰荡光谱(Cavity Ring-Down Spectroscopy)诊断设备可测量离子源内靠近等离子体栅(即离子加速系统朝向等离子体一侧的栅极)区域的负离子密度,以此确定能最大化可引出负离子数量的离子源运行参数。本研究中,SPIDER在无铯条件下分别以氢和氘为工质运行,因此负离子主要通过等离子体体积内的反应产生。本研究阐明了SPIDER中用于限制共引出电子数量的磁过滤场和偏置电流,会如何影响可供引出的负离子密度。结果表明,加速系统前方的磁过滤场应设置在约1.6 mT(该条件下可获得最高的可用负离子密度)至约3.2 mT(该条件下电子电流与离子电流的比值最低)的区间内。当等离子体栅及其周围的偏置板相对于离子源本体加正偏压、且总电流处于0 A÷100 A范围时,负离子密度同样能达到最大值。本文还揭示了在无铯条件下,加速系统内的电场会对离子源内靠近等离子体栅孔处的负离子密度产生多大程度的影响。

英文摘要:

The SPIDER experiment, operated at the Neutral Beam Test Facility of Consorzio RFX, Padua, hosts the prototype of the H-/D- ion source for the ITER neutral beam injectors. The maximization of the ion current extracted from the source and the minimization of the amount of co-extracted electrons are among the most relevant targets to accomplish. The Cavity Ring-Down Spectroscopy diagnostic measures the negative ion density in the source close to the plasma grid (the plasma-facing grid of the ion acceleration system), so to identify the source operational parameters that maximize the amount of negative ions which can be extracted. In this study SPIDER was operated in hydrogen and deuterium in Cs-free conditions, therefore negative ions were mostly produced by reactions in the plasma volume. This work shows how the magnetic filter field and the bias currents, present in SPIDER to limit the amount of co-extracted electrons, affect the density of negative ions available for extraction. The results indicate that the magnetic filter field in front of the acceleration system should be set between about 1.6 mT, condition that maximizes the density of available negative ions, and about 3.2 mT, condition that minimizes the ratio of electron current to ion current. The negative ion density also resulted to be maximized when the plasma grid and its surrounding bias plate was positively biased against the source body with a total current in the range 0 A÷100 A. The paper shows also how much, in Cs-free conditions, the electric fields in the acceleration system can affect the density of negative ions in the source, close to the plasma grid apertures.

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