Negative Ion Source for the Measurement of Plasma Potential by a Heavy Ion Probe

重离子束探针（HIBP）作为一种可靠的测量等离子体局部电位的方法，研究了等离子体的电位和密度波动。然而，对于最近的大型装置，如大型螺旋装置，所需的光束能量增加到MeV区域。由于中性束注入或串联束加速的可能性，基于负重离子源的HIBP具有吸引力。在本工作中，我们研究了在等离子溅射型源中负离子的产生机制，以获得具有最大电流密度的连续光束。提出了一种测量负离子生产表面功函数的新方法，并对功函数与生产效率的关系进行了研究。我们测量了离子源出口激光束的能谱，当溅射能量小于300 eV时，扩散小于10 eV。它足够小，可以进行高质量的波动测量。开发了模拟光束提取和光束光学系统的计算机程序。构建了紧凑型离子源，并对光束光学进行了实验研究。

A Heavy Ion Beam Probe (HIBP) has been used as a reliable method to determine the local plasma potential, and to study the potential and density fluctuations. However, the required beam energy increases up into the MeV region for recent big devices, such as the Large Helical Device. A HIBP based on a negative heavy ion source is attractive because of the possibility of neutral beam injection or Tandem beam acceleration. In this work, we have studied the production mechanism of negative ions in a plasma sputtering type source in order to get a continuous beam with a maximum current density. A new technique to measure the work function of the negative ion production surface has been developed and correlation of the work function to the production efficiency was investigated. We have measured the energy spectrum of the beam at the exit of the ion source, and the spread was less than 10 eV for the sputtering energy less than 300 eV. It is small enough for the high quality fluctuation measurement. A computer code to simulate the beam extraction and beam optic system was developed. A compact ion source was also constructed and the beam optics was studied experimentally.