Lawrie S R, Faircloth D C, Letchford A P, Whitehead M O, Wood T
STFC ISIS Pulsed Spallation Neutron and Muon Facility, Rutherford Appleton Laboratory, Harwell, Oxford, United Kingdom.
Rev Sci Instrum. 2016 Feb;87(2):02B122. doi: 10.1063/1.4934580.
A vessel for extraction and source plasma analyses (VESPA) is operational at the Rutherford Appleton Laboratory (RAL). This project supports and guides the overall ion source R&D effort for the ISIS spallation neutron and muon facility at RAL. The VESPA produces 100 mA of pulsed H(-) beam, but perveance scans indicate that the source is production-limited at extraction voltages above 12 kV unless the arc current is increased. A high resolution optical monochromator is used to measure plasma properties using argon as a diagnostic gas. The atomic hydrogen temperature increases linearly with arc current, up to 2.8 eV for 50 A; whereas the electron temperature has a slight linear decrease toward 2.2 eV. The gas density is 10(21) m(-3), whilst the electron density is two orders of magnitude lower. Densities follow square root relationships with arc current, with gas density decreasing whilst electron (and hence ion) density increases. Stopping and range of ions in matter calculations prove that operating a high current arc with an argon admixture is extremely difficult because cathode-coated cesium is heavily sputtered by argon.
卢瑟福·阿普尔顿实验室（RAL）有一台用于提取和源等离子体分析的装置（VESPA）正在运行。该项目为RAL的ISIS散裂中子与μ子设施的整体离子源研发工作提供支持和指导。VESPA能产生100 mA的脉冲H(-)束流，但导流系数扫描表明，除非增加电弧电流，否则在提取电压高于12 kV时，该源受限于产量。使用高分辨率光学单色仪，以氩气作为诊断气体来测量等离子体特性。原子氢温度随电弧电流呈线性增加，在50 A时可达2.8 eV；而电子温度则略微线性下降至2.2 eV。气体密度为10(21) m(-3)，而电子密度低两个数量级。密度与电弧电流呈平方根关系，气体密度下降，而电子（以及离子）密度增加。物质中离子的阻止本领和射程计算表明，使用氩气混合气体运行高电流电弧极其困难，因为涂覆阴极的铯会被氩气严重溅射。
