The objective of this project is to develop a reliable, compact, high current density, direct current source of cold massive ions for heavy ion beam probe (HIBP) systems. These beam systems have been used successfully to measure plasma potential in magnetically confined high temperature plasma. Currently, the utility of the HIBP diagnostic is being extended to measure fluctuations of space potential and magnetic fields. However, the ability of an HIBP system to measure these fluctuating parameters on a schedule consistent with the magnetic fusion program's needs is at risk because of the unreliable nature, low current density, and poor operational characteristics of the zeolite thallium ion source presently used in this diagnostic. This project plans to solve the operational problems of a zeolite ion source by replacing it with a reliable, steady-state, inductively driven radio frequency (RF) discharge in a heavy metal vapor, from which a high current density of ions can be extracted. The candidate materials include mercury (Hg), lead (Pb), and bismuth (Bi) in addition to thallium (TI). These additional elements are chosen because of their close proximity to TI in the periodic table of the nuclides. Some major design issues that arise from using these materials in an HIBP ion source include the generation and control of the vapor pressure within the plasma chamber of the source and the condensation and migration of material in the region of the electrode structure of the accelerator. The system requirements of the reference beam source are as follows: 200 pA of massive ions at energies ranging from 10 to 15 keV, circular beam with a half angle of beam divergence <0.05', and average cross sectional area of 0. 1 to 1 MM2 over the beam path. Phase I of this project aims: (1) to address the design issues associated with using Hg, TI, Pb, and Bi vapor in an RF driven ion source, (2) to select the element that offers the greatest compatibility to an HIBP system, and (3) to perform a conceptual design of a compact, inductively driven ion source for the Texas Experimental Tokamak HIBP system.Anticipated Results/Potential Commercial Applications as described by the awardee:The improved ion source resulting from this project should significantly improve the capability of an HIBP system to measure magnetic field and potential fluctuation amplitudes and the spectral intensity distributions of those fluctuations in a tokamak plasma. A compact, high quality, low divergent beam source of massive ions, which is DC operable, will find many applications for ion implantation in the semiconductor industry.
