Measurements of neutral beam species, impurities, spatial divergence, energy dispersion, pressure, and reionization using the TFTR U.S. Common Long Pulse Ion Source

Abstract

Results are given from the first comprehensive and complementary measurements using the final production U.S. Common Long Pulse Ion Sources mounted on both the TFTR neutral beam test beamline and the TFTR neutral beam injection system, with actual tokamak experimental conditions, power systems, controls, and operating methods. The set of diagnostics included water calorimetry, thermocouples, vacuum ionization gauges, photodiodes, neutron, gamma-ray, and charged particle spectroscopy, optical multichannel analysis, charge exchange spectroscopy, Rutherford backscatter spectroscopy, and implantation/secondary ion mass spectroscopy. These systems were used to perform complementary measurements of neutral beam species, impurities, spatial divergence, energy dispersion, pressure, and reionization. The measurements were performed either in the neutralizer region, where the beam contained both ions and neutrals, or in the region of the output neutral beam. The average of the neutral particle ratios in the range from 80 to 114 keV is D0[E]:D0[E/2]:D0[E/3]=53(5):27(4):20(4), where the quantities in parentheses are the average experimental uncertainties. The corresponding neutral power ratio is P0[E]:P0[E/2]:P0[E/3]=72(9):19(3):9(2). The half widths (1/e) in the horizontal plane for the full-, half-, and third-energy components were 0.26°, 0.34°, and 0.42°, respectively. The dispersions of the full-, half-, and third-energy components were 1.20 keV, 2.35 keV, and 2.26 keV, respectively. The carbon impurity concentration in a 80 keV D0 beam was not greater than 2×10−4 per D0 beam particle, and exhibited an apparent acceleration state of C+. The oxygen impurity concentration was less than 5×10−4 per D0 beam particle, and exhibited an apparent acceleration state of O+. A variety of vacuum conditions were observed depending on the operating conditions. Typically, pressures in the transition ducts were in the range from 0.3 to 0.7×10−5 Torr at the beginning of injection pulses, and reionized power losses were in the range from 0.75% to 1.5% of incident power. At the end of injection pulses, pressures in the transition ducts were in the range from 0.6 to 2×10−5 Torr and reionized power losses were in the range from 2% to 6% of incident power. This work describes generic results, new apparatus, and advances in measurement techniques for the optimization of tokamak neutral beam heating operations and the analysis of neutral beam heated plasmas.