The development of plasma-sputter-type negative ion sources is underway for the heavy-ion-beam probe system as plasma diagnostic beams of the large helical device ͑LHD͒ for potential and fluctuation field measurements. Our purpose is to increase the doubly charged exchanged Au + beam intensity to enhance the detection signal after passing through the plasmas of the LHD. For this purpose, the characterization of the Au − ion source and the beam optics has been carried out both experimentally and numerically. Based on these results, a new plasma-sputter-type negative ion source is designed and tested.

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An array of nozzles arranged in a bicycle-wheel spoke pattern designed to create a region of high neutral gas density in an H À ion source was tested for its capability to generate a pressure gradient in a vacuum chamber. An experimental setup was designed and built to measure the local pressure around the nozzle array. The two-dimensional direct simulation Monte Carlo (DSMC) technique was employed to simulate the local pressure distribution around the nozzles and to compare the results with the measurements. Pressure measurements and DSMC simulations showed that the streaming neutral gas injection (SNGI) technique was capable of increasing the local pressure to 200% when the ambient pressure was 3:0 Â 10 À2 Pa. At higher ambient pressures, the enhancement factor decreased to 58% when the ambient was 2.8 Pa. A sloshing-type SNGI was also designed and the highest enhancement was 87% at an ambient pressure of 2:6 Â 10 À1 Pa.

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An E×B probe is characterized by investigating its two parameters, namely extraction voltage (Vext) and lens voltage (Vlens). The effects of Vext and Vlens on the extracted H− ion current are examined. The investigation of Vext effects is done with a constant Vlens=0 V. The results show that the optimum value for negative ion extraction is Vext=190 V. With this optimum Vext, the Vlens parameter is examined. Findings show that the optimum Vlens is 0 V. Optimized parameters give the highest ion current and narrowest full width at half maximum. With these optimum settings, the E×B probe is used to study the variation of H− ions as a function of perpendicular distance (i.e., 1 cm to 4 cm) from the center of a magnetized sheet plasma with Bave=6.59 mT.