In experiments on uniformity improvement in a large negative ion source, steep gradients have been observed in the profiles of electron temperature and H- ion beam intensity. It has been observed that the gradient in the H- ion beam intensity is altered by seeding cesium, though the electron temperature distribution is not affected by Cs. Thus in the Cs seeded condition, the H- ion beam intensity is enhanced in local area illuminated by high electron temperature plasmas. A brief analysis suggests possible advantages of high electron temperature plasmas for the negative ion surface production, by enhancement of dissociation to yield proton or atoms as parent particles of the negative ions.
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