Source performance optimization in Cesiated mode in ROBIN

Abstract

ITER reference design, an inductively coupled single driver RF (100 kW, 1 MHz)-source ROBIN is operational at IPR, Gandhinagar. The first phase of the operation yielded H- current density of 22–25 mA/cm2 and with electron to ion ratios > 1. The Cesium (Cs) consumption was very high compared to a similar source BATMAN operated at IPP, Garching. The lessons learned from the operational experience showed the operational limitations in presence of impurities and excessive evaporation of Cs into the source. Since then the source was disassembled, cleaned, and reassembled to enable the restart of operations under improved and controlled conditions. Recent experiments assisted by relevant diagnosis on the cleaned ROBIN source under controlled Cesiated conditions and improvements based on the lessons learned have resulted in achieving H- current densities > 30 mA/cm2 and electron to ion ratios < 1 and with Cs consumption reduced to ∼ 12 mg/hr. The role of plasma grid bias on the H- current densities and electron to ion ratios have been studied in detail. The observations and results related to Cs conditioning, source performance optimization, source parametric dependence on the beam, and related observations and findings related to the effects of the bias voltage on the source performance shall be presented and discussed.