Two RF driver based negative ion source for fusion R&D

Inductively coupled radio frequency (RF) based multi-driver negative ion sources form the basis of the ion sources for Neutral Beam (NB) injectors considered for the fusion devices. Database for such multi-driver operations are limited. A need for supplementing the database is paramount for the development of large size negative ion sources. Under Indian program, experiments initiated with the objective of understanding the physics and technology of multi driver coupling. Radio frequency (RF) based negative NB systems have addressed to this requirement in the form of configuring an experimental system consisting of a two driver based source powered by a single 1 MHz, 180 kW RF generator. Plasma of density ~ 10¹⁸ m^-3, in a volume of ~ 0.5 m³ chamber shall be produced in this experiment from which, extraction of ~ 10-12 A of negative hydrogen ion current @ 50 kV, is foreseen. Power is launched though an actively cooled coil mounted on each of the driver. Adequate flexibility has been incorporated in the system configuration to test configurations of the coupling under atmospheric conditions, or inside a vacuum chamber. Operation of the experiment shall be supported by a PLC based control and PXI based data acquisition system and extensive optical, thermocouple and probe based diagnostics shall provide information related to the essential plasma parameters like uniformity, temperature, density etc. Technical details of the experimental system, including the layout and the supporting systems shall be presented in this paper.