Overview: RF ICP Ion Source Developments for the DIII-D NBI System*

Our collaboration between NC State University and the DIII-D develops radio-frequency (RF) inductively coupled plasma (ICP) positive ion sources to enable a heating power increase of the DIII-D neutral beam injection (NBI) system. We will present an overview of the NC State project scope and progress. Our goal is to design and demonstrate an ion source that is fully compatible with the present NBI accelerator and that operates in hydrogen, deuterium and helium. To inform the prototype ion source design, we perform RF ICP and finite element electromagnetic modeling. We are building two experimental setups at NC State, LUPIN and AMAROK. LUPIN is a reduced scale (cylindrical, 20 cm diameter) ICP source to test a novel, multi-strap RF antenna concept, to characterize plasma uniformity and to validate hybrid kinetic-fluid plasma simulations under NBI-relevant RF power and plasma densities. LUPIN has an internal Faraday screen and up to 20 kW RF power at 2 MHz frequency. AMAROK will be a full-scale pre-prototype ion source that will demonstrate a homogeneous plasma density across the future ion extraction area of 48 by 12 cm, which would translate into an 85 A positive ion beam. It will have at least 150 kW of installed RF power and also match the NBI injector gas flow rate of 15 Torr-L/s at operating pressures 1 to 10 Pa, which is required to study power losses through neutral gas heating. In conjunction with experimental setups that are based at DIII-D, we plan to deliver a prototype ion source design to be installed on a DIII-D NBI.