Power System for Long-Pulse Neutral Beam Injectors

Neutral beam injection (NBI) is an important tool for plasma heating, current drive and a diagnostic at fusion science experiments around the United States, including tokamaks, validation platform experiments, and privately funded fusion concepts. The difficulty in producing power systems that can respond rapidly (10 µs) at high voltage (10 to 100 kV) for beam acceleration or high currents (~ 1 to 5 kA) for control of the ion source is non-trivial. Here the overall cost of the system can be prohibitive with even the cheapest systems costing well above a few hundred thousand to over a million dollars to procure. Currently, there are no vendors in the United States for NBI power systems. Eagle Harbor Technologies (EHT), Inc. proposes to develop new solid-state switching power systems for NBI that takes advantage of the latest developments in solid-state switching. EHT has developed a series resonant converter that can be scaled to the power levels required for NBI at small-scale validation platform experiments. This power system can be used to modulate the NBI voltages over the course of a plasma shot, which can lead to improved control over the plasma. Additionally, these modern solid-state supplies can be made smaller and lower cost that previous generations of NBI power systems. The primary goal of this Phase I program will be to design a new NBI system based on the solid-state resonant converter topology discussed above. The new NBI power system will consist of both a PWM controllable high current ion source power supply and the new modular resonant converter for the HV accelerator section of the NBI. The resonant converter can also be utilized for the other bias grids that are common to NB injectors including the ion and electron repeller grids. The Phase I program will consist of the development of the new supplies and demonstration testing of a prototype unit at EHT. If there is sufficient time, some testing could also be conducted on an installed NBI system at one of the laboratories that are interested in the new technology. Fusion energy offers the promise of an energy source fueled by seawater and lithium, both plentiful on Earth. Additionally, it has the benefit of not producing high level radioactive waste or carbon emissions. The proposed work will develop a new method for the main power systems utilized with neutral beam injection within the fusion science community. Beyond fusion science applications, it could simplify and improve the efficiency of power systems built for other areas including linear particle accelerator supplies, high voltage ion implantation supplies, RF cyclotron power supplies, high power pulse width modulation (PWM) amplifiers, and high power trigger systems. Other commercial and industrial applications will also benefit from continued development of this technology. Additionally, this power system could have applications in fast capacitor charging.