A 15 T Superconducting Magnet for 350 GHz, 1 MW Class Gyrotrons for Commercial Fusion Reactors

C56-30a-273585Electron cyclotron resonance heating is a key fusion technology for: a) plasma heating; b) instability control, to stabilize instabilities such as those from Neoclassical Tearing Modes; and c) electron cyclotron assisted startup. Gyrotrons are a proven vacuum tube technology that can generate sufficient power during continuous operation to satisfy these requirements. In this Phase I program, we propose to perform a conceptual design of a liquid-helium-free—conduction- cooled 15 T/220 mm warm-bore superconducting magnet for a 350 GHz, 1 MW gyrotron operating at >65 % efficiency. The 12 T class tokamaks require ~350 GHz heating frequency and power level ranging from a few hundred kW for electron cyclotron assisted startup to 1-2 MW per gyrotron as part of a 20-40 MW electron cyclotron resonance heating system. Gyrotrons at such frequency and power level require superconducting magnets with ~15 T field with a warm bore diameter of 220 mm. The magnet will be designed with a specific field profile necessary for high performance operation of the electron gun and appropriate beam spreading in the collector to meet the thermal requirements. As a large number of gyrotrons will be necessary in a fusion power plant, they need to be robust and reliable and use liquid cryogen free technology. In this program, we will develop an optimized design of the 15 T gyrotron magnet with a major fraction of the conductor from high-temperature superconducting REBCO material. We will alleviate the stress management that will be encountered in such a high-field/large-bore magnet and develop quench prevention/protection methods to improve operational reliability. We also intend to build and test small REBCO coils to validate our designed winding method, quench detection methods, and reliable electrical joints between coils. The proposed work would leverage the prior well established and successful R&D work on high temperature superconductors like REBCO for high-field and compact tokamaks. Since each tokamak device is expected to use ?50 gyrotrons for its plasma heating and control, the proposed project will result in a new commercial market worth several hundreds of millions of dollars annually and create new business opportunities for US businesses in both magnet and gyrotron technology.