Gyrotron and power supply development for upgrading the electron cyclotron heating system on DIII-D

Abstract

An upgrade of the electron cyclotron heating system on DIII-D to almost 15MW is being planned which will expand it from a system with six 1MW 110GHz gyrotrons to one with ten gyrotrons. A depressed collector 1.2MW 110GHz gyrotron is being commissioned as the seventh gyrotron. A new 117.5GHz 1.5MW depressed collector gyrotron has been designed, and the first article will be the eighth gyrotron. Two more are planned, increasing the system to ten total gyrotrons, and the existing 1MW gyrotrons will subsequently be replaced with 1.5MW gyrotrons.Communications and Power Industries completed the design of the 117.5GHz gyrotron, and are now fabricating the first article. The design was optimized for a nominal 1.5MW at a beam voltage of 105kV, collector potential depression of 30kV, and beam current of 50A, but can achieve 1.8MW at 60A. The design of the collector permits modulation above 100Hz by either the body or the cathode power supply, or both, while modulation below 100Hz must use only the cathode power supply.General Atomics is developing solid-state power supplies for this upgrade: a solid-state modulator for the cathode power supply and a linear high voltage amplifier for the body power supply. The solid-state modulator has series-connected insulated-gate bipolar transistors that are switched at a fixed frequency by a pulse-width modulation regulator to control the output voltage. The design of the linear high voltage amplifier has series-connected transistors to control the output voltage, which was successfully demonstrated in a proof-of-principle test at 2kV. The designs of complete power supplies are progressing.The design features of the 117.5GHz 1.5MW gyrotron and the solid-state cathode and body power supplies will be described and the current status and plans are presented.