Studies towards an upgraded 1.5 MW gyrotron for W7-X

Konstantinos A Avramidis,Felix Mentgen,Tobias Ruess,Gerd Gantenbein,Heinrich P Laqua,Dietmar Wagner,John Jelonnek,Jianbo Jin,C Ioannidis,Stefan Illy,Tomasz Rzesnicki,Ioannis Gr Pagonakis,Manfred Thumm,Robert C Wolf,E Poli,J Oosterbeek,H Laqua

doi:10.1051/epjconf/201920304003

Abstract

Studies towards a 1.5 MW, 140 GHz CW gyrotron, with the capability of MW-class operation also at 175 GHz, are ongoing at Karlsruhe Institute of Technology in view of a possible future upgrade of the ECRH system of the stellarator W7-X. The upgrade of the existing 1.0 MW, 140 GHz European gyrotron for W7-X has been chosen as a development path. Detailed designs of the cavity, the non-linear uptaper, and the quasi-optical launcher for the upgraded gyrotron have been obtained and have been validated numerically. In parallel, a mode generator, intended for low-power tests of the quasi-optical mode converter system of the upgraded gyrotron, has been designed, manufactured, and successfully tested.

Highlights

The stellarator Wendelstein 7-X (W7-X) is equipped with a steady-state (1800 s) Electron Cyclotron Resonance Heating (ECRH) system consisting of ten 1 MW gyrotrons, which operate at 140 GHz [1]
It has been identified that the most promising development path, with respect to risk and cost, would be the upgrade of the existing W7-X TE28,8-mode gyrotron in order to operate in the TE28,10 mode at 140 GHz and in the TE36,12 mode at 175 GHz
The selection of the operating modes and the design parameters for the upgraded gyrotron for W7-X has primarily been driven by the following list of requirements: (i) Continuous Wave (CW) operation at 140 GHz with a power of 1.5 MW (ii) CW MW-class operation at 175 GHz (iii) Minimization of risk and cost of development (iv) Use of the existing gyrotron power supplies at W7-X

Summary

Introduction

The stellarator Wendelstein 7-X (W7-X) is equipped with a steady-state (1800 s) Electron Cyclotron Resonance Heating (ECRH) system consisting of ten 1 MW gyrotrons, which operate at 140 GHz [1]. MW-class microwave power at a frequency around 175 GHz would be attractive for Collective Thomson Scattering (CTS) diagnostics. Motivated by these considerations, studies towards an upgraded 140 GHz, 1.5 MW Continuous Wave (CW) gyrotron, with the option for MW-class operation at 175 GHz, have been initiated at Karlsruhe Institute of Technology [4]. The mode generator is based on the obtained cavity design and is using a coaxial cavity with perforated wall. It has been assembled and experimentally tested, delivering very good results.

Operating mode selection

Cavity and non-linear uptaper

Quasi-optical launcher

Mode generator

Findings

Outlook and discussion