The ECRH system for JET

A.G.A. Verhoeven1, W.A. Bongers1, B.S.Q. Elzendoorn1, M. Graswinckel1,

P. Hellingman1, J.J. Kamp1, W. Kooijman1, O.G. Kruijt1, J. Maagdenberg1,

D. Ronden1, J. Stakenborg1, A.B. Sterk1, J. Tichler1

S. Alberti2, T. Goodman2, M. Henderson2, J.A. Hoekzema3, J.W. Oosterbeek3, A. Fernandez4, K. Likin4, A. Bruschi5, S. Cirant5, S. Novak5, B. Piosczyk6,

M. Thumm6, H. Bindslev7, A. Kaye8, C. Fleming8 H. Zohm9

1FOM-Instituut voor Plasmafysica 'Rijnhuizen', Association EURATOM-FOM;; P.O. Box 1207, 3430 BE Nieuwegein, the Netherlands;

2Euratom/CRPP-Lausanne; 3Euratom/FZJ-Julich;

4Euratom/CIEMAT, Madrid; 5Euratom/CNR-Milano;

6Euratom/FZK-Karlsruhe; 7Euratom/Riso-Denmark;

8Euratom-JET/UKAEA Culham; 9Euratom/IPP-Garching;

An ECRH (electron-cyclotron resonance heating) system is being designed for JET in the frame of the JET-Enhanced Performance project (JET-EP). This project is implemented under the new European Fusion Development Agreement (EFDA). The system will consist of 6 gyrotrons, 1 MW each, in order to deliver 5 MW into the plasma. The system will especially be equipped to enable the control of neo-classical tearing modes (NTM). Furthermore, heating and current drive is foreseen in a large number of different target plasma configurations and the control of the ratio of the electron and ion temperatures. The frequency, 113.3 GHz, is selected to enable a wide range of operating toroidal magnetic fields from 3 to 4 T and at second harmonic at lower fields and also to allow for a future upgrade to 170 GHz using the same systems, including the double-disk diamond windows at the torus side.

The main elements of the ECRH system are:

* gyrotrons with a depressed collector, each 1 MW for 10 s and 0.6 MW for 30 s.

* gyrotrons will have diamond windows, with Gaussian output mode

* evacuated waveguides will transport the mm-wave power

* double disk diamond windows on the tokamak side, with a fast valve to have additional tritium barriers

* a plug-in launcher, steerable in both toroidal and poloidal angle, able to handle 8 mm-wave beams. Four steerable launching mirrors will be installed, handling each two mm-wave beams. Water cooling of the movable mirror is being considered, in order to increase the ITER relevance.

* main power supplies, 60 kV, with a solid-state crowbar to feed two gyrotrons, each

* series IGBT switches will enable independent control of each gyrotron

* body power supplies will stabilise the gyrotron output power and enable fast modulations up to 10 kHz. Solid-state devices are considered the best option.