A NEW GENERATION OF GRIDDED TUBES FOR CW OPERATION ON NEW TOKAMAKS

G. Clerc, A. Boussaton, JP Ichac, C. Robert

THOMSON TUBES ELECTRONIQUES
18 Avenue du Mar'-echal Juin,
92366 MEUDON-LA-FORET

Until now, tetrodes improvements could follow the increase of the RF requirements for the additional heating of plasma in the Tokamaks and other fusion devices. Pulse length was increased from 100 ms to 10, 20 and 30 seconds, and the power from 1.5 MW to 2 or 2.5 MW with a VSWR of 1.5. In these conditions, where the tube's internal elements are an important part of the RF resonant circuits, the repartition of voltages and currents along the tube leads to an utilization of the cathode which is not optimized and to high RF losses. Long operational experience in accelerators, fusion devices and UHF TV transmitters, but also extensive tests conducted with our own high power testing facilities, give TTE a good knowledge of these phenomena. Based on this experience, a new tube named DIACRODE (TM) has been developed. This new structure overcomes the limits reached by conventional tetrodes.

This paper presents an analysis of the Diacrode (TM) concept and an update of the results obtained in the UHF TV and accelerator fields. An extension of this concept to the fusion field gives a neat solution to generate 2 MW cw with a VSWR < or equal to 2, any phase, for the new projects.