THE 8 MW LOWER HYBRID "ELECTRON MODE" SYSTEM FOR THE ADDITIONAL HEATING OF THE PLASMA OF THE FTU TOKAMAK
In the last year and a half after the Workshop Phase II on the FTU project (January 1983), the understanding of the basic physics involved in the RF heating of tokamak plasmas has been considerably improved. This is true especially for the Lower Hybrid (LH) Heating and Current Drive (CD) methods. The "Electron Mode" regime of LH Heating, based on the same physics as the current drive, has been extensively studied and experimentally tested especially with respect to the relation between frequency and density limit. These results have largely contributed to the decision to build a CD system on TORE SUPRA. Based on the same motivations, the Lower Hybrid "Electron Mode" Heating (frequency: 8 GHz), has been chosen to heat the plasma of the FTU Tokamak. This choice is also confirmed due to the uncertain experimental results obtained in the LH ion heating regime at high density, and due to the technical complexity presented by the construction and use of Ion Cyclotron antennas on FTU, which would also imply a plasma size reduction. The RF power required (8 MW at 8 GHz) will be produced by 16 gyrotron oscillators (500 kW unit power) feeding 16 grill couplers installed on 8 equatorial ports of FTU. The dc power supplies will be modularly built to be compatible even with a completely different sort of tubes (e.g. for ICRH). The transmission lines between the generators and the grills will be circular oversized waveguides to reduce the losses to less than 1 dB. Each grill will consist of an 8x8 matrix of rectangular waveguides pressurized and terminated by thick (one wavelength) alumina windows facing the grill mouth. Gyrotron availability has been verified through studies conducted by the two major manufacturers presently on the market. Preliminary quotations and delivery times have been obtained. The design of the grill couplers has been supplemented by a study contract with an industrial research laboratory which is producing a prototype structure and ceramic windows with very promising results. Microwave mode converters and power dividers for the transmission system have been designed and prototypes are being built and will be tested shortly. An 8 GHz, 25 kW cw test bench has been already commissioned and will be used to test all the microwave components. The power level is more than adequate also to process single channels of the coupling structures.
Bibliographic Reference: WRITE TO ENEA, CENTRO RICERCHE ENERGIA FRASCATI, SERVIZIO STUDI E DOCUMENTAZIONE C.P. 65 - 00044 FRASCATI, ROMA (ITALY), MENTIONING REPORT RT/FUS/85/12, 1985
Record Number: 1989124109700 / Last updated on: 1987-01-01
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