T. Eguchi

Development of 28 GHz/35 GHz Dual-Frequency Gyrotron for Fusion Research

The initial design study of 28 GHz/35 GHz dual frequency gyrotron is presented. The design is based on 28 GHz 1 MW gyrotron which we have developed. And it is studied whether 35 GHz oscillation is possible or not using the present 28 GHz gyrotron cavity. From the numerical simulation results, the cavity can form 35.45 GHz TE9,4 mode oscillation of over 1 MW oscillation power with high efficiency. However, in the present mode converter and transmission mirror system, the radiated RF power through the output window is only about 70 % of the 35.45 GHz oscillation power because of the radiation angle difference of 15.85°. For more high efficiency operation for 35 GHz, we will re-design the cavity in which there are good candidate modes such that there is no radiation angle difference.

The Improvement of the ECH Antenna System in the GAMMA 10

This paper shows that the design improvement of the ECH antenna system for high efficient heating of GAMMA 10 tandem mirror plasma. The previous ECH antenna was not large enough to cover the microwave because it was limited by the port size. New antenna system clears this limit and is enlarged as large as possible. And its size becomes twice, which enables to inject the microwave with the efficiency up to 95%. It is about 20% increase as compared with the previous system.

Numerical Calculation of the Gyrotron Oscillator in GAMMA 10 ECH Systems

The computational code for designing the resonant cavity of a gyrotron has been developed to design new gyrotrons for the future GAMMA 10(PDX). The developed code calculates the cavity RF profile function by simultaneously solving a set of relativistic single-particle equations of motion and wave equations to obtain a self-consistent solution in the dynamic system that accounts for the effects of the electron beam on the cavity field profile. Beam-wave interactions mainly occur in the uniform middle section of the resonator. The calculation results explain well experimental data of the gyrotron used in GAMMA 10 ECH system.

2-Dimensional Soft X-Ray Behavior of ECR Heated Plasma in GAMMA 10

The 2-Dimensional soft X-ray behavior during ECR heating have been examined in the GAMMA 10 tandem mirror. The peak position shifts several cm during the ECRH period, and it is found the peak position of the soft X-ray is rotating around the center axis of the vessel and its direction is same as that of E×B drift. In high power heating case, the oscillation of the peak position, decrease of the diamagnetism and line density are observed. The radial ion current measured by the ion sensitive probe increases depending on the ECRH power together with increase in the radius of the SX-peak rotation.

The Performance Test and the Improved Design of 28 GHz 1 MW Gyrotron

For the GAMMA10 tandem mirror, a 28 GHz 1 MW gyrotron has been developed. The output power was achieved 1 MW in short pulse test, and 0.54 MW / 2 s in long pulse test. Moreover, the temperature rise of sapphire single disk window installed in 28 GHz 1 MW gyrotron was measured. The temperature rise was 9 K at 0.45 MW / 2 s. On the basis of the results of the performance test, the designs of 28 GHz 1 MW gyrotron have been improved to enable the operation of 1.5 ~ 2.0 MW several sec. required in GAMMA10 and NSTX, and 0.4 MW CW required in QUEST.

Results of ECH Power Modulation Experimenting High and ELM-Like Heat Flux in GAMMA 10 Tandem Mirror

Electron cyclotron heating (ECH) power modulation experiments in the GAMMA 10 tandem mirror have been started in order to generate and control the high heat flux and to make the ELM (edge localized mode) like intermittent heat load pattern for divertor simulation studies. ECH for potential formation at the plug region (P-ECH) produces the electron flow with high energy along the magnetic filed line. The peak heat-flux of more than 10 MW/m2 was obtained during the ECH injection within the available power of ECH. It is found that arbitrary intermittent heat flux is possible by modulating the ECH power. 0.05 MJ/m2 heat pulse has been obtained with 380 kW 5ms ECH pulse, which indicates possibility of 0.5 MJ/m2 level with multi-MW ECH power.

Development of 154 GHz 1 MW Gyrotron for ECRH of LHD

At the Plasma Research Center (PRC) in University of Tsukuba, development of Mega-Watt Gyrotrons is performed for fusion research. Development of a new 154 GHz 1 MW gyrotron for ECRH system of Large Helical Device (LHD) has been done. The design studies of electron gun (MIG), cavity oscillator, mode converter, transmission mirrors, collector and superconducting magnet (SCM) have indicated more than 1 MW output with efficiency ~33 % for cavity oscillation mode of TE28,8. In the short pulse test of the first test tube, the maximum output power of 1.06 MW and the maximum total efficiency of 35.2 % with CPD were obtained.