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Title: Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system

Abstract

A compact antenna system was designed and fabricated to enable millimeter-wave beam scanning in the toroidal and poloidal directions of the JT-60U tokamak for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) experiments. The antenna consists of a fast movable flat mirror mounted on the tokamak vacuum vessel and a rotary focusing mirror attached at the end of the waveguide that is supported from outside the vacuum vessel. This separate support concept enables a compact structure inside a shallow port (0.68x0.54x0.2 m) that is shared with a subport for an independent diagnostic system. During a plasma shot, the flat mirror is driven by a servomotor with a 3-m-long drive shaft to reduce the influence of the high magnetic field on the motor. The focusing mirror is rotated by a simple mechanism utilizing a push rod and an air cylinder. The antenna has been operated reliably for 3 years after a small improvement to the rotary drive mechanism. It has made significant contributions to ECH and ECCD experiments, especially the current profile control in JT-60U.

Authors:
; ; ; ; ; ;  [1]
  1. Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Mukoyama 801-1, Naka-shi, Ibaraki 311-0193 (Japan)
Publication Date:
OSTI Identifier:
20723246
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 76; Journal Issue: 11; Other Information: DOI: 10.1063/1.2130967; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANTENNAS; CONTAINERS; CURRENTS; ECR CURRENT DRIVE; ECR HEATING; FOCUSING; JT-60U TOKAMAK; MAGNETIC FIELDS; MIRRORS; PLASMA; PLASMA CONFINEMENT; PLASMA DIAGNOSTICS; RF SYSTEMS

Citation Formats

Moriyama, S., Kajiwara, K., Takahashi, K., Kasugai, A., Seki, M., Ikeda, Y., and Fujii, T. Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system. United States: N. p., 2005. Web. doi:10.1063/1.2130967.
Moriyama, S., Kajiwara, K., Takahashi, K., Kasugai, A., Seki, M., Ikeda, Y., & Fujii, T. Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system. United States. doi:10.1063/1.2130967.
Moriyama, S., Kajiwara, K., Takahashi, K., Kasugai, A., Seki, M., Ikeda, Y., and Fujii, T. Tue . "Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system". United States. doi:10.1063/1.2130967.
@article{osti_20723246,
title = {Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system},
author = {Moriyama, S. and Kajiwara, K. and Takahashi, K. and Kasugai, A. and Seki, M. and Ikeda, Y. and Fujii, T.},
abstractNote = {A compact antenna system was designed and fabricated to enable millimeter-wave beam scanning in the toroidal and poloidal directions of the JT-60U tokamak for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) experiments. The antenna consists of a fast movable flat mirror mounted on the tokamak vacuum vessel and a rotary focusing mirror attached at the end of the waveguide that is supported from outside the vacuum vessel. This separate support concept enables a compact structure inside a shallow port (0.68x0.54x0.2 m) that is shared with a subport for an independent diagnostic system. During a plasma shot, the flat mirror is driven by a servomotor with a 3-m-long drive shaft to reduce the influence of the high magnetic field on the motor. The focusing mirror is rotated by a simple mechanism utilizing a push rod and an air cylinder. The antenna has been operated reliably for 3 years after a small improvement to the rotary drive mechanism. It has made significant contributions to ECH and ECCD experiments, especially the current profile control in JT-60U.},
doi = {10.1063/1.2130967},
journal = {Review of Scientific Instruments},
number = 11,
volume = 76,
place = {United States},
year = {Tue Nov 15 00:00:00 EST 2005},
month = {Tue Nov 15 00:00:00 EST 2005}
}
  • Two pilot facilities of advanced negative-ion-based neutral beam injection heating system have been working successfully on the JT-60U tokamak and the LHD heliotron in Japan. These were the first applications of negative-ion technology to the production of high current neutral beam for plasma heating as well as current drive. High energy deuterium beam of 400 keV (5.8 MW) was injected in JT-60U for efficient current drive, and high power hydrogen beam of 9.0 MW (160 keV) was injected in LHD producing high performance plasmas. These results demonstrate the feasibility of negative ion beam system for future fusion reactors such asmore » ITER.« less
  • Research and developments on the ion cyclotron range of frequency (ICRF) heating system in the JT-60 upgrade (JT-60U) are presented. The developments and experiences on the operation of the ICRF heating system contribute to its upgrade and to future ICRF heating systems in ITER. The ICRF heating system for JT-60U started operation in January 1992. RF power up to 7 MW for 1.1 sec at 116 MHz has been coupled to a plasma as a result of the developments described in this paper. New high power tetrodes having pyrolitic graphite grids for higher dissipation of screen and control grids weremore » tested in the ICRF amplifier, and 1.7 MW of the output power at 131 MHz for 5.4 seconds was achieved. This was the highest power level for fusion research above 110 MHz in 1990. A pair of phased loop antenna arrays (2 x 2) showed sufficiently high coupling resistance. To keep the impedance matching between the antenna and the transmission line, a frequency feedback control (FFC) system was developed, and its effectiveness was proved to couple high power RF continuously to the variable plasma. In ITER, enhancement of dielectric loss tangent of ceramics due to neutron irradiation will limit power injection capability of the antenna significantly. To solve this problem, an all-metal support (AMS) was developed in the JT-60U ICRF heating system as a substitute for a ceramic support of a central conductor of a coaxial antenna feeder in the ITER ICRF antenna.« less
  • In the JT-60U negative-ion-based neutral beam injection system, the effect of negative ion and electron deflection by the plasma grid (PG) magnetic filter was studied. After a long-pulse operation of up to 19 s, a local melting was observed on the beamline near the ion source, facing the electron drift side of the PG magnetic field. It is confirmed that the experimental deflection of the negative-ion beam agrees well with the three-dimensional beam simulation result by taking account of the measured magnetic field. By using the code, it is found that some stripped electrons produced in the first acceleration gapmore » pass through the down pitch of the multiple apertures in the next stage of acceleration grids, and then collide on the beamline around the melted location.« less
  • The electron cyclotron range of frequency (ECRF) system was designed and operated on the JT-60U to locally heat and control plasmas. The frequency of 110 GHz was adopted to inject the fundamental O-mode from the low field side with an oblique injection angle. The system is composed of four 1 MW-level gyrotrons, four transmission lines, and two antennae. The gyrotron is featured by a collector potential depression (CPD) and a gaussian beam output through a diamond window. The CPD enables JAERI to drive the gyrotron under the condition of the main DC voltage of 60 kV without a thyristor regulation.more » The gaussian mode from the gyrotron is effectively transformed to HE{sub 11} mode in the 31.75 mm diameter corrugated waveguide. About 75% of the output power of the gyrotrons can be injected into plasmas through the waveguides about 60 m in length. There are two antennae to control the deposition position of the EC wave during a plasma discharge. One is connected with three RF lines to steer the EC beams in the poloidal direction. The other is to control the EC beam in the toroidal and poloidal directions by two steerable mirrors.On the operation in 2000, the power of 1.5 to 1.6 MW for 3 s was successfully injected into plasmas using three gyrotrons. Local profile control was demonstrated by using the antennae. This capability was devoted to improve the plasma performance such as high T{sub e} production more than 15 keV and suppression of the MHD activities. In 2001, the fourth gyrotron, whose structure was improved for long pulse operation, has been installed for a total injection power of {approx}3 MW.« less
  • The phased-array antenna system for Electron Cyclotron/Bernstein Wave Heating and Current Drive experiments has been developed in the QUEST. The antenna was designed to excite a pure O-mode wave in the oblique injection for the O-X-B mode conversion experiments, and its good performances were confirmed at a low power level. The plasma current (<{approx}15 kA) with an aspect ratio of 1.5 was started up and sustained by only RF injection in the low-density operations. The long pulse discharge of 10 kA was also attained for 37 s. The new density window to sustain the plasma current was observed in themore » high-density plasmas. The single-null divertor configuration with the high plasma current (<{approx}25 kA) was attained in the 17 s plasma sustainment.« less