Operation of the Positive-ion Based NBI System for JT-60U
H. Oohara, N. Akino, N. Ebisawa, S. Hikita, A. Honda, T. Itoh, M. Kawai, M. Kazawa, M. Kusama, M. Kuriyama, K. Mogaki, T. Ohga, F. Satoh, H. Seki, Y. Tanai, Y. Toyokawa, N. Umeda, K. Usui and H. Yamazaki
JAPAN ATOMIC ENERGY RESEARCH INSTITUTE, Naka Fusion Research Establishment
Mukoyama, Naka-machi, Naka-gun, Ibaraki-ken, 311-0193 Japan
Abstract.
The JT-60 neutral beam injection system with positive-ion sources (P-NBI) has injected high power neutral beams for 14 years since 1986, and contributed to achieve high performance plasmas in JT-60U. The P-NBI system consists of 14 beam lines, 14 ion source power supply units and subsystems of a refrigeration system, a cooling water system, auxiliary vacuum pumping system and control system including computer system. Each beam line has two ion sources, which has a capability of delivering a deuterium/hydrogen ion beam of 70-80A in total at 80-120keV for 10sec. The original design of the P-NBI was to inject the hydrogen nertral beam power of 20MW at 75keV with 14 beam line units. After achieving the rated injection power of 20MW with hydrogen beam in 1987, the ion sources had been improved to increase an extraction current. The injection power had reached to 27MW at 80keV with hydrogen as a result, which was higher power by more than 30% compared to the rated power. In 1991, the P-NBI system has been modified to be able to operate deuterium beam at 120keV, corresponding to convert the JT-60 plasma operation from with hydrogen to deuterium. An injection power with deuterium beam has achieved 40MW at 95keV using 14 beam line in 1994. Helium-3 and helium-4 beams have been injected for studying D-3He nuclear fusion reaction, and for studying helium ash exhaust capability, respectively. A neutral beam power injected into the plasmas is 4.8MW is 80keV with helium-3 beam using 4 beam lines, and 2.8MW at 60keV with helium-4 beam using 3 beam lines.
In 2000, the computer control system for the NBI has been remodeled from an old-type minicomputer system to a workstation to extend operation capability and flexibility, and to avoid the operation troubles owing to a timeworn computer. In parallel with the alteration of the computer system, data acquisition system has also changed from CAMAC system to VME-bus system. The VME system has reduced the load of the workstation by taking a part of the function in the workstation. After alteration of the computer system, the reliability and flexibility in the neutral beam injection experiments have increased greatly.
In the conference, the developments of the ion sources and power supplies aimed at increasing beam power, and the alteration of the computer system will be presented in detail.