Development of negative ion based neutral beam injector toward JT-60SA

Tanaka, Yutaka; Hanada, Masaya; Kobayashi, Kaoru; Kamada, Masaki; Kisaki, Masashi

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1547 - 1550, 2009/09

This paper reports recent R&D results on negative ion-based NBI system for JT-60 Super Advanced where 10 MW neutral beams is designed to be injected for 100 seconds. There are major two issues to realize such as a high-power and long-pulse injection, i.e., the improvement of voltage holding capability and the reduction of the grid power loading of the JT-60U negative ion source with three acceleration stages. As the first step for improving voltage holding capability, the breakdown location has been examined on site of JT-60U by measuring the lights emitted from spark gaps that are installed outside of the ion source in parallel with acceleration stages. To reduce the grid power to an allowable level, outward deflection of outmost beamlets, due to space charge of the inner beamlets, was suppressed by distorting the acceleration electric field at the edge of the grids. This allowed to reduce the highest grid power loading to acceptable level of 5 %.

Toroidal rotation profiles under the influence of fast-ion losses due to toroidal field ripple

Honda, Mitsuru; Takizuka, Tomonori; Fukuyama, Atsushi*; Yoshida, Maiko; Ozeki, Takahisa

Journal of Plasma and Fusion Research SERIES, Vol.8, p.316 - 320, 2009/09

Characteristics of toroidal rotation profiles in tokamak plasmas are studied under the influence of fast-ion losses due to a toroidal field (TF) ripple by using a one-dimensional multi-fluid transport code, TASK/TX. When a neutral beam (NB) is injected into a plasma, a part of fast ions is lost due to the effect of the TF ripple. The radial current then flows inward in the bulk plasma to keep quasi-neutrality and it exerts a torque on the plasma in the direction opposite to the plasma current. A parametric survey of the toroidal rotation driven by this torque is conducted to quantify the sensitivity to various externally-controllable sources such as a co-tangential NBI power. In the case of a larger ripple amplitude, it is observed that the counter-toroidal rotation develops near the periphery of the plasma as an increase in the co-NBI input power while the co-toroidal rotation velocity on the magnetic axis reaches a maximum value at a certain NBI power. This torque can be mitigated by increasing a gas puff rate. An increase in the plasma current also leads to the reduction in the counter rotation induced by ripple.

Uniform negative ion beam extraction in a cesium-seeded large negative ion source with a tent magnetic filter

Tobari, Hiroyuki; Hanada, Masaya; Inoue, Takashi; Taniguchi, Masaki; Kashiwagi, Mieko; Watanabe, Kazuhiro; Umeda, Naotaka; Sakamoto, Keishi

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1530 - 1533, 2009/09

We applied a tent-shaped magnetic filter combined with a symmetry line-cusp field with a Cesium seeding for the surface production of negative ions. Uniform hydrogen plasma was produced without any localization of primary electrons under low-pressure condition. The negative ion beam extracted from a wide area of 34 cm 17 cm showed spatial deviation of only 7.9%. It was concluded that incident uniform flux of positive ions and/or atoms flux on the surface of the plasma grid was achieved with the tent filter, which enhanced the surface production of negative ions.

Numerical modelling of high energy ion transport in tokamak plasmas

Hamamatsu, Kiyotaka

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1134 - 1137, 2009/09

no abstracts in English

Transport of heavy hydrocarbon and its redeposition on plasma facing walls

Oya, Kaoru*; Inai, Kensuke*; Kikuhara, Yasuyuki*; Nakano, Tomohide; Kawata, Jun*; Kawazome, Hayato*; Ueda, Yoshio*; Tanabe, Tetsuo*

Journal of Plasma and Fusion Research SERIES, Vol.8, p.419 - 424, 2009/09

http://www.jspf.or.jp/JPFRS/PDF/Vol8/jpfrs2009_08-0419.pdf

Redeposition of CH and CH chemically eroded from carbon walls is simulated by EDDY code incorporated with the reflection on a hydrogenated and amorphized carbon surface. The redeposition rate for heavy hydrocarbons is drastically decreased by introduction of the reflection. The redeposition patterns on the surface are enlarged by the reflection, but it is narrower for the heavy hydrocarbons than for CH. The photon emissions of C from CH (CH) decay faster than that of CH from CH in high-temperature (10 eV) plasmas, which reproduces the difference of the decay of the CD and C light intensities observed in the vicinity of the outer diverter plates of JT-60U. For such temperatures, the inverse photon-efficiency, which is defined as the ratio of the number of the launching hydrocarbons to the photoemission events of CH and C, is in good agreement with the values observed in JT-60U experiments.

Measurement of DT and DD neutrons with a TOF spectrometer for determination of fuel ion density ratio in ITER

Okada, Koichi*; Kondo, Keitaro; Ochiai, Kentaro; Sato, Satoshi; Konno, Chikara; Okamoto, Atsushi*; Kobuchi, Takashi*; Kitajima, Sumio*; Sasao, Mamiko*

Journal of Plasma and Fusion Research SERIES, Vol.8, p.666 - 669, 2009/09

Measurement of fuel ion density ratio, /, is required for burning control on ITER. The measured / ratio must be fed back in real time. A neutron measurement system to measure / should be operable at high counting rate. It is estimated that the number of emitted DT neutrons is 200 times higher than that of DD neutrons under the condition of ITER standard operation. A neutron measurement system was developed using a DT/DD generator, where DT neutrons are dominant and DD neutrons are contaminated slightly in the neutron beam. The measurement instrument was a TOF spectrometer. Signals originating from each neutron must be distinguished in order to measure the fuel ratio. We developed a circuit system with discrimination windows to distinguish each signal pulse, and DT and DD neutrons were measured separately and simultaneously with this system. The experimental result indicates a possibility that this system is suitable for measurement of fuel ion density ratio on ITER.

Flight-type-probe for measuring hot core plasmas

Uehara, Kazuya; Sadamoto, Yoshiro*; Amemiya, Hiroshi*; Oyama, Koichiro*; Nagashima, Yoshihiko*

no journal, , 

In the hot and dense fusion plasma, the application of the electrostatic and/or magnetic probe is limited to such a localized region as the scrape off layer (SOL), since the conventional probe would be destroyed in the core plasma region due to the great heat damage and/or the electromagnetic force during the plasma disruption. In order to make the best use of probe methods having a high spatial and time resolution, we consider a flight-type-probe (FTP), in which the probe circuit and memory elements for the signal are installed in a capsule to be thrown into the core hot plasma from one side port with a very fast speed. The data acquired are transmitted through rf antenna to outside observers and/or are saved in the CPU memory elements to be analyzed after reproduction. The dimension of the FTP is designed as small as possible and the launching mechanism is used for a pellet injection or a rail gun. The preliminary design of the FTP is inspected in this issue.

Ultrafast plasma photonics; Measurement and control of laser wakefield

Kondo, Kiminori

no journal, , 

Hydrogen isotope retention in the first wall tiles of JT-60U

Yoshida, Masafumi; Tanabe, Tetsuo*; Sugiyama, Kazuyoshi*; Hayashi, Takao; Masaki, Kei; Yagyu, Junichi; Sato, Masayasu

no journal, , 

We have investigated hydrogen isotopes retention in the graphite outboard first wall tiles of JT-60U by means of TDS, SIMS and SEM. The SEM examination confirms that these tiles are mostly eroded. Differently from graphite divertor tiles, in which H retention was dominated owing to HH discharges preformed after DD discharges to remove tritium, deuterium is dominated in hydrogen isotopes retention of the first wall tiles and penetrates deeper from the surface. This is attributed to injection of high energy D and difficulty of isotopical replacement owing to their lower temperature. Although the total retention of the hydrogen isotopes in the unit area of the first wall region normalized by discharge duration is not large, the integrated amount over the whole surface could be appreciably large. This type of hydrogen retention could be also possible for the metallic wall.

First mirror issues and measures for harsh environment of ITER

Sugie, Tatsuo; Ogawa, Hiroaki; Iwamae, Atsushi; Kawano, Yasunori; Hatae, Takaki; Kajita, Shin*; Kusama, Yoshinori

no journal, , 

Plasma facing first mirrors of ITER will experience relatively higher levels of radiation due to neutron, ray irradiation than in present devices. An additional potential damaging effect for the first mirrors is the formation of coatings of impurities, such as Be, W, C, etc. due to erosion and re-deposition of the materials of the first wall and the divertor. Issues of the first mirror are summarized and the total fluxes and energy distributions of deuterium, helium, carbon and deuterium molecule at the first mirror positions are estimated. Protective and mitigating measures to minimize the degradation of first mirror reflectivity are adopted in the system designs of diagnostics. However, the reflectivity may change due to the environmental effects. An in-situ and remote sensitivity calibration system withstanding in the strong radiation field has been developed. Finally, remaining issues are summarized.