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Journal Articles

Orbit following calculation of energetic ions for design of ferritic insertion on JT-60U

Shinohara, Koji; Suzuki, Yutaka; Sakurai, Shinji; Masaki, Kei; Fujita, Takaaki; Miura, Yukitoshi

NIFS-PROC-63, p.158 - 162, 2006/04

For the further pursuit of the steady-state advanced tokamak research, the ferritic insertion was proposed to reduce the toroidal field (TF) ripple. The reduction of energetic ion loss due to the TF ripple reduction brings: (1) the enhancement of the heating and current drive "effective" efficiency, (2) the extended pulse length and the improved efficiency of RF injection due to the reduced heat flux on antennas and improved coupling between antennas and a plasma, (3) the availability of a wall stabilization without losing heating power, and (4) the possibility of an enhanced availability of the rotation control to improve the MHD stability and transport. The design work of ferritic inserts was carried out aiming at an effective, machine-safe, and short-term installation. Here, the design work for ferritic inserts is described from the viewpoint of the behavior of energetic ions. The confinement of energetic ions and the absence of the unfavorable heat flux on the first wall was assessed by using the Fully three Dimensional magnetic field OFMC code, which was developed for a ferrite insert program in JFT-2M. In the final design, the confinement of energetic ions is improved by about 1.3 times in a large volume plasma with Bt0 = 1.9T.

Oral presentation

Lost alpha diagnostic based on an imaging bolometer and a multi-foil thermal detector

Peterson, B. J.*; Alekseyev, A. G.*; Konoshima, Shigeru; Ashikawa, Naoko*; Parchamy, H.*; Sasao, Mamiko*; Isobe, Mitsutaka*; Miura, Yukitoshi

no journal, , 

The confinement of alpha particles is an important topic for the operation of a fusion reactor as they should transfer their energy to the fuel plasma and then be exhausted safely through the divertor. If their confinement is poor they could escape through the last closed flux surface and scrape off layer in a spatially localized manner that could do serious damage to the first wall. Therefore the diagnosis of lost alpha particles is important for the operational safety and evaluation of an experimental fusion reactor. A diagnostic device has been proposed based on an imaging bolometer and a multi-foil thermal detector. In this paper we discuss ongoing work with testing prototype imaging bolometers on LHD and JT-60U, calibration work using a laser heat source, the testing of a prototype multi-foil thermal detector on an ion accelerator and the design of a diagnostic for ITER. This work is partly supported by Grants-in-Aid for Scientific Research of the JSPS, Nos.16560729 and 16082207.

Oral presentation

Observation of confinement degradation of energetic ions by Alfv$'e$n eigenemodes in weak shear plasmas on JT-60U

Ishikawa, Masao; Shinohara, Koji; Takechi, Manabu; Matsunaga, Go; Kusama, Yoshinori; Krasilnikov, A.*; Kaschuck, Y.*; Isobe, Mitsutaka*; Nishitani, Takeo; Morioka, Atsuhiko; et al.

no journal, , 

Magnetohydrodynamics (MHD) instabilities with a frequency sweeping and then saturation of frequency as qmin decrease have been observed during Negative-ion-based Neutral Beam (NNB) injection in JT-60U Weak Shear (WS) plasmas. The frequency evolution of those MHD instabilities can be explained by Reversed-Shear-induced Alfv$'e$n Eigenemode model or Alfv$'e$n Cascade model. In recent experiments, a confinement degradation of energetic ions by such instabilities was clearly observed. In this work, we evoluate the confinement degradation of energetic ions by the instabilities usigng measurement of total neuron flux and neutron emission profile. Further, we will compare the confinement degradation by the above instabilities with that by Abrupt Large-amplitude Events (ALEs), which are bursting modes.

Oral presentation

Alfv$'e$n eigenmode spectroscopy by application of external magnetic-field perturbations in the compact helical system

Matsunaga, Go; Toi, Kazuo*; Suzuki, Chihiro*; Shimizu, Akihiro*; Takechi, Manabu; Nakajima, Noriyoshi*; Fukuyama, Atsushi*

no journal, , 

no abstracts in English

Oral presentation

Ripple loss of alpha particles in a low-aspect-ratio tokamak reactor

Tani, Keiji; Nishio, Satoshi; Tobita, Kenji; Tsutsui, Hiroaki*; Mimata, Hideyuki*; Iio, Shunji*; Aoki, Takayuki*

no journal, , 

Studies on the loss of fusion produced alpha particles enhanced by toroidal field (TF) ripple in a low-aspect-ratio tokamak reactor (VECTOR) have been made by using an orbit-following Monte-Carlo code. In actual TF coil systems, the ripple loss of alpha particles is strongly reduced as the aspect ratio becomes low (the power loss is proportional to A$$^{8.8}$$ for A$$>$$2.5) and the reduction of the number of TF coils results in a large amount of ripple losses even in a low-aspect-ratio tokamak. To reduce the number of TF coils from 12 to 6, about 40% of coil size enlargement is necessary in VECTOR. Ferrite plates are very effective to reduce ripple losses of alpha particles. By using ferrite plates, the coil size enlargement for N=6 can be relaxed to 15% and the number of coils can be reduced from 12 to 8 without any enlargement of coil size in VECTOR.

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