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22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone
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Rapid Radial Propagation of Momentum Change and Flow Oscillation Associated with a Pellet Injection

24 Oct 2018, 08:30
4h
Mahatma Mandir Conference Centre

Mahatma Mandir Conference Centre

Gandhinagar (nearest Airport: Ahmedabad), India
Poster P3 Posters

Speaker

Dr Tokihiko Tokuzawa (National Institute for Fusion Science)

Description

We report the discovery of rapid momentum change and oscillatory flow as a result of the pellet injection. Novel diagnostics tools with high spatio-temporal resolution applied to the perpendicular flow velocity and turbulence intensity measurements in LHD experiments show the following results. Just after the pellet injection, (1)the damped oscillating flow velocity and the increasing density fluctuation are observed in a few milliseconds. (2)The propagating flow structure towards the core direction is observed, and its speed is faster than the pellet penetration speed. These results are quite meaningful for understanding the physics of pellet penetration in toroidal plasma. Just after the pellet injection, the perpendicular flow velocity is oscillating and damping in a few milliseconds. The damped oscillation model can be applied to fit the observation data. The toroidal mode number of this oscillation is estimated to be 0 or 10. We can also measure the turbulence intensity at the same position. The turbulence increases rapidly and then decreases before the end of the damping of the oscillatory flow. The generation and damping of flow itself might be caused by the turbulence. On the other hand, the electron density increases and the electron temperature decreases with finite delay. Therefore, it is found that the change of local density gradient seems likely not to play an important role for the start of this oscillation. The ballistic propagation of the change of flow structure towards the core direction is observed in the region at r/a<0.97, where the mono-cycle temporal oscillation is observed. In order to measure such a fine velocity profile, a high sampling rate digital storage of 80 GS/s is applied for the frequency comb microwave Doppler reflectometer. The propagation speed increases at the location of r/a~0.97 and exceeds 1.5km/s, which is three times faster than the pellet penetration speed. This indicates that the rapid propagation of information of momentum change is present. Currently, it is also found that the location of the pivot point is not at the rational surface, and the information of momentum change propagates at least r/a~0.86 before the start of the electron density rise. Therefore, it is found that the momentum changes rapidly, and this may lead the global change of the radial electric field and affect the bulk plasma transport.
Country or International Organization Japan
Paper Number EX/P3-7

Primary author

Dr Tokihiko Tokuzawa (National Institute for Fusion Science)

Co-authors

Dr Akira Ejiri (Graduate School of Frontier Sciences, The University of Tokyo) Dr Chihiro Suzuki (National Institute for Fusion Science) Dr Gen Motojima (National Institute for Fusion Science) Dr Hayato Tsuchiya (National Institute for Fusion Science) Prof. Hiroshi Yamada (National Institute for Fusion Science) Dr Ichihiro Yamada (National Institute for Fusion Science) Dr Katsumi Ida (National Institute for Fusion Science) Mr Kazuki Oguri (Nagoya University) Dr Kenji Tanaka (National Institute for Fusion Science) Dr Kiyomasa WATANABE (National Institute for Fusion Science) Dr Masahiko Emoto (National Institute for Fusion Science) Dr Naoki Tamura (National Institute for Fusion Science) Dr Ryuichi Sakamoto (National Institute for Fusion Science) Dr Shigeru Inagaki (Kyushu University) Dr Toru Tsujimura (National Institute for Fusion Science)

Presentation Materials

Paper