Speaker
Laure Vermare
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1062.pdf
Fast ion confinement study by NB blips in the LHD deuterium plasma
Taleo Nishitani1, Kunihiro Ogawa1,2, Sadayoshi Murakami3, Neng Pu2, Hiroki Kawase2,
Mitsutaka Isobe1,2, Masaki Osakabe1,2, and the LHD Experiment Group
1
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan
2
The Graduate University for Advanced Studies, Toki- 509-5292, Japan
3
Kyoto University, Kyoto 615-8520, Japan
The confinement of neutral beam (NB)-injected fast ions has been investigated by neutron
emission rate response to the short pulse NB injection called “NB-blip” at the Large Helical
Device (LHD). This method is widely used in tokamaks with deuterium plasma operation,
however, this is the first time application to the large size helical systems. Generally, neutron
intensity decay time after the NB blip is analysed by a 0-dimensional fast ion slowing down
model, where differences of the beam deposition profile for each shot is not taken into
account. We have developed a neutron emission rate calculation code FBURN based on the
classical slowing down model, which is taking into account of not only the beam deposition
profile but also other plasma parameter profiles such as the electron density and the electron
temperature, and time evolutions of those parameters. The confinement of NB-injected fast
ions is investigated by the discrepancies between measured and calculated neutron emission
decay time τn after the NB blip and between measured and calculated maximum neutron
emission rate Sn during the NB blip. The former is reflected by the collisional diffusion
mainly and the later is reflected by the collision-less diffusion and prompt loss mainly. The
Large Helical Device (LHD) has five NB injectors. NBI#1, #2, and #3 are tangential
direction injectors with typical energy is 180 keV. NBI#4 and #5 are perpendicular
direction injectors with typical energies are 60 keV and 80 keV, respectively. In this
experiment, NBI#1, #2, #3, and #4 each with the pulse width of 40 ms are injected into
different configuration plasmas with various electron densities. It is found that the diffusion
coefficient of NB-injected fast ion evaluated from τn is 1-3 m2/s for perpendicular injections
and 0.3 m2/s or smaller for tangential injections, and the diffusion coefficient evaluated
from Sn is 2-5 m2/s for perpendicular injections and 1.5 m2/s or smaller for tangential
injections. Also, the diffusion coefficient increases as the plasma axis is shifted outward.
