Abstract
Energetic ion driven resistive InterChange modes (EICs) accompanying repeated bursts of the magnetic fluctuations were found in hydrogen campaign of large helical device. The pressure gradient of helically trapped energetic particles, which are mainly produced by perpendicularly injected beams, drives this mode. Recently, perpendicular neutral beam injection (PERP-NBI) systems are upgraded for deuterium plasma campaign. The beam energies of the two PERP-NBIs are increased from 40/40 keV to 60/80 keV, respectively. And the injection powers increase from 6/6 MW to 9/9 MW, as well. As results of these upgrades of NBIs, the β value of helically trapped energetic ions, , has increased up to ∼0.35% and induced EICs with larger bursts and smaller repetition frequencies. It is found that the threshold of to excite EICs increases with deuterium PERP-NBIs. The amplitude of each burst and effect on energetic beam ions become larger when is larger. In addition, a large electrostatic potential about −25 kV is observed when EICs are excited, which is about two times larger than the potential observed in hydrogen campaign. The transient increases of the electron density and temperature in edge regions are clearly observed when the electrostatic potential is formed.
Highlights
Studies of interactions between energetic particles (EPs) and MHD modes are quite important to realize the fusion reactor since EP pressure gradient driven modesExcitation of helically-trapped-energetic-ion driven resistive interchange modes with intense deuterium beam such as fishbone modes cause loss of energetic particles
Offaxis fishbones are studied in DIII-D [8] or JT-60U [9] and it is suggested that the off-axis fishbone is related to external kink modes [8]
The beam energies and injection powers of PERP-NBIs in Large Helical Device (LHD) are increased for the deuterium plasma campaign
Summary
Studies of interactions between energetic particles (EPs) and MHD modes are quite important to realize the fusion reactor since EP pressure gradient driven modes. Excitation of helically-trapped-energetic-ion driven resistive interchange modes with intense deuterium beam such as fishbone modes cause loss of energetic particles. This mode is called the Energetic particle driven resistive InterChange mode (EIC), because EICs are destabilized by the resonance between the resistive interchange mode having an m/n. Excitation of helically-trapped-energetic-ion driven resistive interchange modes with intense deuterium beam from 6/6 MW to 9/9 MW. These upgrades of NBIs lead to a significant increase of the helically trapped EPs β, βh⊥. The stability of the EIC and the effect on energetic beam ions and bulk plasmas with deuterium PERP-NBIs are presented. RMPs are not applied to the plasma because RMPs are considered to affect the stability of interchange modes in LHD [18]
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