Characteristics of neutron emission profile from neutral beam heated plasmas of the Large Helical Device at various magnetic field strengths

Abstract

The neutron emission profile of deuterium plasma in the Large Helical Device was measured with a multi-sightline vertical neutron camera under various magnetic field strength conditions. It was found that the line-integrated neutron emission profile shifts outward in the co-neutral beam (NB) case and inward in the counter NB case. Here, co- and counter directions correspond to enhance and reduce the poloidal magnetic field directions, respectively. The shift becomes more significant when the magnetic field decreased in strength. The experimentally obtained neutron emission profile was compared with the orbit-following models simulated through the DELTA5D code. The calculated neutron emission profiles vary according to the magnetic field strength because of the change of beam ion orbit and the slowing down due to the plasma parameter changes. Although a relatively narrow profile was obtained in the calculations at the inboard side for the co-NB case in the relatively low field condition, the profiles obtained through calculation and experiment were almost qualitatively aligned.

Degradation of fast-ion confinement depending on the neutral beam power in MHD quiescent LHD plasmas

“…However, it is noted that the decrement of the profile of the neutron count per NB power is not necessarily the confinement degradation. This is because the neutron emission profile of the co-direction beam (NB#1) is different from that of the counter-direction beam (NB#2) due to the finite orbit effect [34]. Similarly, the neutron emission profile of NB#1 is not necessarily the same as that of NB#3 because the tangency major radius of NB#1 and NB#3 is slightly different.…”

Fusion product diagnostics based on commercially available chemical vapor deposition diamond detector in large helical device

“…Therefore, advances in energetic particle confinement were expected [38][39][40] through the neutron diagnostics [41][42][43][44][45][46][47][48][49] because neutrons are mainly created by so-called beam-thermal reactions [50]. Energetic particle confinement research, e.g., energetic particle confinement in magnetohydrodynamic quiescent plasmas [51][52][53], visualization of energetic particle transport [54][55][56][57][58][59], and demonstration of MeV ion confinement [60,61], has progressed [62,63]. Recently the beam ion energy spectrum has been studied using D-D neutron energy spectrometers [64][65][66][67][68].…”

Studies of energetic particle transport induced by multiple Alfvén eigenmodes using neutron and escaping energetic particle diagnostics in Large Helical Device deuterium plasmas

“…Moreover, the effect of an energetic-ion-driven resistive interchange mode (EIC) [69][70][71], classified into EPMs on the confinement of helically-trapped beam ions exciting the EIC, has been studied using neutron flux monitors [72,73] and vertical neutron cameras [74][75][76]. Vertical neutron cameras visualized the helically-trapped beam ion density profile [77] and transport of helically-trapped beam ions due to the EIC [78][79][80]. In addition, the transport of passing transit beam ions and 1 MeV tri-tons due to the EIC has been studied [81,82].…”