Effect of the helically-trapped energetic-ion-driven resistive interchange modes on energetic ion confinement in the Large Helical Device

Abstract

The effect of the helically-trapped energetic-ion-driven resistive interchange modes (EICs) on energetic ion confinement is studied in the Large Helical Device (LHD) deuterium plasmas. Neutron diagnostics such as the neutron flux monitor (NFM) and the vertical neutron camera (VNC) are used in order to measure neutrons mainly created by beam-plasma reactions. The line-integrated neutron profiles are obtained by VNC in magnetohydrodynamic-quiet plasma with various neutral beam (NB) injection patterns.The profiles are consistent with that expected by the beam ion density calculated using orbit-following simulations. Significant decreases of the total neutron emission rate (Sn) and the neutron counting rate of the VNC (Cn) in central cords are observed to be synchronized with EIC bursts with perpendicular-NB injection. The drop rates of both Sn and Cn increase with EIC amplitude and reach around 50 %. The line-integrated neutron profiles before and after EIC burst show that in the central cords, Cn decrease due to EIC burst whereas there is almost no change in the other cords. The experimental results suggests that the effect of EIC on helically-trapped beam ion is substantial, however the effect of passing beam ion is not significant.

Analysis of the MHD stability and energetic particles effects on EIC events in LHD plasma using a Landau-closure model

“…Previous studies pointed out that the resistive interchange modes (RIC) are unstable in the magnetic hill region of LHD [42,43,44,45,46]. The RIC can resonate with the precession motion of the helically trapped EP generated by the perpendicular NBI in the range of f = 10 kHz, leading to the enhancement of the EP radial transport [47,48]. Such instability was identified as the trigger of the EIC events in previous studies [2,4].…”

Time-resolved secondary triton burnup 14 MeV neutron measurement by a new scintillating fiber detector in middle total neutron emission ranges in deuterium large helical device plasma experiments

“…In the deuterium experiment performed in the large helical device (LHD) [14][15][16], energetic particle confinement studies are largely advanced using a variety of neutron diagnostics [17][18][19][20][21][22][23]. Sci-Fi detectors play a part in comprehensive neutron diagnostics.…”

“…In the LHD, plasma discharge with MHD instabilities possessing relatively large amplitudes is excited in the S n range of 10 13 n/s to 10 15 n/s [29,30]. Although beam ion transport due to MHD instabilities has been intensively studied by vertical neutron cameras [18][19][20], the effect of deuterium-deuterium (DD) fusionborn triton transport is unclear because there is almost no DT neutron count in vertical neutron cameras [31]. To understand the DD fusion-born triton transport due to the MHD instabilities, time-resolved measurement of secondary DT neutrons with a 1 ms time bin over this S n range is required.…”

Characterization of the New Vertical Neutron Camera Designed for the Low Neutron Emission Rate Plasma in Large Helical Device

“…To study the EP transport in helical devices, the first vertical neutron camera (the so-called VNC1) designed for working at total neutron emission rate (S n ) of 10 16 order, which is the expected maximum S n in LHD [15], has been working since 2017 [16,17]. Studies of classical confinement as well as transport of EPs due to the energetic ion driven magnetohydrodynamic (MHD) instabilities have been reported using VNC1 [18][19][20][21]. In the plasma discharges, where author's e-mail: sangaroon.siriyaporn@nifs.ac.jp the relatively strong MHD instabilities were observed, the time resolution of neutron emission profile was 10 ms with ∼10% error bar because of the relatively low neutron count due to the relatively low S n of 10 14 to 10 15 n/s [21].…”

“…Studies of classical confinement as well as transport of EPs due to the energetic ion driven magnetohydrodynamic (MHD) instabilities have been reported using VNC1 [18][19][20][21]. In the plasma discharges, where author's e-mail: sangaroon.siriyaporn@nifs.ac.jp the relatively strong MHD instabilities were observed, the time resolution of neutron emission profile was 10 ms with ∼10% error bar because of the relatively low neutron count due to the relatively low S n of 10 14 to 10 15 n/s [21]. To study the EP transport with the higher time resolution in relatively low S n discharges, the high detection efficiency vertical neutron cameras (the so-called VNC2 and the socalled VNC3) were developed and were used in LHD from 2018 [22,23].…”