Detection of neutral beam deuterons acceleration by 2nd harmonic radio frequency heating in ASDEX Upgrade via neutron spectrometry

Abstract

Second harmonic absorption of radio frequency in the Ion Cyclotron Range of Frequency (ICRF) by fast D is expected in the case of H minority heating at the fundamental cyclotron frequency, provided the ion Larmor radius is of the order of the RF-wavelength, as it is for Neutral Beam Injection (NBI)-D ions. In tokamaks a strong increase of neutron production is observed when such an ICRF heating is applied on top of NBI, often referred to as "synergy effect".On ASDEX Upgrade a scintillator-based Compact Neutron Spectrometer (CNS) is available outside the torus hall, with perpendicular view through the plasma equatorial plane, measuring Pulse Height Spectra (PHS), which allow to infer the ion distribution functions, in particular the suprathermal tail.The measured PHS exhibit clear energetic tails when ICRF is applied in the presence of NBI, proving there's an overproportional tail in the fast-ion distribution at the high energy end. The PHS in the CNS line-of-sight are modelled coupling kinetic ‡ Corresponding author: git@ipp.mpg.de Detection of neutral beam deuterons acceleration by 2nd harmonic radio frequency heating in ASDEX Upg solvers with wave codes. Unfolding the PHS into neutron emission spectra allows to quantify the maximum fast ion energy with significant occurrence, showing a nonnegligible population around 500 keV, significantly higher than the NBI energy. A sensitivity study assesses the maximum fast ion energy compatible with the measured PHS, confirming the presence of 500 keV D ions.

ICRF heating schemes for the HL-2M tokamak

“…Although the maximum distribution function occurs at v // /v = 0.6, it fills all the values of v // . Figure 10(a) is similar as figures in [19,20].…”

“…Hot plasma correction allows some heating. This is generally not efficient, except for D-NBI ions [17][18][19][20], whose Doppler shift is large enough. Although the antenna is made intentionally to excite the FW, another branch of radio frequency (RF) wave is also parasitically excited.…”

First results from third harmonic ion cyclotron acceleration of deuterium beams in EAST ion heating studies experiments

“…The fishbone oscillation was observed by soft x-ray array and Mirnov coils located in the vessel with high sampling frequency. Meanwhile, harmonic ICRF waves could effectively heat the fast ions on the basis of according to the harmonic absorption mechanism in the experiment, so the plasma fusion reactions in the device increased substantially [20,21]. Thus, the behaviour of fast particles could be obtained by measuring the neutron flux [22,23].…”

Simulation of neutron emission in neutral beam injection heated plasmas with the real-time code RABBIT

“…In NUBEAM, this is calculated with an RF kick operator [21,22] based on the wave fields from TORIC [23]. The kick operator is still under development [24], first comparisons with experiments indicate however already a reasonable agreement [25,26]. In the future, it might be interesting to couple RABBIT with a to be developed real-time capable ICRH code.…”