Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating

Abstract

During the 2015-2016 JET campaigns many efforts have been devoted to the exploration of high-performance plasma scenarios envisaged for DT operation in JET. In this paper we review various key recent hybrid discharges and model the combined ICRF+NBI heating. These deuterium discharges with deuterium beams had the ICRF antenna frequency tuned to match the cyclotron frequency of minority H at the centre of the tokamak coinciding with the second harmonic cyclotron resonance of D. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of D beam ions which allows us to assess its impact on the neutron rate R N T. We evaluate the influence of the resonance position and H concentration which were varied in different discharges in order to test their role in the heating performance. It was found that discharges with a resonance beyond ∼ 0.15 m from the magnetic axis R 0 suffered from impurity accumulation in these plasma conditions. According to our modelling, the ICRF enhancement of R N T increases with the ICRF power absorbed by deuterons as the H concentration decreases. We find that in the recent hybrid discharges this ICRF enhancement varied

First principles and integrated modelling achievements towards trustful fusion power predictions for JET and ITER

“…Ion Cyclotron Ressonant Heating (ICRH) waves with a H minority scheme, is the need to model the damping of the ICRH wave on the fast D obtained from the NBI heating by means of the 2nd harmonic. In particular, for the hybrid scenarios, such interplay can significantly increase the tail of fast ions and boost the beam-target neutron rate generation up to 15-25% [21].This is exemplified in Fig. 5 for the hybrid discharge #86614.…”

“…Extrapolations to 40MW of the hybrid discharge 92398 [21] with a record neutron rate RDD=2.7x10 16 s -1 have been also performed with JINTRAC and the turbulent transport model QuaLiKiz. In this case, the pedestal is kept fixed as a conservative assumption.…”

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

“…However, spectrospic measurements have added significant energy-resolved evidence of energetic ions beyond the injection energy at JET, first for third-harmonic acceleration of D [3][4] [6][7] [8] and very recently also for second-harmonic [9] [10]. For the first time, such evidence both on the experimental and on the modelling side is found for the tokamak ASDEX Upgrade too.…”

Identification of an Optimized Heating and Fast Ion Generation Scheme for the Wendelstein 7-X Stellarator

“…Experimental and modeling efforts into synergetic ICRF-NBI heating in tokamaks, similar to the schemes developed in this Letter for the W7-X stellarator, can be found in Refs. [11,[13][14][15][16][17]. In particular, JET experiments in Ref.…”

“…An alternative approach using on-axis second harmonic n ¼ 2 heating in JET and ASDEX of majority deuterium NBI species was reported in Refs. [14][15][16][17]. rf-heating efficiency for n > 1 minority species heating depends on finite Larmor radius (FLR) effects for rf-power absorption and thus performance decreases for increasing n, and rf interaction occurs with fewer particles than fundamental heating.…”