³He-d fusion reaction rate measurements during ICRH heating experiments in JET

Abstract

In the JET tokamak, ICRF driven fusion reactivity has been determined using measurements of 16.6 MeV γ-ray emission from d[3He, γ]5Li reactions during central RF heating in the (3He)d minority regime. Up to 1 MJ of fast minority ions in the plasma has been produced with the application of up to 15 MW of RF power. The maximum rate produced by d[3He, p]4He fusion reactions has been estimated as 2 × 10l6 s−1 (equivalent to 60 kW of fusion power in charged particle products). The reactivity increased strongly with coupled RF heating power (proportional to (PRF)5/3), with some evidence of a weakening of the dependence leading to a saturation in the energy gain Q at the highest coupled RF power levels (PRF > 8−12 MW). The experimentally measured anisotropic fast ion energies and fusion reaction rates have been simulated using a radially dependent Stix model for a wide variety of discharges. Analysis of the radial profile of fusion reactivity shows that when the RF power density is maximized on the magnetic axis of the discharge, the fusion reactivity is peaked away from the axis. This effect is caused by the minority ions near the centre of the discharge being driven to energies beyond the maximum in the fusion cross-section.

Velocity-space observation regions of high-resolution two-step reaction gamma-ray spectroscopy

“…Gamma-ray spectroscopy (GRS) is an essential diagnostic to study fast ions in fusion plasmas [1,2]. Early GRS measurements in tokamaks have been made at Doublet-III [3], TFTR [4], JET [5][6][7][8][9][10][11][12][13] and JT-60U [14,15]. More recently, high-resolution GRS measurements have been made at JET [16][17][18][19][20][21] and ASDEX Upgrade [22] thanks to the development of new detectors [18,23].…”

“…More recently, high-resolution GRS measurements have been made at JET [16][17][18][19][20][21] and ASDEX Upgrade [22] thanks to the development of new detectors [18,23]. GRS is particularly well-suited for large, hot devices such as JET [5][6][7][8][9][10][11][12][13][16][17][18][19][20][21], ITER [24] or DEMO [25] since high temperatures enhance fusion reaction rates and hence γ-ray fluxes [1,2].…”

“…Many nuclear reactions in hot fusion plasmas lead to γ-ray emission [1,2]. At JET, several species including alpha particles, helium-3, deuterium or hydrogen have been measured using GRS [5][6][7][8][9][10][11][12][13][16][17][18][19][20][21]. These fast ions are generated in fusion reactions, by ion cyclotron resonance heating (ICRH) or by neutral beam injection (NBI) [7].…”

The Tokamak as a Neutron Source

“…In operating modes where the RF power can be coupled well to th • » plasma, combined NBI and RF heating has often led to increased S over that of NBI alone but with no increase in Odd -Using ion cyclotron heating of D-3 He plasmas, JET has produced Q values higher than realized to date in beam-injected plasmas. 76 In the D- 3 He experiments, the RF waves produce energetic 3 He ions with an effective temperature of the tail of the energy distribution well above the optimum one of ~ 500 keV, so that the d( 3 He, 4 He)p fusion reactions are in effect beam-target reactions. But the D- 3 He reactions produce no neutrons, so that these results are not directly relevant to the tokamak's role as a neutron source.…”

Combined heating experiments in ELM-free H modes in JET

“…High electron temperature regimes can be accessed in JET by using (H)D minority heating. Although by choosing different minority heating schemes, in particular ( 3 He)D at high minority concentration, a significant amount of bulk ion heating can be obtained with ICRF alone [9,10], the hot ion regimes characterized by high confinement and DD fusion yield have been accessed in JET only by using high NBI power, either alone or in combination with ICRF.…”