Effective ion tail formation by beam and ion cyclotron heating

Abstract

Ion tail formation by neutral beam (D°) injection and second harmonic ion (D + ) cyclotron heating in a 50:50 D-T plasma is investigated on the basis of a local Fokker-Planck calculation. The deformation of the deuteron velocity distribution function is examined analytically and numerically. The effectiveness of the tail formation is estimated from the enhancement of the D-T fusion reactivity, (ov) = / dv f (v) G(v) (f is the deuteron distribution and G is the 'ov-function', averaged over the isotropic triton distribution). The profile of the integrand typically exhibits two humps in velocity space. This results in a large reactivity enhancement for high energy beam injection. For a radiofrequency (RF) induced tail, a 'wing' or smeared tail rather than a hump is formed. ICRF waves couple well with the beam induced tail ions and enhance the reactivity, especially when the beam is injected perpendicularly to the magnetic field. The efficient use of the power supplied by beam and RF waves to enhance the reactivity is also discussed.

Modification of the DD Neutron Emission Spectrum at the 2.4 - 2.5 MeV Energy Range in Neutral-Beam-Injection-Heated Plasma and Its Application to Fuel Ion Ratio Diagnostics

“…Figure 8 shows the neutron emission rate as a function of the emission angle, which was obtained by integrating the spectra over, first, the 2.4 -2.5 MeV range and, second, the full energy range. The solid lines represent the emission rate when considering an anisotropic D(d,n) 3 He differential cross-section, while the dashed lines represent the rate when assuming an isotropic D(d,n) 3 He differential cross-section. The emission rates while considering an isotropic beam injection (emission spectrum) are indicated by the dotted lines on the same planes.…”

“…In a burning plasma, fast ions are generated via fusion reactions and external heating, and an energetic non-Maxwellian component is formed in the ion-velocity distribution functions [1][2][3][4][5][6]. A rise in the fast-ion population induces a distortion of the emission spectra of fusionproduced particles from a Gaussian distribution [7] and enhances the D(d,n) 3 He fusion reaction rate coefficient, leading to an increase in the total emission rate. As an example of this, Fig.…”

“…2). The anisotropy is also caused by the differential cross-section of the D(d,n) 3 He reaction ( Fig. 3) [13].…”

“…3) [13]. As the beam energy increases, the neutrons produced by the D(d,n) 3 He reaction tend to be emitted in a forward direction toward the NBI. The neutron emission rate measured at the neutron flux monitor near the equatorial port was reported to be greater than that measured above the LHD central axis in large helical device (LHD)-based deuterium plasma experiments using tangential NBI [14,15].…”

“…In this study, we evaluated the modification at the central energy region (2.4 -2.5 MeV for DD neutrons) of the neutron emission spectrum due to NBI heating. It was assumed that the neutrons were produced by the D(d,n) 3 He reaction in NBI-heated DT plasma (e.g., international thermonuclear experimental reactor (ITER)-like plasma). The enhancement of the measurement performance of fuel-ion ratio diagnostics using anisotropic neutron emission spectra was also discussed as an example of the implementation of this specific modification.…”