Loss of alpha particles during slowing-down in an axisymmetric tokamak reactor

Abstract

The containment properties of alpha particles during the slowing-down process in an axisymmetric tokamak reactor are studied by using Monte-Carlo calculations, in which the pitch-anglescattering effects are included. The loss of alpha particles during slowing-down is found to be safely negligible in a pure DT plasma, but increases proportionally to the effective charge number of the plasma and cannot be ignored in a highly contaminated plasma (Z e ff > 4), compared with the loss of 3.5-MeV particles.

Effect of cross-field transport on H− density profile in magnetized plasmas: Comparison between measurement and simulation

“…The following three extinction processes of H − and the elastic collision with neutral particles are considered by using the Monte Carlo method in each time step: ͑1͒ collision with electrons, H − + e → H+2e, ͑2͒ mutual neutralization, H − +H + → 2H, and ͑3͒ collision with H, H − +H → H 2 + e and H − +H→ 2H + e. In addition to these collisional processes, Coulomb collisions with electrons and positive ions are considered. 42,43 The extinction process due to the collision with H 2 is neglected because the extinction rate is substantially lower than that of the collision with H. 44,45 The extinction due to the collision with the chamber wall, which occurs due to the effect of the parallel transport, is considered in each time step by the Monte Carlo method. The extinction probability due to the parallel transport can be determined from the ratio of the negative ion flux toward the wall to the total negative ions.…”

Longitudinal deviation from phase matching in the generation of a second harmonic of cw laser radiation

“…As a result of the pitch-angle scattering, the velocity vector of the alpha-particles may eventually enter the loss cone, and these particles will be lost from the system. To calculate the particle and energy losses [8,9], it is necessary to determine the alpha-particle distribution function in the presence of the loss region.…”

“…Introducing x = Vy /v = cos f, which is evaluated at the equatorial plane of the torus (0 = 0°), Eq. (8) can be written as f + s = a (8) where In and 1 L are the parallel and perpendicular components of the flux density in velocity space. The term f/ra (v) represents a phenomenological damping taking into account effects which can be described by an isotropic damping in velocity space.…”

“…In the case of high damping, i.e. j3 > 1, the The problem of determining the alpha-particle losses during slowing-down and pitch-angle scattering has been considered in Refs [8,9]. In Ref.…”

“…The presence of the corresponding loss regions in velocity-space may have important effects on alphaparticle containment properties. During the slowingdown process the alpha-particles may pitch-anglescatter into the loss regions and thus increase the alpha losses [7][8][9]. In addition, the escape of alpha-particles from the system will result in electrostatic charging of the plasma and the associated electric fields could affect dynamics and confinement properties of the background plasma [5].…”