Boundary Conditions for a Fusion Plasma

Abstract

The boundary conditions in today's plasma experiments and in later fusion plasmas are determined by the interactions of the plasma with the first solid wall. In today's experiments desorption by the plasma hitting the wall dominates, but ion backscattering, trapping and release, as well as sputtering of wall material, will dominate in machines with cleaner walls. The fluxes to the first wall for some of today's plasma experiments are reported and the data about the elementary processes at the first wall are shortly reviewed

Problems of a thermonuclear reactor with a rotating plasma

“…For a reactor with n s 3 X 10 13 cm" 3 , z 0 s 60 cm, assuming that the mean energy of the neutral atoms is s 100 eV (see Ref. [19]), we get zi s 30 cm. This corresponds to an angular distance of the order of 20°a t R = 5 between the ion re-injection region and the 'loss cone' (A0).…”

Plasma-surface interactions in tokamaks

“…The results have been found to be in good agreement with the theoretical energy distributions obtained by Monte Carlo calculations. By using both the calculated and experimental results, Behrisch [65] has derived by interpolation a set of energy distributions for incident ion energies from 10 eV up to 10 keV. It is observed that the relative energy distribution gets 'harder' at low energies, i.e.…”

Alpha transport and blistering in tokamaks

“…Figure 10 shows the calculated helium depth profiles in stainless steel subjected to J = 10 12 alphas-cm" 2 -s" 1 , 0 = 7.5 X 10 14 (D+T) cm^-s" 1 charge-exchange neutral flux, with a first-wall temperature of 300°C. Case (a) corresponds to a recessional velocity of 10" 11 c m s " 1 or a plasma-edge temperature of < 60 eV, while in case (b) the recessional velocity is lO'^cm-s" 1 or the plasma-edge temperature is 700 eV. In case (a), the sputtering rate is low enough to allow the peak helium concentration to reach the critical concentration of 2.9 X 10 22 atoms-cm" 2 (at 300°C, as shown in Fig.…”

“…The operation of present-day tokamaks is strongly influenced by a variety of first-wall erosion processes such as sputtering, vaporization, chemical erosion and arcing from limiters and walls [1][2][3][4]. The onset of thermonuclear burn in future devices will also introduce significant 3.5 MeV alpha (helium) production.…”

“…On the other hand, the 3.5 MeV alpha flux will accumulate at a depth of several microns and, if a sufficiently high helium concentration is reached, could cause serious exfoliation. Two factors broaden the implanted distribution and hence reduce the helium concentration build-up: (1) the angular distribution of the impinging alphas, which produces differing projected ranges; (2) the simultaneous erosion of the surface by the sputtering of the low-energy D-T flux. (An extended abstract of this work has been published [15].)…”