Transport properties of a deuterium, tritium, helium plasma/gas mixture

Abstract

The paper discusses a numerical model for radial transport in a toroidal plasma/gas mixture consisting of all charge states of deuterium, tritium and helium. Solutions of the steady-state momentum and particle balances indicate an enrichment of tritium gas near the reactor wall compared with deuterium. The helium enrichment ratio, although depending strongly on the ion transport model adopted, is always less than unity. Therefore, pumping helium from a cool plasma/gas blanket surrounding the entire plasma body is not attractive.

Optimization of isotope composition of fusion plasmas

“…This finding is in line with observations on TFTR where stronger density peaking has been found in d-t plasmas than in pure deuterium discharges [10]. The present situation is different from the case of plasma fuelling with neutral influx only and pure diffusive anomalous transport of charged particles considered in [4]: for the same neutral density at the separatrix, n t in the plasma core was always lower than n d due to smaller thermal velocity and penetration depth of tritium neutrals.…”

“…The necessity to consider the behaviour of hydrogen isotopes individually has been demonstrated already in earlier reactor studies [4] where the mass dependence has been taken into account by considering the penetration depths of recycling neutrals and neoclassical transport of fuel ions. Modern sophisticated models for anomalous particle transport predict that in the plasma core this is mostly due to ion temperature gradient (ITG) and trapped electron (TE) drift instabilities [5].…”

“…By looking for approaches to control and optimize the plasma composition one has to consider self-consistently the behaviour of both hydrogen isotopes in the core and at the edge including the edge transport barrier (ETB), scrape-off layer (SOL) and divertor volume. In this paper an attempt to perform such an optimization is undertaken by taking into account, additionally to the effects mentioned above, the following aspects: in the ETB, where anomalous transport is strongly reduced, the neoclassical one will be most probable in plateau and banana regimes but not in the Pfirsch-Schlüter regime which was relevant to the conditions considered in [4]; the densities of neutral and charged particles in the SOL, which provide boundary conditions for the profile calculations in the plasma core, may be strongly non-stoichiometric, in particular, due to thermal forces arising with temperature gradients along the magnetic field [8]; in a divertor tokamak with X-point(s) the position where neutral particles enter the confined plasma volume through the separatrix affects significantly the neutral penetration process and, thus, the density profiles of charged particles in the plasma core [9]. The rest of this paper is organized as follows.…”

Modelling the transport of deuterium and tritium neutral particles in a divertor plasma

“…According to [3] this level can be achieved near target plates without noticeable penalties to the fusion power, owing to different transport properties of deuterons and tritons both in the plasma confined region and in the SOL. The rate coefficients for atom ionization and recombination of electrons and ions have been taken from the database AMJUEL of the code EIRENE [4], the dependence of the charge-exchange rate coefficients on the isotope mass-from [11]. In spite of the fact that the present model does not take into account many effects usually involved in a Monte Carlo modelling, these results reproduce satisfactory important features of simulations with the Monte Carlo code EIRENE being a part of the package SOLPS [6].…”

Helium transport in vented divertors and limiters

“…Goedheer and Potters [3,4] considered the elastic scattering process in their studies of the problem of neutral helium transport in plasma. Their based on a numerical solution of the Boltzmann equation and restricted to one-dimensional problems.…”