The depth of penetration of fast hydrogen atoms into a fusion reactor plasma, before they become ionized and held by the magnetic field, is of importance in connection with the heating and refuelling of such a plasma. Here the experimental cross-sections for the important collision processes are reviewed and analytic expressions are formed which describe the data reasonably well.The ion and electron energy distributions to be expected in both toroidal and mirror reactors are used, with the analytic expressions for the cross-sections, to calculate rate coefficients. The plasma thickness T for an 1/e reduction in intensity of the atom beam is then obtained as a function of beam energy and plasma temperature over the range 0.1 to 2000 keV (D+, Do). As an example a 1 MeV deuterium atom beam entering a toroidal reactor plasma has T=1.7×1016 and 2.5×1016cm−2 for plasma temperatures of 1 and 100 keV, respectively.

The dependence of plasma energy confinement on minor radius, density and plasma current is described for Ohmically heated near-circular plasmas in Doublet III. A wide range of parameters is used for the study of scaling laws; the plasma minor radius defined by the flux surface in contact with limiter is varied by a factor of 2 (a = 44, 32 and 23 cm) , the line average plasma density, n̄e, is varied by a factor of 20 from 0.5 to 10 × 1013 cm−3 (n̄e R0/BT = 0.3 to 6 × 1014 cm−2·kG−1) and the plasma current, I, is varied by a factor of 6 from 120 to 718 kA. The range of the limiter safety factor, qL, is from 2 to 12. – For plasmas with a = 23 and 32 cm, the scaling law at low n̄e for the gross electron energy confinement time can be written as (s, cm) where qc = 2πa2BT/μ0IR0. For the 44-cm plasmas, is about 1.8 times less than predicted by this scaling, possibly owing to the change in limiter configuration and small plasma-wall separation and/or the aspect ratio change. At high n̄e, saturates and in many cases decreases with n̄e but increases with I in a classical-like manner. The dependence of on a is considerably weakened. The confinement behaviour can be explained by taking an ion thermal conductivity 2 to 7 times that given by Hinton-Hazeltine's neoclassical theory with a lumped-Zeff impurity model. Within this range the enhancement factor increases with a or a/R0. The electron thermal conductivity evaluated at half-temperature radius where most of the thermal insulation occurs sharply increases with average current density within that radius, but does not depend on a within the uncertainties of the measurements.

Articles you may be interested inInfluence of electric field penetration by a three-electrode beam extraction system on hydrogen negative ion source plasmaa) Rev. Sci. Instrum. 85, 02A720 (2014); 10.1063/1.4833918Broad, intense, quiescent beam of singly charged metal ions obtained by extraction from self-sputtering plasma far above the runaway threshold Experimental results are given for the perveance and beam divergence of a single apenure three electrode extraction system using helium ions at energies between 10 and 30 keY. The apenure radii, the electrode thicknesses, and the spacings were varied and from the results a preferred design was obtained for use in a multiapenure array. The most critical parameter was the ratio (S) of the radius of the. first aperture to the distance between the first and second electrodes, the highest current density being obtained at values of this ratio less than 0.5. The optimum beam divergence observed corresponded to a Gaussian beam profile with a width (0) of ± 1.2 0 at 2 m from the source. The measured perveance at small values of S and at minimum 0) lay between 75% and 90% of the value predicted on the basis of a simple model using the Langmuir-Blodgett fonnula for the spherical diode.