Energy transport of beam-heated high-temperature and high-density plasmas in Doublet-III

Abstract

The empirical scaling of the electron thermal diffusivity, Xe, is investigated for more than 100 beam-heated discharges. These discharges include two major features: 1) high-temperature and highdensity plasma (T e (O)«Tj(O)« 2.5-3 keV at n ^ (5-7) X 10 13 cm" 3 , P NB i £ 4 MW), which will be the basis for the breakeven experiments in the next-generation tokamaks, 2) three types of discharges, i.e. good and poor confinement divertor discharges and limiter discharges. -All kinds of discharges (good heating and poor heating divertor discharges, limiter discharges) have fhe same functional form in x e within ~ 40% at 0.25 a < r <0.65 a, where Xe in the simplest expression scales as Xe a Vn e -The * on t n e r m a l diffusivity, Xi, is consistent with the assumption that the neoclassical Xi can be applicable to our three kinds of discharges. For discharges with different heating efficiency, there is no systematic difference, in the adjustable multiplier, to the neoclassical theory by Hinton-Hazeltine for an ion collisionality of v*= 0.02-0.5.

Experimentally inferred ion thermal diffusivity profiles in the Doublet III tokamak: Comparison with neoclassical theory

“…1. Non-thermal contributions to the measured neutron flux due to knock-on collisions and , n l3 is the line-averaged electron density in units ofl0 13 cm' 3 .…”

“…Neoclassical theory is a well developed body of knowledge which provides the minimum rates of particle and energy transport processes to be expected in toroidal magnetic confinement geometries [1][2][3]. The experimentally inferred ion thermal diffusivity Xj has generally been in the range of one to ten times the predictions of neoclassical theory for tokamak discharges with either Ohmic heating [4,5] or high-power neutralbeam heating [6][7][8][9][10][11][12][13][14][15][16]. In general, the uncertainties in the estimates of Xi are of the order of 100% or larger and it has not been clear whether or not neoclassical theory is sufficient to explain ion confinement in some or all tokamak discharges.…”

Two-dimensional analysis of limiter/divertor transition in scrape-off layer plasmas

“…where Kg = K Q T^1 2 . If we take the Bohm diffusion X e « T e and assume that the connection length L (between midplane and divertor) is affected little by temperature because parallel transport dominates perpendicular transport and the parallel conductivity is Vrnj/me times larger for electrons when T e is equal to Tj.…”

“…Experimental results from ASDEX, D-III, PDX and JFT-2M [1][2][3][4] show that the confinement properties of tokamaks are considerably better with divertor operation than with limiter operation, provided certain conditions are satisfied. A low impurity flux and a low recycled neutral gas flux to the core plasma are necessary for a reduction of radiation and charge exchange energy losses near and/or just inside the separatrix.…”

H-mode experiments with outer and lower divertors in JT-60

“…Discharges with improved energy confinement, called H-mode, were discovered in ASDEX closed divertor experiments with neutral beam (NB) heating [1]. Following this result, H-mode discharges have also been observed in PDX [2], D-UI [3,4], JFT-2M [5], D-ffl D [6,7], PBX [8] and JET [9,10]. In these tokamaks, the divertors are located in the lower and/or upper part of the vessel.…”