3 research outputs found
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Difference in electron thermal diffusivity and profile between interior and exterior of TFTR L-mode plasmas
The local properties such as scale lengths of the electron density (L{sub n{sub e}}), temperature (L{sub T{sub e}}), and pressure (L{sub p{sub e}}), and the electron thermal diffusivity {chi}{sub e}(r) (m{sup 2}/s) for r/a > 0.3 have been studied for TFTR L-mode discharges under the assumption of {chi}{sub e} = {chi}{sub i}. The scale lengths and the electron thermal diffusivity in the interior 0.3 < r/a < 0.55 are significantly different from those on the exterior 0.55 < r/a < 0.8. following are some examples (temperatures in keV, other quantities in MKS units). In the interior (0.3 < r/a < 0.55), most of the scale lengths were constant or a weakly dependent on radius, and {chi}{sub e} can be expressed as (with correlation coefficient R = 0.61), {chi}{sub e}(r) = 1.44 {times} 10{sup 18}(r/a){sup 1.0}T{sub e}(r){sup 0.1}q(r){sup 0.1}/n{sub e}{sup 0.9}(r). In the exterior region (0.55 < r/a < 0.8), the scale lengths decrease monotonically, and {chi}{sub e} can be described as (with R = 0.68), {chi}{sub e}(r) = 2.3 {times} 10{sup 3}(r/a){sup 1.7}T{sub e}(r){sup 0.7}q(r){sup 0.8}/n{sub e}{sup 0.2}(r). It is interesting to note the negative n{sub e} dependence of {chi}{sub e} in the interior and the positive T{sub e} dependence of {chi}{sub e} in the exterior
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Ion confinement and radiation losses in the Advanced Toroidal Facility
Collapses of stored energy are typically observed in low-density ({anti n}{sub e} {approx} 10{sup 13} cm{sup {minus}3}) extensively gettered ATF plasmas when the electron density rises to the ECH cutoff point, and the central heating is supplied only by neutral- beam-injection (NBI). However, the decline of stored energy can be avoided if the density is raised rapidly to about 5 {times} 10{sup 13} cm{sup {minus}3}. Three mechanisms have been proposed to explain the collapses: (1) impurity radiation, (2) excitation of an electron instability driven by the neutral beams, or (3) poor coupling of the beam ions to the thermal plasmas. Detailed spectroscopic studies of plasma cleanliness as a function of the gettering procedure have shown that radiation is an unlikely candidate for initiating collapses, although it may become an important loss mechanism once the electron temperature has fallen to a low level. No specific electron instability has yet been identified with injection, but recent experimental and computational work indicates that losses by shinethrough and charge exchange strongly influence the evolution of low-density plasmas. This report discusses the beam particle losses, thermal ions, and the evolution of radiation profiles
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Bootstrap Current Studies in the Advanced Toroidal Facility
The toroidal current observed during electron cyclotron heating (ECH) in the Advanced Toroidal Facility (ATF) torsatron is identified as bootstrap current. The observed current ranges between +3 kA and {minus}1 kA with negligible Ohmic heating (OH) and ECH-driven currents. The observed currents agree well with predictions of neoclassical theory in magnitude (to within 30%) and parametric dependence (including the reversal of the current), as determined by systematic scans of quadrupole (shaping) and dipole (vacuum axis shift) moments of the vertical field. These results show that the current flow in ATF is well described by the neoclassical theory of bootstrap current despite the presence of anomalies in particle and heat flows. In addition, the results demonstrate the ability to control the toroidal current with the vertical field for currentless operation in stellarators. 5 refs., 5 figs