ISSN:
1089-7674
Source:
AIP Digital Archive
Topics:
Physics
Notes:
A series of scaling studies attempting to correlate the H(high)-mode power threshold (PTH) with global parameters have been conducted. Data from these discharges is also being used to look for dependence of PTH on local edge parameters and to test theories of the transition. Boronization and better operational techniques have resulted in lower-power thresholds and weaker density scaling. Neon impurity injection experiments show that radiation also plays a role in determining PTH. A low-density threshold for the L(low)–H(high) transition has been linked with the locked mode low-density limit, and can be reduced with the use of an error field correcting coil. Highly developed edge diagnostics, with spatial resolution as low as 5 mm, are used to evaluate how the power threshold depends on local edge conditions. Preliminary analysis of local edge conditions for parameter scans of ne, BT, and Ip in single-null discharges, and the X-point imbalance in double-null discharges show that, just before the transition to the H mode, the edge temperatures near the separatrix are approximately constant at 100〈Ti〈220 eV and 35〈Te〈130 eV, even though the threshold power varied from 1.5 to 14 MW. During a density scan, the edge ion collisionality, ν*i, varied from 2 to 17, demonstrating that a transition condition as simple as ν*i=const is inconsistent with the data. The local edge parameters of ne, Te, and Ti do not always follow the same global scaling as PTH. Therefore, theories of the L–H transition need not be constrained by these scalings. © 1996 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.871982
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