DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 53: Test of Paleoclassical Model for Pedestal Electron Temperature Profile | ||
| Name: | Richard Groebner ( |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Requested | Co-Author(s): | J. Callen |
| Description: | Test the paleoclassical theory for electron heat transport (effective chi_e) in the H-mode pedestal. Do this by attempting to make a plasma which has pedestal chi_e which is a factor ~5 less than the effective chi_e predicted by the theory. Perform plasma current scan to vary pedestal chi_e. | ||
| Experimental Approach/Plan: | Vary plasma current (and bt to maintain constant q) from about 0.5 - 1.5 MA (and higher if possible). Perform this in conditions which allow for a long ELM-free period - use moderately high triangularity and low beam power. Obtain good pedestal measurements at each value of current so that good profiles of te, ne and ti can be obtained. Use breathing to improve spatial resolution of pedestal profiles. Enhance the documentation of these discharges by obtaining density fluctuation levels and correlation lengths in the pedestal. | ||
| Background: | The paleoclassical transport model predicts a lower limit for electron thermal transport in a tokamak. In current H-mode tokamaks, this model has been proposed to explain te profiles in the pedestal. There are experimental features which are in rough agreement with the model. These include observations that eta_e is in the vicinity of two, as predicted, that the model can predict the upturn of chi_e that is observed at the very periphery of the pedestal and that some chi_e values from interpretive transport analysis are close to the predictions of the theory. At this time, it is not possible to test the underlying physics mechanism of this model which is that poloidal magnetic field lines diffuse radially and carry electrons with them. The most stringent test that can be made of the model is to attempt to make a pedestal with a low chi_e in an effort to obtain a chi_e value that is well below the predictions of the theory. At this time, we do not have good knowledge of how chi_e values scale in the pedestal. However, the pedestal gradients steepen as the plasma current is increased and it seems likely that chi_e can be varied significantly by varying current. Thus, we propose to vary the current over as wide a range as possible so that the pedestal chi_e can be varied by a large factor. | ||
| Resource Requirements: | 4-5 NBI sources
Cryopumps | ||
| Diagnostic Requirements: | Thomson
CER CO2 interferometer Quadrature reflectometer (desired) BES (desired) | ||
| Analysis Requirements: | Use Osborne python codes to fit profiles to pedestal te, ti and ne. Perform interpretive transport analysis to obtain chi_e values in the pedestal. Evaluate paleoclassical model chi_e. Compare experimental and theoretical values for the effective chi_e. If some experimental values are significantly lower than theoretical values, perform sensitivity analysis to test our confidence in the experimental results. | ||
| Other Requirements: | Some software work may be needed to properly evaluate the best version of paleoclassical theory. This could be done in ONETWO. Alternatively, some of the calculation might be doable in an IDL code. | ||
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