DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 175: Turbulence & transport modifications in ECH plasmas and comparison to gyrokinetic simulation | ||
| Name: | Tony Peebles ( |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation | Presentation time: | Not requested | Co-Author(s): | Anne White, Lothar Schmitz, Terry Rhodes, Guiding Wang, Jon Hillesheim, Troy Carter, Chris Holland, Lei Zeng, E. J. Doyle |
| Description: | Perform local measurements of low and high-k density turbulence and low-k electron temperature turbulence in both Ohmic and ECH heated plasmas. ECH (deposited at r/a ~ 0.4) will be used to significantly modify electron temperature and normalized temperature gradient while keeping density and ion temperature gradients fixed. Resultant modifications in a range of local turbulence parameters at r/a ~0.6 will be used to assess their relative contributions to the increased electron thermal diffusivities. In addition, the phase relationship between low-k density and electron temperature fluctuations will be measured for the first time in the core of a tokamak plasma. The above measurements will be directly compared with predictions of relative fluctuation levels, phase relationships and resultant transport using nonlinear gyrokinetic simulations (e.g GYRO). | ||
| Experimental Approach/Plan: | Lower single null Target plasmas, similar to 120328, will be utilized using at least three gyrotrons (deposited at r/a 0.4) to modify the electron temperature profile. Multichannel reflectometry, microwave backscattering and correlation ECE will be employed to probe the local turbulence response at r/a~ 0.6. These systems will all operate using the same optical path and radial location. Reflectometry and correlation ECE will also be used to determine the phase relationship between density and electron temperature fluctuations. Doppler reflectometry together with CER (beam blips) will be used to determine modifications in ExB flow. Doppler reflectometry together with FIR scattering will also be used to monitor turbulence change at intermediate turbulence scales. Turbulence and transport measurements will be compared with predictions from flux tube gyrokinetic simulations. | ||
| Background: | A previous 2004 experiment in a similar plasma (minus CECE and Doppler reflectometry) indicated that low and intermediate -k density turbulence was only slightly perturbed, whereas high-k density turbulence was strongly modified. A separate 2007 experiment (White et al.), where ECH was applied to a beam heated L-mode plasma, indicated that low-k electron temperature fluctuations increased (~30%) whereas low-k density turbulence did not. Recent GYRO simulations (for the above beam-heated L-mode plasma) predicted density and potential fluctuations to be closely in-phase, whereas temperature and potential fluctuations were clearly out of phase. Since predicted (and measured) fluctuation levels were similar for both density and electron temperature fluctuations this strongly suggests that the turbulent driven electron heat flux, for those plasmas, was dominated by electron temperature fluctuations. Unfortunately no experimental measurement of the phase relationship was available for those plasmas.
In summary, the proposed experiment will (1) Identify which turbulence parameters (low and intermediate-k density, high-k density, low-k electron temperature fluctuations) are modified by application of ECH and allow direct quantitative comparison with predictions from gyrokinetic simulations. (2) Measure the phase relationship between density and electron temperature fluctuations and allow, for the first time, a stringent test of gyrokinetic predictions related to these important transport-related turbulence properties. (3) Correlate measured local changes in turbulence properties with modifications in electron heat diffusivity and predictions from nonlinear gyrokinetic simulations | ||
| Resource Requirements: | Beam blips for Ti profile, Er, MSE, BES
Number of Gyrotrons: 3 to 5 | ||
| Diagnostic Requirements: | All core turbulence systems (correlation ECE, FIR scattering, microwave backscattering, BES, reflectometry, PCI), profile reflectometer, MSE, CER, etc. | ||
| Analysis Requirements: | Non linear gyrokinetic calculations and associated transport analysis, etc. | ||
| Other Requirements: | -- | ||
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