DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 209: Intermediate/high-k turbulence in electron ITBs and tests of gyrokinetic code predictions | ||
| Name: | Lothar Schmitz ( |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation | Presentation time: | Requested | Co-Author(s): | T.L Rhodes, G. Wang, W.A. Peebles, E.Doyle, A.E. White, T.A Carter, G. McKee |
| Description: | Electron heat transport is perhaps the least understood transport channel in tokamak plasmas. Initial experimental evidence exists (Rhodes EPS 2007) linking electron heat transport to increased high-k turbulence. In addition, internal electron transport improvements are thought to occur due to low-k turbulence suppression by sheared rotation. Internal transport barrier formation offers the opportunity to study the transition to regimes dominated by TEM and ETG turbulence. We propose to examine the evolution to this state over a broad range in wavenumber, using the full suite of DIII-D fluctuation diagnostics. The results will significantly constrain the predictions of non-linear simulations (e.g. GYRO) allowing a rigorous (or more stringent) test of their predictive capability. The effects of fluctuating shear flows (Zonal flows) on turbulence level will be measured by Doppler Reflectometry providing simultaneous flow and intermediate-k density fluctuation spectra. Mapping of the transport barrier evolution at different times will be attempted to map out the dependence of flows and fluctuation levels on magnetic shear. | ||
| Experimental Approach/Plan: | Intermediate and high-k turbulence is predicted to be dominant in electron transport barriers in strong negative central shear (NCS) , ECRH-produced, and quiescent double barrier (QDB) discharges. Transport barriers in all four transport channels at r/a ~ 0.5 have been previously seen in DIII-D NCS discharges with injected neutral beam power Pinj >8 MW. While NCS electron barriers tend to be transient, off-axis ECRH heating may be used to trigger/stabilize ITBs in the vicinity of the local minimum in safety factor. QDB discharges offer sustained (but less steep) barriers with improved MHD stability and diagnostic access. Two fields of low-k turbulence (density and electron temperature fluctuations) will be measured via BES, low-k scattering and CECE (correlation ECE) diagnostics. The density will be chosen such that intermediate and high-k density fluctuations can be probed at the same radial location by intermediate/high-k FIR scattering and Doppler Reflectometry. The high-k scattering diagnostic can obtain localized ETG turbulence spectra (k perp ~ 35-40 cm-1) within the transport barrier if the second harmonic cyclotron resonance, used as an internal beam dump, is translated across the barrier region. (this requires a small adjustment of the toroidal magnetic field). The transport barrier region will also be probed by a four channel O-Mode Doppler Reflectometer to obtain the poloidal ExB flow profile within the barrier region, as well as the profile of intermediate-k (6 cm-1 < k pol < 12 cm-1) fluctuation spectra characteristic of TEM and ETG regimes. The measured fluctuation spectra will be compared to gyrokinetic modeling results in these TEM and ETG dominated regimes. Profile reflectometry is crucial for density profile reconstruction. | ||
| Background: | -- | ||
| Resource Requirements: | 7 Beams f; ECH (4 gyrotrons) | ||
| Diagnostic Requirements: | All fluctuation diagnostics, in particular FIR scattering, Doppler reflectometry,CECE,and BES.
Fast ECE, CER, MSE, and profile reflectometry. | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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