Motional Stark Effect Diagnostic Expansion for the DIII-D Tokamak
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
A repositioning of a heating neutral beam on the DIII-D tokamak provides an opportunity to expand and improve the Motional Stark Effect diagnostic (MSE) used to constrain the current profile. Dα emission from the neutral beam is split into components parallel (π) and perpendicular (σ) to the total electric field ETotal = vxB + Eplasma. The MSE diagnostic measures the polarization of the σ component to determine the local magnetic field pitch angle Bz/Bφ and the local radial plasma electric field ER. This is typically done using the EFIT current profile reconstruction code. Two independent measurements of the pitch angle γ at each radius are required to differentiate the contributions from the Stark and plasma electric fields. Presently, three MSE diagnostics provide multiple views of a single neutral beam. Our ability to accurately differentiate Bz and ER is limited because these views do not overlap with sufficient radial resolution in some locations, and this limits the accuracy of the current profile reconstructions. The beam rearrangement allows us to build a fourth MSE view of a second beam injected counter to the plasma current. The combination of the new view with the old will improve radial resolution about a factor of 3, reduce ER uncertainty by a factor of 2 in the core and 5-6 in the edge, and reduce Bz uncertainty by 20-30%. The design of the new system is presented in this paper, focusing on the mechanical and optical details at the tokamak port on which it will be installed.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC52-07NA27344
- OSTI ID:
- 1343023
- Report Number(s):
- UCRL-TR-214210; TRN: US1701918
- Country of Publication:
- United States
- Language:
- English
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