Equilibrium drives of the low and high field side n = 2 plasma response and impact on global confinement
- General Atomics, San Diego, CA (United States)
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
- General Atomics, San Diego, CA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
- General Atomics, San Diego, CA (United States); Oak Ridge Associated Univ., Oak Ridge, TN (United States)
Abstract. The nature of the multi-modal n=2 plasma response and its impact on global confinement is studied as a function of the axisymmetric equilibrium pressure, edge safety factor, collisionality, and L vs. H-mode conditions. Varying the relative phase (ΔφUL) between upper and lower in-vessel coils demonstrates that different n=2 poloidal spectra preferentially excite different plasma responses. These different plasma response modes are preferentially detected on the tokamak high-field side (HFS) or low-field side (LFS) midplanes, have different radial extents, couple differently to the resonant surfaces, and have variable impacts on edge stability and global confinement. In all equilibrium conditions studied, the observed confinement degradation shares the same ΔφUL dependence as the coupling to the resonant surfaces given by both ideal (IPEC) and resistive (MARS-F) MHD computation. Varying the edge safety factor shifts the equilibrium field-line pitch and thus the ΔφUL dependence of both the global confinement and the n=2 magnetic response. As edge safety factor is varied, modeling finds that the HFS response (but not the LFS response), the resonant surface coupling, and the edge displacements near the X-point all share the same ΔφUL dependence. The LFS response magnitude is strongly sensitive to the core pressure and is insensitive to the collisionality and edge safety factor. This indicates that the LFS measurements are primarily sensitive to a pressure-driven kink-ballooning mode that couples to the core plasma. MHD modeling accurately reproduces these (and indeed all) LFS experimental trends and supports this interpretation. In contrast to the LFS, the HFS magnetic response and correlated global confinement impact is unchanged with plasma pressure, but is strongly reduced in high collisionality conditions in both H and L-mode. This experimentally suggests the bootstrap current drives the HFS response through the kink-peeling mode drive, though surprisingly weak or no dependence on the bootstrap current is seen in modeling. Instead, modeling is revealed to be very sensitive to the details of the edge current profile and equilibrium truncation. Holding truncation fixed, most HFS experimental trends are not captured, thus demonstrating a stark contrast between the robustness of the HFS experimental results and the sensitivity of its computation.
- Research Organization:
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
- Sponsoring Organization:
- USDOE
- Contributing Organization:
- Oak Ridge Associated Universities, Oak Ridge, Tennessee 37830, USA Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
- Grant/Contract Number:
- AC02-09CH11466; AC05-06OR23100; FC02-04ER54698
- OSTI ID:
- 1254901
- Alternate ID(s):
- OSTI ID: 1245030; OSTI ID: 1369217
- Report Number(s):
- DOE-GA-54698
- Journal Information:
- Nuclear Fusion, Vol. 56, Issue 5; ISSN 0029-5515
- Publisher:
- IOP ScienceCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Predict-first experimental analysis using automated and integrated magnetohydrodynamic modeling
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journal | May 2018 |
Modal analysis of the full poloidal structure of the plasma response to n = 2 magnetic perturbations
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journal | July 2018 |
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