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# 27th IAEA Fusion Energy Conference - IAEA CN-258

22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone
CONFERENCE MATERIAL NOW AVAILABLE!

## Extending the boundary heat flux width database to 1.3 Tesla poloidal magnetic field in the Alcator C-Mod tokamak

25 Oct 2018, 14:00
4h 45m
Mahatma Mandir Conference Centre

Poster

Dr Maxim Umansky

### Description

The boundary heat flux width ($λ_q$) is an important part of the power exhaust challenge in magnetic confinement fusion reactors. Understanding what sets $λ_q$ has largely been an empirical science [1], however physics understanding is progressing [3-6]. A database of $λ_q$ in H-mode indicated that the poloidal magnetic field ($B_p$) was the only significant parameter associated with the heat flux width: $λ_q~B_p^{-1.19}$ [1]. The maximum $B_p$ in the database was ~0.8 T, whereas ITER at 15 MA will be ~1.2 T.

C-Mod has been the only diverted tokamak capable of operating at reactor-relevant $B_p$, now with measurements up to 1.3 T. These new measurements in EDA H-mode clearly follow the inverse scaling of $λ_q$ with $B_p$ to values exceeding ITER-level. The heuristic drift (HD) model [4,5] has done a remarkable job of reproducing the trend and the magnitude of $λ_q$ in the database. The new high-field data from C-Mod are consistent with the HD model. Perhaps more importantly, the new data provide a benchmark for first principles models [6,7], one of which projects [6] to ~10 times larger $λ_q$ than the empirical $B_p$ scaling for ITER. In addition, we have assembled a database of $λ_q$ consisting of over 300 shots that span nearly the entire operating space of Alcator C-Mod (L-, H- and I-modes) under attached divertor conditions. As in earlier studies [8], $λ_q$ at fixed $B_p$ exhibit significant scatter that appears related to the core plasma confinement. We are presently exploring correlations of $λ_q$ with global and pedestal parameters; we will report on the latest results at this meeting. The database now includes a composite of measurements made by surface thermocouples and Langmuir probes. Improved spatial resolution and heat flux dynamic range over IR thermography allows for more accurate fits of $λ_q$ and resolving the role of transport into the private flux region. We find that the assumption of symmetric spreading of heat flux [1] is not appropriate under many conditions.

[1] T. Eich, et al., Nucl. Fusion 53 (2013) 093031. [2] R.J. Goldston, et al., Nucl. Fusion 52 (2012) 013009. [3] R.J. Goldston, J. Nucl. Mat. 463 (2015) 397-400. [4] C.S. Chang, et al., Nucl. Fusion 57 (2017) 116023. [5] B. Chen, et al., “Progress towards modeling…”, submitted to Phys. Plasmas. [6] B. LaBombard, et al., Phys. Plasmas 18 (2011) 056104.

Country or International Organization United States of America EX/P6-9

### Primary author

Dr Dan Brunner (MIT PSFC)

### Co-authors

Mr Adam Kuang (MIT PSFC) Dr Amanda Hubbard (Massachusetts Institute of Technology, Plasma Science and Fusion Center) Dr Brian LaBombard (MIT Plasma Science and Fusion Center) Dr James Terry (MIT-PSFC) Jerry Hughes (MIT PSFC) Dr Matthew Reinke (ORNL) Dr Steve Wolfe (MIT PSFC)

### Presentation Materials

 Brunner.D-EX-D-1-slide_summary.pptx High-resolution heat flux width measurements at reactor-level magnetic fields and observation of a unified width scaling across confinement regimes in the Alcator C-Mod tokamak