Initial development of the DIII–D snowflake divertor control

Kolemen, Egemen; Vail, P. J.; Makowski, M. A.; Allen, Steve L.; Bray, B. D.; Fenstermacher, Max E.; Humphreys, David A.; Hyatt, Alan W.; Lasnier, Charles J.; Leonard, Anthony W.; McLean, Adam G.; Maingi, R.; Nazikian, Raffi; Petrie, Thomas W.; Soukhanovskii, V. A.; Unterberg, Ezekial A.

doi:10.1088/1741-4326/aab0d3

Initial development of the DIII–D snowflake divertor control

Journal Article · Wed Apr 11 00:00:00 EDT 2018 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/aab0d3· OSTI ID:1435461

Kolemen, Egemen ^[1]; Vail, P. J. ^[2]; Makowski, M. A. ^[3]; Allen, Steve L. ^[3]; Bray, B. D. ^[4]; Fenstermacher, Max E. ^[3]; Humphreys, David A. ^[4]; Hyatt, Alan W. ^[4]; Lasnier, Charles J. ^[3]; ^[4]; McLean, Adam G. ^[3]; Maingi, R. ^[2]; Nazikian, Raffi ^[2]; Petrie, Thomas W. ^[4]; Soukhanovskii, V. A. ^[3]; ^[5]

Princeton Univ., NJ (United States); General Atomics
Princeton Univ., NJ (United States)
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
General Atomics, San Diego, CA (United States)
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Simultaneous control of two proximate magnetic field nulls in the divertor region is demonstrated on DIII–D to enable plasma operations in an advanced magnetic configuration known as the snowflake divertor (SFD). The SFD is characterized by a second-order poloidal field null, created by merging two first-order nulls of the standard divertor configuration. The snowflake configuration has many magnetic properties, such as high poloidal flux expansion, large plasma-wetted area, and additional strike points, that are advantageous for divertor heat flux management in future fusion reactors. However, the magnetic configuration of the SFD is highly-sensitive to changes in currents within the plasma and external coils and therefore requires complex magnetic control. The first real-time snowflake detection and control system on DIII–D has been implemented in order to stabilize the configuration. The control algorithm calculates the position of the two nulls in real-time by locally-expanding the Grad–Shafranov equation in the divertor region. A linear relation between variations in the poloidal field coil currents and changes in the null locations is then analytically derived. This formulation allows for simultaneous control of multiple coils to achieve a desired SFD configuration. It is shown that the control enabled various snowflake configurations on DIII–D in scenarios such as the double-null advanced tokamak. In conclusion, the SFD resulted in a 2.5×reduction in the peak heat flux for many energy confinement times (2–3s) without any adverse effects on core plasma performance.

View Accepted Manuscript (DOE)

Research Organization:: General Atomics, San Diego, CA (United States); Princeton Univ., NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)

Grant/Contract Number:: FC02-04ER54698; AC02-09CH11466; AC52-07NA27344; AC05-00OR22725; SC0015480; SC0015878

OSTI ID:: 1435461

Alternate ID(s):: OSTI ID: 1515659

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 6 Vol. 58; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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Design and simulation of the snowflake divertor control for NSTX–U Vail, P. J.; Boyer, M. D.; Welander, A. S. Plasma Physics and Controlled Fusion, Vol. 61, Issue 3 https://doi.org/10.1088/1361-6587/aaf94a	journal	January 2019
Real time magnetic control of the snowflake plasma configuration in the TCV tokamak Anand, H.; Coda, S.; Felici, F. Nuclear Fusion, Vol. 59, Issue 12 https://doi.org/10.1088/1741-4326/ab4440	journal	October 2019

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