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Title: Plasma Modeling Results and shape control improvements for NSTX

Journal Article · · Nuclear Fusion
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  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Princeton Univ., Princeton, NJ (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
+ Show Author Affiliations

New control implementations and dynamics studies on the National Spherical Torus eXperiment (NSTX) are summarized. In particular, strike point (SP) position, X-point height and squareness control, and two new system-identification methods / control-tuning algorithms were put into operation.The PID controller for the SP was tuned by analyzing the step response of the SP position to the poloidal coil currents, employing the Ziegler-Nichols method. The resulting SP controller was successfully employed to achieve the “snowflake” divertor configuration in NSTX. An offline system identification of the plasma response to the control inputs based on ARMAX input-output models was implemented. With this tool, rough estimates of the improvements were realized and several control improvements were identified.An online automatic relay-feedback PID tuning algorithm was implemented, which has the advantage of tuning the controller in one shot, thus optimizing the use of experimental time. Furthermore, using these new capabilities, we implemented LLD scenarios with control for theall four upper/lower/inner/outer SPs and with a combined X-point height, SP radius control. Separately, an independent squareness control was implemented.

Research Organization:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
DOE Contract Number:
AC52-07NA27344
OSTI ID:
1524726
Report Number(s):
LLNL-JRNL-465267; 462011
Journal Information:
Nuclear Fusion, Vol. 51, Issue 11; ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English

References (12)

Strike point control for the National Spherical Torus Experiment (NSTX) journal September 2010
Physics design requirements for the National Spherical Torus Experiment liquid lithium divertor journal June 2009
Evaporated lithium surface coatings in NSTX journal June 2009
Taming the plasma–material interface with the ‘snowflake’ divertor in NSTX journal December 2010
Exploration of spherical torus physics in the NSTX device journal March 2000
Simulations of NSTX with a Liquid Lithium Divertor Module journal May 2010
Initial results from coaxial helicity injection experiments in NSTX journal February 2001
Impact of MHD equilibrium input variations on the high beta stability boundaries of NSTX journal April 2002
Optimizing stability, transport, and divertor operation through plasma shaping for steady-state scenario development in DIII-D journal May 2009
Aspect ratio scaling of ideal no-wall stability limits in high bootstrap fraction tokamak plasmas journal February 2004
Equilibrium properties of spherical torus plasmas in NSTX journal November 2001
Alfvénic instabilities driven by fusion generated alpha particles in ITER scenarios journal December 2005

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY