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nelsonproceedings.pdf2011-08-26 14:03:37Brian Nelson
nelsonposter.pdf2011-08-26 14:03:08Brian Nelson

Progress on Digital Control of the HIT-SI Power Supply Systems

Author: Brian A Nelson
Requested Type: Poster Only
Submitted: 2011-06-10 15:30:09

Co-authors: A. B. Bourdages, D. Bryant, T. R. Jarboe, M. Mesbahi, T. Moser, A. S. Nelson, and the HIT-SI Team

Contact Info:
University of Washington
120 AERB, Box 352250
Seattle, WA   98195

Abstract Text:
The steady-inductive Helicity Injected Torus (HIT-SI) studies current drive in a toroidal magnetic confinement configuration. Two semi-toroidal helicity injectors produce sinusoidal injector flux and inductively drive injector current in quadrature. This injects helicity into a confinement region in a steady-inductive manor, where self-organization produces a spheromak object.

The HIT-SI power supply system consists of 56 high-power IGBT-based H-bridge switching power amplifiers (SPAs) rated up to 1600 A at 900 V. Each injector has two circuits, one to produce the flux (the "flux circuit") and one to produce the inductive loop voltage (the "voltage circuit"). The higher-power voltage circuit is configured in a resonant LC "tank" circuit, whereas the flux circuit can be either directly-driven or as a tank circuit. High-power variable inductors have been installed to allow rapid fine-tuning of the tank circuits.

Switching signals for the parallel banks of SPAs are generated by Blackfin micro-controller boards manufactured by Analog Devices Inc., running the embedded uClinux operating system. The control program (pre-programmed or real-time feedback) is implemented as a uClinux kernel serial device driver. Once initialized, all interrupts are masked except for an input trigger. Once triggered, the control algorithm is executed for the requested number of cycles, then the Blackfin is restored to normal uClinux operation. Multiple 1 MHz, 12-bit ADC channels are available for the Blackfin to sample signals in real-time and be taken as input for the control programs. The Blackfin 500 MHz CPU time is more than adequate to take several ADC samples per injector period and calculate switching signals. Control parameters are integrated into the MDSplus data acquisition system, and are automatically dispatched to the Blackfin for each shot.

The resonant circuits are being analyzed using a number of methods, including SPICE, MATLAB, and SciPy. A state-space analysis of the circuits has been formalized, and is being used to simulate active feedback control algorithms. These analyses have helped determine optimal operating parameters for HIT-SI.

The injector plasmas can place a significant load on the resonant circuits, particularly the voltage circuit. To refine the simulation parameters for the plasma load, a detailed analysis of the injector impedances is underway. Hilbert transforms of the measured injector voltages and currents are used to create analytic functions for the injector impedance, resolving the resistive and reactive components. The dependence of these components on various plasma parameters is under investigation to further refine the modeling parameters.

Characterization: A3

Please place with other HIT-SI posters.

University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011