Digital Coil Protection System (DCPS) Algorithms For The NSTX Centerstack Upgrade
Authors: R.D. Woolley, P.H. Titus, C.L. Neumeyer and R.E. Hatcher
Abstract:
A significant upgrade is planned for the National
Spherical Torus eXperiment (NSTX) in which plasma current
and confining magnetic field intensities will nearly double while
plasma duration will more than double. Changes will include
replacing the existing centerstack with a new one containing a
thicker TF inner Leg, a new OH solenoid coil, and an expansion
to six of the complement of PF1 coils controlling plasma divertor
shape. Other coils will remain in service with hardware
modifications as needed for their approximately three-fold
increases in magnetic forces.
The new Digital Coil Protection System (DCPS) will avoid the
costly need to further upgrade coils and their mechanical
supports to withstand control misoperations that could otherwise
take them well beyond the operating envelope of critical variables
(i.e., forces, stresses and temperatures) actually needed for the
new regime of plasma experiments. This improvement would be
impossible using the present protective scheme of independent
overcurrent trips for each coil circuit which ignores effects of
current combinations. In the upgraded NSTX, the DCPS will
operate on a fixed cyclic repetition rate fast enough to avoid
latency issues, e.g., 1 millisecond, monitoring currents in the
plasma, in the OH solenoid coil, in 12 PF coil circuits, and in the
TF coil. Its algorithms will calculate in real time the present and
projected maximum future values of each critical variable that
would be reached if protective action were commanded now, with
and without a full plasma disruption event. The DCPS will
command the protective action to begin if any such calculated
critical value exceeds its operating limit; power supplies are then
bypassed by applying zero volts to coil circuit terminals.
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Submitted to: 38th International Conference on Plasma Science & 24th Symposium on Fusion Engineering/ICOPS 2011 SOFE, Chicago, IL, June 26-30, 2011
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Download PPPL-4676 (pdf 1.12 MB 6 pp)
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