"Improving the physical basis of tokamak geometric tolerances," by Carlos Paz-Soldan (General Atomics)

Friday, March 21, 2014 - 1:00pm to 2:30pm
Plasma Seminars

Plasma Seminar

Friday, March 21, 2014
Physics and Astronomy Building (PAB) Room 4-330

Guest Speaker: Carlos Paz-Soldan (General Atomics)

Talk Title: "Improving the physical basis of tokamak geometric tolerances"


Despite its large size, the ITER tokamak is predicted to be very sensitive to non-axisymmetric magnetic “error” fields arising from deformed or misaligned components.  Understanding of this sensitivity at the time of the ITER design resulted in a very severe limit to the permissible deviation from the specified geometry. These limits, called tolerances, are presently set at 1 part in ~10,000, or ~2 mm for the largest ITER electromagnets.  Tolerances this strict may adversely affect both capital cost and construction schedule, especially if one-of-a-kind components fail to meet specification.


This presentation will discuss work which is beginning to cast doubt on this strict limit by improving the physics basis for error field control using non-axisymmetric coils.  Experiments on the DIII-D tokamak allow the comparison of experimentally measured and theoretically predicted control coil currents which optimally correct the error field, with good agreement found across several plasma scenarios.


Furthermore, recent experiments have demonstrated a very strong recovery of the plasma performance after the control coils are used to correct intentionally applied error fields.  As ITER will be equipped with several arrays of non-axisymmetric control coils, further exploration and predictive understanding of this performance recovery may support relaxation of the strict geometric tolerance currently enforced.