The Trim Coils for the Wendelstein 7-X Magnet System

Abstract

Abstract-The magnet system of the fusion experiment Wendelstein 7-X (W7-X) consists of superconducting as well as normal conducting coils. 50 non planar superconducting coils are forming the main field, 20 planar superconducting coils allow varying the shape of the plasma. Inside of the plasma vessel 10 normal conducting control coils will be placed to modify the strike points of the plasma at the divertor. In addition a set of five normal conducting trim coils has been designed to allow the correction of error fields and to increase the experimental flexibility. The coils will be placed at the outer surface of the outer vessel of W7-X. Four out of five coils have identical size and shape. They have dimensions of 3.5x3.3 meters with 48 turns and will be operated with currents of up to 1.8 kA. The other coil type has a smaller size of 2.8x2.2 meters, but a higher number of turns and a higher operating current of 1.95 kA. Both types of trim coils will be made of square copper hollow profile with an integrated cooling channel. Five independent power supplies will be used to energize the coils. The present concept is based on four-quadrant power supplies. The control system will allow the local control as well as the remote control of the five power supplies from an external control room.

Service oriented architecture for scientific analysis at W7-X. An example of a field line tracer

“…The tracer service was applied to estimate the W7-X target loads with a 1/1 perturbation produced by the W7-X trim coils [46]. A scaling of the divertor overload with the 1/1 amplitude was obtained.…”

“…In order to compensate possible field errors, five trim coils will be installed at W7-X [46]. These coils are designed to minimize the low order resonant modes from 1/1 to 4/4.…”

Transition From Construction to Operation Phase of the Wendelstein 7-X Stellarator

“…In addition, five so-called trim coils are mounted on the outside of the cryostat (symmetrically to the midplane) [13]. These, again independently supplied, coils can correct for asymmetries in the stellarator magnetic field, as it could result from an out-of-tolerance assembly of the 70 modular field coils, and can be used for physics studies on the plasma edge.…”

Error field measurement, correction and heat flux balancing on Wendelstein 7-X a

“…A series of experiments durring the first experimental campaign on W7-X made use of the trim coil [3,4]. These coils provided by correcting and perturbing magnetic fields.…”