Resistive sensor and electromagnetic actuator for feedback stabilization of liquid metal walls in fusion reactors

Abstract

Liquid metal walls in fusion reactors will be subject to instabilities, turbulence, induced currents, error fields and temperature gradients that will make them locally bulge, thus entering in contact with the plasma, or deplete, hence exposing the underlying solid substrate. To prevent this, research has begun to actively stabilize static or flowing free-surface liquid metal layers by locally applying forces in feedback with thickness measurements. Here we present resistive sensors of liquid metal thickness and demonstrate j × B actuators, to locally control it.

Space- and time-resolved resistive measurements of liquid metal wall thickness

“…Embedded in the container are 3×4 copper electrodes of 2 mm diameter and various lengths, for comparison (1,16 and 25 mm, each with its own advantages and disadvantages 14 ). Adjacent electrodes are spaced by 25 mm in one direction and 15 mm in the other.…”

“…In a previous work 14 we had shown that, quite simply, and on the net of small corrections, the electrical conduca) fvolpe@columbia.edu tance between two electrodes immersed in the LM scales linearly with the local LM thickness. Resistive measurements were used to infer the LM thickness in a single location and at a single time 14 .…”

“…An additional diagnostic requirement is posed by the very fact that these walls are liquid and thus can deform 10 under the effect of instabilities, turbulence, as a result of non-uniform force fields or currents from the plasma [11][12][13][14] . Deformations are undesired for various reasons 14 , therefore they need to be monitored as a function of space and time, with resolutions of the order of a centimeter (in the poloidal and toroidal direction) and 10 ms 14 .…”

Passive and active electromagnetic stabilization of free-surface liquid metal flows

“…However, free-surface liquid metal (LM) layers will tend to be uneven [9] as a result of nonuniform force fields, liquid metal instabilities and turbulence [10]. Uneven LM surfaces could enter in contact with the plasma, contaminate it, cool it, and possibly disrupt it, or they might expose the underlying solid wall to damage by heat and neutrons, and expose the plasma to a material with less benign erosion and wall recycling properties.…”

“…As a result, the j × B force-density will change, and adjustments of the applied current-pattern might be required, in feedback with multi-point measurements of liquid metal thickness. This is the subject of separate works [10,11].…”