Bootstrap current

A current that a tokamak plasma drives through itself, without any external current-drive system, as a side effect of the fall in pressure from its hot centre to its cooler edge. It arises from the way particles trapped on the outer, weaker-field side of the ring collide with the particles circulating freely around it. A tokamak needs a current in its plasma to confine it, and a transformer can only drive that current for a limited time, so a machine meant to run steadily must supply it some other way. The larger the share of current the plasma drives itself, the less external current drive is needed, saving both the equipment and the electricity it consumes. Advanced and spherical tokamak designs aim for a high bootstrap share.

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concept:bootstrap-current

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