Hybrid magnet for use in fusion reactors
A toroidal field coil for generating a toroidal magnetic field in a nuclear fusion reactor comprising a toroidal plasma chamber having a central column. The toroidal field coil comprises a portion passing through the central column. The portion passing through the central chamber comprises: ●a low temperature superconductor, LTS, layer ( 21 ) formed from LTS; ●a high temperature superconductor, HTS, layer ( 22 ) formed from HTS and located radially outward of the LTS layer. ●a non-superconducting conductive layer ( 23 ) formed from electrically conducting, non-superconducting material and located radially outward of the HTS and LTS layers.
1. A toroidal field coil for generating a toroidal magnetic field in a nuclear fusion reactor comprising a toroidal plasma chamber having a central column, the toroidal field coil comprising a portion which comprises:
a low temperature superconductor (LTS) layer formed from LTS material;
a high temperature superconductor (HTS) layer formed from HTS material and located radially outward of the LTS layer;
a non-superconducting conductive layer formed from electrically conducting, non-superconducting material and located radially outward of the HTS and LTS layers.
2. A toroidal field coil according to claim 1 , and comprising an insulating layer located between the HTS layer and the non-superconducting conductive layer.
3. A toroidal field coil according to claim 2 , and comprising a further insulating layer located between the LTS layer and the HTS layer.
4. A toroidal field coil according to claim 1 , and comprising a plurality of HTS layers and/or a plurality of LTS layers, each HTS and/or LTS layer being made from a different material, wherein every HTS layer is located radially outwards of every LTS layer, and the non-superconducting conductive layer is located radially outwards of all HTS and LTS layers.
5. A toroidal field coil according to claim 4 , and comprising further insulating layers located between each pair of adjacent HTS and/or LTS layers.
6. A toroidal field coil according to claim 1 , wherein the insulating layer(s) comprises a region of vacuum.
7. A toroidal field coil according to claim 1 , wherein the non-superconducting conductive material comprises copper, beryllium and/or aluminium.
8. A nuclear fusion reactor comprising a plasma chamber having a central column and the toroidal field coil of claim 1 , wherein the portion of the toroidal field coil passes through said central column.
9. The fusion reactor of claim 8 , comprising four or more toroidal field coils.
10. The fusion reactor of claim 8 , configured to confine plasma in the plasma chamber with a major radius of the confined plasma of 1.5 m, preferably less than 1.0 m, more preferably less than 0.5 m.
11. The fusion reactor of claim 8 , which reactor has an aspect ratio of 2.5 or less and is preferably a spherical tokamak reactor with aspect ratio of 2.0 or less.
12. The fusion reactor of claim 8 , in which shielding is provided around the central column in order to reduce or eliminate damage from neutrons.