Repairing a surface of a divertor or first wall in a tokamak via deposit of refractory metal while maintaining a vacuum
A method of repairing a divertor or first wall surface in a tokamak plasma vessel. The divertor or first wall surface comprises a refractory metal having a melting point of at least 2000° C. A pressure of less than 25 mbar is maintained within the plasma vessel following the end of operation of the plasma vessel. The refractory metal is deposited onto the divertor or first wall surface within the plasma vessel via a deposition process which is one of: additive manufacturing; physical vapour deposition; thermal spray; arc ion plating; diode laser cladding; and chemical vapour deposition.
1 . A method of repairing a divertor or first wall surface in a tokamak, the tokamak comprising:
a vacuum chamber;
a vacuum maintenance system configured to maintain a pressure of less than 25 mbar within the vacuum chamber;
a first wall and a divertor within the vacuum chamber, each having a surface comprising a refractory metal having a melting point above 2000° C.; and
a refractory metal deposition system comprising:
a refractory metal source;
a heating system; and
a positioning system, the method comprising:
the vacuum maintenance system maintaining a pressure of less than 25 mbar within the vacuum chamber during suspension of operation of the tokamak;
during the suspension of operation of the tokamak, depositing the refractory metal of the refractory metal source onto the divertor or first wall surface via a deposition process comprising:
operating the positioning system to position at a target area of the first wall surface or the divertor surface each of:
a portion of the refractory metal of the refractory metal source; and
the heating system; and
operating the heating system to melt the portion of the refractory metal;
thereby depositing the portion of the refractory metal against the target area.
2 . A method according to claim 1 , and comprising, prior to depositing the portion of the refractory metal against the target area, heating the target area.
3 . A method according to claim 1 , and comprising performing the step of depositing the refractory metal for each of a plurality of target areas within a region of the first wall surface, thereby coating the region of the first wall surface in the refractory metal.
4 . A method according to claim 1 , wherein the refractory metal is provided as a powder, and the refractory metal source comprises a powder dispenser configured to dispense the refractory metal powder to the target area.
5 . A method according to claim 4 , wherein the powder dispenser comprises an inert gas source and a refractory metal powder source, and the powder dispenser dispenses the refractory metal powder by blowing the refractory metal powder from the refractory metal powder source to the target area via an output channel.
6 . A method according to claim 1 , wherein the refractory metal source comprises a refractory metal wire, and wherein the portion of the refractory metal source is one end of the refractory metal wire.
7 . A method according to claim 1 , wherein the heating system comprises a laser or an electron beam.
8 . A method according to claim 1 , and comprising, prior to depositing the refractory metal, scanning, by a scanning system, the divertor or first wall surface in order to identify regions in need of repair, and wherein the step of depositing the refractory metal comprises depositing the refractory metal onto the regions needing repair.
9 . A method according to claim 1 , and comprising providing a mask over a portion of the divertor or first wall surface prior to depositing the refractory metal, and removing the mask following deposition of the refractory metal.
10 . A method according to claim 1 , and comprising milling a portion of the divertor or first wall surface onto which the refractory metal was deposited following deposition.
11 . A method according to claim 1 , wherein the tokamak comprises first and second vacuum pump systems, wherein
the first vacuum pump system is used during operation of the tokamak, and
the second vacuum pump system is used during deposition of the refractory metal, and following deposition of the refractory metal in order to remove waste products from the deposition
and/or subsequent milling.
12 . A method according to claim 11 , wherein the secondary vacuum pump system comprises a scroll pump.
13 . A method of operating a tokamak, the method comprising:
forming and maintaining a first plasma within the tokamak;
extinguishing the first plasma;
repairing a divertor or first wall of the tokamak by a method according to claim 1 ;
forming a second plasma within the tokamak;
wherein the pressure within the tokamak remains below 25 mbar between the extinguishing of the first plasma and the forming of the second plasma.
14 . A tokamak comprising:
a vacuum chamber;
a vacuum maintenance system configured to maintain a pressure of less than 25 mbar within the vacuum chamber during suspension of operation of the tokamak;
a first wall and a divertor within the vacuum chamber, each having a surface comprising a refractory metal having a melting point above 2000° C.; and
a refractory metal deposition system comprising:
a refractory metal source;
a heating system configured to heat a portion of the refractory metal of the refractory metal source;
a positioning system configured to position the heating system and the portion of the refractory metal of the refractory metal source to any region of the first wall surface or the divertor surface;
a controller configured to function during the suspension to:
operate the positioning system to position at a target area of the first wall surface or the divertor surface each of:
a portion of the refractory metal of the refractory metal source; and
the heating system; and
operate the heating system to melt the portion of the refractory metal;
thereby depositing the portion of the refractory metal against the target area during the suspension.
15 . Apparatus according to claim 14 , wherein the heating system is further configured to heat the target area of the first wall or divertor surface.
16 . Apparatus according to claim 14 , wherein the controller is further configured to perform the steps of operating the positioning system and operating the heating system for each of a plurality of target areas within a region of the first wall surface, thereby coating the region of the first wall surface in the refractory metal.
17 . A tokamak according to claim 14 , wherein the vacuum chamber comprises a port, and wherein at least a portion of the refractory metal deposition system is configured to enter the vacuum chamber via the port.
18 . A tokamak according to claim 14 , wherein the vacuum maintenance system comprises first and second vacuum pump systems,
wherein the controller is configured to use the first vacuum pump system to maintain the vacuum during operation of the tokamak, and
to use the second vacuum pump system to maintain the vacuum during deposition of the refractory metal and removal of waste products from the deposition
and/or subsequent milling.
19 . A tokamak according to claim 18 , wherein the second vacuum pump system comprises a scroll pump.