Double null liquid metal diverters

Abstract

A tokamak plasma vessel. The tokamak plasma vessel comprises a toroidal plasma chamber, a plurality of poloidal field coils, an upper divertor assembly, and a lower divertor assembly. The plurality of poloidal field coils are configured to provide a poloidal magnetic field having a substantially symmetric plasma core and an upper and lower null, such that ions in a scrape off layer outside the plasma core are directed by the magnetic field past one of the upper and lower nulls to divertor surfaces of the respective upper and lower divertor assembly. Each of the upper and lower divertor assembly comprises a liquid metal inlet and a liquid metal outlet located below the liquid metal inlet. Each of the upper and lower divertor assembly is configured such that in use liquid metal flows from the liquid metal inlet to the liquid metal outlet over at least one divertor surface of the divertor assembly.

1 . A tokamak plasma vessel comprising:
 a toroidal plasma chamber;   a plurality of poloidal field coils;   an upper divertor assembly;   a lower divertor assembly;   wherein the plurality of poloidal field coils are configured to provide a poloidal magnetic field having a substantially symmetric plasma core and an upper and lower null, such that ions in a scrape off layer outside the plasma core are directed by the magnetic field past one of the upper and lower nulls to divertor surfaces of the respective upper and lower divertor assembly;   wherein each of the upper and lower divertor assembly comprises:
 a radially inboard divertor surface formed from solid meal and positioned to receive ions from the scrape off layer which is radially inward of the plasma envelope; 
 a radially outboard divertor surface positioned to receive ions from the scrape off layer which is radially outwards of the plasma envelope, 
 a liquid metal inlet; and 
 a liquid metal outlet located below the liquid metal inlet; 
 configured such that in use liquid metal flows from the liquid metal inlet to the liquid metal outlet over at least the respective radially outboard divertor surface. 
   
     
     
         2 . A tokamak plasma vessel according to  claim 1 , wherein the poloidal field coils are configured to provide a symmetric magnetic field. 
     
     
         3 . A tokamak plasma vessel according to  claim 1 , wherein the poloidal field coils are configured to provide a magnetic field which is asymmetric outside the plasma core so as to optimise interaction with the upward facing divertor surfaces. 
     
     
         4 . A tokamak plasma vessel according to  claim 1 , and comprising a liquid metal supply means configured to supply liquid metal to each liquid metal inlet at a respective flow rate. 
     
     
         5 . A tokamak plasma vessel according to  claim 1 , wherein each divertor surface over which the liquid metal flows is generally upward facing. 
     
     
         6 . A tokamak plasma vessel according to  claim 4 , wherein the upper divertor assembly comprises at least one divertor surface over which liquid metal flows which is generally downward facing, and wherein that divertor surface is at an angle such that, when the liquid metal supply means supplies liquid metal to the surface at the respective flow rate, the wetting of the liquid metal to the divertor surface prevents liquid metal from falling from the divertor surface. 
     
     
         7 . A tokamak plasma vessel according to  claim 6 , wherein the divertor surfaces are arranged with reflective symmetry, such that the divertor surfaces of the upper divertor assembly are a reflection of the divertor surfaces of the lower divertor assembly in an equatorial plane of the tokamak plasma vessel. 
     
     
         8 . A tokamak plasma vessel according to  claim 6 , wherein the generally downward facing divertor surface comprises channels. 
     
     
         9 . A tokamak plasma vessel according to  claim 1 , wherein the liquid metal inlet of at least one of the divertor surfaces is located radially outwards of the respective liquid metal outlet. 
     
     
         10 . A tokamak plasma vessel according to  claim 1 , wherein the liquid metal is lithium or tin.