Tungsten Construction Parts for Plasma Technique

Applications which might gain more importance in the future are construction material for the tungsten alloy plasma technique in magneto hydrodynamic power generation (W and W-Cu) and target plates in fusion reactors (W, W-La2O3).

Recent plasma technique and theoretical and numerical studies show that tungsten may be the best, if not the only, material to withstand the extraordinary operating conditions in a nuclear fusion reactor diverter. The diverter, being that part of the vacuum vessel where the tungsten alloy plasma technique particles interact with the first wall, and where a large fraction of the fusion heat is removed, consists of water-cooled copper heat-exchanger element covered with a plasma facing armor. The tungsten alloy plasma techniqueparticles (electrons, protons, and α-particles) are directed by the magnetic field toward the diverter target plates, where they are neutralized and pumped. The convective heat flux reaches 20 MW.m-2 and the attendant surface temperature more than 3000℃. Therefore, a suitable armor material must have a high thermal conductivity (in order to transfer high heat fluxes), low thermal expansion coefficient and low Young’s modulus (in order to keep thermal stresses low), and a high melting point and low sputtering yield (in order to keep erosion low). Although tungsten does not have as high a thermal conductivity and as low a Young’s modulus as carbon-carbon composite materials, which are foreseen for the sections of the diverter with the highest heat flux, many experts believe that, in the long run, reasonable lifetimes will only be achieved by tungsten diverter plates, which have the lowest erosion rates of all materials in sections of the diverter with relatively low plasma temperature but high particle density.

For the technical realization of low-pressure plasma processes, one requires equipment with the following components:
Vacuum system (pump, vessel)
Energy supply
Gas supply
Measurement and control components for the reproducible adjustment of the process parameter
Due to the necessity of a vacuum system in most cases, batch operation method is the easiest solution.

The processes can be flexibly and complexly configured, in order to change the mode of action of the tungsten alloy plasma technique through variation of the process parameters (pressure, gas flow, gas composition, power) and can attain different effects in one process step. So that, i.e. without great expenditure a secondary cleaning can be carried out and immediately thereafter a corrosion protection layer becomes deposited, without having to aerate in between.


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