Fundamental processes of fuel removal by cyclotron frequency range plasmas and integral scenario for fusion application studied with carbon co-deposits

Abstract Plasma impact removal using radio frequency heated plasmas is a candidate method to control the co-deposit related tritium inventory in fusion devices. Plasma parameters evolve according to the balance of input power to losses (transport, radiation, collisions). Material is sputtered by the ion fluxes with impact energies defined by the plasma sheath. H₂, D₂ and ¹⁸O₂ plasmas are produced in the carbon limiter tokamak TEXTOR. Pre-characterised a-C:D layers are exposed to study local removal rates. The D₂ plasma exhibits the highest surface release rate of 5.7 ± 0.9 ∗ - 10¹⁹ D/m²s. Compared to this the rate of the O₂ plasma is 3-fold smaller due to its 11-fold lower ion flux density. Re-deposition of removed carbon is observed, indicating that pumping and ionisation are limiting the removal in TEXTOR. Presented models can explain the observations and allow tailoring removal discharges. An integral application scenario using ICWC and thermo-chemical removal is presented, allowing to remove 700 g T from a-C:DT co-deposits in 20 h with fusion compatible wall conditions using technical specifications similar to ITER.