H-phase in ITER: what can be learned about divertor and SOL behaviour in the D and D-T phases

1. H-phase in ITER: what can be learned about divertor and SOL behaviour in the D and D-T phases W. Fundamenski (UKAEA, EFDA-JET)

2. Complex system of i, e, n and g Coupled system of ions, electrons, neutrals and fields Kinetic equation for electrons, ions, impurities and neutrals Accelaration due to both internal and external fields Coulomb collisions for charged species, described by the Fokker-Planck operator, neutral collisions by the Boltzmann operator Maxwell’s equations for internal fields Closure only via 0th and 1st Suggests themoment approach

3. Ion mass in edge/SOL plasma physics • fully ionised plasma physics (dimensionless parameters), scaling with ion mass • All electron quantities independent of A, e.g. rene vTece A0  const • Ion quanties typically scale as a square root (or its inverse) of the ion mass, e.g. r*  1/n*  1/vTi 1/vA 1/k||ike A1/2, kib A0  const • The combination of these include the range of derived quantities, including plasma-neutral interactions (cross-sections) • D and H are chemically identical (to fairly high accuracy), hence electron impact reactions are quite similar (ionisation, excitation, etc). • In contrast, ion impact reactions can differ substantially, eg. CX, elastic scattering. • plasma-surface interactions (erosion yields) • Physical sputtering of C, Be, W,… depends on ion mass • Chemical sputtering of C comparable for H and D • SOL plasma transport • Parallel convection at roughly the plasma sound speed, cs vTi A-1/2 • Parallel conduction, k||i A-1/2

4. Interactions in the tokamak edge Tokamak core is largely a classical, fully ionised plasma (relativistic corrections for runaway electrons, quantum corrections for impurities) Tokamak edge involves quantum effects due to interaction of ions-electrons, photons, atoms-molecules and solid surface (eg. ionisation-recombination, excitation-emission, charge exchange, surface chemistry,…) The relative importance of quantum effects complicates a general theory of a tokamak edge plasma, which is typically described by severely truncated forms plasma fields (photons) neutrals surface

5. Selected plasma-neutral cross-sections In practice, quantum effects included via interaction cross-sections 1) e + H2 H2+ + 2e 2) e + H2 2H0 + e 3) e + H2 H0 + H+ + 2e 4) e + H2+ 2H0 5) e + H2+ H0 + H+ + 2e 6) e + H0 H+ + 2e 7) H0 + H+ H+ + H0

6. Extrapolation to ITER D-phase • Due to the complexity of the above scalings, a simple ‘wind-tunnel’ similarity experiment not possible within a single machine • i.e. not possible to directly extrapolate from the H-phase to the D-phase of ITER based on a simple dimensionless scaling • However, all of the above scalings can be (are) included in edge transport codes, • multi-fluid plasma/MC neutrals codes, eg. SOLPS (B2/EIRENE), … • local or global turbulence codes, e.g. ESEL, GEM, XG2, etc. • plasma filament transport, • Therefore, from the DSOL perspective, the validation of these codes should be the primary task of the H-phase in ITER, • For instance, consider divertor plasma detachment (discussed on Monday) • Once validated, the extrapolation to ITER D phase becomes more credible from the ITER H-phase, then from, say, the JET D phase, e.g. r*, div.closure, etc. • To facilitate this extrapolation in the ion mass, it is desirable to perform reference (matched) H vs D experiments in existing tokamaks, • The focus should be on Ohmic and L-mode edge/SOL conditions, in order to empirically infer (whenever possible) isotopic scalings of unknown plasma parameters • This should be supplemented by detailed modelling effort