Beam-plasma atomic data needs for fusion devices

Transcription

1 Beam-plasma atomic data needs for fusion devices

2 Contemporary areas of application on fusion machines: Beam stopping (H/D/T heating beams) Beam shinethrough in small machines and/or at low density. Power from heating beams transmitted through the plasma can damage the inner wall. Cross section data could make the protection calculations more or less conservative Beam density in the centre of the plasma, especially in large machines. Data would affect calculations for ITER diagnostic performance Charge exchange (impurity and hydrogen) population cross sections Stark effect for magnetic field magnitiude and direction measurement Non-statistical population of sub-states affecting line ratios (for magnetic field direction measurements that are based on the intensity ratios) Magnetic field magnitude Lithium beam stopping: density profile dependent on cross-section for stopping (but eliminated from calculation by boundary conditions?) Zeeman effect in Lithium: population of sub-levels (as Stark) when used to measure magnetic field direction. Thermal He 'beam' excitation and charge-exchange Helium (high energy) beam excitation. Ion source physics, especially negative ion formation Neutral beam reionisation by neutral collisions (Positive and negative) ion neutralisation in neutral gas

3 Beam stopping cross-section (E Delabie) Neutral beam stopping above 40 kev/amu dominated by proton impact ionisation from ground state (Below 40 kev/amu CX dominated) Recommended data from Janev & Smith, 1993 (and ADAS) based on experimental data (Shah & Gilbody, 1982) which at the time agreed with theoretical predictions Theory later found to be unconverged (Toshima, 1998). Several theoretical studies since then consistently predict 10% higher cross sections

4 Beam stopping cross-section (E Delabie) Impact of a 10% change in beam-stopping cross sections f =e σx n f f = σ σ ln f For JET-like conditions, f=0.22, reduces core density by 15% mild effect (although reduces shinethrough by 30%) For ITER conditions, f=0.01, reduces core density by 46% significant impact on the performance of the core charge-exchange system Uncertainties in modelling (not just atomic data) acknowledged: need to measure local beam emission for quantitative analysis of impurity spectra 30% discrepancy in total emission (but potential causes other than atomic physics) Enhanced Lorentz ionisation from upper n-levels thought to be adequately trreated

5 Seems like it needs experiments to check atomic data. Experiment is not a 'clean' measurement of a single crosssection, (CX as well as impact excitation involved) so needs to have a self-consistent modelling of the experimental results. Can an experiment achieve the required accuracy (propagation of errors in electron density etc)?

6 FIDASIM (Heidbrink, Grierson) Code to fully model the beam emission spectrum of hydrogen beam into a hydrogen plasma. Attempts to model all processes, including Thermal charge exchange from the edge (donor energies below 1 kev) Effect of 'halo': charge transfer between C 5+ and D +, want to add this process to the modelling

7 FIDASIM (Heidbrink, Grierson) Code to fully model the beam emission spectrum of hydrogen beam into a hydrogen plasma. Attempts to model all processes, including Thermal charge exchange from the edge (donor energies below 1 kev) Effect of 'halo': charge transfer between C 5+ and D +, want to add this process to the modelling Data on nl resolved cross sections for D 0 +D + D + +D 0 for energies below 1 kev (62eV 2.5keV) seems to be available already in ADAS for n=1, 2, 3, 4 /home/adas/adas/adf24/scx#h0 no data on C 5+ +D + C 6+ +D 0

8 Charge-exchange from high n-states of the beam (R E Bell) Intensity ratio of C VI n=8-7 to C VI n=14-10 are 28:1 (TFTR) and 30:1 (DIII-D). Using Einstein A-coeffefficients, deduce the population ratio of the respective upper n-levels (n=14 and n=8): about 1.5x This ratio is larger than can be explained by a collisional-radiative model based on donor n=1 and n=2 populations only Implies that n>2 donor populations need to be considered, but there is no data for these.

9 Charge-exchange from high n-states of the beam (R E Bell) Some data exists in ADAS for n=3,4 donor to C receiver, but derivation uncertain. Was studied briefly in the early days of JET but dismissed as contributions found insignificant for the spectral features of interest. Suggestions from M O'Mullane: There is very little in the literature for H(n>3) donor and nothing which resolves the spread in the n-shells of the capturing carbon Without more fundamental data one could: Extrapolate total cross section data to H(n>2) donor based on [Janev, Phys Lett A160, p67, 1991] Split the total cross-section over n-states, using 'universal scaling' developed for W Beam populations in the n>2 levels adequately covered in existing models/data. Fundamental calculations could be done instead to provide this data

10 Thermal helium 'beam' data (M Brix) Important processes for thermal helium beam diagnostics ~.1 10 ev proton impact excitation Charge exchange with impurities Collisional redistribution Data is pre-1990's and no-longer 'state of the art' Lithium beam Electron impact excitation dominant at low energies data believed to be good (need to check with the Garching group) Thermal sodium beams being considered for machines that are lithium wall conditioning how reliable is this data?

11 Neutral beam ion sources (E Surrey) Electron collision processes, Te from ev, depending on whether filament or RF driven (cf ITER) Accuracy of atomic data thought to be % but this is probably adequate (since many microscopic processes involved tends to average out the errors). Overall comparison with extracted beam properties is okay. Probably not worth investing a lot of effort to improve. Three ionisation processes: H H + H 2 H 2 + H 3 H 3 + Neutralisation occurs on surfaces: concept of cross section may not be appropriate Formation of H - occurs at surfaces, processes not well understood. Caesium coating improves yield. (ITER importance)

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