View from the US and the DIII-D programme

1. View from the US and the DIII-D programme T. E. Evans* General Atomics, San Diego, CA 15th ADAS Workshop 3-6 October 2010 Armagh, Northern Ireland *In collaboration with: N. H. Brooks, N. Eidietis, D. Humphreys, A. Hyatt,P. Parks, E. Strait, J. Wesley (GA)O. Schmitz (FZ-Jülich)J. Canik, N. Commaux, J. Harris, D, Hillis,T. Jernigan, R. Maingi, M. W. Shafer, E. A. Unterberg (ORNL)D. J. Battaglia (ORNL-ORISE)E. Hollmann, A. James, J. Yu (UCSD)S. Ohdachi (NIFS)A. Wingen (Dusseldorf)

2. The DIII-D program is strongly focused on addressing ITER urgent issues • Global performance and stability • Scenario II H-mode startup, core stability and energetic particle physics • Core fueling, heating and current drive • Neoclassical tearing mode, sawtooth and resistive wall mode control • Development of advance inductive operating scenarios (high-bN, high-gain) • Pedestal, scrape-off layer and divertor • L-H power threshold, energy, particle and momentum transport • ELM stability, suppression and mitigation • Resonant magnetic perturbation (suppression and pacing) • Pellet pacing • Off-normal events • Vertical stabilization • Disruption mitigation • Thermal quench • Non-axisymmetic currents and vessel forces (i.e., halo currents) • Runaway electron generation, control and suppression

3. The DIII-D program is strongly focused on addressing ITER urgent issues • Global performance and stability • Scenario II H-mode startup, core stability and energetic particle physics • Core fueling, heating and current drive • Neoclassical tearing mode, sawtooth and resistive wall mode control • Development of advance inductive operating scenarios (high-bN, high-gain) • Pedestal, scrape-off layer and divertor • L-H power threshold, energy, particle and momentum transport • ELM stability, suppression and mitigation • Resonant magnetic perturbation (suppression and pacing) • Pellet pacing • Off-normal events • Vertical stabilization • Disruption mitigation • Thermal quench • Non-axisymmetic currents and vessel forces (i.e., halo currents) • Runaway electron generation, control and suppression

4. Two sets of non-axisymmetric coils produce a variety of RMPs in DIII-D • The 4-turn C-coil and single-turn upper/lower I-coil can be configured for n=3 RMP experiments or n=1 field-error correction

5. 2 stable branches enter the X-point as  2 unstable branches exit the X-point as  3D magnetic perturbations split the separatrix into a homoclinic (self-intersecting) tangle Homoclinic tangle produced by DIII-D I-coil RMP fields Axisymmetric (no 3D perturbations) Non-axisymmetric (with 3D perturbations) • 3D perturbations cause the separatrix to bifurcate into stable and unstable invariant manifolds T. E. Evans, et al., J. Physics: Conf. Ser., 7(2005) 174

6. Stochastic field lines formed by n=3 RMPs intersect divertor targets through homoclinic tangle lobes 1.08 1.06 1.04 1.02 1.38 1.36 1.34 • I-coil perturbations create stable and unstable invariant manifolds • Field lines escape though lobes formed by the manifolds R (m) 0 100 200 300 f (deg) -300 -200 -100 0 f (deg) I-Coil current = 4.1 kA (n=3) 1.0 0.5 0.0 -0.5 -1.0 1.0 0.5 0.0 -0.5 -1.0 Z (m) - BT + BT 1.0 1.5 2.0 2.5 R(m) 1.0 1.5 2.0 2.5 R(m) M. W. Shafer (ORNL) 132731:2750

7. Peak divertor heat flux bifurcates due RMP fields during ELM suppression • Split heat flux peaks are consistent with vacuum field line calculations of magnetic footprint patterns on the divertor target plates

8. ELM suppression correlated with a reduction in peak p Experiment Theory • Expectation based on quasilinear transport theory: • stochastic layer reduces peak p and shifts it inward • Experimental data has outward shifted p peak rather than inward • High-resolution ne and Te pedestal profiles diagnostics are being developed

9. He-I line ratio electron density and temperature diagnostic for DIII-D • He-I line ratio technique: basic approach • Application to H-mode plasmas • Assessment of feasibility for DIII-D using existing hardware: He-I intensity examples post-boronization residual helium He-I intensity examples from post-helium glow residual helium neutrals He-I intensity examples from low order He gas puffing into far SOL • Proposed He-I line ratio setup for DIII-D Upgraded filterscope system for ne(r,t), Te(r,t) and simultaneous nn(r,t) measurement Proposed set of helium gas capillaries for SOL characterization Modeling effort for adaptation of collisional radiative model for H-mode application

10. Based on ne and Te dependence of the atomic level population densities in both spin systems Electron temperature Te sensitivity Maximum of normalized population density at lower Te for triplet system (Result of different rate coefficients for spin forbidden transitions) Comparison yields Te sensitivity Electron density ne sensitivity • Suitable transitions: Employ ratio of levels predominantly depopulated by (a) collisions and (b) spontaneous radiation 31D 21P @ l1=667.8 nm ne(r,t) 31S 21P @ l2=728.1 nm Comparison yields ne sensitivity Te(r,t) 33S 23P @ l3=706.5 nm Hintz E and Schweer B 1995 Plasma Phys. Control. Fusion 37 A87

11. Proposed DIII-D system based on TEXTOR He beam implemnetation 667.8 nm ne(r,t) 728.1 nm Te(r,t) 706.5 nm ne(r,t) 670.8 nm Range of wavelengths Accessible quantities Standard system characteristics: • time resolution: > 100Hz • digital resolution: 12 bit or higher • spatial resolution: 15 cm coverage (0.7 < r < 1.1) with Dr=1.2mm • He gas puff capability (rate needed < 8 x 1018 s-1) • Lithium oven for beam attenuation on Lithium as ne reference O. Schmitz et al. PPCF 50 (2008) 115004

12. Atomic data and Collisional Radiative Model (CRM) need to be optimized for H-mode conditions • Te lower than reference measurements with increasing heating Improve atomic data Include high energy states by cascading and bundled solutions Develop fast algorithm for automated non-stationary solution Analysis needs to be pushed beyond actual boundaries for good H-mode measurements • at low ne<1.0 1018 m-3, relaxation issues Develop fast algorithm for automated non-stationary solution Include beam geometry and change in velocity distribution into CRM We are aiming at ne and Te measurements in the SOL radial up to the separatrix under H-mode conditions at different poloidal positions Use line ratio technique for 2D imaging and as divertor diagnostic Need to determine if He line intensities provide sufficient signals-to-noise levels in H-mode SOL plasmas

13. Proof-of-concept testing done with existing hardware Midplane filter scope system Divertor video cameras MDS spectrometer DiMES TV views tanTV view • He-I filters on cameras • tanTV captured two lines simultaneously • One channel equipped with He-I filters and PMT • Check carbon back- ground for He-I lines used

14. Residual helium after boronization gives sufficient signal for ~15 discharges 706.5nm 728.1nm Signal from residual helium after boronization only, no puffing! Discharge #15 after boronization recovery Decays slowly but not sufficient for quantitative evaluation by CRM How much gas injection do we need for a robust signal? 667.8nm

15. Helium images of the divertor provide high-resolution profiles of magnetic footprints 2 667.8nm Strike line striation due to n=1 LM during TBM application observed in high contrast 1 Strong density and temperature dependence of level populations makes He attractive for imaging purposes Camera views can be used as two dimensional ne and Te monitors in the divertor if calibrated 15

16. Mid-plane filterscope system has sufficient signal when a low-flow He puff is introduced in the SOL Signals from chord 6 at separatrix Signal from residual helium glow discharge Midplane filterscope system Residual helium gas from glow discharge is marginal but a small He puff sufficient for ne and Te measurement Signal from 0.2 torr-L-s-1helium gas puff into far SOL 16

17. An H-mode relevant collisional radiative model is being developed for the proposed He beam system Population density ni is established by: • radiative transitions to and from other levels with Einstein coefficient Aij • electron impact excitation and de-excitation with rate coefficient qej->i=<sej->i v> and qei->j=<sej->j v> • ion impact excitation and de-excitation with rate coefficient qij->i=<sij->i v> and qii->j=<sii->j v> • electron and ion impact ionization with rate coefficients Seiand Sii Same processes included but improvement towards H-mode challenges: • Including pseudo states to calculate rate coefficients for high n levels • Atomic data manufactured in particular for He problem with comparison to experiment • Introduced linearization method for time dependent CRM solution to overcome relaxation issues • Include line of sight effects of diagnostic setup for net line emission correction due to ionization Further improvement ongoing but readily available for basic studies J. M. Munoz Burgos, O. Schmitz, S. D. Loch and C. P. Balance, paper in process

18. The proposed DIII-D He beam system will use proven nozzle technology Design is based on a local gas puff with direct tangential/perpendicular views Strong active and therefore localized signal Well defined beam geometry and velocity distribution Pulsed system possible for optimized background subtraction Standard TEXTOR nozzle • 340 micro tubes • 210 µm diameter each • 30 mm in length • beam with +/- 10 degree divergence • thermal velocity (1.4-1.6 km s-1) • puff rate 0.3-4.0 1018 He atoms s-1 • local beam density 0.2-2.0 1017 at. m-3 DiMES • effect on local plasma parameters negligible (<5%)

19. Additional poloidal locations are being evaluated as an upgrade option System I: HFS and LFS profile diagnostic • 1 filter scope system, 12 radial chords, Dr=3 mm with 2 mm spot size • automated view adjustment to one of six puff locations • tangential view with radial fine adjustment System II: UD and LD ne and Te diagnostic • 2 filter scope systems – one in each divertor • 12 radial chords, Dr=3 mm with 2 mm spot size • automated view adjustment to one of six puff locations • tangential view with radial fine adjustment System III: DiMES capillary • 1 filter scope system • 2-3 channel observation from UD on capillary DiMES • 1 additional channel observation of DiMES sample (PPI)

20. Tore Supra TRIPND Visible light A soft X-ray imaging system is being designed to study magnetic islands in DIII-D L- and H-modes TEXTOR Poincaré Plot CIII Image Inner Wall Evans et al. PoP (2002) Schmitz et al. RMP Workshop (2008) • Ohmic & L-Mode magnetic islands images agree with vacuum field modeling • Better validity for vacuum field modeling • Are islands screened in diverted H-mode plasmas? • Visible diagnostics restricted to LCFS-PSI region

21. The proposed DIII-D system is largely based on the LHD SXR imaging system design • Pinhole/Foil with Fiber image guide to fast camera • Tangential View • Analysis uses tomographic inversion with regularization techniques • SVD used to isolate core modes Ohdachi, et al, Plasma Science Tech. (2006).

22. The design and installation of DIII-D SXR imaging system is constrained by port structures & TF coil locations • Relies on efficient scintillator with high resolution: CsI:Tl • Sensitivity: ~ 0.11 e-/ 1 kev X-ray • Scintillator Efficiency, Light Coupling Losses, Detector Efficiency CsI:TlScintillator Pinhole Tangency Plane O. Schmitz et al. PPCF 50 (2008) 115004

23. The DIII-D program is strongly focused on addressing ITER urgent issues • Global performance and stability • Scenario II H-mode startup, core stability and energetic particle physics • Core fueling, heating and current drive • Neoclassical tearing mode, sawtooth and resistive wall mode control • Development of advance inductive operating scenarios (high-bN, high-gain) • Pedestal, scrape-off layer and divertor • L-H power threshold, energy, particle and momentum transport • ELM stability, suppression and mitigation • Resonant magnetic perturbation (suppression and pacing) • Pellet pacing • Off-normal events • Vertical stabilization • Disruption mitigation • Thermal quench • Non-axisymmetic currents and vessel forces (i.e., halo currents) • Runaway electron generation, control and suppression

24. Runaway Electron (RE) current decay may be related to multi-step ionization energy loss • RE beam position controlled to avoid wall contact • Understanding the physics of the natural decay phase may be important for mitigating RE beams in ITER • avalanche process inhibited due to E < Ec? • RE beam instabilities? • RE energy loss due to background impurity ionization processes? • Cross sections needed for mono-energetic MeV electron inner shell ionization and radiation processes

25. Summary and conclusions • DIII-D program focused on ITER urgent issues • Advanced diagnostic development for boundary control with 3D magnetic perturbation fields • High-resolution He-I beam system for edge profile analysis • Soft x-ray imaging system for studying 3D lobe structures and magnetic islands in L- and H-mode • Develop ELM suppression approachs for ITER • Runaway electron beam physics • Develop an understanding of RE beam generation and decay processes • Develop RE beam control and mitigation approach • Progress is being made on developing CRM analysis tools and specifying atomic data needs

26. DIII-D