10_ADASWS_tee-1/25 View from the US and the DIII-D programme T. E. Evans * General Atomics, San Diego, CA 15 th 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)

10_ADASWS_tee-2/25 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-  N, 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

10_ADASWS_tee-3/25 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-  N, 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

10_ADASWS_tee-4/25 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

10_ADASWS_tee-5/25 3D magnetic perturbations split the separatrix into a homoclinic (self-intersecting) tangle 2 unstable branches exit the X-point as  2 stable branches enter the X-point as  3D perturbations cause the separatrix to bifurcate into stable and unstable invariant manifolds Axisymmetric (no 3D perturbations) Non-axisymmetric (with 3D perturbations) Homoclinic tangle produced by DIII-D I-coil RMP fields T. E. Evans, et al., J. Physics: Conf. Ser., 7 (2005) 174

10_ADASWS_tee-6/25 Stochastic field lines formed by n=3 RMPs intersect divertor targets through homoclinic tangle lobes I-coil perturbations create stable and unstable invariant manifolds – Field lines escape though lobes formed by the manifolds M. W. Shafer (ORNL) + B T - B T : R(m) R(m)  (deg)  (deg) I-Coil current = 4.1 kA (n=3) Z (m) R (m)

10_ADASWS_tee-7/25 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

10_ADASWS_tee-8/25 ELM suppression correlated with a reduction in peak  p 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 n e and T e pedestal profiles diagnostics are being developed Theory Experiment

10_ADASWS_tee-9/25 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 n e (r,t), T e (r,t) and simultaneous n n (r,t) measurement Proposed set of helium gas capillaries for SOL characterization Modeling effort for adaptation of collisional radiative model for H-mode application He-I line ratio electron density and temperature diagnostic for DIII-D

10_ADASWS_tee-10/25 Based on n e and T e dependence of the atomic level population densities in both spin systems Suitable transitions: 3 1 D =667.8 nm 3 1 S =728.1 nm 3 3 S =706.5 nm n e (r,t) T e (r,t) Maximum of normalized population density at lower T e for triplet system Comparison yields T e sensitivity Electron temperature T e sensitivity Employ ratio of levels predominantly depopulated by (a) collisions and (b) spontaneous radiation Electron density n e sensitivity (Result of different rate coefficients for spin forbidden transitions) Comparison yields n e sensitivity Hintz E and Schweer B 1995 Plasma Phys. Control. Fusion 37 A87

10_ADASWS_tee-11/25 Proposed DIII-D system based on TEXTOR He beam implemnetation nm nm nm n e (r,t) T e (r,t) nm n e (r,t) Range of wavelengths Accessible quantities Standard system characteristics: time resolution: > 100Hz digital resolution: 12 bit or higher spatial resolution: 15 cm coverage (0.7 <  < 1.1) with  r=1.2mm He gas puff capability (rate needed < 8 x s -1 ) Lithium oven for beam attenuation on Lithium as n e reference O. Schmitz et al. PPCF 50 (2008)

10_ADASWS_tee-12/25 Atomic data and Collisional Radiative Model (CRM) need to be optimized for H-mode conditions Need to determine if He line intensities provide sufficient signals-to-noise levels in H-mode SOL plasmas Analysis needs to be pushed beyond actual boundaries for good H-mode measurements We are aiming at n e and T e 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 T e lower than reference measurements with increasing heating at low n e < m-3, relaxation issues Improve atomic data Include high energy states by cascading and bundled solutions Develop fast algorithm for automated non-stationary solution Include beam geometry and change in velocity distribution into CRM

10_ADASWS_tee-13/25 Proof-of-concept testing done with existing hardware Midplane filter scope system One channel equipped with He-I filters and PMT Divertor video cameras He-I filters on cameras tanTV captured two lines simultaneously MDS spectrometer Check carbon back- ground for He-I lines used tanTV view DiMES TV views

10_ADASWS_tee-14/25 Residual helium after boronization gives sufficient signal for ~15 discharges 706.5nm 728.1nm 667.8nm 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?

10_ADASWS_tee-15/25 Helium images of the divertor provide high- resolution profiles of magnetic footprints 15 Strong density and temperature dependence of level populations makes He attractive for imaging purposes Camera views can be used as two dimensional n e and T e monitors in the divertor if calibrated 667.8nm 2 1 Strike line striation due to n=1 LM during TBM application observed in high contrast

10_ADASWS_tee-16/25 Mid-plane filterscope system has sufficient signal when a low-flow He puff is introduced in the SOL Signal from residual helium glow discharge Signal from 0.2 torr-L-s -1 helium gas puff into far SOL Signals from chord 6 at separatrix Midplane filterscope system Residual helium gas from glow discharge is marginal but a small He puff sufficient for n e and T e measurement 16

10_ADASWS_tee-17/25 An H-mode relevant collisional radiative model is being developed for the proposed He beam system Population density n i is established by: radiative transitions to and from other levels with Einstein coefficient A ij electron impact excitation and de-excitation with rate coefficient q e j->i = i v> and q e i->j = j v> ion impact excitation and de-excitation with rate coefficient q i j->i = i v> and q i i->j = j v> electron and ion impact ionization with rate coefficients S e i and S i i 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

10_ADASWS_tee-18/25 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 beam with +/- 10 degree divergence 30 mm in length thermal velocity ( km s -1 ) puff rate He atoms s -1 local beam density at. m -3 effect on local plasma parameters negligible (<5%) DiMES

10_ADASWS_tee-19/25 Additional poloidal locations are being evaluated as an upgrade option System I: HFS and LFS profile diagnostic System II: UD and LD n e and T e diagnostic System III: DiMES capillary DiMES 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 2 filter scope systems – one in each divertor automated view adjustment to one of six puff locations 12 radial chords, Dr=3 mm with 2 mm spot size tangential view with radial fine adjustment 1 filter scope system 1 additional channel observation of DiMES sample (PPI) 2-3 channel observation from UD on capillary

10_ADASWS_tee-20/25 A soft X-ray imaging system is being designed to study magnetic islands in DIII-D L- and H-modes 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 CIII Image Inner Wall Poincaré Plot TEXTOR Tore Supra Visible light TRIPND Schmitz et al. RMP Workshop (2008) Evans et al. PoP (2002)

10_ADASWS_tee-21/25 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).

10_ADASWS_tee-22/25 O. Schmitz et al. PPCF 50 (2008) 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 Tangency Plane Pinhole CsI:Tl Scintillator

10_ADASWS_tee-23/25 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-  N, 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

10_ADASWS_tee-24/25 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 < E c ? 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

10_ADASWS_tee-25/25 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

10_ADASWS_tee-26/25 DIII-D