Boundary Physics Science Focus Group Meeting Wednesday 16th November 2005 9:30 AM B 318

1. Boundary Physics Science Focus Group Meeting Wednesday 16th November 2005 9:30 AM B 318 Agenda: Joint BP / RF meeting on edge conditioning and RF coupling - tba. Input for ITPA meeting in Shanghai in January. Proposed titles by Thursday 17th please. (3 mins) Bob: Opportunities for research on LTX (5 mins + 3 mins discussions) Henry: Opportunities with Li on NSTX (5+3 mins) Rajesh: Opportunities for heat and particle transport and ELM research (5+3 mins) Bateman,Kritz/Rajesh: Benchmarking of CPES (5+3 mins) Vlad: Opportunities in Divertor Physics (5+3 mins) Charles: Opportunities to study dust and deposition (5+3 mins) Leonid: Opportunities for ELM stabilization on JET (5+3 mins). _____________________ 10:45 preparations for 11:00 AM DIII-D ROF this room

2. Divertor SOL ITPA Shanghai Jan 9-12th 2006 • Topic 1 - D/T retention (long pulse, saturation.. processes) • Topic 2 - Wall conditioning • Topic 3 - Flux consumption and startup on outside limiter • Topic 4 - Flow characterization • Topic 5 - Melt layer stability & vapor shielding • Topic 6 - Spectroscopy of hydrocarbons in low T plasmas Other suggested topics which could be included: • A) Radial transport and ELMs • B) ELMs & wall loading. • C) Wall loading during disruptions • Bruce Lipschultz summary comments: - Certainly topics 1-2 are strongly supported.- We should get started on topics 3 & 5 as these have not been covered before. So, we should solicit additional talks. Please suggest- We have not dealt with topic 4 in quite a while. It might be worth revisiting. But there is not much being volunteered.- We should drop topic 5 until we get more participation- Of the new suggested topics radial transport is the strongest. I say let's keep it if the people come. Bruce Lipschultz.

3. Opportunities for Boundary Physics Research • on the Lithium Tokamak Experiment (LTX) • R. Majeski & R. Kaita • Equilibrium and Stability of Plasmas with Low-Recycling Walls • • Burning Plasma Relevance: • - Improved fueling control with low-recycling boundary • Increased MHD stability with reduction of temperature gradients • Unique Combination of LTX Features: • - Close-fitting conducting shell with plasma-facing surface coated with liquefied lithium • - Injectors for supersonic gas, deuterium pellets, & compact toroids (UC Davis proposal) • Equilibrium reconstructions with Equilibrium and Stability Code (ESC - L. Zakharov) • Theory collaboration on confinement and transport (S. Krasheninnikov at UCSD) • • Research Opportunities: • - Tests of theory predictions for low-recycling on discharge performance • Exploration of potentially reactor-relevant techniques for plasma core fueling

4. Opportunities for Boundary Physics Research • on LTX (continued) • R. Majeski and R. Kaita • Power Handling Under High Heat Load Conditions • • Burning Plasma Relevance: • - Present materials considered for ITER may not survive high instantaneous heat loads • • Unique Combination of LTX Features: • - Heat loads up to 50 MW/m2 dissipated with liquid lithium in CDX-U toroidal tray • - Electron beam used to discover efficient convective cooling of liquid lithium available • - Access to simulator of free liquid metal surface flow in toroidal field (QTOR at UCLA) • • Research Opportunities: • - Studies of dependence of heat dissipation on B-field in static and flowing liquid metal • Heat transfer analysis including convective effects with liquid metal MHD codes (UCLA)

5. Kugel: NSTX Lithium Experiments Are Focusing on Particle Control (FY’05-07) & Power Handling (FY’08) • A partial lithium coating has been demonstrated to provide strong edge pumping (reduction of recycling).• The NSTX 5-Year Plan describes a 3 phased approach to lithium PFCs: (I) Lithium Pellet Injection, (II) Lithium Evaporators, (III) Liquid Lithium Divertor.• Phase I, Lithium Pellet Injection is in progress; Phase II is starting. • The NSTX Experimental Schedule calls for the capability to perform routine thick lithium coating depositions over a significant fraction of the plasma facing surfaces for the first XP’s in 2006.

6. NSTX Lithium Evaporator (LITER-1) Approach • Wide coverage over CS and Inner Divertors for high performance DND plasmas. • Thick deposition on Lower Divertor for LSN plasmas. • Start with 100mg/min Lithium deposition on existing graphite PFCs. • Characterize Lithium morning deposition, & between-shot deposition. • Later replace existing graphite PFC tiles with suitable PFC upgrade as required.

7. NSTX Lithium Research and ITPA, ITER, BP, and FSEAC Priorities* • NSTX lithium facility will have unique and complementary characteristics that may enable important advances in boundary physics and technology research • Among the three major U.S. facilities, NSTX is unique in its study of lithium coatings and its planned exploration of liquid lithium for particle and heat flux management. • NSTX lithium contributions to boundary physics and technology research may enhance the vitality of the U.S. fusion program • NSTX is also confronting edge heat and particle flux management issues through its unique program on lithium coatings and its investigation of liquid lithium as solution for both particles and heat. • This is unique research with the potential of offering a revolutionary solution to burning plasmas in any toroidal confinement configuration if the issues of concern can be understood and managed. • NSTX lithium research opens a unique and probably vital strategic option for fusion development, that of a cost-effective Component Test Facility (CTF) • Success on NSTX could lead to consideration of liquid lithium as a back-up option, perhaps for a target at the bottom of the divertor Vee on ITER, and CTF. *NSTX Research and Its Role in Advancing Fusion Energy Science: A Report Prepared for the FESAC Facilities Review, May 28, 2005

8. Maingi: Opportunities for Pedestal and ELM Research • ITER needs the confinement accompanying large, Type I ELMs, but has potential problem with target ablation with present material choices • Several promising alternatives • “Grassy” ELMs - high bp, low toroidal rotation • Type II ELMs - access to second stability? with high k or d, and/or proximity to double-null • Enhanced Da; High Recycling Steady: ne* ~ 1 too high? • Type V ELMs - only ST? similar to Type II? high b EDA? • Quiescent H-mode - low recycling and counter NBI • ELM control through vertical modulations and edge resonant magnetic perturbations • Physics understanding needed to assess extrapolability

9. Opportunities for Pedestal and ELM Research • Picture of an ELM as an MHD instability set by peeling-ballooning boundaries has some experimental support P. Snyder, H. Wilson PoP 2002 P. Snyder, H. Wilson PPCF 2004

10. Opportunities for ELM Research • Picture of an ELM as an explosive MHD instability being investigated S. Cowley, PPCF 2003 Kirk, PRL 2004

11. Opportunities for ELM Research • However, ELMs can have single or double filamentary structure, and can seemingly last much longer than predicted detonation times ~ (ta2tE)1/3~100 msec Maingi, NF 2005 Strait, PoP 1997 • Detailed imaging of structure of different kinds of ELMs would enable more rigorous experiment-theory comparison • Diagnostics: USXR with multiple filters, fast cameras(s), FIRTiP, GPI, Magnetics, Fast probe - more diagnostics needed or more experiments or both?

12. Opportunities for Pedestal and ELM Research • Are the DIII-D edge resonant magnetic perturbation experiments at odds with peeling/ballooning picture? • What is role of rotation? • What is role of collisionality? • What is role of TF ripple? • What is the mechanism by which ELM flux actually leaks onto the open field lines? • What is ratio of power to the wall vs. divertor during ELMs? • Pedestal research: what is the role of aspect ratio? • Pedestal research: can stability be optimized by controlling the fueling source?

13. Diagnostics for ELM and Pedestal Research • Existing Diagnostics: • USXR with multiple filters - localizes Te at perturbation • Tangential USXR camera • Fast camera(s): fisheye, midplane, divertor structure • FIRTiP - toroidal propagation and physical size • Magnetics - toroidal propagation and current size • Fast probe - number of filaments • Proposed Diagnostic Enhancements: • Extra edge Thomson channels - 5 more? - - better Pe’ • Upgrade of spatial and time resolution for ERD - better Pi’ • Additional edge MSE channels - better Jped • Midplane tangential view for fast camera? Better midplane stucture

14. Opportunities for heat and particle control research • Edge plasma transport: • Balance between parallel and perpendicular - any impact of high mirror ratio and short midplane-divertor conection length? • Roles of diffusive, convective, and intermittent radial transport • What goes to divertor vs. wall? • Role of SOL flows and ballooning-like transport - uniqueness of 2-D imaging at multiple poloidal locations • Role of shape? • Disruptions: characterization and mitigation

15. What is Needed from Experimentsfor Verification and Validation ofIntegrated Edge Simulations Arnold H. Kritz Glenn Bateman Lehigh University Physics Department Bethlehem, PA 23 October 2005

16. Benchmarking of CPESWhat is Needed from Experiments for V&V • Well diagnosed profiles during ELM cycle • Electron and ion temperatures, densities, velocities, current density • Turbulence spectra, non-Maxwellian characteristics of distributions • Need estimates of error bars and systematic uncertainties • Core plasma profiles needed together with pedestal and ELMs • ELM crashes • Timing: period, inherently random variation of period • Conditions that produce different kinds of ELM crashes • Characteristics of instability structure and growth • Change in plasma profiles produced by ELM crashes • Currents induced in walls • External conditions • Such as: divertor geometry, gas puffing, pumping • Systematic scans of data • As a function of density, heating power, triangularity, isotope mass • For trends as well as pointwise comparisons

17. Experimentally Measured Profiles During ELM cycle Used to Calibrate ASTRA Pedestal Model • Experimental data for DIII-D 98889 obtained from Tom Osborne at GA • Noise reduced by overlaying data from consecutive ELM cycles • ELM period 16-18 msec

18. NSTX divertor research is an integral part of NSTX 5-year Boundary Physics Research Plan Soukhanovskii • NSTX divertor research focuses on • ST divertor physics - basis for modeling and scaling of CTF • Tokamak divertor physics (P/R ~ 8, q ~ 4-6 MW/m2, opacity) • Scope of experimental and modeling work on NSTX is limited by available budget and manpower (diagnostics, …) • List of “divertor opportunities on NSTX” is not a wishlist but a list of topics most likely to be addressed in the next few years based on realistic expectations of available manpower, diagnostics, research trends, in accordance with the 5 year Research Plan. • Some of these topics are being addressed on NSTX in FY05-FY06, and some are ITER-relevant and ITPA Div-SOL hot topics

19. Exp. divertor research opportunities on NSTX • Heat flux mitigation - development of steady-state dissipative divertor scenarios (D2, impurity puffing) for NSTX long pulses (BP+ISD ETs) SOL-Div ITPA active topic, ITER-relevant • Experimental divertor physics on NSTX: • Effect of divertor geometry on heat flux reduction (ST magnetic geometry effects - extend divertor database, Open divertor geometry effects) • Atomic and molecular physics effects (Role of opacity and recombination, role of molecular source and processes in recycling - SOL-Div ITPA active topic, ITER-relevant) • Plasma transport and flows (Divertor heat and particle flux asymmetry, impurity production and transport, role of drifts, role of flows, SOL kinetic effects, e-i partition effects) • Divertor operation and optimization (pumping - cryo-pump, lithium) • MARFE physics: properties, source/sink, effect on core performance (density limits, MHD stability) • These exp. efforts will be supported by modeling: multi-fluid (UEDGE, …), MC neutral transport (DEGAS 2), plasma turbulence (BOUT), kinetic (?), opacity and CRM (CRETIN) . SOL-Div ITPA: http://efdasql.ipp.mpg.de/divsol/

20. NSTX divertor research is an integral part of NSTX 5-year Boundary Physics Research Plan

21. NSTX scrape-off layer and divertor diagnostics • Divertor IRTV two Indigo Alpha 160 x 128 pixel microbolometer cameras, 7-13mm range, 30 ms frame rate • Divertor/SOL cameras with Da, Dg, C III filters four Dalsa 1 x 2048 pixel CCDs, filter FWHM 10-15 A, frame rate 0.2 - 1 ms • Neutral pressure gauges four microion gauges on top and at midplane, two Penning gauges in lower and upper divertor, time response 5-10 ms • High-resolution divertor UV-VIS spectrometer ARC Spectro-Pro 500i, 3 input fibers, time response 15-30 ms, FWHM > 0.6 A • Midplane and divertor bolometry midplane (AXUV radiometer array), divertor - ASDEX-type four channel bolometer, time response 20 ms • Divertor Langmuir probes midplane - fast probe, tile LPs - Isat, Te measurements • Midplane Multi-point Thomson scattering with 2-4 points in SOL • Gas Injectors at various poloidal locations, R<1022 s-1 • Enhanced shaping capability - Lower Single • Null, k1.8 - 2.5, d0.4 - 0.9

22. Opportunities to study dust and deposition on NSTX ITER • ITPA DSOL priority topic: “Improve understanding of SOL plasma interaction with the main chamber” Concerns on ITER Be wall: • heat load, erosion lifetime, repair difficulty • tritium migration, • coating diagnostic mirrors… • ITPA Diagnostics priority topic:“…assessment of techniques for measurement of dust and erosion.” Concerns: high dust levels are expected in ITER from long plasma duration and more intense plasma surface interactions. • How to assure dust levels are below safety limit ? • Will dust transport impurities to plasma core reducing fusion reactivity ? • Limits for C-and Be-dust are related to an explosion (e.g., H produced by Be reactivity with steam). • The limit for W-dust is related to the containment function of the ITER building (is more flexible). Open ST geometry facilitates diagnostic access and cost effective progress on these topics.

23. Three pronged approach: • Study dust in NSTX plasma via fast cameras. • Plan to use intersecting views to define dust trajectory for detailed comparison to DUSTY model of S. Pigarov (UCSD). • Study dust settling in surfaces on NSTX and ASDEX-U • Work (resources ($)) needed to increase sensitivity of electrostatic dust detector. • Continue to study deposition with quartz crystal microbalances • Cross machine comparisons now an ITPA proposal. • Dedicated XPs to pin down correlations next campaign. • Modeling comparisons with Hogan / Brooks

28. Quiescient H-mode