Observations of impurity transport in NSTX

NSTX Supported by Observations of impurity transport in NSTX College W&M Colorado Sch Mines Columbia U CompX General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Illinois U Maryland U Rochester U Washington U Wisconsin Luis F. Delgado-Aparicio Princeton Plasma Physics Laboratory and the NSTX Research Team Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec 4th ITPA Transport & Confinement Meeting Culham, Oxford, UK, 22-25 March 2010

In collaboration with… D. Stutman, K. Tritz, M. Finkenthal and D. Kumar Plasma Spectroscopy Group (PSG) The Johns Hopkins University (JHU, USA) R. Bell, S. Kaye, W. Solomon, B. LeBlanc, J. Menard, S. Paul and C. H. Skinner Princeton Plasma Physics Laboratory (PPPL)

Outline • Motivation and main diagnostic • Impurity transport experiments in NSTX • a) r* scan at fixed q-profile • b) n* scan of NBI heated H-modes • c) First-cut results from momentum & particle pinch • experiment • Toroidal rotation effects on particle diffusivity • Future experiments, diagnostic needs & possible “areas” of collaborations

Motivation • The understanding of impurity transport in magnetically confined fusion plasmas is one of the challenges facing the current fusion research. • Study the properties of impurity particle transport in a spherical tokakak (ST) in a variety of scenarios. • Important for extrapolation to the next step ST devices such as CTF and for comparison with the large aspect ratio tokamaks like ITER. Melted tungsten for the ITER-DT phase?

The main diagnostic for impurity transport used in NSTX is the tangential ME-SXR array L. Delgado-Aparicio, et al., RSI, 75, 4020, (2004). JAP, 102, 073304 (2007). PPCF, 49, 1245 (2007). NF, 49, 085028, (2009). NSTX top view Magnetic axis (core)

Example 1: r* scan at fixed q-profile Ne puff Ne puff Ne puff L. Delgado-Aparicio, et al., PPCF, 49, 1245 (2007). L. Delgado-Aparicio, et al., NF, 49, 085028, (2009).

Experimental and simulated SXR profiles at low vs. high field L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

Experimental diffusivity in agreement with theoretical models Note large increase in Dneo and Dexp at r/a>0.8 L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

Convective velocity changes sign with BT VZ<0 at r/a>0.5 at low-field is anomalous ⇒ instabilities? L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

Example 2: n* scan of NBI heated H-modes 4 MW 6 MW 2 MW • n* scan of NBI heated H-mode plasmas with n, Ip and Bf held constant. • The high-power discharges have as much as twice the Ti,e in the gradient region (r/a~0.6-0.8). • n* vary up to a factor of four with nearly identical density profiles.

Reconstructions show differences in SXR emissivities for low- & high- NBI power in the regions where n* changed The low-energy emissivities (εLE-SXR~nNe8+, Ne9+) indicate that the core emissivity decreases with NBI power while increasing at the gradient region. However, the high-energy emissivity (εHE-SXR~nNe10+) indicate that both the core and gradient region emissivity increases with NBI power.

Charge state distribution can explain the differences in emissivity without the need of changing the transport Preliminary results from MIST simulations indicate that a factor of two increases of Te (0.6<r/a<0.8) could be solely responsible for modifying the Ne charge state distribution and thus the SXR emissivity, without the need of changing the underlying transport properties.

Results from the momentum and particle transport experiments are on the way (w/W. Solomon and S. Kaye) • The flattening effect during the n=3 braking seems to be stronger in the core than in the edge region. • Get D & V from time-dependent MIST modeling. • After the n=3 pulses the core impurity pile-up seem to be stronger; need to invoke inward Vpinch?

Core impurity diffusivity can be affected by rotation in NSTX (×10-100 static DNeo) Charge-states from heavy impurities (Z≠A/2) can have different DPS(w). DPS(w) can be several times larger than that of the neoclassical transport for stationary plasmas. This is an additional mechanism to explain enhanced core diffusivities without the need of invoking the presence of long wavelength electrostatic turbulence. b) Ti a) Mo Vf MD Fe Ne Ar C O Neon-like Fe DPS(w) d) Wong (‘87) & Romanelli (‘98) Pfirsch-Schlüter Dneon(w) c) Neon DPS(w) DPS(w=0) DPS(w=0)

Pellet injection can probe enhanced core impurity transport • Ablation resistant, vitreous C pellets deposits impurity deep in the plasma. • Evolution of nZ much slower than that of Te. • DC around 1 m2/s for r/a > 0.6 (Neoclass. range). • DC(r/a→core) > 1m2/s nC (×1012 cm-3) nC (×1012 cm-3) NCLASS range

Density and impurity control is goal of multi-year Li program on NSTX Lithium Research (LR) Topical Science Group: • XP-1002: Core impurity density and radiated power reduction using variations in LLD divertor conditions (V. Soukhanovskii, LRNL). • XP-1024: Controlling Impurity Sources by Diffusive Lithium Injection (C. Skinner, PPPL). • XP-1027: RMPs below the ELM triggering threshold for impurity screening (J. Canik, ORNL). • XP-1056: Can Li Aerosol injection mitigate high-Z impurity accumulation during ELM-free H-modes (D. Mansfield, PPPL)? Advanced Scenario Topical Science Group: • XP-1005: Modifications to the early discharge evolution to reduce late impurity content evolution (J. Menard, PPPL). • XP-1006: Development of High-Elongation Beam Heated Scenarios with Reduced Impurity Content and Increased Non-Inductive Fraction (S. Gerhart, PPPL). • XP-1007: Use of HHFW heating to increase the non-inductive current fraction in NBI produced H-mode plasmas with triggered ELMs to control impurity buildup (M. Bell, PPPL).

New ME-SXR diagnostics will enable transport experiments probing also Z-dependence • Increased spatial resolution (~1 cm) probing the edge and gradient region. • Five broadband energy ranges will allow estimates of C, O, Ne, Ar and Fe transport. (Courtesy of K. Tritz - JHU)

Possibility of joint experiments(…just some ideas for 2011) • Study relationship between D & V and rotation (important for NSTX, NHTX and CTF). • Use NBI and/or n=3 magnetic braking. • Use different impurities. • Exp. tests vs. Wong/Romanelli’s • model. • Relationship between Vp and central electron heating in NSTX. • Use HHFW heating →Te/Ti~1-4. • Compare with NBI→Te/Ti~1 • Z-scaling of impurity transport. • C, O, Ne, Ar and metals! • Reviving the pellet injector. • Study relationship between resonant magnetic perturbations and edge transport. • 3D-non-axisymmetric perturbations. • MHD events such as RWMs & ELMs. • Magnetic ELM-pace experiments. • Impurity transport. • “Flushing” impurities from core. • Measuring He transport in NSTX. • Right diagnostic not working yet! • Good time/spatial resolution. • (5-10 ms, 1-4 cm) • Diagnostic based on beam emission. • SXR trans. grating spectro. (JHU). • Scanning visible spectro. (PPPL).

Acknowledgements • The Johns Hopkins University: Gaib Morris, Scott Spangler, Steve Patterson, Russ Pelton and Joe Ondorff. • Princeton Plasma Physics Laboratory: Bill Blanchard, Patti Bruno, Thomas Czeizinger, John Desandro, Russ Feder, Jerry Gething, Scott Gifford, Bob Hitchner, James Kukon, Doug Labrie, Steve Langish, Jim Taylor, Sylvester Vinson, Doug Voorhes and Joe Winston (NSTX). • This work was supported by U.S. DoE Contract No. DE-AC02-09CH11466 at PPPL and DoE grant No. DE-FG02-99ER5452 at Johns Hopkins University.

EXTRAS

Add an extrinsic impurity for transport studies

Ne gas-puff technique proven useful in MHD experiments Studying the correlations between magnetic and kinetic diagnostics for resistive wall mode identification Study of radiation induced tearing modes The earlier appearance of the NTM appear to be due to the enhanced Prad. Verifying the linear-dependence of the island-width growth-rate with w∙Prad is important, as it predicts that tokamaks can be susceptible to TM destabilization by impurity radiation.

Rotation can increase the stationary DPfirsch-Slüter • K. L. Wong, et al., PRL, 59, 2643, (1987); Phys. Fluids B 1, 545, (1989). • M. Romanelli, et al., Plasma Phys. Control. Fusion, 40, 1767, (1998). • Although Wong and Romanelli’s results were derived using different • methods, the neoclassical enhancement due to rotation is the SAME! ∴ Neoclassical diffusivity for heavy impurities can be one to two orders of magnitude higher in a rotating plasma than in a stationary one without the need of invoking the presence of long wavelength electrostatic turbulence.

Core impurity diffusivity can be affected by rotation in NSTX (×10-100 static DNeo) b) Ti a) Mo Vf MD • Can be tested using: • Pellet injection • Laser blow-off • Balanced NBI • n=3 mag. braking • Argon injection Fe Ne Ar C O Neon-like Fe DPS(w) d) Wong (‘87) & Romanelli (‘98) Pfirsch-Schlüter Dneon(w) c) Neon DPS(w) DPS(w=0) DPS(w=0)

Observations of impurity transport in NSTX