Recent Results in Impurity Transport in Tokamaks D R Mikkelsen PPPL 2nd Coordinated Working Group Meeting Greifswald, June 4-6, 2007 D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Original motivation for this presentation Density dependent impurity accumulation in stellarators is very striking Nakamura, et al., Nucl. Fusion 43 (2003) 219; PPCF 44 (2002) 2121 Burhenn, et al., Fusion Sci. Tech. 46 (2004) 115 Why does transport qualitatively change with only a small change in collisionality? Expect collisionality to be important in both neoclassical and turbulent transport. Good topic for CWG study. Experimental data exists Apply the transport simulation codes. For this talk I searched for evidence of impurity accumulation in tokamaks with similar density thresholds or windows. No one could provide any examples in tokamaks. Plan B for talk: summarize recent work on tokamak impurity transport. D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Overview Historical background: general characterization of impurity transport in tokamaks Recent experiments in JET and TCV Gyrokinetic simulations of impurity transport Multi-color soft X-ray system on NSTX New crystal X-ray spectrometer on C-Mod D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Characterization of Impurity Transport in Tokamaks While neoclassical-level transport is occasionally observed: Wade, et al., Phys. Rev Letters 84 (2000) 282, ion temperature gradient screening Neu, et al., Nucl. Fusion 45 (2005) 209, tungsten accumulation with low anomalous D Adding some RF heating removes the accumulation Dux, et al., Nucl. Fusion 44 (2004) 260, accumulation in ITB region, Z dependence Takenaga, et al., Nucl. Fusion 45 (2003) 1235, argon accumulation with low anomalous D Additional ECH can exhaust the argon. Helium and carbon don t accumulate. Scavino, et al., Plasma Phys. Control. Fusion 46 (2004) 857 868 Neoclassical pinch traps silicon inside sawtooth mixing radius in TCV. Impurity diffusivity is mainly much higher than the neoclassical level. This prevents strong neoclassical accumulation! Giroud, Nuclear Fusion 47 (2007) 313 Guirlet, et al., Plasma Phys. Control. Fusion 48 (2007) B63 Comprehensive discussion of experiment and theory, little original data Scavino, et al., Plasma Phys. Control. Fusion 45 (2003) 1961 Shape dependence in anomalous impurity transport in TCV Rice, et al., Phys. Plasmas 7 (2000) 1825 Ohmic and L-mode plasmas characterized by strong D, weak pinch D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Impurity Accumulation in Tokamaks This page summarizes Guirlet, et al., Plasma Phys. Control. Fusion 48 (2007) B63 Most comprehensive recent discussion of experiment and theory. Impurity densities are often more peaked than the electron density: Ida K et al 1987 Phys. Rev. Lett. 58 116 Pasini D et al 1992 Plasma Phys. Control. Fusion 34 677 Dux R et al 1999 Nucl. Fusion 39 1509 Takenaga H et al 2003 Nucl. Fusion 43 1235 Zablotsky, et al., 2006 IAEA, EX/P3-7 This is neoclassically expected, Hirshman and Sigmar 1981 Nucl. Fusion 21 1079, but neoclassical predictions are seldom quantitatively correct. Turbulence is believed to be generally more important, but some enhanced confinement regimes allow neoclassical accumulation to occur. Dux R et al 1999 Nucl. Fusion 39 1509 Sunn-Pedersen T et al 2000 Nucl. Fusion 40 1795 Wade M R et al 2000 Phys. Rev. Lett. 84 282 Jackson G L et al 1991 Phys. Rev. Lett. 67 3098 Additional electron heating raises D and prevents accumulation (enhances turbulent transport?) Van Oost G et al 1995 22nd EPS Conf., vol 19C p III-345 Neu R et al 2003 J. Nucl. Mater. 313 316 116 Puiatti M-E et al 2003 Plasma Phys. Control. Fusion 45 2011. D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Impurity Transport in ITBs C-Mod density-itb Without central heating electron and impurity densities rise, Z eff rises. Rice J.E. et al 2001 Nucl. Fusion 41 277 Rice J.E. et al 2002 Nucl. Fusion 42 510 With central heating (added after ITB formation!) steady state is achieved in AUG and C-Mod. Rice J.E. et al 2002 Nucl. Fusion 42 510 Wukitch S.J. et al 2002 Phys. Plasmas 9 2149 Stober J. et al 2002 Dependence of particle transport on the heating profile in ASDEX Upgrade Proc. 19th Int. Conf. on Fusion Energy (Lyon, 2002) EX/C3-7Rb Low impurity diffusivities in Temperature ITBs are not much larger than neoclassical: Takenaga H et al 2003 Nucl. Fusion 43 1235 Efthimion P C et al 1999 Nucl. Fusion 39 1905 Dux R et al 2004 Nucl. Fusion 44 260. D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Additional historical references from J. E. Rice, et al., Phys. Plasmas 7 (2000) 1825 Impurity confinement in tokamak plasmas has been studied extensively (Ref. 25 and references therein). Impurity transport in Ohmic L-mode plasmas is generally characterized as anomalous,26 32 with diffusion coefficients ranging from 100 to 1000 times larger than neoclassical predictions.33 In neutral beam and ICRF H-mode plasmas, longer impurity confinement is observed, characterized by a large edge inward convection velocity,34 39 similar to neoclassical predictions. There are few direct measurements of impurity transport in Ohmic H-mode plasmas, other than some documented increases in the global Zeff 25 M. Mattioli, R. Giannella, R. Myrnas et al., Nucl. Fusion 35, 1115 ~1995. 26 E. S. Marmar, J. E. Rice, and S. L. Allen, Phys. Rev. Lett. 45, 2025 ~1980. 27 TFR Group, Phys. Lett. 87A, 169 ~1982. 28 E. S. Marmar, J. E. Rice, J. L. Terry, and F. Seguin, Nucl. Fusion 22, 1567 ~1982. 29 TFR Group, Nucl. Fusion 23, 559 ~1983. 30 B. C. Stratton, A. T. Ramsey, F. P. Boody, C. E. Bush, R. J. Fonck, R. J. Groebner, R. A. Hulse, R. K. Richards, and J. Schivell, Nucl. Fusion 27, 1147 ~1987. 31 R. Giannella, L. Lauro-Taroni, M. Mattioli et al., Nucl. Fusion 34, 1185 ~1994. 32 M. Mattioli, C. DeMichelis, and A. L. Pecquet, Nucl. Fusion 38, 1629 ~1998. 33 R. Hawryluk, S. Suckewer, and S. Hirshman, Nucl. Fusion 19, 607 ~1979. 34 G. Fussman, J. Hofmann, G. Janeschitz et al., J. Nucl. Mater. 162, 14 ~1989. 35 K. Ida, R. J. Fonck, S. Sesnic, R. A. Hulse, B. LeBlanc, and S. F. Paul, Nucl. Fusion 29, 231 ~1989. 36 M. E. Perry, N. H. Brooks, D. A. Content, R. A. Hulse, M. A. Mahdavi, and H. W. Moos, Nucl. Fusion 31, 1859 ~1991. 37 D. Pasini, M. Mattioli, A. W. Edwards, et al., Nucl. Fusion 30, 2049 ~1990. 38 D. Pasini, R. Giannella, L. L. Taroni, M. Mattioli, B. Denne-Hinnov, N. Hawkes, G. Magyar, and H. Weisen, Plasma Phys. Controlled Fusion 34, 677 ~1992. 39 J. E. Rice, J. L. Terry, J. A. Goetz, et al., Phys. Plasmas 4, 1605 ~1997. D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Theoretical Turbulent Impurity Transport General discussion of different effects contributing to impurity convection found in Garbet, et al., Plasma Phys. Control. Fusion 46 (2004) B557 Angioni, ITPA meeting, 7-10 May 2007, Lausanne Quasi-linear calculations of density peaking factor, V/D for many impurity species and for many plasma conditions: Giroud, Chengdu IAEA, EX/8-3 Work of Angioni on AUG & JET simulations is compared with experiment. Angioni, Phys. Plasmas 14 (2007) 055905 Z dependence of RV/D in AUG from simulations. Angioni and Peeters, Phys. Rev. Letters 96 (2006) 095003 Idealized ITG and TEM regimes; comparison with analytic fluid pinches Estrada-Mila, et al., Phys. Plasmas 12 (2005) 022305 Nonlinear gyrokinetic particle transport: He-D and He-D-T D/V model is consistent with simulations (flux is offset-linear with grad-n I ) (also in my C-Mod nonlinear simulations); quasi-linear work assumes this form. Someone will compare this with the JET helium transport experiments? Many opposing convection terms in the theory, only one simple generalization is possible: no strong anomalous pinch is found that creates impurity accumulation turbulent impurity pinches are certainly common, but density peaking saturates. Turbulent diffusivity minimizes impurity density peaking. D. R. Mikkelsen, Coordinated Working Group Meeting, Greifswald, 4-7 June 2007
Applications of the multi-color m optical SXR array in the National Spherical Torus Experiment (NSTX-PPPL) L. F. Delgado-Aparicio The Johns Hopkins University, The Plasma Spectroscopy Group
Principle of the optical soft x-ray x (OSXR) array Conversion of XUV emission to visible light To discrete channels and light detectors (PMT and/or APDs) + (RC/TIA) amplifiers It s a system that uses a fast (~1 μs) and efficient scintillator (CsI:Tl) in order to convert soft x-ray photons (0.1<E ph <10 kev) to visible green light (λ~550 nm). (L. F. Delgado-Aparicio, et. al., RSI 2004, submitted to Appl. Opt., 2007)
Tangential multi-color optical SXR array R 0 ~100-120 cm OSXR head r TF7 T,0 r T,15 G J H Multi-color (multi-foil) capability I X-rays from NSTX plasma (midplane: 0<ρ<1.0) SXR filters (e.g. Be 10, 100, 300, 500 μm) Ec1 Ec2 Ec3 To fiber optics + PMTs + TIAs (L. F. Delgado-Aparicio, et. al., PPCF, 2007)
RF HHFW electron heating experiments (L. F. Delgado-Aparicio, et. al., submitted to JAP, 2007)
Neon buildup in impurity transport experiments (L. F. Delgado-Aparicio, et. al., PPCF, 2007)
Experiment Department Diagnostic Developmeny Division Diagnostic Initiatives: X-ray Crystal Diagnostic: The new X-ray imaging crystal spectrometer for profile measurements of the ion temperature and toroidal rotation on Alcator C-Mod was installed on April 12, 2007 and provided the first spatially resolved spectra of H-like and He-like argon on April 13, 2007. The spectrometer is equipped with two spherically bent quartz crystals and four PILATUS II detector modules. Spectra of He-like argon were recorded from the entire 70 cm high cross-section of the plasma with a spatial resolution of 1 cm and use of three PILATUS II detector modules; spectra of H-like argon spectra were recorded with only one PILATUS II detector module from the central region of the plasma. (The spectra of H-like argon are important for Ti & rotation measurements at higher electron temperatures when the emissivity profile for He-like argon is expected to be hollow.) The layout of the spectrometer and the first spectral data from C-Mod are shown. 1
Experiment Department Diagnostic Development Division Spatially Resolving X-ray Imaging Crystal Spectrometer - PPPL/C-Mod Collaboration Spherically bent crystal spectrometer looking at H & He-like Argon emissions lines Provides impurity temperature and rotation profiles for r/a ~<0.8 He-like Crystal Gate Valve B-port H-like Crystal He-like Detectors H-like Detector Spectrometer Layout Pilatus X-ray Detector Module 2
Hirex SR on Alcator 4
Raw Data: He-like Spectra Bottom Core Top 6
Raw Data: He-like Spectra Bottom Core Top 7
Raw Data: H-like spectra 9
Hirex Sr. Moments H-like Ar x4 Ne-like Mo T I (kev) ΔV φ (km/s) Counts 10