Zscaling of impurity C, Ne, Ar transport in beam heated NSTX Hmode discharges

1
Z-scaling of impurity (C, Ne, Ar) transport in
beam heated NSTX H-mode discharges

• L. F. Delgado-Aparicio, D. Stutman, K. Tritz, and
  M. Finkenthal
• The Johns Hopkins University, The Plasma
  Spectroscopy Group
• R. E. Bell, M. Bell, R. Kaita, S. Kaye, B. P.
  LeBlanc, S. Paul and L. Roquemore
• Princeton Plasma Physics Laboratory
• F. Levinton, H. YuhNOVA Photonics, Inc.

NSTX Results/Research Forum December, 12-17,
2005 Princeton, New Jersey, USA
2
Motivation

• Continue the impurity particle transport studies
  in NSTX (done already for L-mode) for the H-mode,
  estimating the dependence of DZ vZ for
  different Z and plasma parameters (Bf, q, Wf,
  Ti).
• Preliminary estimates in H-mode indicate that we
  might have small (close to neoclassical) impurity
  DZ as well as vZgt0.
• Convective impurity transport could play an
  important role in NSTX (flat ne and peaked Ti)
  H-modes, where temperature screening might be
  shielding the plasma core from low Z impurities.
• These impurities studies are relevant for NSTX
  scaling of high confinement (high b) plasmas and
  ITER operational scenarios where screening of
  high-Z impurities will be invoked to shield the
  plasma core.

3
First assessment of impurity transport in NSTX
H-modes
Hollow carbon distribution
Wf (km/s)
NSTX 108730

• DZ falling into the neoclassical range also
  outside r/a gt 0.5
• VZ gt0 (convective outward velocity)

GOAL
1 D. Stutman, et. al., EPS Conference on Plasma
Physics and Controlled Fusion (2002).
4
Impurity transport technique applied in NSTX
L-modes

• Filtered diode arrays measure peripheral, mid
  and core Neon ions.
• The Neon contribution is obtained from
  consecutive, reproducible shots.
• Inclusion of peripheral charge states (Prad)
  improves D, V estimate

1 D. Stutman, et. al., EPS Conference on Plasma
Physics and Controlled Fusion (2002). 2 D.
Stutman, et. al., POP, 10, 4387, (2003).
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Diagnostics to be used for the H-mode impurity
transport XP
Tangential optical (scintillator-based) soft
X-ray array (tOSXR)

• Carbon diagnostics
• Poloidal (diode-based) USXR arrays with a Ti 0.3
  mm foil (Ecgt0.1 keV) discriminate between the
  peripheral C line emission and the core C
  continuum.
• CHERS system (C6 and ??).
• BOLOMETER Prad

• Neon diagnostic
• The poloidal USXR tOSXR arrays will be
  selectively filtered for energy bands covering
  the entire neon spectrum in NSTX.
• Ne10 for r/a0.4 (Ecgt1.4 keV, use of Be 100
  mm).
• Ne8 and Ne9 (He- and H-like) for 0.4r/a0.7
  (Ecgt0.4 keV, use of Be 10 mm).
• Ne6 and Ne7 Be- and Li-like for 0.7r/a0.9
  (Ecgt0.1 keV, use of Ti 0.3 mm).
• BOLOMETER Prad

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Plasma parameters and needed diagnostics

• Parameters to be changed
• Bf
• Wf
• Ip ? q
• Ti ? ? Ti

• Needed plasma diagnostics
• CHERS
• MSE
• Bolometer
• MPTS

Small gas puffs to be used CD4, Ne, Ar
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EXTRA SLIDES
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Neoclassical cross-field impurity flux

• depend on the details of momentum transfer
  between the various plasma
• particle species ? dependent on local plasma
  conditions.

• can generally be neglected because momentum
  transport between electrons
• and impurities is small

For steady state (GZ0)

• In plasmas with a peaked main ion density
  profile, low and high Z impurities would be
• expected to concentrate in the plasma
  center regardless of the Ti profile.

• HOWEVER, in cases of small ?nD, the GZ driven
  by ?Ti does become important.

• If the main ions impurities of interest are in
  the bannana plateau regime ? gTilt0

1 P. H. Rutherford, POF, 17, 1782, (1974). 2
M. R. Wade, et. al., PRL, 84, 282, (2000). 3 D.
R. Baker, et. al., GA-A23485, (2000)
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Impurities accumulation due to neo-classical
effects ?

• Generally gD?ZgtgtgTigt0
• If peaked nD(r), impurities are expected to
  concentrate in the plasma center, regardless of
  the Ti(r).
• Confirmed in experiments with strong central
  fueling either by pellet injection 4 or NBI
  fueling 5.

DIII-D NCS L-mode 3
4 S. L. Milora, et. al., NF, 35, 657,
(1995). 5 E. J. Synakowski, et. al., POF B, 5,
2215, (1993).
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Transport coefficients in the banana-plateau (BP)
regime
Diffusion
Convective velocity
is the weighted viscosity coefficient m00 of the
impurity and main ions
is connected to the ratio of the viscosity
coefficients m01/ m00 of the impurity and main
ions
6 W. A. Houlberg, et. al., POP, 4, 3230,
(1997). 7 R. Dux, et. al., NF, 39, 1509, (1999).
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Is the accumulation a rotational effect
(centrifugal forces)?
From a simple 2-fluid-model picture

• For the case of a trace impurity (I) and a
  working ion (i)
• ZI2nIltltni
• Ti TI
• Rotational velocity of the heavy ion impurity
  is vth,I
• The impurity and background ions are rotating
  at the same toroidal speed.
• Temperature varies slowly with the radius.

8 M. Romanelli, et. al., EPS Conference on PPCF
(Berchtesgaden, Germany, June 1997)