Two fluid simulations of RMP penetration and comparison with ...

Two fluid simulations of RMP penetration and comparison with experiments

S. Günter

Available codes for resonant field penetration

Code Geometry Physics model

XTOR Tokamak, but no separatrix

•  two-fluid, but no polarization current •  bootstrap current •  no neoclassical rotation damping and drive •  anomalous diffusion/viscosity

JOREK Full tokamak geometry

•  two-fluid, but no polarization current •  no bootstrap current •  neoclassical rotation damping but no drive •  anomalous diffusion but no viscosity

M3D-C1 Full tokamak

geometry

•  Full two-fluid, including polarization current •  no bootstrap current •  neoclassical rotation damping/drive •  anomalous diffusion/viscosity

TM1 circular cylinder

•  Full two-fluid, including polarization current •  bootstrap current •  no neoclassical rotation damping/drive •  anomalous diffusion/viscosity

Experimental opportunities:

ASDEX Upgrade: 2x8 coils Planned upgrade (2013): rotating fields (~1 kHz), current rise time: ~2 ms

NSTX: so far 1x6 (midplane) coils

Trigger of magnetic islands by external perturbation fields

•  „clean“ experiment for forced reconnection, triggering magnetic islands (much slower than sawtooth trigger but well defined amplitude)


•  „clean“ experiment for forced reconnection, triggering magnetic islands (much slower than sawtooth trigger but well defined amplitude) •  test density dependence of error field penetration

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(!BR0(!R-  relevant for ITER error fields, empirical scaling

has large error bars in prediction for acceptable error fields


•  „clean“ experiment for forced reconnection, triggering magnetic islands (much slower than sawtooth trigger but well defined amplitude) •  test density dependence of error field penetration

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Fitzpatrick, PPCF 2012

-  relevant for ITER error fields, empirical scaling has large error bars in prediction for acceptable error fields

-  so far no theoretical explanation for the density dependence, and weak empirical basis for αs

-  Recent theory by Fitzpatrick can be tested


•  islands triggered so far in low density L-mode discharges only on ASDEX Upgrade

n=1 perturbation field



max external field (2.4 s) no perturbation (1.6 s)

q=2 surface




•  very small rotation at the rational surface

•  plasma rotation speeded up to lock the electron fluid

max external field (2.4 s) no perturbation (1.6 s)

q=2 surface


For mode locking, plasma “wants” to rotate with , can be achieved by changing density and/or rotation profile

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electron direction

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Test Fitzpatrick‘s scaling for error field penetration

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Experiments: •  First test physics scaling (β ρ*) using measured plasma parameters

and – if found – explore relevant parameter range -  density variation -  Ohmic vs. ECRH heated discharges

•  Test validity of applied scaling law (neo-Alcator assumed in Fitzpatrick‘s paper) -  scaling law should connect Ohmic regime with low density L mode -  affects density scaling even if physics model for penetration is right -  momentum confinement assumed to be proportional to energy

confinement (but in Ohmic discharges dominated by electron transport)


Test Fitzpatrick‘s scaling for error field penetration

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Theory: compare theory (β ρ* scaling) with code results Theory assumes that ion polarization current is the main stabilizing effect, minimum code requirements •  plasma inertia (at least in the vicinity of the rational surfaces) –

discuss PIES project! •  anomalous viscosity

To determine the plasma rotation against the perturbation field: •  Neoclassical viscosity and rotation drive


Edge ergodization on ASDEX Upgrade ?

Vacuum fields ergodic, but no evidence for ergodization inside plasma separatrix: -  no significant changes in pressure gradient nor rotation profiles (pedestal density

increases) -  ELM suppression works anyway

Chirikov parameter

W. Suttrop, 2012

Edge ergodization on ASDEX Upgrade ?

Vacuum fields ergodic, but no ergodization observed inside plasma separatrix: probably due to high rotation velocity of electron fluid

E. Viezzer, 2012

Evans et al., NF 2008

In the pedestal region plasma rotates in the electron diamagnetic drift direction: •  torque to force plasma rotation into ion diamagnetic direction •  reduction of density gradient

AUG (higher density) results in contradiction to low density discharges on DIII-D

low density discharges planned on AUG

Edge ergodization on NSTX?

ELMs triggered by RMPs (due to larger pressure gradients?)

J. Canik et al., NF 2010

Example: JOREK simulations for ITER edge

M. Becoulet et al., 2012

Combine topics of error field penetration and island excitation by sawteeth/fishbones:

•  Experiments on exciting magnetic islands by external fields and background MHD activity, examine details of plasma perturbation (see talk by Igoshine)

•  Simulations using appropriate codes

-  M3D-C1/TM-1 for sawtooth dynamics and seed island trigger

-  M3D-C1/TM-1/PIES for test of Fitzpatrick‘s results (ion polarization current for PIES needed)

Understand modification of the pedestal by external error fields: •  try to find edge ergodization in low-density ASDEX Upgrade

discharges, situation for NSTX?

•  Simulations by XTOR, JOREK, possibly M3D-C1 and PIES

Two fluid simulations of RMP penetration and comparison with ...

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