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Title: Intrinsic rotation in DIII-D

Abstract

In the absence of any auxiliary torque input, the DIII-D plasma consists of nonzero toroidal angular momentum, in other words, it rotates. This effect is commonly observed in tokamaks, being referred to as intrinsic rotation. Measurements of intrinsic rotation profiles have been made in DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] H-mode discharges, with both Ohmic heating (OH) and electron cyclotron heating (ECH) in which there is no auxiliary torque. Recently, the H-mode data set has been extended with the newly configured DIII-D simultaneous co- and counter-directed neutral beam injection (NBI) capability resulting in control of the local torque deposition, where co and counter refer to the direction relative to the toroidal plasma current. Understanding intrinsic rotation is important for projection toward burning plasma performance where any NBI torque will be relatively small. The toroidal velocity is recognizably important regarding issues of stability and confinement. In DIII-D ECH H-modes the rotation profile is hollow, co-directed at large minor radius and depressed, or actually counter-directed, nearer the magnetic axis. This profile varies with the ECH power deposition profile to some extent. In contrast, OH H-modes have a relatively flat co-directed rotation profile. There is a scaling of the DIII-D intrinsicmore » toroidal velocity with W/I{sub p}, as seen in intrinsic rotation in Alcator C-Mod [J. Rice, Nucl. Fusion 39, 1175 (1999)], where W is the total plasma thermal energy and I{sub p} is the magnitude of the toroidal plasma current. This common scaling resulted in a dimensionless similarity experiment between DIII-D and Alcator C-Mod on intrinsic rotation, obtaining a single spatial point match in the toroidal velocity normalized to the ion thermal velocity. The balanced NBI capability in DIII-D is a useful tool to push scaling studies to higher values of the plasma normalized energy, notwithstanding the details of torque deposition for co-NBI versus counter-NBI. There are theories which address intrinsic rotation, both extensions of neoclassical theory and related to turbulent transport. At this time, the comparisons with theory are qualitative.« less

Authors:
; ; ; ;  [1];  [2];  [2];  [2]
  1. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20975053
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 5; Other Information: DOI: 10.1063/1.2539055; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALCATOR DEVICE; ANGULAR MOMENTUM; COMPARATIVE EVALUATIONS; CONTROL; DOUBLET-3 DEVICE; ECR HEATING; ELECTRIC CURRENTS; H-MODE PLASMA CONFINEMENT; IONS; NEOCLASSICAL TRANSPORT THEORY; PLASMA; PLASMA BEAM INJECTION; RF SYSTEMS; ROTATION; SCALING; VELOCITY

Citation Formats

DeGrassie, J. S., Rice, J. E., Burrell, K. H., Groebner, R. J., Solomon, W. M., Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, General Atomics, P.O. Box 85608, San Diego, California 92186-5608, and Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451. Intrinsic rotation in DIII-D. United States: N. p., 2007. Web. doi:10.1063/1.2539055.
DeGrassie, J. S., Rice, J. E., Burrell, K. H., Groebner, R. J., Solomon, W. M., Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, General Atomics, P.O. Box 85608, San Diego, California 92186-5608, & Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451. Intrinsic rotation in DIII-D. United States. doi:10.1063/1.2539055.
DeGrassie, J. S., Rice, J. E., Burrell, K. H., Groebner, R. J., Solomon, W. M., Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, General Atomics, P.O. Box 85608, San Diego, California 92186-5608, and Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451. Tue . "Intrinsic rotation in DIII-D". United States. doi:10.1063/1.2539055.
@article{osti_20975053,
title = {Intrinsic rotation in DIII-D},
author = {DeGrassie, J. S. and Rice, J. E. and Burrell, K. H. and Groebner, R. J. and Solomon, W. M. and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 and General Atomics, P.O. Box 85608, San Diego, California 92186-5608 and Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451},
abstractNote = {In the absence of any auxiliary torque input, the DIII-D plasma consists of nonzero toroidal angular momentum, in other words, it rotates. This effect is commonly observed in tokamaks, being referred to as intrinsic rotation. Measurements of intrinsic rotation profiles have been made in DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] H-mode discharges, with both Ohmic heating (OH) and electron cyclotron heating (ECH) in which there is no auxiliary torque. Recently, the H-mode data set has been extended with the newly configured DIII-D simultaneous co- and counter-directed neutral beam injection (NBI) capability resulting in control of the local torque deposition, where co and counter refer to the direction relative to the toroidal plasma current. Understanding intrinsic rotation is important for projection toward burning plasma performance where any NBI torque will be relatively small. The toroidal velocity is recognizably important regarding issues of stability and confinement. In DIII-D ECH H-modes the rotation profile is hollow, co-directed at large minor radius and depressed, or actually counter-directed, nearer the magnetic axis. This profile varies with the ECH power deposition profile to some extent. In contrast, OH H-modes have a relatively flat co-directed rotation profile. There is a scaling of the DIII-D intrinsic toroidal velocity with W/I{sub p}, as seen in intrinsic rotation in Alcator C-Mod [J. Rice, Nucl. Fusion 39, 1175 (1999)], where W is the total plasma thermal energy and I{sub p} is the magnitude of the toroidal plasma current. This common scaling resulted in a dimensionless similarity experiment between DIII-D and Alcator C-Mod on intrinsic rotation, obtaining a single spatial point match in the toroidal velocity normalized to the ion thermal velocity. The balanced NBI capability in DIII-D is a useful tool to push scaling studies to higher values of the plasma normalized energy, notwithstanding the details of torque deposition for co-NBI versus counter-NBI. There are theories which address intrinsic rotation, both extensions of neoclassical theory and related to turbulent transport. At this time, the comparisons with theory are qualitative.},
doi = {10.1063/1.2539055},
journal = {Physics of Plasmas},
number = 5,
volume = 14,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • The first measurements of turbulent stresses and flows inside the separatrix of a tokamak H-mode plasma are reported, using a reciprocating multitip Langmuir probe at the DIII-D tokamak. A strong co-current rotation layer at the separatrix is found to precede intrinsic rotation development in the core. The measured fluid turbulent stresses transport toroidal momentum outward against the velocity gradient and thus try to sustain the edge layer. However, large kinetic stresses must exist to explain the net inward momentum transport leading to co-current core plasma rotation. The importance of such kinetic stresses is corroborated by the success of a simplemore » orbit loss model, representing a purely kinetic mechanism, in the prediction of features of the edge corotation layer.« less
  • A detailed description is presented of the experiment reported in [S. H. Mueller et al., Phys. Rev. Lett. 106, 115001 (2011)], which reported the first measurements of fluid turbulent stresses in a tokamak H-mode pedestal. Mach probe measurements disclosed a narrow co-current rotation layer at the separatrix, which is also seen in some L-modes [J. A. Boedo et al., Phys. Plasmas 18, 032510 (2011)]. Independent evidence for the existence of the edge co-rotation layer is presented from main-ion rotation measurements by charge-exchange-recombination spectroscopy in comparable helium plasmas. The probe measurements are validated against density and electron temperature profiles from Thomsonmore » scattering and in terms of the measured turbulent particle transport, which is consistent with the global density rise. Non-diffusive non-convective angular momentum transport is required by two independent experimental observations: (1) A persistent dip in the rotation profile separates the edge layer from the evolving core region during intrinsic rotation development. (2) The rotation profiles with co- and counter-current neutral beam injection appear well described as the simple sum of a constant intrinsic part and the beam-driven part, also demonstrating the profile-independence of the intrinsic torque. Characteristics of the turbulent fluctuations composing the fluid turbulent stresses are discussed: Up to 0.5 cm inside the separatrix, the low amplitude of the Reynolds stress (<0.05 Nm of torque) is due to both a reduction of the fluctuation amplitudes at the peak of the edge co-rotation layer and weak correlations between the toroidal and radial velocity fluctuations. Further into the core, the correlations increase significantly up to a value of +0.75, resulting in an almost unidirectional character of the turbulent Reynolds stress, generating substantial counter-current torques up to -2 Nm. Additional mechanisms must be present to balance these torques and explain the co-current core-plasma spin-up at a rate of +0.3 Nm.« less
  • No abstract prepared.
  • The effect of electron cyclotron heating (ECH) on the intrinsic rotation profile in DIII-D is shown experimentally. Former DIII-D experiments have shown that ECH tends to cause an interior reduction in the normally co-Ip directed intrinsic rotation profile, and this core rotation can be fully reversed to the opposite direction. This effect is due to a turbulent rearrangement of the interior rotation profile. Here, we show results that there is more than one mechanism causing this. We compare two low density L-mode discharges where the only operational difference is the location of the ECH deposition. At low ECH power, comparablemore » to the Ohmic power, the primary change is in the q-profile accompanied by a reversal of the core intrinsic rotation direction for the more off-axis deposition. The change in the shear of the q-profile fits well with a recent theoretical prediction for this rotation reversal. At higher ECH power, the primary change is in the core electron temperature, Te, accompanied by a hollowing of the rotation profile near the magnetic axis. This effect appears to be due to the change in electron collisionality, consistent with another theoretical, gyrokinetic prediction. The variety of phenomena that could allow ECH to modify the intrinsic rotation profile give some expectation that regions of large velocity shear in the interior could be generated, with the possibility of triggering internal transport barriers.« less