Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST

S.S. Henderson, L. Garzotti, F.J. Casson, D. Dickinson, M.F.J. Fox, M. O'Mullane, A. Patel, C.M. Roach, H.P. Summers, M. Valovic

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Time-dependent helium gas puff experiments have been performed on the Mega Ampère Spherical Tokamak (MAST) during a two point plasma current scan in L-mode and a confinement scan at 900 kA. An evaluation of the He II (n = 4 → 3) spectrum line induced by charge exchange suggests anomalous rates of diffusion and inward convection in the outer regions of both L-mode plasmas. Similar rates of diffusion are found in the H-mode plasma, however these rates are consistent with neoclassical predictions. The anomalous inward pinch found in the core of L-mode plasmas is also not apparent in the H-mode core. Linear gyrokinetic simulations of one flux surface in L-mode using the GS2 and GKW codes find that equilibrium flow shear is sufficient to stabilize ITG modes, consistent with beam emission spectroscopy (BES) observations, and suggest that collisionless TEMs may dominate the anomalous helium particle transport. A quasilinear estimate of the dimensionless peaking factor associated with TEMs is in good agreement with experiment. Collisionless TEMs are more stable in H-mode because the electron density gradient is flatter. The steepness of this gradient is therefore pivotal in determining the inward neoclassical particle pinch and the particle flux associated with TEM turbulence.
LanguageEnglish
Article number093013
Number of pages12
JournalNuclear Fusion
Volume54
Issue number9
DOIs
Publication statusPublished - 19 Aug 2014

Fingerprint

helium
transmission electron microscopy
equilibrium flow
gradients
plasma currents
flux (rate)
charge exchange
line spectra
convection
turbulence
slopes
shear
evaluation
estimates
predictions
gases
spectroscopy
simulation

Keywords

  • tokamaks
  • helium transport
  • pinch devices
  • plasma turbulence

Cite this

Henderson, S. S., Garzotti, L., Casson, F. J., Dickinson, D., Fox, M. F. J., O'Mullane, M., ... Valovic, M. (2014). Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST. Nuclear Fusion, 54(9), [093013]. https://doi.org/10.1088/0029-5515/54/9/093013
Henderson, S.S. ; Garzotti, L. ; Casson, F.J. ; Dickinson, D. ; Fox, M.F.J. ; O'Mullane, M. ; Patel, A. ; Roach, C.M. ; Summers, H.P. ; Valovic, M. / Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST. In: Nuclear Fusion. 2014 ; Vol. 54, No. 9.
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abstract = "Time-dependent helium gas puff experiments have been performed on the Mega Amp{\`e}re Spherical Tokamak (MAST) during a two point plasma current scan in L-mode and a confinement scan at 900 kA. An evaluation of the He II (n = 4 → 3) spectrum line induced by charge exchange suggests anomalous rates of diffusion and inward convection in the outer regions of both L-mode plasmas. Similar rates of diffusion are found in the H-mode plasma, however these rates are consistent with neoclassical predictions. The anomalous inward pinch found in the core of L-mode plasmas is also not apparent in the H-mode core. Linear gyrokinetic simulations of one flux surface in L-mode using the GS2 and GKW codes find that equilibrium flow shear is sufficient to stabilize ITG modes, consistent with beam emission spectroscopy (BES) observations, and suggest that collisionless TEMs may dominate the anomalous helium particle transport. A quasilinear estimate of the dimensionless peaking factor associated with TEMs is in good agreement with experiment. Collisionless TEMs are more stable in H-mode because the electron density gradient is flatter. The steepness of this gradient is therefore pivotal in determining the inward neoclassical particle pinch and the particle flux associated with TEM turbulence.",
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Henderson, SS, Garzotti, L, Casson, FJ, Dickinson, D, Fox, MFJ, O'Mullane, M, Patel, A, Roach, CM, Summers, HP & Valovic, M 2014, 'Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST' Nuclear Fusion, vol. 54, no. 9, 093013. https://doi.org/10.1088/0029-5515/54/9/093013

Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST. / Henderson, S.S.; Garzotti, L.; Casson, F.J.; Dickinson, D.; Fox, M.F.J.; O'Mullane, M.; Patel, A.; Roach, C.M.; Summers, H.P.; Valovic, M.

In: Nuclear Fusion, Vol. 54, No. 9, 093013, 19.08.2014.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST

AU - Henderson, S.S.

AU - Garzotti, L.

AU - Casson, F.J.

AU - Dickinson, D.

AU - Fox, M.F.J.

AU - O'Mullane, M.

AU - Patel, A.

AU - Roach, C.M.

AU - Summers, H.P.

AU - Valovic, M.

PY - 2014/8/19

Y1 - 2014/8/19

N2 - Time-dependent helium gas puff experiments have been performed on the Mega Ampère Spherical Tokamak (MAST) during a two point plasma current scan in L-mode and a confinement scan at 900 kA. An evaluation of the He II (n = 4 → 3) spectrum line induced by charge exchange suggests anomalous rates of diffusion and inward convection in the outer regions of both L-mode plasmas. Similar rates of diffusion are found in the H-mode plasma, however these rates are consistent with neoclassical predictions. The anomalous inward pinch found in the core of L-mode plasmas is also not apparent in the H-mode core. Linear gyrokinetic simulations of one flux surface in L-mode using the GS2 and GKW codes find that equilibrium flow shear is sufficient to stabilize ITG modes, consistent with beam emission spectroscopy (BES) observations, and suggest that collisionless TEMs may dominate the anomalous helium particle transport. A quasilinear estimate of the dimensionless peaking factor associated with TEMs is in good agreement with experiment. Collisionless TEMs are more stable in H-mode because the electron density gradient is flatter. The steepness of this gradient is therefore pivotal in determining the inward neoclassical particle pinch and the particle flux associated with TEM turbulence.

AB - Time-dependent helium gas puff experiments have been performed on the Mega Ampère Spherical Tokamak (MAST) during a two point plasma current scan in L-mode and a confinement scan at 900 kA. An evaluation of the He II (n = 4 → 3) spectrum line induced by charge exchange suggests anomalous rates of diffusion and inward convection in the outer regions of both L-mode plasmas. Similar rates of diffusion are found in the H-mode plasma, however these rates are consistent with neoclassical predictions. The anomalous inward pinch found in the core of L-mode plasmas is also not apparent in the H-mode core. Linear gyrokinetic simulations of one flux surface in L-mode using the GS2 and GKW codes find that equilibrium flow shear is sufficient to stabilize ITG modes, consistent with beam emission spectroscopy (BES) observations, and suggest that collisionless TEMs may dominate the anomalous helium particle transport. A quasilinear estimate of the dimensionless peaking factor associated with TEMs is in good agreement with experiment. Collisionless TEMs are more stable in H-mode because the electron density gradient is flatter. The steepness of this gradient is therefore pivotal in determining the inward neoclassical particle pinch and the particle flux associated with TEM turbulence.

KW - tokamaks

KW - helium transport

KW - pinch devices

KW - plasma turbulence

U2 - 10.1088/0029-5515/54/9/093013

DO - 10.1088/0029-5515/54/9/093013

M3 - Article

VL - 54

JO - Nuclear Fusion

T2 - Nuclear Fusion

JF - Nuclear Fusion

SN - 0029-5515

IS - 9

M1 - 093013

ER -