Momentum losses by charge exchange with neutral particles in H-mode discharges at JET

T. W. Versloot (Corresponding Author), P. C. de Vries, C. Giroud, M. Brix, M. G. von Hellermann, P. J. Lomas, D. Moulton, M. O'Mullane, I. M. Nunes, Antti Salmi, Tuomas Tala, I. Voitsekhovitch, K.-D. Zastrow, JET-EFDA collaborators

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Abstract

The effect of a neutral density background on the toroidal angular momentum and kinetic energy profiles has been investigated in JET. Under equivalent conditions but with increasing gas fuelling during the flat top phase, it has been observed that both the edge rotation and temperature decrease. The increase in electron density was not sufficient to compensate the rotation and temperature loss such that both energy and momentum confinement times are significantly reduced. The edge localized mode behaviour is observed to be significantly affected by the increased neutral influx. A simple 1.5D fluid model has been used to qualitative capture the neutral transport response within the plasma, followed by a forward model of the passive charge-exchange (CX) emission of carbon to obtain a corrected radial neutral density profile. It has been found that the neutral density is sharply attenuated over the edge region, with similar edge magnitudes in both the non-fuelled (Γ0/ne ~ 1.2 m s−1) and maximum fuelled case (Γ0/ne ~ 2.5 m s−1). Discharges with reversed-B operation exhibited even higher normalized neutral fluxes related to first orbit effects and increased wall interactions. Over the full neutral influx range, a decrease in pedestal thermal Mach number from 0.25 to 0.14 was observed. Increased neutral penetration up to the pedestal top (r/a ~ 0.9) due to multiple CX interactions is obtained from the interpretive model. Under these multiple neutral–ion interactions, the impact on the CX loss of angular momentum is larger compared with the CX energy loss. The drag torque was seen to increase up to 10% of the total applied torque, while energy losses appeared to be smaller. The accuracy of this global approach method is unfortunately limited; however, the estimated momentum sink was found comparable to the torque required to explain the discrepancy between observed global energy and momentum confinement.
Original languageEnglish
Article number065017
Number of pages14
JournalPlasma Physics and Controlled Fusion
Volume53
Issue number6
DOIs
Publication statusPublished - 2011
MoE publication typeA1 Journal article-refereed

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neutral particles
charge exchange
Momentum
Torque
Angular momentum
momentum
torque
Energy dissipation
Fueling
angular momentum
energy dissipation
kinetic energy
Kinetic energy
Mach number
Carrier concentration
refueling
Drag
Orbits
interactions
profiles

Cite this

Versloot, T. W., de Vries, P. C., Giroud, C., Brix, M., von Hellermann, M. G., Lomas, P. J., ... JET-EFDA collaborators (2011). Momentum losses by charge exchange with neutral particles in H-mode discharges at JET. Plasma Physics and Controlled Fusion, 53(6), [065017]. https://doi.org/10.1088/0741-3335/53/6/065017
Versloot, T. W. ; de Vries, P. C. ; Giroud, C. ; Brix, M. ; von Hellermann, M. G. ; Lomas, P. J. ; Moulton, D. ; O'Mullane, M. ; Nunes, I. M. ; Salmi, Antti ; Tala, Tuomas ; Voitsekhovitch, I. ; Zastrow, K.-D. ; JET-EFDA collaborators. / Momentum losses by charge exchange with neutral particles in H-mode discharges at JET. In: Plasma Physics and Controlled Fusion. 2011 ; Vol. 53, No. 6.
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title = "Momentum losses by charge exchange with neutral particles in H-mode discharges at JET",
abstract = "The effect of a neutral density background on the toroidal angular momentum and kinetic energy profiles has been investigated in JET. Under equivalent conditions but with increasing gas fuelling during the flat top phase, it has been observed that both the edge rotation and temperature decrease. The increase in electron density was not sufficient to compensate the rotation and temperature loss such that both energy and momentum confinement times are significantly reduced. The edge localized mode behaviour is observed to be significantly affected by the increased neutral influx. A simple 1.5D fluid model has been used to qualitative capture the neutral transport response within the plasma, followed by a forward model of the passive charge-exchange (CX) emission of carbon to obtain a corrected radial neutral density profile. It has been found that the neutral density is sharply attenuated over the edge region, with similar edge magnitudes in both the non-fuelled (Γ0/ne ~ 1.2 m s−1) and maximum fuelled case (Γ0/ne ~ 2.5 m s−1). Discharges with reversed-B operation exhibited even higher normalized neutral fluxes related to first orbit effects and increased wall interactions. Over the full neutral influx range, a decrease in pedestal thermal Mach number from 0.25 to 0.14 was observed. Increased neutral penetration up to the pedestal top (r/a ~ 0.9) due to multiple CX interactions is obtained from the interpretive model. Under these multiple neutral–ion interactions, the impact on the CX loss of angular momentum is larger compared with the CX energy loss. The drag torque was seen to increase up to 10{\%} of the total applied torque, while energy losses appeared to be smaller. The accuracy of this global approach method is unfortunately limited; however, the estimated momentum sink was found comparable to the torque required to explain the discrepancy between observed global energy and momentum confinement.",
author = "Versloot, {T. W.} and {de Vries}, {P. C.} and C. Giroud and M. Brix and {von Hellermann}, {M. G.} and Lomas, {P. J.} and D. Moulton and M. O'Mullane and Nunes, {I. M.} and Antti Salmi and Tuomas Tala and I. Voitsekhovitch and K.-D. Zastrow and {JET-EFDA collaborators}",
year = "2011",
doi = "10.1088/0741-3335/53/6/065017",
language = "English",
volume = "53",
journal = "Plasma Physics and Controlled Fusion",
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Versloot, TW, de Vries, PC, Giroud, C, Brix, M, von Hellermann, MG, Lomas, PJ, Moulton, D, O'Mullane, M, Nunes, IM, Salmi, A, Tala, T, Voitsekhovitch, I, Zastrow, K-D & JET-EFDA collaborators 2011, 'Momentum losses by charge exchange with neutral particles in H-mode discharges at JET', Plasma Physics and Controlled Fusion, vol. 53, no. 6, 065017. https://doi.org/10.1088/0741-3335/53/6/065017

Momentum losses by charge exchange with neutral particles in H-mode discharges at JET. / Versloot, T. W. (Corresponding Author); de Vries, P. C.; Giroud, C.; Brix, M.; von Hellermann, M. G.; Lomas, P. J.; Moulton, D.; O'Mullane, M.; Nunes, I. M.; Salmi, Antti; Tala, Tuomas; Voitsekhovitch, I.; Zastrow, K.-D.; JET-EFDA collaborators.

In: Plasma Physics and Controlled Fusion, Vol. 53, No. 6, 065017, 2011.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Momentum losses by charge exchange with neutral particles in H-mode discharges at JET

AU - Versloot, T. W.

AU - de Vries, P. C.

AU - Giroud, C.

AU - Brix, M.

AU - von Hellermann, M. G.

AU - Lomas, P. J.

AU - Moulton, D.

AU - O'Mullane, M.

AU - Nunes, I. M.

AU - Salmi, Antti

AU - Tala, Tuomas

AU - Voitsekhovitch, I.

AU - Zastrow, K.-D.

AU - JET-EFDA collaborators

PY - 2011

Y1 - 2011

N2 - The effect of a neutral density background on the toroidal angular momentum and kinetic energy profiles has been investigated in JET. Under equivalent conditions but with increasing gas fuelling during the flat top phase, it has been observed that both the edge rotation and temperature decrease. The increase in electron density was not sufficient to compensate the rotation and temperature loss such that both energy and momentum confinement times are significantly reduced. The edge localized mode behaviour is observed to be significantly affected by the increased neutral influx. A simple 1.5D fluid model has been used to qualitative capture the neutral transport response within the plasma, followed by a forward model of the passive charge-exchange (CX) emission of carbon to obtain a corrected radial neutral density profile. It has been found that the neutral density is sharply attenuated over the edge region, with similar edge magnitudes in both the non-fuelled (Γ0/ne ~ 1.2 m s−1) and maximum fuelled case (Γ0/ne ~ 2.5 m s−1). Discharges with reversed-B operation exhibited even higher normalized neutral fluxes related to first orbit effects and increased wall interactions. Over the full neutral influx range, a decrease in pedestal thermal Mach number from 0.25 to 0.14 was observed. Increased neutral penetration up to the pedestal top (r/a ~ 0.9) due to multiple CX interactions is obtained from the interpretive model. Under these multiple neutral–ion interactions, the impact on the CX loss of angular momentum is larger compared with the CX energy loss. The drag torque was seen to increase up to 10% of the total applied torque, while energy losses appeared to be smaller. The accuracy of this global approach method is unfortunately limited; however, the estimated momentum sink was found comparable to the torque required to explain the discrepancy between observed global energy and momentum confinement.

AB - The effect of a neutral density background on the toroidal angular momentum and kinetic energy profiles has been investigated in JET. Under equivalent conditions but with increasing gas fuelling during the flat top phase, it has been observed that both the edge rotation and temperature decrease. The increase in electron density was not sufficient to compensate the rotation and temperature loss such that both energy and momentum confinement times are significantly reduced. The edge localized mode behaviour is observed to be significantly affected by the increased neutral influx. A simple 1.5D fluid model has been used to qualitative capture the neutral transport response within the plasma, followed by a forward model of the passive charge-exchange (CX) emission of carbon to obtain a corrected radial neutral density profile. It has been found that the neutral density is sharply attenuated over the edge region, with similar edge magnitudes in both the non-fuelled (Γ0/ne ~ 1.2 m s−1) and maximum fuelled case (Γ0/ne ~ 2.5 m s−1). Discharges with reversed-B operation exhibited even higher normalized neutral fluxes related to first orbit effects and increased wall interactions. Over the full neutral influx range, a decrease in pedestal thermal Mach number from 0.25 to 0.14 was observed. Increased neutral penetration up to the pedestal top (r/a ~ 0.9) due to multiple CX interactions is obtained from the interpretive model. Under these multiple neutral–ion interactions, the impact on the CX loss of angular momentum is larger compared with the CX energy loss. The drag torque was seen to increase up to 10% of the total applied torque, while energy losses appeared to be smaller. The accuracy of this global approach method is unfortunately limited; however, the estimated momentum sink was found comparable to the torque required to explain the discrepancy between observed global energy and momentum confinement.

U2 - 10.1088/0741-3335/53/6/065017

DO - 10.1088/0741-3335/53/6/065017

M3 - Article

VL - 53

JO - Plasma Physics and Controlled Fusion

JF - Plasma Physics and Controlled Fusion

SN - 0741-3335

IS - 6

M1 - 065017

ER -