Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D

E. M. Hollmann; A. Bortolon; F. Effenberg; N. Eidietis; D. Shiraki; I. Bykov; B. E. Chapman; J. Chen; S. Haskey; J. Herfindal; A. Lvovskiy; C. Marini; A. McLean; T. O'Gorman; M. D. Pandya; C. Paz-Soldan; Popović

doi:10.1063/5.0080385

Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D

E. M. Hollmann, A. Bortolon, F. Effenberg, N. Eidietis, D. Shiraki, I. Bykov, B. E. Chapman, J. Chen, S. Haskey, J. Herfindal, A. Lvovskiy, C. Marini, A. McLean, T. O'Gorman, M. D. Pandya, C. Paz-Soldan, Popović

Advanced Tokamak Physics

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Abstract

The first dynamic (time-dependent) measurements of impurity ion radial (cross field) and parallel (along-field) diffusion coefficients for post-disruption runaway electron plateaus are presented. Small (∼1 mm diameter) carbon or silicon pellets are fired into the edge of steady-state runaway electron (RE) plateaus, and the resulting radial and toroidal transport of singly charged impurity ions (C+ or Si+) is monitored with spatially distributed visible spectrometers. Consistent with previous steady-state particle balance estimates of Ar+ radial transport, radial (cross field) diffusion coefficients D⊥ ≈ 2-5 m2/s are obtained, about 10 × larger than expected from neo-classical theory. Parallel diffusion coefficients D∥ ≈ 30-80 m2/s are estimated, also much (≈ 50 ×) larger than classical. It is speculated at present that these large diffusion coefficients may be due to turbulent transport. Indications of fairly significant (almost 2 ×) toroidal variation in electron density are seen in the RE plateaus, and this appears to cause some toroidal variation in impurity radial diffusion rates. Indications of slow (≈1 Hz) toroidal rotation in the impurity ions are observed, although the uncertainty in this measurement is large.

Original language	English
Article number	022503
Journal	Physics of Plasmas
Volume	29
Issue number	2
DOIs	https://doi.org/10.1063/5.0080385
State	Published - Feb 1 2022

Funding

This work was supported in part by the U.S. Department of Energy under Contract Nos. DE-FG02-07ER54917, DE-FC02-04ER54698, DE-AC02-09CH11466, DE-AC05-00OR22725, DE-AC52-07NA27344, DE-FG02-04ER54744, and DE-AC05-06OR23100. The technical support of L. Chousal, J. Kulchar, and D. Ayala is gratefully acknowledged, as is diagnostic support of M. Austin, C. Chrystal, C. Lasnier, A. Moser, and M. Van Zeeland. Permission to use PrismSPECT from I. Golovkin is gratefully acknowledged.

Funders	Funder number
U.S. Department of Energy	DE-AC05-00OR22725, DE-AC02-09CH11466, DE-FC02-04ER54698, DE-FG02-04ER54744, DE-AC52-07NA27344, DE-FG02-07ER54917, DE-AC05-06OR23100

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10.1063/5.0080385

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Hollmann, E. M., Bortolon, A., Effenberg, F., Eidietis, N., Shiraki, D., Bykov, I., Chapman, B. E., Chen, J., Haskey, S., Herfindal, J., Lvovskiy, A., Marini, C., McLean, A., O'Gorman, T., Pandya, M. D., Paz-Soldan, C., & Popović (2022). Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D. Physics of Plasmas, 29(2), Article 022503. https://doi.org/10.1063/5.0080385

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title = "Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D",

abstract = "The first dynamic (time-dependent) measurements of impurity ion radial (cross field) and parallel (along-field) diffusion coefficients for post-disruption runaway electron plateaus are presented. Small (∼1 mm diameter) carbon or silicon pellets are fired into the edge of steady-state runaway electron (RE) plateaus, and the resulting radial and toroidal transport of singly charged impurity ions (C+ or Si+) is monitored with spatially distributed visible spectrometers. Consistent with previous steady-state particle balance estimates of Ar+ radial transport, radial (cross field) diffusion coefficients D⊥ ≈ 2-5 m2/s are obtained, about 10 × larger than expected from neo-classical theory. Parallel diffusion coefficients D∥ ≈ 30-80 m2/s are estimated, also much (≈ 50 ×) larger than classical. It is speculated at present that these large diffusion coefficients may be due to turbulent transport. Indications of fairly significant (almost 2 ×) toroidal variation in electron density are seen in the RE plateaus, and this appears to cause some toroidal variation in impurity radial diffusion rates. Indications of slow (≈1 Hz) toroidal rotation in the impurity ions are observed, although the uncertainty in this measurement is large.",

author = "Hollmann, {E. M.} and A. Bortolon and F. Effenberg and N. Eidietis and D. Shiraki and I. Bykov and Chapman, {B. E.} and J. Chen and S. Haskey and J. Herfindal and A. Lvovskiy and C. Marini and A. McLean and T. O'Gorman and Pandya, {M. D.} and C. Paz-Soldan and Popovi{\'c}",

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doi = "10.1063/5.0080385",

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Hollmann, EM, Bortolon, A, Effenberg, F, Eidietis, N, Shiraki, D, Bykov, I, Chapman, BE, Chen, J, Haskey, S, Herfindal, J, Lvovskiy, A, Marini, C, McLean, A, O'Gorman, T, Pandya, MD, Paz-Soldan, C & Popović 2022, 'Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D', Physics of Plasmas, vol. 29, no. 2, 022503. https://doi.org/10.1063/5.0080385

TY - JOUR

T1 - Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D

AU - Hollmann, E. M.

AU - Bortolon, A.

AU - Effenberg, F.

AU - Eidietis, N.

AU - Shiraki, D.

AU - Bykov, I.

AU - Chapman, B. E.

AU - Chen, J.

AU - Haskey, S.

AU - Herfindal, J.

AU - Lvovskiy, A.

AU - Marini, C.

AU - McLean, A.

AU - O'Gorman, T.

AU - Pandya, M. D.

AU - Paz-Soldan, C.

AU - Popović,

PY - 2022/2/1

Y1 - 2022/2/1

N2 - The first dynamic (time-dependent) measurements of impurity ion radial (cross field) and parallel (along-field) diffusion coefficients for post-disruption runaway electron plateaus are presented. Small (∼1 mm diameter) carbon or silicon pellets are fired into the edge of steady-state runaway electron (RE) plateaus, and the resulting radial and toroidal transport of singly charged impurity ions (C+ or Si+) is monitored with spatially distributed visible spectrometers. Consistent with previous steady-state particle balance estimates of Ar+ radial transport, radial (cross field) diffusion coefficients D⊥ ≈ 2-5 m2/s are obtained, about 10 × larger than expected from neo-classical theory. Parallel diffusion coefficients D∥ ≈ 30-80 m2/s are estimated, also much (≈ 50 ×) larger than classical. It is speculated at present that these large diffusion coefficients may be due to turbulent transport. Indications of fairly significant (almost 2 ×) toroidal variation in electron density are seen in the RE plateaus, and this appears to cause some toroidal variation in impurity radial diffusion rates. Indications of slow (≈1 Hz) toroidal rotation in the impurity ions are observed, although the uncertainty in this measurement is large.

AB - The first dynamic (time-dependent) measurements of impurity ion radial (cross field) and parallel (along-field) diffusion coefficients for post-disruption runaway electron plateaus are presented. Small (∼1 mm diameter) carbon or silicon pellets are fired into the edge of steady-state runaway electron (RE) plateaus, and the resulting radial and toroidal transport of singly charged impurity ions (C+ or Si+) is monitored with spatially distributed visible spectrometers. Consistent with previous steady-state particle balance estimates of Ar+ radial transport, radial (cross field) diffusion coefficients D⊥ ≈ 2-5 m2/s are obtained, about 10 × larger than expected from neo-classical theory. Parallel diffusion coefficients D∥ ≈ 30-80 m2/s are estimated, also much (≈ 50 ×) larger than classical. It is speculated at present that these large diffusion coefficients may be due to turbulent transport. Indications of fairly significant (almost 2 ×) toroidal variation in electron density are seen in the RE plateaus, and this appears to cause some toroidal variation in impurity radial diffusion rates. Indications of slow (≈1 Hz) toroidal rotation in the impurity ions are observed, although the uncertainty in this measurement is large.

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U2 - 10.1063/5.0080385

DO - 10.1063/5.0080385

M3 - Article

AN - SCOPUS:85124691718

SN - 1070-664X

VL - 29

JO - Physics of Plasmas

JF - Physics of Plasmas

IS - 2

M1 - 022503

ER -

Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D

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