## This content will become publicly available on May 20, 2020

# Tokamak parameter regimes with low toroidal momentum diffusivity

## Abstract

The strong, sharp flow structures that are seen frequently in tokamak cores, and large amplitude spontaneous global toroidal rotation are both surprising in light of current theories where toroidal flow evolution is dominantly diffusive. Mechanisms for spontaneously generating strong poloidal shear flows have been extensively investigated, but these processes were thought not to apply to toroidal flows. We confirm, however, that there is a regime with near-zero toroidal momentum diffusivity, where toroidal flow structures are spontaneously generated, as shown in earlier global gyrokinetic simulations. This allows strong rotation with negligible applied external torque, and the regime where this occurs is also favourable for strong turbulence stabilisation by rotation. In conclusion, the transition to low momentum diffusivity occurs for tight aspect ratio, low safety factor and at low levels of heat flux, in agreement with a simple zero-dimensional model for the flow–turbulence interaction.

- Authors:

- Univ. of Warwick, Coventry (United Kingdom)
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

- Publication Date:

- Research Org.:
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

- Sponsoring Org.:
- USDOE

- Contributing Org.:
- Partially supported by EPSRC grants EP/N035178/1 and EP/R034737/1

- OSTI Identifier:
- 1558751

- Grant/Contract Number:
- AC02-09CH11466

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Journal of Plasma Physics

- Additional Journal Information:
- Journal Volume: 85; Journal Issue: 3; Journal ID: ISSN 0022-3778

- Publisher:
- Cambridge University Press

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; fusion plasma; plasma confinement; plasma flows

### Citation Formats

```
McMillan, B. F., and Dominski, J. Tokamak parameter regimes with low toroidal momentum diffusivity. United States: N. p., 2019.
Web. doi:10.1017/S0022377819000333.
```

```
McMillan, B. F., & Dominski, J. Tokamak parameter regimes with low toroidal momentum diffusivity. United States. doi:10.1017/S0022377819000333.
```

```
McMillan, B. F., and Dominski, J. Mon .
"Tokamak parameter regimes with low toroidal momentum diffusivity". United States. doi:10.1017/S0022377819000333.
```

```
@article{osti_1558751,
```

title = {Tokamak parameter regimes with low toroidal momentum diffusivity},

author = {McMillan, B. F. and Dominski, J.},

abstractNote = {The strong, sharp flow structures that are seen frequently in tokamak cores, and large amplitude spontaneous global toroidal rotation are both surprising in light of current theories where toroidal flow evolution is dominantly diffusive. Mechanisms for spontaneously generating strong poloidal shear flows have been extensively investigated, but these processes were thought not to apply to toroidal flows. We confirm, however, that there is a regime with near-zero toroidal momentum diffusivity, where toroidal flow structures are spontaneously generated, as shown in earlier global gyrokinetic simulations. This allows strong rotation with negligible applied external torque, and the regime where this occurs is also favourable for strong turbulence stabilisation by rotation. In conclusion, the transition to low momentum diffusivity occurs for tight aspect ratio, low safety factor and at low levels of heat flux, in agreement with a simple zero-dimensional model for the flow–turbulence interaction.},

doi = {10.1017/S0022377819000333},

journal = {Journal of Plasma Physics},

number = 3,

volume = 85,

place = {United States},

year = {2019},

month = {5}

}

Works referenced in this record:

##
Mechanisms for generating toroidal rotation in tokamaks without external momentum input

journal, May 2010

- Solomon, W. M.; Burrell, K. H.; Garofalo, A. M.
- Physics of Plasmas, Vol. 17, Issue 5

##
Observation of Spontaneous Toroidal Rotation Inversion in Ohmically Heated Tokamak Plasmas

journal, December 2006

- Bortolon, A.; Duval, B. P.; Pochelon, A.
- Physical Review Letters, Vol. 97, Issue 23

##
Influence of the centrifugal force and parallel dynamics on the toroidal momentum transport due to small scale turbulence in a tokamak

journal, April 2009

- Peeters, A. G.; Strintzi, D.; Camenen, Y.
- Physics of Plasmas, Vol. 16, Issue 4

##
Turbulent transport of toroidal angular momentum in low flow gyrokinetics

journal, March 2010

- Parra, Felix I.; Catto, Peter J.
- Plasma Physics and Controlled Fusion, Vol. 52, Issue 4

##
Transport of Parallel Momentum Induced by Current-Symmetry Breaking in Toroidal Plasmas

journal, March 2009

- Camenen, Y.; Peeters, A. G.; Angioni, C.
- Physical Review Letters, Vol. 102, Issue 12

##
Anomalous momentum transport from drift wave turbulence

journal, November 1993

- Dominguez, R. R.; Staebler, G. M.
- Physics of Fluids B: Plasma Physics, Vol. 5, Issue 11

##
Simulating background shear flow in local gyrokinetic simulations

journal, March 2019

- McMillan, B. F.; Ball, J.; Brunner, S.
- Plasma Physics and Controlled Fusion, Vol. 61, Issue 5

##
Nonlinear gyrokinetic turbulence simulations of E×B shear quenching of transport

journal, June 2005

- Kinsey, J. E.; Waltz, R. E.; Candy, J.
- Physics of Plasmas, Vol. 12, Issue 6

##
The toroidal momentum diffusivity in a tokamak plasma: A comparison of fluid and kinetic calculations

journal, January 2008

- Strintzi, D.; Peeters, A. G.; Weiland, J.
- Physics of Plasmas, Vol. 15, Issue 4

##
Field‐aligned coordinates for nonlinear simulations of tokamak turbulence

journal, August 1995

- Beer, M. A.; Cowley, S. C.; Hammett, G. W.
- Physics of Plasmas, Vol. 2, Issue 7

##
Residual parallel Reynolds stress due to turbulence intensity gradient in tokamak plasmas

journal, November 2010

- Gürcan, Ö. D.; Diamond, P. H.; Hennequin, P.
- Physics of Plasmas, Vol. 17, Issue 11

##
Dependence of intrinsic rotation reversals on collisionality in MAST

journal, February 2015

- Hillesheim, J. C.; Parra, F. I.; Barnes, M.
- Nuclear Fusion, Vol. 55, Issue 3

##
Spontaneous toroidal flow generation due to negative effective momentum diffusivity

journal, February 2015

- McMillan, Ben F.
- Physics of Plasmas, Vol. 22, Issue 2

##
Jets

journal, June 1994

- Rhines, Peter B.
- Chaos: An Interdisciplinary Journal of Nonlinear Science, Vol. 4, Issue 2

##
Global gyrokinetic simulations of intrinsic rotation in ASDEX Upgrade Ohmic L-mode plasmas

journal, March 2018

- Hornsby, W. A.; Angioni, C.; Lu, Z. X.
- Nuclear Fusion, Vol. 58, Issue 5

##
Intrinsic momentum transport in up–down asymmetric tokamaks

journal, July 2014

- Ball, Justin; Parra, Felix I.; Barnes, Michael
- Plasma Physics and Controlled Fusion, Vol. 56, Issue 9

##
Anomalous parallel momentum transport due to E×B flow shear in a tokamak plasma

journal, September 2009

- Casson, F. J.; Peeters, A. G.; Camenen, Y.
- Physics of Plasmas, Vol. 16, Issue 9

##
Accuracy of momentum transport calculations in full- *f* gyrokinetic simulations

journal, January 2012

- Idomura, Yasuhiro
- Computational Science & Discovery, Vol. 5, Issue 1

##
The nonlinear gyro-kinetic flux tube code GKW

journal, December 2009

- Peeters, A. G.; Camenen, Y.; Casson, F. J.
- Computer Physics Communications, Vol. 180, Issue 12

##
Spectral treatment of gyrokinetic shear flow

journal, March 2018

- Candy, J.; Belli, E. A.
- Journal of Computational Physics, Vol. 356

##
Experimental observations and modelling of intrinsic rotation reversals in tokamaks

journal, January 2017

- Camenen, Y.; Angioni, C.; Bortolon, A.
- Plasma Physics and Controlled Fusion, Vol. 59, Issue 3

##
Up-down symmetry of the turbulent transport of toroidal angular momentum in tokamaks

journal, June 2011

- Parra, Felix I.; Barnes, Michael; Peeters, Arthur G.
- Physics of Plasmas, Vol. 18, Issue 6

##
Core intrinsic rotation behaviour in ASDEX Upgrade ohmic L-mode plasmas

journal, March 2014

- McDermott, R. M.; Angioni, C.; Conway, G. D.
- Nuclear Fusion, Vol. 54, Issue 4