# Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculations

## Abstract

Stiffness measurements are presented in the quasi-helically symmetric experiment (HSX), in which the neoclassical transport is comparable to that in a tokamak and turbulent transport dominates throughout the plasma. Electron cyclotron emission is used to measure the local electron temperature response to modulated electron cyclotron resonant heating. The amplitude and phase of the heat wave through the steep electron temperature gradient (ETG) region of the plasma are used to determine a transient electron thermal diffusivity that is close to the steady-state diffusivity. The low stiffness in the region between 0.2 ≤ r/a ≤ 0.4 agrees with the scaling of the steady-state heat flux with temperature gradient in this region. These experimental results are compared to gyrokinetic calculations in a flux-tube geometry using the gyrokinetic electromagnetic numerical experiment code with two kinetic species. Linear simulations show that the ETG mode may be experimentally relevant within r/a ≤ 0.2, while the Trapped Electron Mode (TEM) is the dominant long-wavelength microturbulence instability across most of the plasma. The TEM is primarily driven by the density gradient. Non-linear calculations of the saturated heat flux driven by the TEM and ETG bracket the experimental heat flux.

- Authors:

- HSX Plasma Laboratory, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States)

- Publication Date:

- OSTI Identifier:
- 22410387

- Resource Type:
- Journal Article

- Journal Name:
- Physics of Plasmas

- Additional Journal Information:
- Journal Volume: 22; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ECR HEATING; ELECTRON EMISSION; ELECTRON TEMPERATURE; FLEXIBILITY; HEAT FLUX; INSTABILITY; NEOCLASSICAL TRANSPORT THEORY; NONLINEAR PROBLEMS; PLASMA; PLASMA SIMULATION; STEADY-STATE CONDITIONS; SYMMETRY; TEMPERATURE GRADIENTS; THERMAL DIFFUSIVITY; TOKAMAK DEVICES; TRANSMISSION ELECTRON MICROSCOPY; TRAPPED ELECTRONS; WAVELENGTHS

### Citation Formats

```
Weir, G. M., Faber, B. J., Likin, K. M., Talmadge, J. N., Anderson, D. T., and Anderson, F. S. B.
```*Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculations*. United States: N. p., 2015.
Web. doi:10.1063/1.4921146.

```
Weir, G. M., Faber, B. J., Likin, K. M., Talmadge, J. N., Anderson, D. T., & Anderson, F. S. B.
```*Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculations*. United States. doi:10.1063/1.4921146.

```
Weir, G. M., Faber, B. J., Likin, K. M., Talmadge, J. N., Anderson, D. T., and Anderson, F. S. B. Fri .
"Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculations". United States. doi:10.1063/1.4921146.
```

```
@article{osti_22410387,
```

title = {Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculations},

author = {Weir, G. M. and Faber, B. J. and Likin, K. M. and Talmadge, J. N. and Anderson, D. T. and Anderson, F. S. B.},

abstractNote = {Stiffness measurements are presented in the quasi-helically symmetric experiment (HSX), in which the neoclassical transport is comparable to that in a tokamak and turbulent transport dominates throughout the plasma. Electron cyclotron emission is used to measure the local electron temperature response to modulated electron cyclotron resonant heating. The amplitude and phase of the heat wave through the steep electron temperature gradient (ETG) region of the plasma are used to determine a transient electron thermal diffusivity that is close to the steady-state diffusivity. The low stiffness in the region between 0.2 ≤ r/a ≤ 0.4 agrees with the scaling of the steady-state heat flux with temperature gradient in this region. These experimental results are compared to gyrokinetic calculations in a flux-tube geometry using the gyrokinetic electromagnetic numerical experiment code with two kinetic species. Linear simulations show that the ETG mode may be experimentally relevant within r/a ≤ 0.2, while the Trapped Electron Mode (TEM) is the dominant long-wavelength microturbulence instability across most of the plasma. The TEM is primarily driven by the density gradient. Non-linear calculations of the saturated heat flux driven by the TEM and ETG bracket the experimental heat flux.},

doi = {10.1063/1.4921146},

journal = {Physics of Plasmas},

issn = {1070-664X},

number = 5,

volume = 22,

place = {United States},

year = {2015},

month = {5}

}