# Compressional Alfvén eigenmodes in rotating spherical tokamak plasmas

## Abstract

Spherical tokamaks often have a considerable toroidal plasma rotation of several tens of kHz. Compressional Alfvén eigenmodes in such devices therefore experience a frequency shift, which if the plasma were rotating as a rigid body, would be a simple Doppler shift. However, since the rotation frequency depends on minor radius, the eigenmodes are affected in a more complicated way. The eigenmode solver CAE3B (Smith et al 2009 Plasma Phys. Control. Fusion 51 075001) has been extended to account for toroidal plasma rotation. The results show that the eigenfrequency shift due to rotation can be approximated by a rigid body rotation with a frequency computed from a spatial average of the real rotation profile weighted with the eigenmode amplitude. To investigate the effect of extending the computational domain to the vessel wall, a simplified eigenmode equation, yet retaining plasma rotation, is solved by a modified version of the CAE code used in Fredrickson et al (2013 Phys. Plasmas 20 042112). Lastly, both solving the full eigenmode equation, as in the CAE3B code, and placing the boundary at the vessel wall, as in the CAE code, significantly influences the calculated eigenfrequencies.

- Authors:

- Max-Planck-Inst. fur Plasmaphysik, Greifswald (Germany). Max-Planck/Princeton Center for Plasma Physics
- 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

- OSTI Identifier:
- 1368183

- Grant/Contract Number:
- AC02-09CH11466

- Resource Type:
- Journal Article: Accepted Manuscript

- Journal Name:
- Plasma Physics and Controlled Fusion

- Additional Journal Information:
- Journal Volume: 59; Journal Issue: 3; Journal ID: ISSN 0741-3335

- Publisher:
- IOP Science

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; spherical tokamak; compressional Alfven eigenmode; rotation

### Citation Formats

```
Smith, H. M., and Fredrickson, E. D.
```*Compressional Alfvén eigenmodes in rotating spherical tokamak plasmas*. United States: N. p., 2017.
Web. doi:10.1088/1361-6587/aa58fd.

```
Smith, H. M., & Fredrickson, E. D.
```*Compressional Alfvén eigenmodes in rotating spherical tokamak plasmas*. United States. doi:10.1088/1361-6587/aa58fd.

```
Smith, H. M., and Fredrickson, E. D. Tue .
"Compressional Alfvén eigenmodes in rotating spherical tokamak plasmas". United States.
doi:10.1088/1361-6587/aa58fd. https://www.osti.gov/servlets/purl/1368183.
```

```
@article{osti_1368183,
```

title = {Compressional Alfvén eigenmodes in rotating spherical tokamak plasmas},

author = {Smith, H. M. and Fredrickson, E. D.},

abstractNote = {Spherical tokamaks often have a considerable toroidal plasma rotation of several tens of kHz. Compressional Alfvén eigenmodes in such devices therefore experience a frequency shift, which if the plasma were rotating as a rigid body, would be a simple Doppler shift. However, since the rotation frequency depends on minor radius, the eigenmodes are affected in a more complicated way. The eigenmode solver CAE3B (Smith et al 2009 Plasma Phys. Control. Fusion 51 075001) has been extended to account for toroidal plasma rotation. The results show that the eigenfrequency shift due to rotation can be approximated by a rigid body rotation with a frequency computed from a spatial average of the real rotation profile weighted with the eigenmode amplitude. To investigate the effect of extending the computational domain to the vessel wall, a simplified eigenmode equation, yet retaining plasma rotation, is solved by a modified version of the CAE code used in Fredrickson et al (2013 Phys. Plasmas 20 042112). Lastly, both solving the full eigenmode equation, as in the CAE3B code, and placing the boundary at the vessel wall, as in the CAE code, significantly influences the calculated eigenfrequencies.},

doi = {10.1088/1361-6587/aa58fd},

journal = {Plasma Physics and Controlled Fusion},

number = 3,

volume = 59,

place = {United States},

year = {Tue Feb 07 00:00:00 EST 2017},

month = {Tue Feb 07 00:00:00 EST 2017}

}