Gyrokinetic simulations of the nonlinear upshift of the critical density gradient for TEM turbulence in tokamak fusion plasmas

The effect of collisionality on a new nonlinear upshift of the critical density gradient for onset of Trapped Electron Mode (TEM) turbulence is investigated in detail. Both linear and nonlinear, high resolution simulations were performed on massively parallel computers using the gyrokinetic code, GS2. The TEM nonlinear upshift is analogous to the Dimits Shift for ion temperature gradient driven (ITG) turbulence, but exists in the density gradient as opposed to the temperature gradient. In the ITG case, increasing ion-ion collisions damp the zonal flows but have little effect on the linear growth rate. In contrast, electron-ion collisions strongly damp the TEM growth rate, while ion-ion collisions weakly damp zonal flows, causing an increase in the TEM upshift. Numerous simulations were run, scanning different density gradients to determine the critical density gradients for each collisionality and to examine the upshift caused by increasing collisionality. The linear critical density gradient was not significantly affected by collisionality, while both critical density gradients were determined to be larger for the nonlinear runs.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Nuclear Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Zeller, Kyle M. (Kyle Montgomery)

Advisor dc:contributor.advisor

• Darin Ernst.

• Nuclear Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/41592

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/41592