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Darin Ernst. Zeller, Kyle M. (Kyle Montgomery) Massachusetts Institute of Technology. Dept. of Nuclear Science and Engineering. Massachusetts Institute of Technology. Department of Nuclear Science and Engineering 2008-05-19T15:58:07Z 2008-05-19T15:58:07Z 2006 http://hdl.handle.net/1721.1/41592 213497083 Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006. "June 2006." Includes bibliographical references (p. 44). 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. by Kyle M. Zeller. S.B. 47 p. eng Massachusetts Institute of Technology 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. http://dspace.mit.edu/handle/1721.1/7582 Nuclear Science and Engineering. Gyrokinetic simulations of the nonlinear upshift of the critical density gradient for TEM turbulence in tokamak fusion plasmas Thesis application/pdf Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="f0662fc9-dd58-43b1-8e87-4aae87fd6661"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Gyrokinetic simulations of the nonlinear upshift of the critical density gradient for TEM turbulence in tokamak fusion plasmas</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2006</PublicationDate> <Authors> <Author> <DisplayName>Zeller, Kyle M. (Kyle Montgomery)</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Nuclear Science and Engineering.</Keyword> <Abstract>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.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>