DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 418: Does the Pedestasl spin the plasma? | ||
| Name: | Francis Perkins ( |
Affiliation: | University of Colorado |
| Research Area: | Rotation Physics | Presentation time: | Not requested | Co-Author(s): | -- |
| Description: | http://web.gat.com/diii-d_global/rof08/submit.php#http://web.gat.com/diii-d_global/rof08/submit.php# | ||
| Experimental Approach/Plan: | Measure trapped ions with large toroidal precession. | ||
| Background: | Remarks on Rotation.
As is the case for n, T, the pedestal region sets the boundary condition for angular momentum transport. This takes the form of a prescribed value for the pedestal angular rotation frequency. What physics determines this angular rotation frequency? The MHD answer is zero -- all open field lines are line-tied to the vessel. Alcator C-Mod Ohmic-H data support a model in which angular momentum is created in the pedestal and diffuses inward. The boundary condition for angular momentum transport must be determined by pedestal physics. What physics can apply torque to the pedestal? One possible scenario involves the potential determined by electron sheaths on open field lines just outside the separatrix. This sheath potential is several electron temperature. Alcator C-Mod observes very high temperature gradient just outside the separatrix, which implies a large radial electric field and a very high toroidal precession frequency for trapped ions. Collisions between trapped and passing ions would provide the friction to transfer momentum to the bulk plasma and create Ware pinches. Note that this model uses trapped particles and would not be found by a fluid model code. It also suggests that divertor biasing could be used to insert angular momentum into a plasma. Experimentally, it would be interesting to distiguish trapped vs passng particles. It strikes me that a common scenario for the pedestal, including direct ion-orbit loss, would serve your Rotaion, ELM Pedestal, Thermal Transport efforts well. | ||
| Resource Requirements: | Diagnostic capability to measre trapped ions | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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