DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
Login | Review | Submit | Logout | Help
Questions about this website? Contact Andrew LeBlanc Questions about ROF? Contact Chuck Greenfield
| Title | 121: Reliable, flexible formation of 100% noninductive discharges | ||
| Name: | John Ferron ( |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation | Presentation time: | Not requested | Co-Author(s): | -- |
| Description: | Improve the startup of steady-state scenario discharges by implementing: 1) routine use of feedback control of the q evolution, 2) counter-injection beams and gyrotrons as the heat sources, 3) avoidance of tearing modes probably using ECCD for preemptive stabilization, and 4) access to higher q_min made possible by startup at higher betaN with preemptive NTM stabilization. | ||
| Experimental Approach/Plan: | 1) Start using the feedback control of q routinely during experiments with steady-state scenario discharges. Use this control to specify the target q_min value at the start of the high-performance phase and enable the timing of the high-performance phase and corresponding q_min value to be varied independently. Also use the q_min control to enable experiments with the target q_min >2. 2) Develop the capability to use counter beams and gyrotrons as the heat source during the discharge formation without the appearance of tearing modes or mode locking. This will require a robust method to avoid tearing modes. A possibility is to use the gyrotrons for ECCD stabilization of NTMs. The maximum gyrotron power could be applied for preemptive stabilization. Then, the necessary amount of counter beam power to maintain the desired q evolution would be added by the PCS. As the tearing modes are typically observed at rather low beta, they may be classical tearing rather than neoclassical tearing. In this case, a different approach to stabilization will be required. Either way, as tearing modes are observed on a large fraction of the discharges, it is important to find a way to avoid them. It may be necessary to dedicate the gyrotrons to use during the discharge formation in order to do this development. However, in the future when real-time steerable mirrors are installed, gyrotrons can be used for one purpose at the beginning of the shot and another purpose during the high-performance phase. Also, it may be possible to design the gyrotron aiming in combination with an evolution of the toroidal field or major radius that makes a particular fixed gyrotron aiming compatible with the needs during both the beginning of the discharge and the high-performance phase. 3) Access higher values of q_min at the start of the high-performance phase by using preemptive NTM stabilization to allow relatively high betaN values during the discharge formation. In order to maintain the q_min at high values, relatively high electron temperatures are required leading to higher beta because of the correspondingly higher input power. 4) Try varying the plasma current ramp rate to test whether improvements in q control and tearing mode avoidance are possible. | ||
| Background: | During 2004-2007 techniques for feedback control of the q evolution during discharge formation were developed. This capability is now ready for routine use and will improve capability to reliably specify the q profile at the start of the high-performance phase and will improve flexibility to vary this target q profile from shot to shot. Difficulties with the startup of steady-state scenario discharges remain, however. Tearing modes often appear, even at relatively low beta. Also, there is a need to avoid use of the co-injection beams for discharge formation in order to conserve their energy injection capability to maximize beta and pulse length in the high-performance phase. This means using the counter beams and the gyrotrons to provide the necessary electron heating during discharge formation. Initial tests using the counter beams indicated that tearing modes are more likely to occur. | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
Print this page