Corsica free-boundary scenario and controller studies for ITER

1. Corsica free-boundary scenario and controller studies for ITER L. L. LoDestro, T. A. Casper, W. H. Meyer, and L. D. Pearlstein 12th ITPA Confinement Database and Modelling Topical Group Meeting EPFL, Lausanne May 7--10, 2007 Ackn: A. Portone, EFDA-CSU Barcelona Work supported by the U.S. DOE Contract W-7405-48.

2. Recent Corsica ITER modelling is focussed on free-boundary predictive simulation: ITER scenarios: Assess VS consumption, PF-coil currents, strike- point locations. Verify the equilibria pass through the fiducial shapes. Test the plasma shape-and-position controller. We are developing code capability. Physics results here are illustrative.

3. Outline • Start-up simulations for ITER and DIII-D • ITER scenario studies • ITER controller studies • Corsica and Corsica/Simulink • Summary/Conclusions

4. EFIT01 shapes Corsica computed Ip equilibria ITER start-up experiments at DIII-D will be used for code validation • EFIT boundaries at selected times provide “fiducial” shapes • Corsica evolves internal flux/current densities using N,T measurements

5. sawteeth sawteeth Corsica is also being used to design and model the DIII-D experiments simulating ITER Ip Ip DIII-D ITER • DD 1st day of expt’s. Without trying very hard, q0 & li come close. Ref. 2 with faster Ip ramp. L-mode . More expt.’s to follow. q0 li

6. Simulations of ITER scenarios (following) employ a special free-boundary technique Prescribed shape scenario technique: • Developed for Snowmass • Plasma boundary is linearly interpolated between fiducials • Coil currents and Volt-seconds (VS) are backed out • Result is similar to that with a perfect controller Faster and simpler than using a controller.

7. Simulation of ITER reference scenario 2 finds PF-coil currents and VS are within limits • Simulation includes neo, neo, GLF23, analytic Paux,  heating & diffusion. • n is prescribed.

8. Ref. 2 simulation indicates JBS has a significant impact on the plasma boundary (preliminary result). With JBS Without JBS • Divertor strike-points were not prescribed here. When they are prescribed along with the boundary and JBS is included, the plasma shape can not be held “close” to the fiducials---suggesting control might be problematic. • Note increased range of divertor strike-points and limiter point with JBS.

9. ITER reference scenario 2, no JBS, cont. • Simulation includes coil ramp-down through return of VS.

10. Two implementations for simulating control with Corsica • Corsica solves circuit equations • Can run with implicit time-step  speed • Corsica is coupled to Mathworks Matlab/Simulink ($$$) • Circuit eqn’s solved by Simulink -- state-space controllers, explicit • Modular • Rapid installation of new controllers • Entire coil description can reside outside the 1&1/2D code • Corsica can serve as the plasma model in D. Humphrey’s (GA) PCS, continue collaboration on devel. of Simulink environment. • Can split the control: fast (VS) with Corsica, slow (shape) with Simulink

11. Corsica on beowulf cluster MDSPlus server mdsip Xwindows and jScope Rpc & mdsip X Matlab node Corisca/Simulink simulation is distributed over network

12. We have successfully controlled VDEs & MD1,2 in Corsica/Simulink with the JCT Feb 2001 controller • Ohm’s law transport only. • Inputs to controller: Vertical Stability: d ZCS/dt Shape: gaps, Ip, IPFC • Outputs: VS: voltage to PFC2--5 Shape: CS and PF voltages • Delays, etc., included Tested 0 ok (nec for implicit) • Linear plasma model tests were successful

13. Corsica – JCT/Feb 2001 controller during Vertical Displacement Event

14. Corsica models the large-scale plasma disturbances Minor Disruptions: MD1 Instantaneous li drop of 0.2(li -0.5) and p drop of 0.2p followed by a 3s exponential recovery. MD2 Instantaneous p drop of 0.2p followed by a 3s exponential recovery. Corsica p drop Prescribed p drop Corsica lidrop

15. Corsica – JCT/Feb 2001 Controller during MD1 Graphics produced with MDSPlus jScope

16. Corsica – JCT/Feb 2001 Controller during MD2 Graphics produced with MDSPlus jScope

17. Controlled simulations with Te,i transport are being carried out with Corsica performing the control • Capability was developed for original ITER-EDA • Exercised with Ohm’s law only • ITER-FEAT results agree with Corsica/Simulink • Here we include JBS. Other transport and sources as before. • Plasma bulges toward the upper x-point.

18. Summary and conclusions • Physics conclusions: • Reasonable VS & PF currents found for ITER reference scenario 2 (Ohm’s law + Te,i transport). • Large edge bootstrap current is an issue • affects shape & divertor strike-points • The ITER-FEAT controller successfully controls 1cm VDE’s and MD1, MD2 minor disruptions • tested with Ohm’s law only, without large edge JBS • Location of upper control point cf. upper X-point with large edge JBS is an issue

19. Summary and conclusions, cont. • Code status: • Two types of predictive free-boundary simulation are available: backing out PF currents (ready); and solving circuit equations with controllers. • Two environments for plasma control simulations are available (same physics): Corsica/Simulink code-coupling; or all Corsica. • Ohm’s law: working well. • Ohm’s law plus Te,i transport: minor warts. • Not in this talk: alternative start-up and performance scenario simulation; profile control; synthetic diagnostics.