SIMULATION OF MULTIPARAMETRIC CONTROL OF BURNING PLASMA

1. SIMULATION OF MULTIPARAMETRIC CONTROL OF BURNING PLASMA

2. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) Feedback control of plasma parameters in a reactor-tokamak is in principle a multiparametric task Big set of parameters for control Different parameters require for theirs control contradictive conditions in the same time -- Acceptable divertor heat loads require high Ar concentration what contradict with good CD efficiency and high Pfus -- PCD changes not only JCD(r) but changes Pfus(r) and plasma pressure too -- Decrease ne increase CD efficiency but decrease Pfus and increase divertor plates heat loads... and so on ... Different characteristic time scales for different parameters Equilibrium ~ a fraction of a sec Transport ~ some sec Current profile change ~ some hundred sec

3. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov)  Different possible ways to control the same parameter Pfus can be controlled by change of ne, Paux, Ar concentration and He pumping speed ( all these parameters can change it ) Nonlinear interaction between different feedback loops transport Change J(r) ne(r), T(r) CD efficiency Task of plasma parameters control requires multiparametric optimization and special algorithms. This task is facilitates because of plasma selforganization which decreases first perturbations.

4. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov)  plasma selforganization decreases first perturbations 2 time scales connected with transport and J(r) profile reorganization

5. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) Time of j(r) profile reorganization for ITER ~ 3000 s Evolution of plasma parameters for WNS-like scenario after sudden switch-on Paux and increase of <ne>.

6. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) Evolution of plasma parameters in reference ITER discharge • Δtflat-top~ 400-600s • Δtstart-up ~ 100s • ΔtJ(r)reorganization~3000s • difficulties for • J(r) changes • J(r) profile once • achieved can exist • some hundred sec • without Paux

7. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) Radial profiles for t = 40s of ITER WNS scenario

8. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) t = 70 s (start of high-Q operation) t = 250 s (end of high-Q operation) High-Q operational scenario (Paux=0) Possibility for control without Paux Q=Pfus / Paux Pfus feedback control by ne (Paux=0) ne feedback control by fuelling Ploss feedback control by Ar seeding

9. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) Time response of plasma parameters and control capability on the 30% reduction in the thermalized He pumping speed ___without control ___ with control Control of ne by fuelling Control of Pfus by PNBI PNBI(t+dt)= PNBI(t) + k.[1-(Pfus(t)/PfusSS] Control of SS conditions (Uloop= 0) by PRF PRF(t+dt) = PRF(t) + k.Uloop(t) dt = 0.02s  Elimination of ne and Pfus perturbations  Essential decrease of Uloop perturbation

10. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) Influence of feedback control at 0.7% increase of Carbon density with control without control

11. ITPA Joint Meeting on Control, 14July 2003, St.Petersburg. (V. Leonov) CONCLUSIONS  Feedback control of plasma parameters in a reactor-tokamak is amultiparametrictask. It is important to develop algorithms of such control and test them on the up-to-date experiments. One must takes into accounta nonlinear interaction between different feedback loops.  Plasma selforganization decreases first perturbations and facilitates task of the plasma parameters control.  Long time of j(r) profile reorganizationfor ITER (~ 3000s) makes difficult of this profile changes.  Simulations showpossibility to control of the main plasma parametersin the burning experiment and essentially decrease of possible perturbations by using the simplest proportional feedback systems.