MODELLING OF TIME DEPENDENT HIGH Q OPERATIONAL SCENARIO FOR ITER-LIKE DEVICE.

1. MODELLING OF TIME DEPENDENT HIGH Q OPERATIONAL SCENARIO FOR ITER-LIKE DEVICE.

2. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE Motivation  One of the ITER goals is “to explore the possibility of high-Q operation if favourable confinement conditions can be achieved”.  High-Q operation is interesting for investigations of burning stability, control of plasma parameters and burning conditions by different feedback loops at the small Paux  0.

3. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE Issues  Analysis of ITER operational diagrams show that for high Q (Paux 0) operation it is desirable to have: --- plasma current higher than 15MA (q<3) (MHD stability-?) --- enhanced density (close to the Greenwald limit) (E (n) - ?) --- enhanced confinement (RS regimes with ITB) (Paux = 0 -?).  The subject of this work is to investigate the possibility of ITER operation in enhanced confinement regime with ITB at Paux = 0 during the time ~ some hundreds sec ( >> E ). (to test burning dynamics and possibility to control performance and plasma parameters in regimes with Paux= 0 ).

4. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE  Simulations show that RS configuration can’t be achieved by bootstrap current only and some auxiliary off-axis CD (or Paux) is necessary. It does difficult to achieve high Q values but ... ... the main idea:  To use very long skin time (~ 3000s) which >> E (~ some s). If the RS configuration is once achieved on the initial stage of the discharge the operation in this configuration with the enhanced confinement can be then continued for some hundred sec during j(r) profile reorganization at Paux = 0.

5. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE Example of simulation of plasma parameters evolution for WNS-like scenario after switch on Paux and <ne>.  Time of j(r) profile reorganization ~ 3000 s (see also D.Moreau, I. Voytsekhovitch Nucl. Fus.V.39 (1999), 685)

6. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE We use other strategy including a simultaneous ramp-up of the plasma current in accordance with the plasma minor radius and plasma density increase which gives possibility to decrease time of j(r) profile formation to some tens sec (in our case ~ 50 s). (In this case profile forms layer after layer) In D.Moreau, I. Voytsekhovitch paper (Nucl. Fus.V.39 (1999), 685) strategy of the initial stage of the discharge (which consists of some stages) with the total time duration ~ some thousand sec is suggested. This strategy for discharges with a plasma current flat-top ~ some hundred sec (as in our case) is not effective. J(r) 0 0.5 1 rmax

7. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE The model : 1.5D ASTRA transport code: 2D equilibrium + 1D transport ci,e =ci,e,of(r). Fi, e (S) + ci,eneo, D = Dof(r).Fe(S)cio = ceo = Deo f(r) = 1 + 3.r2 - radial dependence, DHe= ce , Vp= Vp He= 0 Fi, e (S) = exp{4. (S-1)}/(1 + exp{4. (S-1)}) , S = r .(q`/ q) ceo is fitted to provide tE=tEscaling (OH, L or H-98(y2)) Boundary conditions: on the basis of B2-Eirine results approximation: (Ts/1eV)3/2ns/1019m-3=90 Ploss/1MW Thermalized Helium pumping speed: to produce t*He/tE = 5. Impurity: in the coronal approximation Mean plasma density : is controlled by the gas puff in the kinetic approach. H & CD: NBI, ECR, LH

8. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE High-Q operational scenario with RS configuration Pfus feedback control by ne (Paux=0) ne feedback control by fuelling Ploss feedback control by Ar seeding

9. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE t = 70 s (start of high-Q operation) t = 250 s (end of high-Q operation) Radial profiles during high-Q operation

10. 3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache. V. Leonov: Modelling of High-Q Scenario RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»NUCLEAR FUSION INSTITUTE CONCLUSIONS Operational strategy including j(r) profile formation layer after layer by ramp-up of the plasma current simultaneously and in accordance with the increase of plasma minor radius gives possibility to decrease time of j(r) profile formation to some tens sec.  Long time scale of j(r) profile reorganization gives possibility after the achieving of RS configuration to work in this configuration some hundreds sec with enhanced confinementatvery high Q (Paux= 0). Simulations demonstrates possibility to control fusion power, plasma density, power losses to the divertor and some other parametersby feedback loops in high-Q regime at Paux = 0.