ITER STEADY-STATE OPERATIONAL SCENARIOS A.R. Polevoi for ITER IT and HT contributors ITER-SS 1

OUTLINE: (1)Definitions (2)Basis for choice of operational parameters (3)Transport simulations for ITER (4)Types of SS scenarios proposed for ITER SS Type-I:NB + LH CD SS Type-II:NB + EC CD (5)Discussion on physics needs Projection of experimental scenarios to ITER Experimental demonstration of feasibility

DEFINITIONS Steady State scenario = scenario with full noninductive current drive ITER Hybrid reference scenario = scenario with partial noninductive current drive with Q > 5 and duration of the current flat top  t > 1000 s ITER Steady State reference scenario = scenario with full noninductive current drive with Q > 5 and duration of the current flat top  t > 3000 s

BASIS FOR CHOICE OF OPERATIONAL PARAMETERS (2.1) CD systems for ITER are defined P CD,ITER : NB33 MW 2 NBIs with 1 MeV D EC20 MW 170 GHz LH40 MW ( ) 5 GHz (2.2)For ITER divertor configuration and pumping system power flux to SOL should be limited P sep < P max,ITER ( ~ 100 MW) (for more accurate parametric dependence see ITER PDD)

BASIS FOR CHOICE OF OPERATIONAL PARAMETERS (2.3)Plasma contamination by He can be relatively small   */  e < 2 [1] for ITER reference inductive scenario (2.4) Codes for CD simulation are benchmarked vs some experiments and can be used for CD predictions (2.5) Transport model for SS and hybrid operation in present day experiments is not identified yet [1] Kukushkin et al NF 43 (2003) 716

TRANSPORT SIMULATIONS FOR ITER (3.1) To find the requirements for transport HH y,2 = ? which provide SS operation 100% Noninductive CD with the ITER CD tools and P fus /P CD = Q > 5;P CD < P CD,ITER (3.2)To study whether such operation can be stable against NTMs, ballooning, MHD modes, RWMs:  N <  ITER-wall (3.3)To use He pumping and recycling consistent with SOL/divertor simulations with B2/Eirene (3.4)To study whether such operation is compatible with ITER divertor loads: P sep < P max,ITER ~ 100 MW (3.5)Taking account of density limit

TYPES OF SS SCENARIOS PROPOSED FOR ITER SS TYPE-I GOAL: q min > 2 RS to avoid NTMs TOOLS: NB CD + edge LH CD ~50% I bs / ~ 50% I CD (+):Moderate requirements for confinement HH y,2 = (-):Low li3 ~ 0.6 =>  N close to  ITER-wall => narrow operational space with pressure peaking p(0)/ SS TYPE-II GOAL: q min > 1 WS to avoid ST high li3 to increase stability TOOLS:NB CD + EC CD ~50% I bs / ~ 50% I CD (+):High li3 ~ 0.9 => stable n = 1 (-):Higher HH y,2 = is required -NTM stability ? -n = 2, 3 stability ?

SS TYPE-I:q min > 2 RS, NB+LH CD Suggested transport:Ion neoclassical at the edge pedestal and RS areas, D =  e =  i

FEASIBILITY OF TYPE-I SCENARIO (-) low inductance li3 ~ 0.6 => low no wall limit  N < 2.5 STABLE OPERATIONAL SPACE SHRINKS WITH PRESSURE PEAKING FIG.4Stabilising wall position a w /a vs.    for q=const scan of SS operational points 4.1.1, 2, 3 from Table I at a = 1.85 m. No-wall ideal MHD stability limits are shown by vertical dashed lines. a w,ITER /a  Lines 1,2,3 correspond to 4.1.1, 4.1.2, from the Table I with different pressure peakednss: p(0)/ = 2.7, 2.9,3.1

SS TYPE-II:q min > 1 WS, NB+ECCD Suggested transport:D =  e = 0.5  i ~1+ 3x 2 and ion neoclassical at the edge pedestal D =  e =  i =  i,neo

(1)  N IN ALL SCENARIOS IDEAL n=1 KINKS ARE STABLE (2)SCENARIOS CAN REQUIRE CONSIDERATION OF THE NTM STABILIZATION TABLE II: ITER PLASMA PARAMETERS FOR THE SS Type-II SCENARIOS Scenario N I p, MA9“ a / R, m2 / / 6.35 H H98(y,2) P fus, MW P los, MW8886 P NB /P EC, MW33/20,10 19 m n/n G, a.u l i3, a.u I BS /I p, % I NB /I p, % I EC /I p, %4.75 (q = 2)7.0 (q = 1.5)  N, a.u /, % /,% q(0)/q min /q /1.52/ /1.45/5.25

DISCUSSION ON PHYSICS NEEDS Projection of experimental scenarios to ITER (5.1) Pressure and q profiles,  N are similar to those required for ITER SS operation. Thus, at least the ideal stability features and active RWM control do not require extrapolation (5.2)In ITER heating of electrons dominates P e > P i,T i /T e ~ 1 is expected In experiments with  N and HH similar to ITER P e 1. Thus, projection to ITER with T i /T e ~ 1 (rather than with T i /T e > 1) with the same  N and HH is required to avoid overestimation of P fus ~ T i 2 (and Q) and underestimation of I CD ~ T e

DISCUSSION ON PHYSICS NEEDS Constraints from SOL/DIV simulations (B2/EIRENE) For ITER divertor configuration and pumping system power flux to SOL should be compatible with divertor constraints (P max,ITER ~ 100 MW ) (for more accurate parametric dependence see ref. [1,2] ) Plasma contamination by He can be relatively small   */  e < 2 [1] Core fuelling saturates with increase of the separatrix density. Thus, ITER operation requires dominant core fuelling [1]. Pellet injection is suggested as a major source of the core fuelling. Thus, the experimental scenario can be considered as ITER relevant if results of projection to ITER fulfil: (5.3)P sep < P max,ITER (5.4) with moderate contamination by He. (5.5) scenario should be compatible with pellet fuelling [1]Kukushkin et al NF 43 (2003) 716 [2]ITER PDD

DISCUSSION ON PHYSICS NEEDS Experimental demonstration of ITER SS feasibility For experimental support of the ITER SS scenarios feasibility the following directions are suggested: I.Data supply for validation of transport which fulfil the SS requirements II.Data supply for validation of predictive capabilities of CD codes III.Demonstration of active control of instabilities IV.Demonstration of compatibility with pellet fuelling V.ITER relevant discharges should be selected taking account of limitations and rules ( ) discussed in a previous section