Effect of low aspect ratio data on H-mode confinement

M Valovic, 9th ITPA CDBM Meeting, Oct 2005

Why we want to know the a/R scaling ?

Preparation for ITER operation: better understanding of scaling with dimensionless parameters *, , *. Aspect ratio is contained in their definitions and thus the a/R scaling gives additional insight into the physics.

DEMO optimisation.

Physics basis for Component Test Facility

For ITER like shape the a/R scalingis given by MAST and NSTX data.

STPP

MAST NSTX

M Valovic, 9th ITPA CDBM Meeting, Oct 2005

Spherical tokamaks are naturally high machines.

START, MAST and NSTX extent the H-mode tokamak database of conventionally shaped plasmas simultaneously in =a/R and .

At the same time the ST data broadly agree with the scaling derived from conventional aspect ratio tokamaks. Thus the data make powerful constraint on and dependencies BE x x :

Unfavourable scaling gives positive exponent weak scaling gives negative exponent M Valovič et al. Nucl. Fusion 2005S Kaye et al. H-mode Workshop 2005

- interplay

M Valovic, 9th ITPA CDBM Meeting, Oct 2005

Summary and plans

Low aspect ratio data from NSTX, MAST are significant in determining the aspect ratio and dependencies for ITER like shaped plasmas. Expanding the range of a/R and raises the question of validity of log-linear scaling. It is known that * exponent is not constant across the whole * range (C C Petty).

Therefore dimensionless scans at low A are important to test whether exponents depend on a/R. Beta scan on MAST is planned.

Expansion of MAST H-mode dataset is planned.