Heat transport and L-H threshold in He4 majority experiments in JET

1. Heat transport and L-H threshold in He4 majority experiments in JET D C McDonald, M Beurskens, G Calabro, P Gohil, F Ryter, C Giroud, K-D Zastrow, I Voitsekhovitch, E Surrey, R Sartori, G Maddison, E de la Luna, I Nunes, P J Lomas, I Day, J Lonnroth

2. Goals • Goals of experiment (largely those of TC-4) • Extend the physics basis for predicting H-mode transition and performance in the ITER He4 phase. • first aim is to predict ITER He4 L-H threshold • second aim is basis for predicting ITER D-T operation from that in He4 • improved diagnosis, since 2001, enables us to advance in these areas • Key areas • Threshold • Explore role of density and ICRH/NBI fraction on L-H threshold • Determine L-H threshold at ITER relevant shape, relative to D • Document JET L-H threshold for subsequent ELMy H-mode studies • Confinement • Obtain first measurements of ETB in He4 and determine its physics • Diagnose core transport • Determine role of ETB and transport physics on global confinement • Type I-III transition • Determine Type I-III threshold at ITER relevant shape, relative to D, in He4 plasmas • Multimachine • Contribute to common multimachine physics basis for L-H threshold, ETB and H-mode confinement for H and He4 plasmas

3. L-H results: He4 concentration • 2001 data: clear difference (factor of ≈1.4) between the D and He4. • AUG pre-2008 and DIII-D 2009 broadly in line. • AUG 2008 found D and He4 almost equal • In 2009 JET performed first concentration scan. • Results show no or a very weak change in L-H power as concentration varies from 1-87% • Clearly at odds with 2001 data and several other studies. • Does agree with AUG 2008. • Including the rest of the 2009 He4 (>80% He) and D references (<1% He), a more complicated picture is seen.

4. L-H results: He4 density 1.7MA/1.8T, JET V5 (d=0.2) shape 2001 2009 D He4 • Density scan was performed at fixed B, I and shape. Results show • D: L-H power rises broadly monotonically with density • He4: L-H power rises broadly monotonically for ne≥2.51019m-3, but power is higher at ne=2.1 1019m-3 than at 2.5 1019m-3 • Comparing the 2009 concentration scan with 2001 data at same field, 1.8T, it is seen that the density ranges differ. • 2009 concentration scan: ne=2.0-2.7 1019m-3 • 2001 data: ne=1.0-1.6 1019m-3 • Comparing these regions on the density scan plot, we see that • 2009 data lies in the region where He4 and D L-H is similar • 2001 data lies in the region where He4 L-H > D L-H • Consistent with concentration trends • However, the difference between the JET and AUG, or the JET and DIII-D, data is not explained.

5. L-H theory and modelling • No agreed universal model for L-H threshold • He4 concentration: In 2003 study, Kiviniemi modelled neoclassically driven electric fields in edge region of plasmas using ASCOT • Took a JET plasma configuration with fixed shape and ne for H, D, T and He4. • Found qualitative agreement with the trends in temperature threshold for L-H in experiments (used JET 2001 for He4) and those in the predicted E-field. • Quality of JET 2001 profile data meant that it did not impose a very strong constraint • Would certainly be interested in repeating this ASCOT modelling • Density dependence: Kalupin proposed that density rollover in the L-H threshold is related to the impact of the ratio of conductive to convective thermal transport on the edge temperature gradient. Not clear how isotope charge fits into this model, but could attempt a study. • Other models: several exist. Would certainly be interested in projects to test these using our available data. Welcome ideas. • NB: CX data is unlikely to be available, ie no Ti or rotation

6. Type I-III ELM threshold PI-III (D) = 6.7-9.3 MW PI-III (He4) = 7.5-9.1 MW PI-III/PMartin08(He4) = 1.4-1.6 PI-III/PMartin08(D) = 1.2-1.8 D scan - NBI: 4-10MW He4 scan - NBI: 4-12MW increasing NBI power pulno: Ploss (MW) pulno: Ploss (MW) 79197: 5.4 79195: 6.3 79198: 7.5 79193: 9.1 79192: 12.3 79742: 5.4 79743: 6.7 79744: 9.3 79745:10.7 time (seconds) time (seconds)

7. Type I ELMs on ITER? Extrapolating this ratio to a Type I ELMy H-mode in the ITER half-field baseline conditions: B=2.65T, I=7.5MA, ne=51019 m-3, S=678 m2 gives a required power for Type I ELMs of 42-48MW Including the 95% confidence interval estimate of the Martin08 scaling, the power that would be required for Type I ELMs is, 23-86MW Most of this range lies within the proposed available auxiliary power for He4 ITER plasmas PI-III/PMartin08(He4) = 1.4-1.6

8. Confinement results ELMy H-modes: B=1.8T, I=1.7MA, d=0.4, n=51019m-3 NTM island • 2001 data: Global confinement significantly poorer in He4 compared with D references. • For matched plasmas (ne fixed) He4 global confinement was ≈68±8% of D equivalent • AUG 2008 data is broadly in line with this • 2009 JET: very similar results. In the 60-70% range. • Quality of electron density and profile data is considerably better. Possibility of CX data too.

9. Confinement theory and modelling • Core transport modelling: • TRANSP validation of data underway. TRANSP now includes ADAS cross-section database which is seen as vital for He4, particularly for NBI • Aim to make predictive runs with GLF23 and/or Weiland models to validate these models on He4 plasmas and to understand the D to He4 (or He4 to DT) scaling. Voitsekhovitch (PoP 2002) made a similar study of He4 plasmas in Tore Supra using the Weiland model. • r*M½/Z  r*(He4) = √½ r*(D) • It’s been noted that the ≈75% ratio of He4 to D confinement is consistent with saying that, for the same input power and electron density, the temperature profiles will be the same. Not clear how this links to theory. • Would certainly welcome theoreticians or modellers interested in this work. • Studying He4 plasmas is both potentially important for ITER and provides interesting physics in its own right.