1. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 1 H-mode pedestal characteristics on MAST A.Kirk, T. O’Gorman, R. Scannell Addition of new data at low pedestal collisionality New data from LFS Yag system Comparison of SND with CDN shots

2. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 2 Recap: Inboard versus outboard n e widths Inboard and outboard widths in mm similar far from ELM n e pedestal width is not a function of  N alone Can be explained if density pedestal width determined by neutrals If we mapped inboard data to outboard we would get the wrong answer But what about the temperature/pressure width ?

3. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 3 Recap: Comparison of HFS and LFS T e ped width The outboard temperature pedestals are approaching the limit of the spatial resolution of the system and care is needed

4. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 4 New results on CDN discharges Looking at more shots from the Ruby system Using the new edge Yag data

5. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 5 New Ruby data on Inboard versus outboard widths Again confirm that the density pedestal width is NOT a flux surface quantity Temperature pedestal width: error bars are too large to be certain Some indication that different to density dependence

6. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 6 Edge Thomson Scattering on MAST Edge TS System Optics Core System View Edge System View Core System Optics Laser Beam Path Edge TS system views the laser from 1.25-1.45m The outboard pedestal and SOL region Uses the same lasers as the core system but different viewing optics Scattered light from 16 laser centres is transmitted to 8 spectrometers via fibre optics

7. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 7 Comparison of Yag and Ruby at LFS New Yag system allows measurement of lower temperature pedestals on the outboard side

8. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 8 Comparison of HFS(Ruby) with LFS(Yag) As reported previously the density pedestal is wider on the LFS Temperature looks in good agreement but need statistics to be sure

9. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 9 Comparison of HFS(Ruby) with LFS(Yag) Good agreement in the pedestal heights measured at the HFS and LFS

10. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 10 Comparison of HFS(Ruby) with LFS(Yag) Confirms that the density pedestal width is NOT a flux surface quantity

11. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 11 Comparison of HFS(Ruby) with LFS(Yag) BUT the temperature pedestal width does seem to be a flux surface quantity

12. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 12 Ratio of the temperature to density pedestal width This factor of two would be sufficient to allow  T e to be a flux surface quantity

13. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 13 What about the pressure pedestal? The HFS and LFS pressure pedestal heights are similar The ratio of the widths is consistent with the pressure being a flux surface quantity

14. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 14 What about the pressure pedestal? The HFS and LFS pressure pedestal widths are similar in flux space –in spite of the fact that the density pedestal widths aren’t!! Possible because the density and temperature barrier locations are different

15. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 15 Pedestal heights and dependencies

16. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 16 Pedestal heights New low collisionality branch- “type IV ELMs” The operational space in CDN discharges has been greatly expanded – including a

17. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 17 Pedestal width dependencies The “type IV” ELMs have a different pedestal width dependence - Generally on MAST  Te  T e ped - The “type IV” have a relatively narrow pedestal width that does not change with T e ped

18. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 18 SND Discharges For CDN no mapping required as Z TS ~Z mag For SND need to take into account that  Zmag ~ 0.85*  Z=0

19. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 19 SND vs CDN discharges – Pedestal characteristics The SND discharges are at a higher T e ped and predominantly in the type I region  Te increases linearly with T e

20. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 20 SND vs CDN discharges – Pedestal width For the SND discharges the density pedestal width IS a flux surface quantity Ruby data

21. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 21 SND vs CDN discharges Widths on the LFS are similar the difference is at the HFS Is the HFS being modified through the SOL?

22. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 22 Pedestal width scalings

23. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 23 Scalings – banana orbit As previously observed the MAST pedestal widths fall below the banana orbit scaling

24. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 24 Scalings –  pol or  pol ? Originally JT-60U had claimed that the temperature pedestal width scaled with  * pol More recent experiments on JT-60U comparing pedestal widths in H and D plasmas have shown that it is really a  pol scaling BUT  pol and  pol are correlated

25. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 25 Scalings on MAST –  pol or  pol  pol and  pol are correlated but the low n e high T e branch and the SND shots allow some separation

26. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 26 Scalings –  pol or  pol Using CDN data only and choosing similar   pol and different  pol Width depends on  pol for the same  * pol

27. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 27 Using CDN data only and choosing similar  pol and different   pol Scalings –  pol or  pol No positive correlation with  * pol

28. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 28 Adding SND data and choosing similar  pol and different  * pol Scalings –  pol or  pol No positive correlation with  * pol

29. A. Kirk, ITPA Pedestal meeting, GA, 30 April 2008 29 Summary 1) In CDN shots the density pedestal width is not a flux surface quantity but the temperature pedestal width is! 2) In SND shots Both the density and temperature pedestal widths are flux surface quantities. This suggest that in addition to neutrals playing a role the SOL helps to determine the density pedestal width 3) The temperature pedestal width scales with  pol rather than  * pol.