A.Kirk ITPA Pedestal meeting, Milan, October 2008 1 H-mode access on MAST Presented by Andrew Kirk UKAEA With thanks to Anthony Field, Hendrik Meyer and Martin Valovic • Effect of magnetic configuration • Effect of gas puff location • Effect of divertor leg length • Effect of pellets
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H-mode access on MAST Presented by Andrew Kirk UKAEA
H-mode access on MAST Presented by Andrew Kirk UKAEA With thanks to Anthony Field, Hendrik Meyer and Martin Valovic. Effect of magnetic configuration Effect of gas puff location Effect of divertor leg length Effect of pellets. Comparison of P thr with P s. P thr = 0.53 0.03 MW. - PowerPoint PPT Presentation
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A.Kirk ITPA Pedestal meeting, Milan, October 2008 1
H-mode access on MAST
Presented by Andrew Kirk UKAEA
With thanks to Anthony Field, Hendrik Meyer and Martin Valovic
• Effect of magnetic configuration
• Effect of gas puff location
• Effect of divertor leg length
• Effect of pellets
A.Kirk ITPA Pedestal meeting, Milan, October 2008 2
• Flows driven by Flows driven by B drifts B drifts (V.A. Rozhansky et.al.)(V.A. Rozhansky et.al.)
The Rozhansky explanation The Rozhansky explanation predicts an Increase in predicts an Increase in toroidal flow with HFS gas toroidal flow with HFS gas puff ratepuff rate
A.Kirk ITPA Pedestal meeting, Milan, October 2008 8
Possible explanations
Increase in toroidal flow with HFS gas puff rate supports flows driven by B drifts interpretation
A.Kirk ITPA Pedestal meeting, Milan, October 2008 9
Divertor leg length
Repetitive L-mode phases induced by Repetitive L-mode phases induced by change of the connection length on MAST.change of the connection length on MAST.
Loss of bootstrap current pulls leg inwardsLoss of bootstrap current pulls leg inwards
Shortening of leg Shortening of leg H-mode H-mode
Similar effects have been observed on JET with the X-point height scan
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Fuelling Pellets can induce L-H transition
• Explained by increased density gradient due to a pellet
Similar to what has been observed in DIII-D
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Summary
H-mode access on MAST is facilitated near to CDN and using HFS gas fuelling. Studies have been performed trying to understand these effects
In addition the effect of
• Loop voltage and Density• Error fields • Effect of co vs cntr NBI
have been studied.
A.Kirk ITPA Pedestal meeting, Milan, October 2008 12
Backup material
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