h-mode access on mast presented by andrew kirk ukaea
DESCRIPTION
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 PresentationTRANSCRIPT
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
Comparison of Pthr with Ps
PPss=0.061=0.061nnee0.620.62
BBTT0.690.69
SS0.880.88
F.Ryter et.al., Plasma Phys. Contr. Fusion F.Ryter et.al., Plasma Phys. Contr. Fusion 4444 (2002) A415-A421 (2002) A415-A421
• Pthr= 0.530.03 MW
Minimised by requiring:Minimised by requiring:• Inboard fuellingInboard fuelling• DND configurationDND configuration..
• Pthr> 1.8 Ps (Ps = 0.29 MW)
PPss=0.072=0.072nnee0.70.7
BBouTouT0.70.7
SS0.9 0.9 (Z(Zeffeff/2)/2)0.70.7F(A)F(A)
T. Takizuka et.al., Plasma Phys. Contr. Fusion T. Takizuka et.al., Plasma Phys. Contr. Fusion 4646 (2004) A227-A233 (2004) A227-A233
• Pthr ~ Ps
A.Kirk ITPA Pedestal meeting, Milan, October 2008 3
•Pth reduced in DN (| rsep| < i/2) by more than factor 2
Effect of magnetic configuration
This effect is also observed on AUG and NSTX
LDND: Pthr= LDND: Pthr= 1.21.20.15 MW0.15 MW
A.Kirk ITPA Pedestal meeting, Milan, October 2008 4
Possible explanations
In the L-mode phase: • No change of Te, ne or Ti for CDN, LSN, USN• Er ~ - 1kV/m between CDN and LSN - B2SOLPS modelling also
produces these changes
L-modeL-mode
Similar effect observed on AUG
A.Kirk ITPA Pedestal meeting, Milan, October 2008 5
Possible explanations
In the L-mode phase: • No change of Te, ne or Ti for CDN, LSN, USN• Er ~ - 1kV/m between CDN and LSN - B2SOLPS modelling also
produces these changes • SOL Flow patterns change – similar to effects observed on C-MOD
A.Kirk ITPA Pedestal meeting, Milan, October 2008 6
Effect of gas puff location
I/B O/B
H-mode access easier using Inboard Gas puff
A.Kirk ITPA Pedestal meeting, Milan, October 2008 7
Possible explanations
HFS fuelling changes the toroidal HFS fuelling changes the toroidal rotation of the plasma due to rotation of the plasma due to
• Neoclassical toroidal Neoclassical toroidal viscosity (P. Helander viscosity (P. Helander et.al.)et.al.)
• 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
A.Kirk ITPA Pedestal meeting, Milan, October 2008 10
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
A.Kirk ITPA Pedestal meeting, Milan, October 2008 11
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
A.Kirk ITPA Pedestal meeting, Milan, October 2008 13
Possible explanations for gas puff location
• HFS ionisation source drives outward parallel flow.
• Net toroidal torque due to B-drift of ions. v in counter-current direction
– observed in experiment.
• Radial transport of toroidal momentum from SOL.
• v in co-current direction
• Balance of both toroidal torques determines toroidal rotation Er
A.Kirk ITPA Pedestal meeting, Milan, October 2008 14
Possible explanations for gas puff location
• HFS ionisation source drives outward parallel flow.
• Net toroidal torque due to B-drift of ions. v in counter-current direction
– observed in experiment.
• Radial transport of toroidal momentum from SOL.
• v in co-current direction
• Balance of both toroidal torques determines toroidal rotation Er
• Predicts an Increase in toroidal flow with HFS gas puff rate
1.24 1.28 1.32 1.36 1.40 1.44 1.48
-20
-15
-10
-5
0
5
10
separatrix
outer midplaneT
e=120eV, T
i=120eV
at the inner boundary
SOLcore
6467 6468 experiment 6467 6468 code 6468 code, small puff
Tor
oida
l ve
loci
ty (km
/s)
Radial coordinate Y, (m)
B2SOLPS Toroidal Velocity
-6 -4 -2 0 2 4 6 8 101214
-6
-4
-2
0
2
outer midplaneT
e=120eV, T
i=100eV
at the inner boundary
separa
trix
SOLcore
6467 6468
Rad
ial el
ectric
fie
ld (kV
/m)
Radial coordinate Y, (cm)
Radial E-field
A.Kirk ITPA Pedestal meeting, Milan, October 2008 15
B2SOLPs Modelling shows that the shorter divertor leg leads to:
• Lower edge temperature results in strong reduction of V||
• More negative Er, and increased shear lower Pth(?)
Possible explanations for shorter divertor leg