1 Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Gr P.C. de Vries JET-EFDA Culham Science Centre Abingdon OX14 3DB UK Internal Transport Barriers and Rotational Internal Transport Barriers and Rotational Shear Shear
22
Embed
1Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group P.C. de Vries JET-EFDA Culham Science Centre Abingdon OX14.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
P.C. de Vries
JET-EFDA Culham Science CentreAbingdon OX14 3DB UK
Internal Transport Barriers and Rotational ShearInternal Transport Barriers and Rotational Shear
2Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
IntroductionIntroduction Why Internal Transport Barriers?
– ITBs may play a role in advanced tokamak scenario for ITER1.– Studying ITBs may improve our understanding of transport physics
Scope of this presentation– Present experimental observations on ITBs at JET
• Especially focussing on the role of rotation(al) shear
– How do these relate to turbulence and transport physics?– Present results on other recent transport studies at JET– Provide a reference to various experimental papers– Start a discussion
3Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Turbulence and TransportTurbulence and Transport Transport in Tokamak plasma is predominantly driven by turbulence. Temperature gradient driven turbulence stiff profiles
– Non-diffusive behaviour T does not change with Heat Flux
‘Temperature Gradient’
‘Hea
t F
lux’
Neo-classical
Tcrit
eff
4Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Internal Transport BarriersInternal Transport Barriers Profile stiffness locally broken in the presence of and Internal
transport barrier (ITB).– Studying ITBs may improve our understanding of transport physics
minor radius
pla
sma
pre
ssu
re
ITB
H-mode
pedestalTcrit
5Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
How to make an ITB How to make an ITB Empirical recipe to form strong ion internal transport barriers
– Optimised q-profiles with low or negative magnetic shear (q’/q)– Often significant Neutral Beam Injection (NBI) heating– Similar recipe used in various Tokamaks (JT-60U, DIII-D, AUG … )
GC GC
m/n=5/22/1
6Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
How to make an ITBHow to make an ITB In plasmas with negative magnetic shear a specific class of
ITBs are ‘triggered’ when qmin reaches an integer value1,2,3
– Confirmed by the onset of an Grand-Cascade of Alfven waves4.
16Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Turbulence and Profile StiffnessTurbulence and Profile Stiffness Profile stiffness locally broken in the presence of and Internal
transport barrier (ITB).
Normalised Gradient R/LT
‘No
rmal
ised
Hea
t F
lux,
qi
Neo-classical
Tcrit
eff
ITB
growth
17Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Turbulence and Profile StiffnessTurbulence and Profile Stiffness But what about plasmas without ITBs? Does the rotation affect
turbulence too?
Normalised Gradient R/LT
‘No
rmal
ised
Hea
t F
lux,
qi
Neo-classical
Tcrit
eff
qi qires ni q
1.5 s Ti
2ieBR2
R
LTifR
LTiR
LTi crit
H
R
LT iR
LTi crit
Tcrit usually set by ITG growth rate
Stiffness factor: s
Tcrit
18Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Turbulence and Profile StiffnessTurbulence and Profile Stiffness But what about plasmas without ITBs? Does the rotation affect
turbulence too?
Normalised Gradient R/LT
‘No
rmal
ised
Hea
t F
lux,
qi
Neo-classical
Tcrit
eff
qi qires ni q
1.5 s Ti
2ieBR2
R
LTifR
LTiR
LTi crit
H
R
LT iR
LTi crit
Tcrit usually set by ITG growth rate
Stiffness factor: s
s
s
19Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Stiffness and rotation(al shear)Stiffness and rotation(al shear) Detailed experiments at JET indicate that the stiffness is
affected by the plasma rotation/rotational shear– from power balance and modulation experiments
1 MANTICA, P. , et al., Phys. Rev. Lett. 102 (2009) 175002
20Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Stiffness and rotation(al shear)Stiffness and rotation(al shear) Latest analysis in suggest that the impact of the rotation on the profile stiffness may depend on q or q’/q
Question: Does a flat q profile enables the rotation(al shear) to affect the ion stiffness?
Stiffness decreases with rotation Stiffness high for any rotation
Core region (R=3.33 m) = lower q’/q
1 MANTICA, P. , JET Science Meeting (2009)
Outer region (R=3.60 m) = higher q’/q
21Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
Conclusions/DiscussionConclusions/Discussion Ion ITBs are triggered independent of the rotation
– Strong player in the triggering process is the q profile
The ITB growth is strongly affected by the rotational shear– ITBs do not grow after triggering if the rotational shear is too low
Note that these results do not excluded other mechanisms that aid the growth of ITBs
– such as fast-particles, etc.– The physics of electron ITBs differ all together (q-profile).
GYRO modelling suggest that ITG turbulence is suppressed in strong ITBs
– Rotational shear affects the growth rate/critical gradient
Or is it the stiffness that is affected by the rotational and q?
22Peter de Vries – ITBs and Rotational Shear – 18 February 2010 – Oxford Plasma Theory Group
List of PublicationsList of Publications Experimental observations of ITBs