control of mhd instabilities. similarities and differences between tokamak and rfp
DESCRIPTION
Control of MHD instabilities. Similarities and differences between tokamak and RFP. V. Igochine, T. Bolzonella, M. Maraschek, W. Suttrop, D.Yadykin. Outline of the talk. Control of MHD instabilities in ASDEX Upgrade Tokamak scenarios and corresponding instabilities - PowerPoint PPT PresentationTRANSCRIPT
RFX workshop /20.01.2009/ Valentin IgochinePage 1
Control of MHD instabilities. Similarities and differences between tokamak and RFP
V. Igochine, T. Bolzonella, M. Maraschek, W. Suttrop, D.Yadykin
RFX workshop /20.01.2009/ Valentin IgochinePage 2
Outline of the talk
• Control of MHD instabilities in ASDEX Upgrade– Tokamak scenarios and corresponding instabilities – Conventional scenario: Neoclassical tearing mode and sawteeth
• Main stabilizing/destabilizing factors• ECCD as a main active control tool• ITER requirements for active control
– Advanced scenario: Resistive wall mode • External coils design in ASDEX Upgrade• Present status and start of the operation
• Control of the RWMs in RFPs in comparison with tokamaks– Similarities and differences in RWM behavior and drive – Open questions in RWM physics
• Conclusions
RFX workshop /20.01.2009/ Valentin IgochinePage 3
Tokamak scenarios and typical safety factor profiles
C. M. Greenfield et. al. ITER scenarios:
1. H-mode2. Improved H-mode3. Advanced tokamak
scenario
RWM
NTM,Sawtooth
ρ
q
2
1.5
Safety factor
1
qI
RFX workshop /20.01.2009/ Valentin IgochinePage 4
Tokamak scenarios and typical safety factor profiles
C. M. Greenfield et. al. ITER scenarios:
1. H-mode2. Improved H-mode3. Advanced tokamak
scenario
RWM
NTM,Sawtooth
ρ
q
2
1.5
Safety factor
1
qI
RFX workshop /20.01.2009/ Valentin IgochinePage 5
Control of MHD instabilities is a key issue to obtain a high-performance plasma
MHD instabilities in the core regime• Neoclassical Tearing Modes (NTMs) - appear in a high beta plasma - limit the achievable beta at N<N
ideal
• Sawtooth Oscillations - have smaller effects on global parameters - are able to trigger an NTM at low N values
Active control is important for both!
Control tool: Electron Cyclotron Current Drive (ECCD) - highly localized current drive fill the hole in bootstrap current - flexible ECCD location is necessary
MHD instabilities in conventional scenario
flat pressure in the island↓
no bootstrap current
↓ growth of NTM
RFX workshop /20.01.2009/ Valentin IgochinePage 6
EC resonanceThe island position varies during the discharge
We have to match position of the island with current drive position
• ASDEX Upgrade (changes of Btor)Bt changes is not possible in superconductor device like ITER
• DIII-D (moves the plasma radial)No free volume for radial movement in ITER
Both variants are not acceptable for ITER!
• Changes of ECCD deposition • system of mirrors to change position of the depositionForeseen for ITER
(3,2) NTM
Possible variant of NTMs suppression
RFX workshop /20.01.2009/ Valentin IgochinePage 7
ASDEX Upgrade enhances its capabilities in this area
EC resonance(3,2) NTM
Currentdrive
4 new gyrotrons (1 MW & 10s each) with movable mirror system each.
Present status: 1 gyrotron is already installed. The others would be installed in 2009-2010.
RFX workshop /20.01.2009/ Valentin IgochinePage 8
EC resonance Possible problems in ITER:
• Deposition width is largeSolution: Current drive should be done in O-point only (Maraschek PRL, 2007)
• Locking of NTM to the wallIn line ECE diagnostic to detect the island (F. Volpe)
(3,2) NTM
Possible problem in ITER and their solutions
Now ITER
Current drive is only inside the island
RFX workshop /20.01.2009/ Valentin IgochinePage 9
• ECE can detect modulated ECRH (every 0.2s 2ms off)• MSE migrated to realtime-acquisition and transfers data• standard data transfer framework established• 80ms realtime TORBEAM for deposition predictions
Complete realtime-loop for NTM control
RFX workshop /20.01.2009/ Valentin IgochinePage 10
Why do we need to control sawteeth?
• Long Sawteeth have been shown to trigger Neo-classical Tearing Modes
– Long Sawteeth NTMs
– Short Sawteeth Avoid NTMs
• NTMs degrade plasma confinement
• Even bigger problem in ITER
Time (s)
ICRH/MW
NBI/MW
termination
Magnetics: #58884 only
Expanded intime: 15-18s
2/1
3/2
4/3
0
15kHz
long sawtooth
SXR/a.u.
[Sauter et al, PRL, 88, 2002]
Fusion born ’s
Long sawtooth periods
More likely to trigger NTMs
JET
RFX workshop /20.01.2009/ Valentin IgochinePage 11
Stability of the (1,1) mode strongly depends from shear at q=1 surface.
ECCD is able to destabilize the mode and make more frequent and smaller sawteeth.
Sawtooth control
Example: Change of shear at q=1 with co-ECCD and counter-ECCD in ASDEX Upgrade [A.Mueck, PPCF, 2005]
RFX workshop /20.01.2009/ Valentin IgochinePage 12
Complete realtime-loop for NTM and Sawtooth control
The same system can be used for NTMs and Sawteeth control!
NTM
(1,1), Sawteeth
RFX workshop /20.01.2009/ Valentin IgochinePage 13
Tokamak scenarios and typical safety factor profiles
C. M. Greenfield et. al. ITER scenarios:
1. H-mode2. Improved H-mode3. Advanced tokamak
scenario
RWM
NTM,Sawtooth
ρ
q
2
1.5
Safety factor
1
qI
RFX workshop /20.01.2009/ Valentin IgochinePage 14
Bu - coils
Bl - coils
A - coils
END 2009: Installation of 4 Bu and 4 Bl coils.
Coils system for ELMs and RWMs control in ASDEX-U
RFX workshop /20.01.2009/ Valentin IgochinePage 15
Drilling holes for coils in support structures is the most time consuming work which would be done at the end of 2009.
Actively cooled coils
Coil system design for ASDEX Upgrade
RFX workshop /20.01.2009/ Valentin IgochinePage 16
ASDEX Upgrade (8x3) ITER (9x3)
The coil system is similar to ITER design
Comparison of coils geometry in ASDEX-U and ITER
RFX workshop /20.01.2009/ Valentin IgochinePage 17
Time schedule (from W.Suttrop, Ringberg 2008)
RFX workshop /20.01.2009/ Valentin IgochinePage 18
ELM control is one of the main priorities
Time schedule (from W.Suttrop, Ringberg 2008)
RFX workshop /20.01.2009/ Valentin IgochinePage 19
RWM: tens of Hz rotation
particles
Plasma flow: kHz rotation
Coupling:(m, n)(m±1,n)(m±2,n)
RWM is the main common issue for tokamaks and RFPs
• RWM is the main common issue for tokamak and RFP
• RWM is static in RFP and slowly rotates in tokamaks
• Static RWM typically destroys the plasma confinement
Study of RWM locking & unlocking & rotation is important for tokamaks and can be studied in RFPs
RFX workshop /20.01.2009/ Valentin IgochinePage 20
• The RWM can be unlocked in RFPs.• Successful experiments on active rotation in RFX-mod.
V. Igochine et.al. EPS2008/ T.Bolzonella et.al., PRL, 2008
RWM rotation experiments in RFX-mod
RFX workshop /20.01.2009/ Valentin IgochinePage 21
Result is in very good agreement with ideal mode assumption.
The mode rotation depends on phase shift between feedback and RWM
RWM rotation experiments in RFX-mod. Summary.
RFX workshop /20.01.2009/ Valentin IgochinePage 22
Result is in very good agreement with ideal mode assumption.
No effect of plasma rotation up to now. The same rotation in both directions
The mode rotation depends on phase shift between feedback and RWM
RWM rotation experiments in RFX-mod. Summary.
RFX workshop /20.01.2009/ Valentin IgochinePage 23
Result is in very good agreement with ideal mode representation.
No effect of plasma rotation up to now.
Next step: increase frequency of the rotation by changing Δφ
Any asymmetry?
RWM rotation experiments in RFX-mod. Next step.
RFX workshop /20.01.2009/ Valentin IgochinePage 24
Result is in very good agreement with ideal mode representation.
No effect of plasma rotation up to now.
Next step: increase frequency of the rotation by changing Δφ
IF YES, THEN PLASMA ROTATION COULD BE IMPORTANT
Any asymmetry?
RWM rotation experiments in RFX-mod. Next step.
RFX workshop /20.01.2009/ Valentin IgochinePage 25
Conclusions
Different tokamak scenarios require different types of control.
RWM physics is a natural common issue for RFPs and Tokamak
In spite of several differences the mode is the same and advanced knowledge about mode control can be moved from RFPs to Tokamaks.
Further experiments with rotation could help better understand the physics of the RWM.