Post on 08-Jan-2016
description
JT-60U JT-60U
Resistive Wall Mode (RWM) Study on JT-60U
Resistive Wall Mode (RWM) Study on JT-60U
Go Matsunaga松永 剛
Japan Atomic Energy Agency, Naka, Japan
JSPS-CAS Core University Program 2008 in ASIPP Plasma and Nuclear FusionFeb. 16-21, 2009 in ASIPP
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 2
JT-60U JT-60U
Outline
Introduction Current driven RWM in OH plasmas RWM in high- plasmas Recent RWM topics Summery & Suggestion for EAST experiments
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 3
JT-60U JT-60U
Introduction
Toward fusion reactors, the high-N operation is very attractive and advantageous, because high bootstrap current (fBS) and high fusion output (Pfus) are expected.
Finite wall resistivity makes another mode, Resistive Wall Mode (RWM)
that limits achievable N.(RWM is characterized
by wall diffusion time, w)
However, achievable N is limited by low-n MHD instability.
No-wall No-wall N-limit -limit ((N==Nno-wallno-wall ->C->C=0)=0)
Ideal-wall Ideal-wall N-limit-limit ((N==Nideal-wallideal-wall ->C->C=1)=1)
Therefore, RWM stabilization is a key issue for high-N operation in ITER and a fusion reactor.
DeviceSize
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 4
JT-60U JT-60U
What is key for RWM study?
RWM behaviors Wall location effect Rotation stabilization effect
→Stabilization Mechanisms Feedback control
→Establishment, Mode controllability Interaction with other instabilities
→ELMs, Energetic particle driven modes Error field effect
→Resonant field amplification (RFA), Active sensing
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 5
JT-60U JT-60U
Useful tools for RWM study onJT-60U
Plasam-Wall clearance feedback control
Plasam-Wall clearance feedback control
Positive ion based NBs (PNB) 4 tangential
CO ~ 4MW CTR ~ 4MW
7 perpendicular Negative ion based NBs (NNB)
2 tangential CO ~ 4MW
Positive ion based NBs (PNB) 4 tangential
CO ~ 4MW CTR ~ 4MW
7 perpendicular Negative ion based NBs (NNB)
2 tangential CO ~ 4MW
Various NB injectionsVarious NB injections
JT-60U JT-60U
Current driven RWM in OH plasmas
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 7
JT-60U JT-60U
Current driven RWM experiments
In order to investigate wall location effect on MHD instability, plasma-wall gap scan has been performed in OH plasma.
→ since only q-profile can determine the stability, wall effect can be clearly measured.
To destabilize current driven external kink mode, surface q was decreasing by plasma current ramping up.
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 8
JT-60U JT-60U
m/n=3/1 Current driven RWM is observed
qeff was just below 3, m/n=3/1 instability appeared and thermal collapse occurred.
The growth time of this mode is about 10ms.
→ On JT-60U, w is several milliseconds.
Current driven RWM↑
external kink mode +
wall stabilizing effect
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 9
JT-60U JT-60U
Wall location effect for RWM
G. Matsunaga, PPCF, Vol. 49, p.95(2007)
Wall stabilizing of current-driven kink mode on OH plasma
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 10
JT-60U JT-60U
RWM growth rates vs. wall location
G. Matsunaga et al., PPCF, Vol. 49, pp.95-103 (2007)
G. Matsunaga et al., PPCF, Vol. 49, pp.95-103 (2007)
Increasing d/a, RWM growth rate increased.
According to AEOLUS-FT with taking into account a resistive wall, m/n=3/1kink and m/n=2/1 tearing modes are unstable.
The dependence qualitatively agrees with RWM dispersion relation without plasma rotation.
m/n=2/1tearing modes
m/n=3/1kink mode
JT-60U JT-60U
RWM in high- plasmas
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 12
JT-60U JT-60U
Identification of critical rotation for RWM stabilizing
To identify critical plasma rotation for RWM stabilization, we only changed plasma rotation.
At 5.9s : Stored energy FB was started
→ keeping N constant
At 6.0s : Tang NBs were switched from CTR-NB to CO-NB
→ slowly reducing Plasma rotation
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 13
JT-60U JT-60U
High- RWM was observed by reducing plasma rotation
Just before collapse, n=1 radial magnetic field was growing with ~10ms growth time.
→ RWM
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 14
JT-60U JT-60U
Plasma rotation profiles
Since N was kept constant, deceleration of plasma rotation was thought to make the RWM unstable.
Focusing on the plasma rotation at the q=2, critical plasma rotation is less than 1kHz.
This value is corresponding to 0.3% of Alfvén velocity.
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 15
JT-60U JT-60U
Dependence of critical rotation on C
Target value of stored energy FB was changed to get the dependence of the critical plasma rotation.
The dependence of the critical rotation on C is weak.
This means that we can sustain the high-βup to the ideal wall limit.
JT-60U JT-60U
Recent RWM topics
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 17
JT-60U JT-60U
Challenge of sustainment of high- discharge
Previously, on JT-60U, the high-N plasmas > N
no-wall were transiently obtained.
In this campaign, we have tried to sustain the high-N plasma > N
no-wall with plasma rotation larger than Vt
cri.
We have successfully obtained the high-N plasma for several seconds.
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 18
JT-60U JT-60U
Best discharge; N~3.0, ~5sec
On the best discharge,
N~3.0 (C~0.4) was sustained by plasma rotation > Vt
cri.
Sustained duration is ~5s, which is ~3 time longer than R.
Time duration is determined by the increase of N
no-wall due to gradual j(r) penetration.
According to ACCOME, fCD80% and fBS~50% were also achieved.
~5s (~3~5s (~3RR))
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 19
JT-60U JT-60U
What limits for high-N long discharges
However, the sustainment of high-N is not straightforward.
Because almost all discharges were limited by
Resistive Wall Mode (RWM) Neoclassical Tearing Mode (NTM)
Furthermore, many discharges have been lost by new instabilities:
Energetic particle driven Wall Mode (EWM)
directly induces RWM despite Vt > Vtcri
RWM Precursor
strongly affects Vt-profile at q=2,
finally, induces RWM onset
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 20
JT-60U JT-60U
EWM can directly induce RWM
In the wall-stabilized high-bN region, Energetic particle driven Wall Mode (EWM) is newly observed.
At RWM onset, rotation was At RWM onset, rotation was enough for stabilization.enough for stabilization.
The EWM is dangerousThe EWM is dangerous for RWM
n=1
n=1
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 21
JT-60U JT-60U
Features of EWM
Toroidal mode number : n=1Poloidal mode number : m~3 (Kink Ballooning-like)Radial mode structure : globally-spreadGrowth time : 1~2ms
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 22
JT-60U JT-60U
Trapped energetic particle by PERP-NBs (85keV)
Mode frequency is chirping down as mode amplitude is increasing.
Initial mode frequency agrees with the precession frequency of the energetic particles from the PERP-NB.
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 23
JT-60U JT-60U
Hot pressure of PERP-NB seems to drive
hh//total total ~ -10%~ -10%
EWM is stabilized by reducing PERP-NB injection power while keeping N constant.
→ Driving source is trapped energetic particle pressure
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 24
JT-60U JT-60U
N>Nno-wall (C>0) is required to drive EWM
The EWM were observed in high-N plasmas.
However, the EWM requires C>0, NOT only high-N.
CC>0>0,, NN<3.0<3.0CC>0>0,, NN<3.0<3.0
EWMEWM
CC>0>0,, NN~3.0~3.0CC>0>0,, NN~3.0~3.0
EWMEWM
CC~0~0,, NN~3.0~3.0CC~0~0,, NN~3.0~3.0
No EWMNo EWM
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 25
JT-60U JT-60U
EWM stability domains
If the no-wall limit is changed by j(r), EWM is always destabilized above the no-wall limit.
Increasing plasma rotation, EWM boundary seems to follow it.→ EWM has a similar stability to RWM
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 26
JT-60U JT-60U
Summery
RWM is a key issue in an economical aspect for future fusion reactors.
On JT-60U, RWM has been well studied; Current driven RWM → Wall location effect, High- RWM → Plasma rotation stabilizing, Instability related to RWM → Coupling to energetic particles.
JT-60U has been shut down in last August. We must wait for JT-60SA for further RWM study.
Our corroborations become important!
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 27
JT-60U JT-60U
m/n=1/1 Internal-kinkm/n=1/1 Internal-kink
FishboneFishbone
Possible interpretation for EWM
EWM is a coupling mode between energetic particles
andmarginally stable RWM.
Kinetic contribution Kinetic contribution of fast particlesof fast particles
MHD MHD
marginally stablemarginally stable marginally stablemarginally stable unstableunstable unstableunstable
•RWMRWM
Energetic particle driven Wall mode (EWM)Energetic particle driven Wall mode (EWM)
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 28
JT-60U JT-60U
Suggestion for EAST experiment
Current driven RWM by Ip ramping Wall location effect Stabilizing by fast ion tail by ICRF
External coils Feedback control Active sensing (RFA) Rotation control (Error field effect)
Neutral Beam High- RWM Energetic particle effect ELM interaction
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 29
JT-60U JT-60U
RWM dispersion relation
KineticKineticEnergyEnergyIntegralIntegral
PlasmaPlasmaPotentialPotentialEnergyEnergy
VacuumVacuumEnergyEnergy
withwithNo WallNo Wall
M. S. Chu et al., Phys. Plasma, Vol. 11, p.2497(2004) M. S. Chu et al., Phys. Plasma, Vol. 2, p.2236(1995) M. S. Chu et al., Phys. Plasma, Vol. 11, p.2497(2004) M. S. Chu et al., Phys. Plasma, Vol. 2, p.2236(1995)
WallWallSkinSkinTimeTime
KineticKineticEnergyEnergyIntegralIntegral
PlasmaPlasmaPotentialPotentialEnergyEnergy
Vacuum Energy with Ideal WallVacuum Energy with Ideal Wall
VacuumVacuumEnergyEnergy
withwithResistiveResistive
WallWall
DissipationDissipationEnergyEnergyIntegralIntegral
Vacuum EnergyVacuum Energywithout Wallwithout Wall
ComplexComplexGrowthGrowth
RateRate
PlasmaRotation
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 30
JT-60U JT-60U
Plasma rotation stabilizing effect on RWM
Some models predict that the critical rotation is several % of Alfven speed at the rational surface.
→ Dissipation and rotation are required for RWM stabilization.
How much is the critical rotation for RWM stabilization?
Future devices will have low plasma rotation.
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 31
JT-60U JT-60U
m/n=1/1 Internal-kinkm/n=1/1 Internal-kink
FishboneFishbone
RWMRWM
Energetic particle driven Wall mode (EWM)Energetic particle driven Wall mode (EWM)
Possible interpretation for EWM
EWM is originated from energetic particles and marginally stable RWM.
Kinetic contribution Kinetic contribution of fast particlesof fast particles
MHD MHD
marginally stablemarginally stable
marginally stablemarginally stable
unstableunstable
unstableunstable
Feb. 16-21, 2009 G. Matsunaga JAEA, CUP in ASIPP 32
JT-60U JT-60U
Ideal MHD analysis by MARG2D
This mode is unstable w/o wall, however, stable with ideal wall.
The mode structure is localized in the LFS
→ Kink-Ballooning mode structure