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Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
March 19th, 2019
Hyunyeong Leea,b, Y. G. Kima, S. C. Kima, J. G. Joc, S. C. Honga, Y. S. Naa and Y. S. Hwanga
brbbebbero@snu.ac.kr
hylee@nfri.re.kr
Solenoid-free start-up utilizing outer PF coils with the help of EBW pre-ionization in VEST
aSeoul National University, 151-742, San 56-1, Shillim-dong, Gwanak-gu, SeoulbNational Fusion Research Institute, 169-148,Gwahak-ro, Yuseong-gu, Daejeon
2/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
IntroductionSolenoid free start-up in tokamak
Solenoid-free start-up in tokamak
• Plasma current in all tokamak devices has relied on central solenoid intrinsically
• Essential for current drive without CS : Low aspect ratio, SSO, COE
• Solenoid free start-up : helicity injection, induction from outer PF, using RF [1]
Previous works for solenoid free start-up
[1] R. Raman, et. al., Plasma Physics and Controlled Fusion 56 103001 (2014)[2] S.P. Hirshman, et. al., Plasma Fluids 29 790 (1986)
Helicity injection Using RF Induction from outer PFPros Many results in
experimentsSSO, many results in
experimentsIntrinsic flux from outer PF coils. Flux from external inductance [2]
Cons Complexinjector system,
Based on ST
Huge power of RF system, Efficiency
CFS formation, Based on ST, huge power for pre-ionization
Devices PEGASUS, NSTX
TST-2, LATE, QUEST, MAST
NSTX, TST-2, JT60-U
3/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
IntroductionPrevious works for Solenoid free start-up (1)
Previous works in LATE [3]• Solenoid free start-up : ECH assisted pressure driven current• Vertical field for only force balance• Plasma current jumps after closed flux surface (CFS) formation
Previous works in PEGASUS [4]• Solenoid free start-up : Local helicity injection• CFS formation near outboard : Plasma current sheet from LHI• Successful plasma current evolution with aid of flux from external inductance
[3] T. Yoshinaga, et. al., Physical Review Letter 96 125005 (2006)[4] D. J. Battaglia, et. al., Nuclear Fusion 51 073029 (2011)
4/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
IntroductionPrevious works for Solenoid free start-up (2)
Previous works in NSTX [5]• Solenoid free start-up using outer
PF induction• The failure of CFS formation
- Difficult for sustaining fieldnull configuration
- Shortage of ECH pre-ionization
Previous works in JT60-U [6]• CS less start-up with outer PF• 1 MW with ECH power• Without external inductance flux
The study on CFS formation with helpof Electron Bernstein wave (EBW)pre-ionization
[5] W. Choe, et. al., Nuclear Fusion 45 1463-1473 (2005)[6] M. Ushigome, et. al., Nuclear Fusion 46 207-213 (2006)
5/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
OXB(O cutoff & UHR)
OXB(CS & UHR)
XB(UHR)
Pros Many results in experiments Simple designSingle Mode conversion
Cons Complex ScenarioDensity fluctuationAngular dependant
Complex Scenario Need : polarizer
Limitation of O cutoff
Limit of R cutoff – tunnelingControl on density profile
Devices MAST, NSTX, W7, WEGA, LHD, TCV CDX-U, TST-2, COMPASS-D
IntroductionElectron Bernstein Wave via direct XB MC
Electron Cyclotron Resonance Heating (ECRH)• Widely used in fusion devices : pre-ionization, local heating and CD• In ST, it has limitations due to low toroidal field.
Electron Bernstein Wave (EBW)• Electrostatic wave of transition from electromagnetic wave (MW)• Alternatives for heating and CD in ST : No cutoff density
Previous Works for EBW assisted start-up and heating experiments
6/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux Surface
7/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux SurfacePrevious works for CFS formation
An essential factor of successful start-up : formation of Closed Flux Surface (CFS) Previous works for formation of CFS
• DYON : 0D model for start-up in JET and ITER [7]- Dominant parallel transport when Ip reaches 100 kA (empirical CFS).
• ECH assisted start-up with TPC in KSTAR [8]- Start-up Failure : Faster convective loss time than CFS formation time
It is important to understand the mechanism of CFS formation quantitatively for successful start-up.
[7] H. Kim, et, al., Nuclear Fusion 52 103016 (2012)[8] J. W. Lee, et. al.,Nuclear Fusion 57 126033 (2017)
Convective loss timeClosed surface formation time
8/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux SurfacePlasma evolution : before CFS, CFS and after CFS
CFS formation experiments with TPC• Decreasing Bv with different ECH power• Vloop is supplied continuously after 400 ms• Earlier Ip initiation with larger ECH
What determines the CFS formation and Ip initiation?• Decreasing Bv & Pre-ionization
Open field current : Pfirsch-Schulter currents in openfield line with TPC
402.0 402.5 403.0 403.5 404.0 404.5 405.0 405.50
1000
2000
3000
4000
5000
6000 B0~500 G / ECH 6 kW B0~500 G / ECH 4 kW B0~500 G / ECH 2 kW
Time (ms)Pl
asm
a Cu
rrent
(kA)
0
5
10
15
20
25
30
35
40Vertical Field (G)Open field
current
CFS Formation
After CFSformation
9/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Pfirsch-Schluter currents in open field• Low toroidal field with high plasma current• Different gradient B effect near ECR
• The incline : gradient B• B0 ~ 500 G : 1st ECR R=0.23 m (inboard)• B0 ~ 1000 G : 1st ECR R = 0.40 m (central)
• The plasma startup has been affected to more openfield current from low vertical field than current fromelectric field
Formation of Closed Flux SurfacePS current in open field line with TPC
0 20 40 60 80 100 120 140 160 180 2000
500
1000
1500
2000
2500
3000
3500
4000
Plas
ma
Curre
nt (A
)
Bt/Bv
B0 ~ 500 G B0 ~ 700 G B0 ~ 1000 G
297.0 297.5 298.0 298.5 299.0 299.5 300.00
200400600800
100012001400160018002000
Pl
asm
a Cu
rrent
(A)
Time (ms)
B0 ~ 500 G B0 ~ 700 G B0 ~ 1000 G
297.0 297.5 298.0 298.5 299.0 299.5 300.0 300.5 301.00
1000
2000
3000
4000
5000
Plas
ma
curre
nt (A
)time (ms)
High Bv High E Low Bv Low E
10/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux SurfaceModel for CFS formation along ECH power (1)
The model for CFS formation• The poloidal field from plasma
current along the resistivity of pre-ionization plasma
• CFS formation : the time whenBp overcomes the decreasing Bv
• Measurement of Pre-ionization- Movable Langmuir Probe- Electron density and
temperature profile0.2 m < R < 0.8 m
• Initial condition of CFS formation- Ip from open field
Resistivity 1D profile (experiment)
Span resistivity 2D (R:0~1 m, Z:-0.5~0.5 m)
Current density 2D (R:0~1 m, Z:-0.5~0.5 m)
Normalized J2D from plasma current
Psi 2D calculation (R:0~1 m, Z:-0.5~0.5 m)
Br, Bz calculation (R:0~1 m, Z:-0.5~0.5 m)
Net magnetic field calculation adding experiment B
with eddy current (R:0~1 m, Z:-0.5~0.5 m)
Plot normalized J2D (R:0~1 m, Z:-0.5~0.5 m)
Plot magnetic field line (R:0~1 m, Z:-0.5~0.5 m)
11/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux SurfaceModel for CFS formation along ECH power (2)
ECH 6 kW : 404.4 ms
ECH 4 kW : 404.5 ms
ECH 2 kW : 404.8 ms
400 401 402 403 404 405 406 407 408 409 410
0
1000
2000
3000
4000
5000
6000 B0~500 G / ECH 6 kW B0~500 G / ECH 4 kW B0~500 G / ECH 2 kW
Time (ms)
Plas
ma
Curre
nt (k
A)
-30
-20
-10
0
10
20
30
Vertical Field (G)
The 2D model for CFS formation• The magnetic field line makes CFS
during the start-up (red line)• Background : normalized 2D current
density profile from experiment• The timing of CFS formation is similar
to plasma current initiation in all cases• CFS has important factors of plasma
current kickup
12/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux SurfaceCFS formation with decreasing Bv along Bt
Formation of CFS occurs at the differenttiming and location
• Different current density profile ofresistivity profile from Bt
In all cases, the Ip initiates when CFShas been formed.
CFS formation is essential forsuccessful start-up and the poloidalfield from Ip overcomes the existingvertical field.
B0 ~ 1000 G : 404.5 ms
B0 ~ 700 G : 404.2 ms
B0 ~ 500 G : 404.2 ms
400 401 402 403 404 405 406 407 408 409 410-1000
0100020003000400050006000700080009000
10000 B0~1000 G / ECH 6 kW B0~ 700 G / ECH 6 kW B0~ 500 G / ECH 6 kW
Time (ms)
Plas
ma
Curre
nt (A
)
-30
-20
-10
0
10
20
30
Vertical Field (T)
13/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
General criteria for CFS formation• Importance of consideration of pre-
ionization resistivity• a : minor radius of CFS• The timing and location of startup may
be determined by how to make pre-ionization plasma as we want to start.
Formation of Closed Flux SurfaceGeneral Criteria for CFS formation
𝐸𝐸𝑡𝑡𝐵𝐵𝑡𝑡𝐵𝐵𝑣𝑣
> 1000 𝑉𝑉𝑚𝑚
→ 100[𝑉𝑉𝑚𝑚
] with relaxationLloyd condition :
500G 2kW 500G 4kW 500G 6kW 700G 6kW 1000G 6kW0
50
100
150
200
250
300
LLoy
d co
nditi
on (V
/m)
Relaxed Lloyd condition
500G 2kW 500G 4kW 500G 6kW 700G 6kW 1000G 6kW100
150
200
250
300
E t*a/B
v*res
istiv
ity(V
/G*O
hm*m
)
Bp/Bv > 1
𝐸𝐸𝑡𝑡𝑎𝑎𝐵𝐵𝑣𝑣𝜂𝜂
> 1.6 × 102 [𝑉𝑉
𝐺𝐺Ω𝑚𝑚]
𝐵𝐵𝑝𝑝𝐵𝐵𝑣𝑣
=𝜇𝜇0𝐸𝐸𝑡𝑡𝐴𝐴𝐵𝐵𝑣𝑣2𝜋𝜋𝑎𝑎𝜂𝜂
> 1
14/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Solenoid Free Startup Scenario using outer PF coils
15/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Solenoid free start-up scenario using outer PF coils 0D Power balance model
After CFS formation, the plasma current evolution will be predicted with 0D powerbalance model by PEGASUS [9]
0D power balance model for VEST solenoid free start-up• Source from PF coil : Voltage from the change of vertical field for equilibrium• Source from external inductance : decrease of Lext, shape change(ɛ, κ) [2]
[9] J. L. Barr, et. al., Nuclear Fusion 58 076011 (2018)[2] S.P. Hirshman, et. al., Plasma Fluids 29 790 (1986)
LossResistive
Dissipation
SourcePF coil
SourceExternal
Inductance
LossInternal
Inductance
[6]
16/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Solenoid free start-up scenario using outer PF coils Solenoid free startup scenario in VEST
SF start-up scenario• After successful CFS
formation• (a)~(b) : 𝜂𝜂~ 7 × 10−6• Flux from external
inductance change isdetermined with thelocation and size of CFS
• (c)~(d) : 𝜂𝜂~ 5 × 10−5• Enormous resistive
dissipation disrupt theplasma current ramp-up
• The balance betweendriving flux (Vgeo) and antidriving flux (VR)
17/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Solenoid free start-up scenario using outer PF coils Correlation between Vgeo and Resistive dissipation
• In the same resistivity, the aspect ofplasma current is different from thelocation and the size of CFS
• The correlation between the fluxfrom external inductance changeand resistive dissipation exists
• With lower resistivity, Vgeo can beutilized with plasma current ramp-upefficiently.
0.0 0.5 1.0 1.5 2.0 2.5 3.00
500
1000
1500
2000
2500
3000
Plas
ma
Curre
nt (A
)
Time (ms)
R~0.60a~0.15 R~0.65a~0.10 R~0.70a~0.05
0.0 0.5 1.0 1.5 2.0 2.5 3.00
500
1000
1500
2000
Plas
ma
Curre
nt (A
)
Time (ms)
R~0.60a~0.15 R~0.65a~0.10 R~0.70a~0.05
0.0 0.5 1.0 1.5 2.0 2.5 3.00
1000
2000
3000
4000
5000
6000
Plas
ma
Curre
nt (A
)
Time (ms)
R~0.60a~0.15 R~0.65a~0.10 R~0.70a~0.05
Resistivity ~ 7E-6
Resistivity ~ 5E-5
Resistivity ~ 1.6E-5
18/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Solenoid free start-up scenario using outer PF coilsResistivity calculation for successful CFS formation
The CFS region of successful SF start-up using outer PF coils• Successful startup has been determined by the location and size of CFS• The region for successful start-up has been broadened along lowering the
resistivity of pre-ionization plasma• The external inductance flux and resistive dissipation has been differed from the
location and size of CFS• The increase on electron temperature is essential for the change of resistivity of
pre-ionization plasma
10 15 20 25 30 350.0
5.0x1016
1.0x1017
1.5x1017
2.0x1017
2.5x1017
3.0x1017
Dens
ity (#
/m3)
Electron Temperature (eV)
resistivity~5E-5 resistivity~2.5E-5 resistivity~2.0E-5 resistivity~1.5E-5
Outer limiter location R~0.75 m
19/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
EBW Pre-ionization Experiments in VEST
20/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Enhancement of pre-ionization under TPC with EBW collisional damping In case of B0 ~ 500 G
• The density peak exists near ECR with low ECH power• With increasing ECH power, steep density gradient is produced near UHR :
improvement on XB mode conversion• Over dense plasma is generated due to EBW collisional damping
In case of B0 ~ 1000 G• Over dense plasma production between ECR and UHR
Collisionless heating is more favorable for lower resistivity of pre-ionization plasma
0.2 0.3 0.4 0.5 0.6 0.7 0.80.0
5.0x1016
1.0x1017
1.5x1017
2.0x1017
2.5x1017
3.0x1017 ECR
R cutoffUHR
De
nsity
(#/m
3)
Radius (m)
only TF : ECH 6 kW TPC : ECH 3 kW TPC : ECH 6 kW TPC : ECH 16 kW
L cutoff
(a) B0 ~ 0.5 kG
0.2 0.3 0.4 0.5 0.6 0.7 0.80.0
5.0x1016
1.0x1017
1.5x1017
2.0x1017
2.5x1017
3.0x1017
Den
stiy
(#/m
3)
TPC : ECH 6 kW only TF : ECH 6 kW TPC : ECH 16 kW
Radius (m)
R cutoff
L cutoff
UHR
ECR
(b) B0 ~ 1 kG
EBW Pre-ionization Experiments in VESTEnhancement of Pre-ionization with TPC
21/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
EBW Pre-ionization Experiments in VESTIncrease of Te near harmonics
• TF field control for 2nd or 3rd harmonics near outboard : Collisionless heating• Electron temperature increases near outboard for lower resistivity• Higher mirror ratio in TPC makes higher particle confinement time
22/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
EBW Pre-ionization Experiments in VESTPower Estimation for Successful SF Startup
• Minimum resistivity for successful SF startup using outer PF coils : 3 × 10−5
• To achieve the target resistivity, the estimation using ECH 5 kW & 14 kW• With mirror ratio ~ 2.3, the power estimation is about 60 kW• With mirror ratio ~ 3.5, the power estimation is about 45 kW• The higher mirror ratio has the higher particle confinement time
23/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Conclusion
CFS formation, main factor of successful start-up, is convinced with 2D model andexperiments with decreasing vertical field. The general criterion for CFS formation issuggested by considering quantitative resistivity of pre-ionization and the size of CFS.
The power of mode converted EBW has been deposed moving toward ECR bycollisional damping and electron temperature increases in ECR harmonics by EBWcollisionless heating near 2nd or 3rd harmonic resonance.
The lower resistivity of pre-ionization plasma has been required for successfulsolenoid free start-up utilizing outer PF coils with 0D power balance modelling. It canbe confirmed for the region of CFS location and size with lower resistivity and theECH power of 45 kW in mirror ratio ~ 2.3 and 60 kW in mirror ratio ~ 3.5 has beenestimated to achieve the target resistivity 3.0 × 10−5 for successful solenoid freestart-up utilizing outer PF coils.
24/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Back Up
25/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
IntroductionStart-up in Spherical Torus
Spherical Torus (ST)
• Limited space for central solenoid : restricted inductive flux
• It is important to develop efficient start-up scheme
• VEST : First ST in Korea
Objectives : innovative start-up and non-inductive CD
Previous works for start-up
• Long connection length with low vertical field – Field null
[1]
• The empirical condition for reliable start-up – Lloyd condition
[2-3]
• Relaxation with pre-ionization [3]
• However, the previous study on start-up does not represent the quantitative
study on effect of pre-ionization. [1] R. Yoshino, et. al., Plasma Physics and Controlled Fusion 39 205 (1997)[2] A. Tanga, et. al., in Tokamak start-up(Knoepfel, H., Ed), Plenum Press, New York p. 159 (1986)
[3] B. Lloyd, et. al., Nuclear Fusion 31 2031 (1991)
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Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
2nd ECR
IntroductionTrapped Particle Configuration (TPC)
(a) (b) Previous works for start-up
(a) Field null configuration (FNC)
• Long connection length
• Requirement of transition
time for stable decay index
[4] Y.H. An, et. al., Nuclear Fusion 57 016001 (2017)[5] J. W. Lee, et. al., Nuclear Fusion 57 126033 (2017)
(b) TPC configuration [4]
• Short connection length
• Enhancement of particle confinement
• Intrinsic stable decay index – no transit time
• Efficient Vs consumption – prompt Ip initiation
• Excellent experimental results in VEST and
KSTAR [4-5]
27/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
IntroductionTPC Startup Experiments in VEST & KSTAR
TPC 3kW TPC 5kW TPC 6kW400
450
500
550
600
650
Curre
nt R
ampu
p Ra
te (k
A / s
)
400.0 400.5 401.0 401.5 402.0-0.4
-0.3
-0.2
-0.1
0.0
Loop
vol
tage
[V]
R~0.2434 R~0.2633 R~0.28327 R~0.3020
Time [msec]
Experiments in VEST & KSTAR
• Wide operation regime [4-5]
• Successful extremely low loop
voltage startup in VEST [6]
- E ~ 0.16 V/m
• Many advantages using TPC
despite of short connection length[6] H. Y. Lee, et. al., IAEA FEC EX P4-53 (2016)
28/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
• Commercial MW power supply(6 kW 2.45 GHz : 1ea)
• LFS injection• X/O mode injection
• Magnetron (30 kW 2.45 GHz Microwave)• LFS injection• X mode injection• Not Controllable pulse duration• Synchronization with VEST trigger system
ECH System New ECH System
Experimental Setup in VESTECH System in VEST
29/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
IntroductionFormation of Closed Flux Surface (CFS)
An essential factor of successful start-up : CFS formation Previous works for formation of CFS
• The plasma current jumps after formation of CFS [7]• DYON : 0D model for start-up in JET and ITER [8]
- Dominant parallel transport when Ip reaches 100 kA (empirical CFS). • ECH assisted start-up with TPC in KSTAR [5]
- Failure : Faster convective loss time and low ionization rate from TECHP0D• How can CFS be formed with existing vertical field (short connection length)?
[7] T. Yoshinaga, et. al., PRL 96 125005 (2006)[8] H. Kim, et, al., Nuclear Fusion 52 103016 (2012)
Convective loss timeClosed surface formation time
30/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux SurfaceIncrease of Ne and Te inside CFS
In case of B0 ~ 0.05 T,• After formation of CFS, Ne and Te increases.• Density increases R = 0.4 m and then R = 0.3 m
but no increase in R = 0.2 m.• With increasing plasma current, the size of CFS is
enlarged and it may affects to the order ofincreasing Ne
• After density increases, the electron temperatureincreases inside CFS
• The plasma current inside CFS may be dominantamong total plasma current and ohmic heatingfrom Ip affects to the Ne and Te increase
0.4040 0.4042 0.4044 0.4046 0.4048 0.4050 0.40520
1x1017
2x1017
3x1017
4x1017
5x1017
Time (s)
0.2 m 0.3 m 0.4 m
0.4040 0.4042 0.4044 0.4046 0.4048 0.40500
10
20
30
40
50
Tem
pera
ture
(eV)
Time (s)
0.2 m 0.3 m 0.4 mCFS Time CFS Time
403.5 403.8 404.1 404.4 404.7 405.0
0
2000
4000
6000
8000
10000
Plas
ma
Curre
nt [A
]
Time [ms]
B0~1000 G / ECH 6 kW B0~ 700 G / ECH 6 kW B0~ 500 G / ECH 6 kW
CFS Formation
Ne
31/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Formation of Closed Flux SurfaceIncrease of Ne and Te inside CFS
In case of B0 ~ 0.075 T• After formation of CFS, Ne and Te increases.• Density increases R = 0.4 m and then in R = 0.3 m, and
in R = 0.2 m.• Also, the electron temperature increases inside CFS
but the order of the increase is opposite to the density,R = 0.25m, 0.3 m and 0.4 m. It might be the differenceof loop voltage inside CFS.
• The ohmic heating from increasing Ip and EBW heatingaffects to the ne and te increase inside CFS and thefuture works are planned to distinguish the two effects.
CFS Time CFS Time
0.4040 0.4042 0.4044 0.4046 0.4048 0.40500
1x1017
2x1017
3x1017
4x1017
5x1017
Dens
ity (#
m3)
Time (s)
0.25 m 0.3 m 0.4 m
0.4040 0.4042 0.4044 0.4046 0.4048 0.40500
10
20
30
40
50
Tem
pera
ture
(eV)
Time (s)
0.25 m 0.3 m 0.4 m
403.5 403.8 404.1 404.4 404.7 405.0
0
2000
4000
6000
8000
10000
Plas
ma
Curre
nt [A
]
Time [ms]
B0~1000 G / ECH 6 kW B0~ 700 G / ECH 6 kW B0~ 500 G / ECH 6 kW CFS
Formation
32/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
EBW Pre-ionization Experiments in VESTPre-ionization with only TF - Power
ECH pre-ionization experiment using only TF field in VEST• At the lower power, density peak exists near ECR but with increasing the MW
power, the density peak moves outward : Steep density gradient near UHR• Density peak between UHR and ECR : EBW collisional damping in low Te [10-11]• Te increase near ECR : collisionless heating by non-converted X wave and EBW
30 35 40 45 50 55 60 65 70 75 80 850.0
0.2
0.4
0.6
0.8
1.0
1.2
n e [10
17m
-3]
R [cm]
X-mode_2kW X-mode_3kW X-mode_4kW X-mode_6kW
Electron Cyclotron Resonance
Chamber Port
30 35 40 45 50 55 60 65 70 75 80 853
6
9
12
15
18
21
24
T e [eV
]
R [cm]
X-mode_2kW X-mode_3kW X-mode_4kW X-mode_6kW
Electron Cyclotron Resonance
Chamber Port
UHR
[10] S. Pesic, Physica C, 125 118-126 (1984)[11] S.J.Diem, et. al., Physical Review Letter 103 015002 (2009)
33/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
20 30 40 50 60 70 800.0
0.2
0.4
0.6
0.8
1.0
1.2 ECRUHRUHR
ECRUHR
n e [10
16m
-3]
R [cm]
B0~500G B0~700G B0~1000G
ECR
EBW Pre-ionization Experiments in VESTPre-ionization with only TF – Toroidal field
The change of density profile along the toroidal field• In case of B0 ~ 1000 G, the density peak exists between ECR and UHR.• In case of B0 ~ 700 G, no density peak exists
- moderate density gradient near UHR : low efficiency of XB MC• In case of B0 ~ 500 G, high density plasma generates near ECR
34/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
EBW Pre-ionization Experiments in VESTLower Resistivity : Te increase
To lower pre-ionization plasma resistivity• The limitation of collisional damping : density increase• Electron Temperature increase : collisionless heating• Lower operation pressure (under 1E-5 Torr) & GDC cleaning• ECR Harmonics near outboard region (2nd & 3rd harmonics)• Particle confinement time : Mirror ratio change
0.2 0.3 0.4 0.5 0.6 0.7 0.80.0
5.0x10-5
1.0x10-4
1.5x10-4
2.0x10-4
2.5x10-4
3.0x10-4
3.5x10-4 1st ECR
Without GDC With GDC
Tota
l Res
istiv
ity
Radius (m)
2nd ECR
0.2 0.3 0.4 0.5 0.6 0.7 0.80.0
5.0x10-5
1.0x10-4
1.5x10-4
2.0x10-4
2.5x10-4
2nd ECR
1st ECR1st ECR 3rd ECR2nd ECR
B0 ~ 500 G B0 ~ 750G
Tota
l Res
istivi
ty
Radius (m)
35/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
[16] J. S. Yoon, et. Al., JPCRD 37 913 (2008)
53/2
ln5.2 10
[ ]eff
ei spitzere
ZT eV
η η − Λ= = ×
220
2 fevm
ennvm
enm mee
e
mee
e
meen
σσνη ===
eien ηηη +=
EBW Pre-ionization Experiments in VESTResistivity Calculation of Pre-ionization plasma
Resistivity calculation• Total resistivity is the sum of electron-
neutral collision and electron-ion collision (Spitzer)
• Average electron velocity : Ve (Te)• Total Momentum transfer cross section
σm (Te) [16]• Spitzer resistivity is dominant for total
resistivity in this regime : essential for Teincrease
10 15 20 25 30 350.0
5.0x1016
1.0x1017
1.5x1017
2.0x1017
2.5x1017
3.0x1017
Dens
ity (#
/m3)
Electron Temperature (eV)
resistivity~5E-5 resistivity~2.5E-5 resistivity~2.0E-5 resistivity~1.5E-5
0.0 5.0x1017 1.0x1018 1.5x1018 2.0x10180.0
0.2
0.4
0.6
0.8
1.0
Spitz
er/T
otal
Res
istiv
ity
Density (#/m3)
36/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
Solenoid free start-up using outer PF coils
[14] D. J. Battaglia, et. al., Nuclear Fusion 51 073029 (2011)[15] S.P. Hirshman, et. al., Plasma Fluids 29 790 (1986)
1.0 1.5 2.0 2.5 3.0-0.5
0.0
0.5
1.0
Aspect ratio
1 2 3 4 5 6 7 8 9 10-0.5
0.00.5
1.01.5
2.0 Hirshman and Neilson Large aspect ratio
Norm
alize
d ex
tern
al in
duct
ance
Aspect ratio
κ~1.8
With successful CFS formation at any position, solenoid free start-up near outboard isfavorable startup method.
PEGASUS has succeeded in this method using Local Helicity Injection [14] 0D power balance model for VEST solenoid free start-up with EBW pre-ionization
• Source from PF coil : Voltage from the change of vertical field for equilibrium• Source from external inductance : decrease of Lext, shape change(ɛ, κ) [15]
37/23LHY_KJHCDW_MAR19
Korea-Japan Workshop on Physics and Technology of Heating and Current Drive
on March 19th 2019, at SNU
EBW Pre-ionization Experiments in VESTChange of particle confinement along mirror ratio
45 50 55 60 65 70 755.0x1016
1.0x1017
1.5x1017
2.0x1017
Dens
ity (#
/m3)
Radius (cm)
5kW 8kW 11kW L cutoff UHR
2nd ECR
45 50 55 60 65 70 755.0x1016
1.0x1017
1.5x1017
2.0x1017
Dens
ity (#
/m3)
Radius (cm)
3kW 5kW 8kW L cutoff UHR
2nd ECR45 50 55 60 65 70 75
7
8
9
10
11
12
13
Tem
pera
ture
(eV)
Radius (cm)
5kW 8kW 11kW
2nd ECR
B0 ~ 750 GTPC Mirror ratio ~ 3.5
B0 ~ 750 GTPC Mirror ratio ~ 2.3
• Collisionless heating by converted EBW near 2nd harmonic : Te increase• The change of particle confinement time along mirror ratio• The higher mirror ratio has the higher particle confinement time
- The huge pressure change is expected with more high power
2 4 6 8 10 12 14 166.0x1017
8.0x1017
1.0x1018
1.2x1018
1.4x1018
1.6x1018
Mirror ratio ~ 3.5 @ R=0.65 m Mirror ratio ~ 2.3 @ R=0.65m
Plas
ma
Pres
sure
ECH Power (kW)
45 50 55 60 65 70 756
7
8
9
10
11
12
13
Te
mpe
ratu
re (e
V)
Radius (cm)
3kW 5kW 8kW
2nd ECR
Recommended