Hyunyeong Leea,b Y. G. Kim , S. C. Kim , J. G. Jo , S. C. Hong Y. S. …psl.postech.ac.kr/kjws19/talks/20190319_KJHCDW_Oral... · 2019. 3. 23. · 0 ~ 500 G : 1st ECR R=0.23 m (inboard)

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

[email protected]

[email protected]

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

mailto:[email protected]

mailto:[email protected]

2/23LHY_KJHCDW_MAR19


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




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)




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)




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




Formation of Closed Flux Surface




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




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




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




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)




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




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)




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




Solenoid Free Startup Scenario using outer PF coils




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]




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)




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




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




EBW Pre-ionization Experiments in VEST




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




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




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




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.




Back Up




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)




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]




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)




• 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




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




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

발표자

프레젠테이션 노트

Current jump and saturation in open field line only for low toroidal field?




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




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)




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




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)




[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)




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]




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

Documents

Hyunyeong Leea,b Y. G. Kim , S. C. Kim , J. G. Jo , S. C. Hong Y. S. …psl.postech.ac.kr/kjws19/talks/20190319_KJHCDW_Oral... · 2019. 3. 23. · 0 ~ 500 G : 1st ECR R=0.23 m (inboard)