KSTAR ICRF transmission line system upgrade for load resilient operation

H. J. Kim, S. J. Wang, Y. S. Bae, H. L. Yang, J.-G. Kwak, S. H. Kima and M. Parka

KSTAR Research Center, NFRIa Fusion Plasma Ion Heating Research Center, KAERI

Japan-Korea Workshop on Physics and Technology of

Heating and Current Drive

Haeundae, Busan, Korea Jan. 28-30, 2013

Outline

q Motivation

q KSTAR ICRF transmission line system upgrade in 2012

q Stable ICRF operation with load resilient T/L system

q Conclusion

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 2

Motivation

q Reliable high power ICRF operation in 2012 KSTAR Campaign

– Fusion plasma is not quiescent and exhibits many transient phenomena such as mode transitions or edge localized modes (ELMs) bursts.

– Plasma density changes and the characteristic of wave propagation is affected.– Plasma density changes and the characteristic of wave propagation is affected.

– An effective load resilient operation is mandatory for reliable ICRF operation.

– In 2011 campaign, we found unstable transmitter power by high reflection.

– Transmitter unstable power at 30.45 MHzà frequency: 30.8 MHz (2012 campaign)

– Tuning problem; inter-strap coupling effect is large.

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 3

2011 campaign

KSTAR ICRF transmission line system upgrade2011 Campaign

2012 CampaignDe-coupler Hybrid splitter

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 4

transmitter

Dummy load

transmitter

Load resilient ICRF T/L system upgrade2011 ICRF system 2012 ICRF system

Dummyload

90 deg. difference

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 5

w/ decoupler

w/o decoupler

90 deg. difference

q Operation of a decoupler

Installation and measurement of a decoupler*

YL

Loop 12

M X dcLoop 34Y

1

2

q Installation and RF test of a decoupler

– Decoupler cancels reactive mutual admittance by adjusting Xdc.

– power balance by allowing coupled power flow through decoupler branch.

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013

– *S. J. Wang et al., Fusion Engineering and Design (In press in FED, 2013)

6

30.8 MHz

High power operation with a decoupler

q Operation of a decoupler at 180 deg. between loop A and B (2011 vs. 2012)

– Power ratio (PA/PB): ~ 1 (2012)à Decoupler works very well.

– 400 kW, 3 s stable operation: FWD ~ 400 kW, REF: 60 kW, VSWR : ~ 2

2011campaign

2012campaign

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 7

Simulation on 3dB coaxial hybrid splitter

q Quadrant hybrid splitter

– when power is reflected from the resonant loops, the reflected power will go to the dummy load and will not be seen by the generator.

– S21, S31: -3.01 dB / S11, S41: -38.1 dB @ 30.8 MHz– S21, S31: -3.01 dB / S11, S41: -38.1 dB @ 30.8 MHz

– Phase difference (port 2 and 3): 90 deg.

-30

-20

-10

0

180

240

300

360

S11S21S31S41

S-pa

ram

eter

s (dB

)

Phas

e di

ffer

ence

(Deg

.)

input Output-3 dB

90 Deg.

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 8

-60

-50

-40

0

60

120

20 25 30 35 40

S41

S21-S31 (Deg.)S-pa

ram

eter

s (dB

)

Phas

e di

ffer

ence

(Deg

.)

Frequency (MHz)

30.8 MHz

Output-3 dBisolated

90 Deg.difference

Ultra-wideband 3dB coaxial hybrid splitter

q Proposed two-section 3dB hybrid splitter*

– Port 2&3: -3.10 ± 0.15 dB(amplitude)

– 90° ± 2° (phase difference)

– Bandwidth : 37% (proposed), VSWR < 1.3 -30

-20

-10

0Single-sectionTwo-sectionThree-sectionProposed circuit

Ret

urn

loss

(dB

)

– Bandwidth : 37% (proposed), VSWR < 1.3

-50

-40

-30

25 30 35 40

Ret

urn

loss

(dB

)

Frequency (MHz)

0.2

0.4

0.6Two-sectionThree-sectionProposed circuit

Am

plitu

de im

bala

nce

(dB

)

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 9

– *H. J. Kim et al., Applied Physics Letters 100 (2012) 263506-0.6

-0.4

-0.2

0

25 30 35 40A

mpl

itude

imba

lanc

e (d

B)

Frequency (GHz)

BW: 11.7MHz

Measurements on 3dB coaxial hybrid splitter

q RF measurement results

– S21, S31: -3.05 dB @ 30.8MHz

– S11, S41: -34.8 dB @ 30.8MHz

– Phase difference (port 2 and 3): 90.2 deg.– Phase difference (port 2 and 3): 90.2 deg.

-30

-20

-10

0

180

240

300

360

S11S21S31S41

S21-S31 (Deg)

S-pa

ram

eter

s (dB

)

Phas

e di

ffer

ence

(Deg

.)

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-60

-50

-40

0

60

120

20 25 30 35 40

S21-S31 (Deg)

S-pa

ram

eter

s (dB

)

Phas

e di

ffer

ence

(Deg

.)

Frequency (MHz)

30.8 MHz

q Power measured at resonant loop A, B and hybrid splitter(HS)

– Total reflected power, P_total_ref = P_ref_A + P_ref_B

– Power ratio (P_HS/P_total_ref) becomes around 1à HS working is very good. (load resilient operation)

Load resilient operation with a hybrid splitter

good. (load resilient operation)

8

10

4

5P_HSP_total_ref

Ratio (P_HS/ P_total_ref)

ICR

F re

flect

ion

pow

er (k

W)

Ref

lect

ion

pow

er ra

tio

# 7899

15

20P_fwd_AP_fwd_BP_ref_H/SP_ref_AP_ref_B

ICR

F po

wer

(kW

)

# 7899

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 11

0

2

4

6

0

1

2

3

3 3.2 3.4 3.6 3.8 4IC

RF

refle

ctio

n po

wer

(kW

)

Ref

lect

ion

pow

er ra

tio

Time (s)

0

5

10

3 3.2 3.4 3.6 3.8 4

ICR

F po

wer

(kW

)

Time (s)

q Load resilient operation (200 kW, 1s) using a 3dB hybrid splitter

– Forward power: 200 kW, reflected power: 20 kW, averaged VSWR : ~ 2

– Stable operation of ICRF transmitter with 10% reflection (L–mode)

Typical load resilient ICRF operation

150

200

250

300

3

4

5

6ForwardReflected

VSWR

ICR

F po

wer

(kW

)

VSW

R

# 7398

90deg.àload resilient

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0

50

100

0

1

2

6 6.2 6.4 6.6 6.8 7

ICR

F po

wer

(kW

)

Time (s)

àload resilient

q Load resilient operation in H-mode plasma

– Plasma density in the area of antenna changes rapidly in H-mode plasma

– The characteristic of wave propagation from antenna to plasma is affected

– High reflection from antenna plasma loading changed (high VSWR:2~6)

Stable ICRF operation in H-mode plasma

– High reflection from antenna plasma loading changed (high VSWR:2~6)

– Stable ICRF operation with a load resilient T/L in ELMy plasmas

3

4

5

6

6

8

10

12VSWR_loop AVSWR_loop B

Ratio

VSW

R

Rat

io (P

_HS

/ P_t

otal

_ref

)

# 7907

15

20

25P_fwd_AP_fwd_BP_ref_AP_ref_B

ICR

F po

wer

(kW

)

# 7907

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0

1

2

3

0

2

4

6

6.5 7 7.5

VSW

R

Rat

io (P

_HS

/ P_t

otal

_ref

)

Time (s)

0

5

10

5 5.5 6 6.5 7 7.5 8

ICR

F po

wer

(kW

)

Time (s)

q Increase in the ICRF averaged coupled power in ELMy plasmas

– Effective protection of transmitter using a 3dB hybrid coupler

– Load resilient TL system leads to a stable power transmission in ELMy plasmas

– An effective load resilient operation is mandatory for reliable and efficient ICRF

Typical ICRF shot in ELMy plasmas

– An effective load resilient operation is mandatory for reliable and efficient ICRF power transmission

1000

1500

2000

2500

3000

600

800

1000

Ip (kA)NBI_total (kW)ICRF_forward (kW)ICRF_reflected (kW)

H_alphaW_TOT

NB

I (kW

), IC

RF

(kW

)

W_s

tore

(kJ)

, H_a

lpha

(a.u

.)

# 7273

200

400

600

800

150

200

250

300

Ip (kA)ICRF_forward (kW)ICRF_reflected (kW)W_TOT

H_alpha

ICR

F (k

W),

W_s

tore

(kJ)

H_a

lpha

(a.u

.)

# 7273

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-500

0

500

1000

0

200

400

0 2 4 6 8 10 12

Ip (k

A),

NB

I (kW

)

W_s

tore

(kJ)

Time (s)

-400

-200

0

0

50

100

7.4 7.5 7.6 7.7 7.8 7.9 8 8.1

Ip (k

A),

ICR

F (k

W),

H_a

lpha

(a.u

.)

Time (s)

Conclusion

q We have newly installed a decoupler and a 3 dB hybrid coupler.

q Load resilient operation has been successfully performed in 2012 campaign.

– In L/H-mode plasmas, we found load resilient transmission line system – In L/H-mode plasmas, we found load resilient transmission line system leads to stable ICRF transmitter operation and high power transmission.

q We expect that the load resilient KSTAR ICRF system enables not only the stable transmitter operation but also enhancement of power coupling to the plasma in 2013 KSTAR campaign.

Japan-Korea Workshop Haeundae, Busan Jan. 28-30, 2013 15

q We also designed an ultra-wideband two-section 3 dB coaxial hybrid coupler by configuring asymmetric impedance matching using HFSS.

Thank you for your attention

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