Status of ICRF heating system and steady-state experiment in LHD

T. Seki, T. Mutoh, K. Saito, H. Kasahara, R. Seki,G. Nomura and LHD Experiment Group

National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, JapanJapan

Japan-Korea Workshops on Physics and Technology of Heating and Current Drive

Hanwha Resort, Haeundae, Busan, KoreaJanuary 28-30, 2013

Contents

• ICRF heating system and technology for • ICRF heating system and technology for steady-state operation in LHD- status of ICRF heating system

• long pulse plasma experiment in LHD- ICRF conditioning by 10 sec injection-- ICRF conditioning by 10 sec injection- recent result of steady state experiment

• Summary and future plan

Status of ICRF antennaPoloidal array (PA) antenna (HAS) antenna

Strap width30cm (PA)20cm (HAS)20cm (HAS)

Strap length70cm (PA, HAS)

Strap region3 ~ 73 cm (PA)-30cm ~ + 40cm (HAS)

Toroidal wavenumberk ~ 0 m-1 (PA)

In order to control toroidal wavenumber and reduce RF sheath loading on dipole excitationA handshake form antenna (HAS)“HA-SU-U” means wavenumber in Japanese.

k|| ~ 0 m-1 (PA)k|| ~ 7 m-1 (HAS)

Frequency38.47MHz

Protector (C, CFC)Cooling (water)Movable (~15 cm)

Experimental setup-ICRF heating antennas-

3.5U,L portHAS: hand shake antenna(Toroidal array antenna)(Toroidal array antenna)Capable of controlling k// with changing phase between applied RF power.Better heating efficiency

7.5U,L portPA antenna(Poloidal array antenna)Better loading resistance

# 1 IPA

# 2 IPA

# 1 DPA

# 2 DPA

# 1 FPA

# 2 FPA

Im pedance

m atching

device

Impedance

m atching

3 .5 U

Antenna

3 .5 L

~ 4 kW ~ 1 0 0 kW ~ 1 MW

Hall for Heat ing Devices Basem ent

of LHD

LHD Hall

Six steady state transmitters can be operated simultaneously

RF transmitterLiquid stub tuner Antenna

CPI

CPI# 2 IPA

# A IPA

# 2 DPA

# A DPA

# 2 FPA

SG

m atching

device

Im pedance

m atching

Antenna

4 .5 U

Antenna

4 .5 L

Antenna

7 .5 U

# 5 A FPA

# 3 IPA # 3 DPA # 3 FPAIm pedance

m atching

device

# 4 IPA # 4 DPA # 4 FPA

Im pedance

m atching

device

installed in near future

CPI

Thales

Eimac

# A IPA

# B IPA

# A DPA

# B DPA

# 5 B FPA

# 6 B FPA

m atching

device

Impedance

m atching

device

Antenna

7 .5 L

Antenna

IPA: Intermediate Power Am plifier

DPA: Driver Power Am plif ier

FPA: Final Power Am plif ier

# 6 A FPA

5changeable from 25 to 100 MHz

Thales

Thales

Eimac

Operational test of RF transmitters were carried out using steady state dummy load

•#1: 4CM2500KG– =>3.5U antenna– 0.55MW / 1h

0.8

1.01GJ 2GJ

– 0.55MW / 1h

•#2: 4CM2500KG– =>3.5L antenna– 0.54MW / 1h

•#6A: TH525A– =>7.5U antenna– 0.52MW / 0.5h– 0.23MW / 1h0.2

0.4

0.6

0.8

RF

Pow

er [M

W]

#1#2#6A

#6B

0.1GJ

– 0.23MW / 1h

•#6B: TH525A– =>7.5L antenna– 0.49MW / 0.5h– 0.24MW / 1h

•Total input energy: 6 GJ

0.0

0.2

100 1000 10000Time [s]

achieved in 2007

Stub3Stub2Stub1

Automatic impedance feedbackcontrol by Liquid stub tuner

Time evolution of liquid length of stubDouble or triple stub configuration

1.4

1.5

gth[

m] Oscillator Side

Time evolution of reflectivity

1.1

1.2

1.3

0 500 1000 1500 2000

Liqu

id L

eng

Time[s]

Antenna Side

•Necessary for steady state operation•Applicable from several sec to CWoperation•Automatic control of antenna phase is also introduced for HAS antenna

Real-time phasing system is installed

114021 Phase (I,Q)Antenna loading has time evolution in a short time.Impedance matching changes with the antenna phase, and the antenna phase changes impedance matching.

The difference for the time evolution is not so large at the initial phase in short time discharge, and there is no guarantee for keeping phase in the discharge.

In order to achieve effectively phasing experimentsthe real-time impedance matchingthe real-time phase feedback

114039 Phase (I,Q)the real-time phase feedbackkeeping forward power in various antenna loadingare needed.

Stable current phasing is demonstrated in the LHD, and accurately phasing experiment is able to be carried out.With phase feedback

Experimental condition for ICRF heating

- minority ion heating -• Magnetic field and axis are B=2.75T, Rax=3.6mare B=2.75T, Rax=3.6m

• Wave frequency: 38.47MHz

• He plasma mixed with minority H ionsminority H ions

• Ion cyclotron resonance layers are located at saddle point of magnetic configuration

ICRF discharge was used for plasma conditioning

IAEA2012 by H. Takahashi

• Repeated 10 sec ICRF discharge decreased the hydrogen minority ratio

–ECH assist is effective in high minority situation at the beginning of conditioning

–useful for remove the hydrogen from helium plasma• Electron density profile changed from hollow to flat or center-peaked

–contributed for high ion temperature achievement

Highest ion temperature was achieved after ICRF conditioning

IAEA2012 by H. Takahashi

• High ion temperature was obtained • High ion temperature was obtained after ICRF conditioning

• Change of electron density profile led to increase of Pi/ne

Plasma parameters of SSO is steadily improved

• HAS (dipole mode) antenna has better antenna has better performance than HAS (monopole) and PA antennas.

• Plasma density was increased almost proportionally to Pproportionally to PRF

(PICH+PECH).

Highest density ICRF plasma was achieved

ne=3.6x1019m-3 with PRF~2.4MW for 10s

•High density plasma with ne=3.6x1019m-3 , Te~Ti~1keV ne=3.6x1019m-3 , Te~Ti~1keV and Wp=300kJ was sustained with PICRF=2MW and PECH=0.37MW for 10 seconds.

•Plasma parameters were constant after 5 seconds.constant after 5 seconds.•could be extended more.

Steady state operation by minority ion heating was successfully carried out

discharge time: 54min and 28sec, average input power: 490kW

• Power control during plasma discharge with watching sparks in vacuum vessel

• Rax=3.64-3.67m, ne~0.4x1019m-3, Te~Ti~1keV• Plasma was terminated by sudden increase of density

caused by influx of iron impurity

Long pulse operation was carried out with high density and high RF power

ne=2.4x1019m-3 with PRF~1.8MW for 60s

•Plasma of higher density with higher RF power was higher RF power was sustained for 60 sec.

•The long pulse operation was extended to the new region of duration time vs. PRF.

Fusion triple product :nôETi~3.5x1018m-3 sec keV

Longest pulse discharge with 1x1019m-3

•pulse length: 18min. 55sec. (1135sec.)

•total ICRF power: 0.7MW- 3.5U: 0.22MW- 3.5U: 0.22MW- 3.5L: 0.22MW- 7.5L: 0.27MW

•ECH power: 0.27MW

•antenna-plasma gap- 3.5: 7.5cm- 3.5L: 12.5cm

•line-averaged electron 19 -3

•line-averaged electron density: 1x1019m-3

•highest temperature at 7.5 antenna is higher than that of 3.5 HAS antenna

Movie for 19 min. discharge

tangential view of 7.5 PA antenna From 3.5L to upper From 3.5U to lower

From 7.5U to lower

Discharge was terminated with spark around 7.5 PA antenna

tangential view of 7.5 PA antenna From 3.5L to upper From 3.5U to lower

From 7.5U to lower

Observing a spark event with low minority ratio

• A spark event is happened with low H minority ratio afterrepeated steady-state operation.

• By injecting hydrogen super sonic gas puffing (SSGP), the spark event is reduced and vanished in a few minutes(approximately 2 minutes in this discharge after SSGP(0.01Pa･m3/s)).

One of the candidate of sparking place

LightLight

• The spark position is not confirmed, but it seems to be outside at next port by the light of sparks. (flakes on divertor tiles ?)

• As RF power for the PA antenna is increased, the sparks is easy to be happened.

• Checking the relationship between the accelerated tail and this spark.

From 3.5L From 3.5U

Red light emission of divertor trace on the carbon plate protecting coaxial line of ICRF

Carbon plate was curved

From 7.5U

protecting coaxial line of ICRF antenna

From 7.5U

Curved surface of carbon by divertor legWater leak occurred at the support of the carbon plate(7.5L PA antenna)

Summary of recent long pulse discharges

• Density is different in year by year:

• former exp.: less than 19 -3

Duration Time vs. PRF

• former exp.: less than 1x1019m-3

• 2011: more than 1x1019m-3

• 2012: about 1x1019m-3

• extend pulse length in injection of MW level and density of 1x1019m-3

• Spark is still important issue for steady state operation

• Sparks from HAS (dipole mode) antenna is a little

temporary

Summary and future plpan• ICRF discharge was useful for plasma

conditioning

• Reduce H ratio, modify density profile • Reduce H ratio, modify density profile

• Higher density was achieved by HAS antenna with PA antenna

• 1019m-3 plasma was sustained about 19 minutes by ICRF heating and ECHby ICRF heating and ECH

• New antenna will be installed in next campaign

- PA type antenna aiming at high power injection