Improvements in ECH and ECCD Properties by Upgrade of ECH...

Korea-Japan Workshop on Physics and Technology of Heating and Current Drive, 2016.12.14–16, Pohang

Improvements in ECH and ECCD Properties by

Upgrade of ECH Antenna System on LHD

Y. Yoshimura, S. Kubo, T. Shimozuma, H. Igami, H. Takahashi, T.I. Tsujimura,R. Makino, S. Kobayashi, S. Ito, Y. Mizuno, K. Okada, K. Yanagihara*, and the LHD Experiment Group

National Institute for Fusion Science, 322-6 Oroshi, Toki 509-5292, Japan* Graduate School of Engineering, Nagoya Univ., Nagoya 464-8601, Japan

[email protected]

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Contents of This Presentation

> Brief introduction of LHD and its ECH system

> Recent upgrade of ECH system on LHD> Installation of a second 154 GHz gyrotron> Relocation of a 77 GHz injection port from top to horizontal> Installation of two new ECH antenna systems in a horizontal port

> Experimental achievements using the upgraded ECH system> High-Te0 of 10 keV at electron density of 2×1019 m−3

> Simultaneous achievements of high-Te0 and high-Ti0

> 39 min stable plasma sustainment> High density plasma heating by 154 GHz EC-waves> High current drive by combination of ECCDs

> Conclusions2

> LHD Specifications-Major radius

3.4 ~ 4.1 m-Minor radius

~ 0.6 m (at Rax=3.6 m)-Plasma Volume

~ 30 m3 (at Rax=3.6 m)-Magnetic field on axis≦ 2.85 T (at Rax=3.6 m)

> Heating power -ECH (77 GHz×3,154 GHz×2, 82.7

GHz×1)5.4 MW 0.6 MW/CW

-NBI (Neg.×3, Pos.×2)27.0 MW 0.5 MW/10 min

Cryostatvessel

Poloidal coilsHelical coilsPlasma

Vacuum Chamber

DivertorLegs

Height: 8.8 mOuter Diameter: 13.5 mTotal Weight: 1,500 ton

Horizontal(O) port

Top (U) port

Large Helical Device (2017, next 19th experimental campaign: LHD's first DD experiment)

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Specification of 77 and 154 GHz Gyrotrons

Items Design

Frequency

Power/ Pulse length

Cavity mode

Tube type

Collector type

Output window

77GHz / 154GHz

1.0MW for 5s (77GHz #1)1.3MW for 1s (77GHz #2)1.8MW for 1s (77GHz #3)1MW for 5s (154GHz#1, 2)

0.3MW / 0.5MW for CW

TE18,6 / TE28,8

Triode

Collector potential depression

CVD diamond

4

Specification of ECH System after 2014

> New high power, long pulse 77 GHz (#1: working from 2007, #2: from 2008 and #3: from 2009) and 154 GHz (#1: from 2012 and #2: from 2014) gyrotrons> Maximum total injection power in pulse operation to LHD simultaneously became up to 5.4 MW> One of the 77 GHz gyrotron relocated its power injection port from 9.5-U top port to 2-O horizontal port

2

2

5

Relocation of a 77 GHz Injection Port from Top to Horizontal

2

2

6

top port injection horizontal port injection

> In the case of top port injections, beam path and resonance layer are nearly tangential --> power deposition profile tends to be broad, and slight refraction of beam path results in large change of ρdep, even results in no power deposition

> In the case of horizontal port injections, beam path and resonance layer are nearly normal --> precise control of power dep. is possible

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Installation of Two ECH Power Injection Antenna Systems in LHD Horizontal Port 2-O

> Two sets of new ECH antenna mirrors were installed at horizontal port, corresponding to the increase in the number of gyrotron and to the change of one of the injection ports from top to horizontal

2-OLR, 77GHz2-OUR, 77GHzNEW

2-OLL, 154GHz

2-OUL, 154GHzNEW

2-O port top view

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Four EC-wave Injection Mirror Antenna Systemsin 2-O Port of LHD

new 2-OUR 77GHz

new 2-OUL 154GHz

old 2-OLL 154GHzold 2-OLR 77GHz

> Power injection antenna systems of four of five high power gyrotrons are concentrated in the 2-O port

inside view of 2-O port

Experimental achievements using the upgraded ECH system 1

High-Te0 of 10 keV at line average ne of 2×1019 m−3

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> Plasma parameter region is extended to high-Te and high-ne side

> Concentrated on-axis ECH power deposition realizes highly peaked Te profile with electron ITB


Simultaneous achievements of high-Te0 and high-Ti0

10

> Concentrated on-axis focused EC-waves are additionally applied to high-Ti

plasmas sustained by high power NBI

> Despite the flattening of Ti profile due to ECH, Te0=7.6 keV with Ti0=6 keV at ne_ave=1×1019 m−3 was achieved

Ti,

Te

[keV

]

ne [

10

19

m−

3]

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Stable High Performance 39 Min Discharge by ECH

> 154GHz powers of 120kW and 91kW, and 77GHz powers of 163kW and 110kW were applied all from 2-O port for CW plasma sustainment

> Two 154GHz powers are applied continuously and two 77GHz powers alternately: time averaged injection power was 350kW

> One more 77GHz power is applied from top port for plasma start-up and additional heating in the cases of density increase

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> Data acquisition of Thomson scattering measurement was in failure in the 39 min discharge #131059: Te0 in nearly the same discharge #131054 is plotted for reference

> A higher performance plasma of Te0 > 2.5keV, Ti = 1keV, ne_ave = 1.1×1019 m−3 was sustained for 39 min by higher ECH power

> Stable plasma: no intense impurity signals except for the timing of termination



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> 154GHz powers of 120kW and 91kW were applied continuously

> 77GHz powers of 163kW and 110kW were applied alternately

> 77GHz power of 247kW (5.5-U) was applied in case of ne rise

> Due to the variation of combination of ECH powers, total injection power varies such as 320kW, 370kW and 620kW

> Te0 increases and Te profile becomes fat with ECH power: robust plasmas against impurity influx can be generated



time (s)


High density plasma heating by 154 GHz EC-waves

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> Cutoff density of 77GHz 1st-O is 7.4×1019 m−3

> Cutoff density of 154GHz 2nd-X is 14.7×1019 m−3

> Even at density of 13.1×1019 m−3, application of 154GHz EC-wave demonstrated heating efficiency of 64% while 77GHz wave had no heating effect

TRAVIS code: N.B. Marushchenko et al., Nuclear Fusion, 48 (2008) 054002, 49 (2009) 129801


Combination of two 77 GHz ECCDs for high current drive

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> 77GHz on-axis 2nd harmonic ECCDs in this presentation> Focused Gaussian beam injections from horizontal 2-O port> Beam directions are two dimensionally steerable> EC-wave beams are injected obliquely aiming at magnetic axis> Beam direction is defined by N//: projection of beam unit vector on toroidal direction at magnetic axis> Polarization of waves is controlled using polarizers> Low-field side injection: current will be driven oppositely to beam direction according to the Fisch-Boozer theory> Positive (negative) N// <ー> positive (negative) Ip

ECCD by Use of EC-Wave Beams Injected from 2-O Port

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Low Magnetic Ripple with Magnetic Axis Position of 3.75m

> 10th symmetry in toroidal direction in LHD: 1 period is 36 degrees> EC-wave beam injection from the horizontal 2-O port at toroidal angle of 18 deg.> Variation of magnetic field on magnetic axis is negligible with Rax=3.75m> Mirror-trapping effect in magnetic well which degrade ECCD efficiency can be reduced by setting Rax at 3.75m1.4

1.45

1.5

1.55

1.6

0 6 12 18 24 30 36

Rax=3.6mRax=3.75mRax=3.9m

toroidal angle (degree)

magnetic field on axis (T)

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Dependence of IECCD on N// calculated with TRAVIS code

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> Rax=3.75m, ne0=0.3×1019 m−3 with flat profile, Te0=3keV with peaked profile, and 1MW ECCD power PECCD were assumed for the calculations> Maximum IECCDs are expected with N//

~±0.2 > In the experiment, EC-wave beam directions were controlled by a parameter Tf (toroidal position of beam center on the R=3.9m plane) so that N//

to be ~±0.2 and IECCD to be maximum

UR, co-ECCD: Tf =0.3m, N// =0.195LR, co-ECCD: Tf =0.5m, N// =0.204UR, ctr-ECCD: Tf =−0.3m, N// =−0.195LR, ctr-ECCD: Tf =−0.2m,N// =−0.229

Waveforms in Two ECCDs Combination Exp. 1Rax=3.75m, Bt=1.375T

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020406080

100#128315

0 2 4 6 8 10

plas

ma

stor

eden

ergy

(kJ)

time (s)

0

0.1

0.2

0.3

0.4#128315

2-OUR, ctr-ECCD2-OLR, ctr-ECCD5.5-U, ECH

ECH

pow

er (M

W)

0

0.5

1

1.5#128315

ne (1

019 m

-3)

NBI0

0.1

0.2

0.3

0.4#128317

2-OUR, co-ECCD2-OLR, co-ECCD5.5-U, ECH

0

0.5

1

1.5#128317

020406080

100#128317

0 2 4 6 8 10

time (s)

NBI

counter-ECCDs co-ECCDs

-40

-30

-20

-10

0

10

20

30

40

0 2 4 6 8 10

plas

ma

curr

ent (

kA)

time (s)

#128317ECH + co-ECCDx2

#128315ECH + ctr-ECCDx2

NBIs

-46.761+57.574*exp(-t/6.63)

47.409-71.482*exp(-t/5.45)

Waveforms in Two ECCDs Combination Exp. 2

20

> 730kW ECCD power PECCD : 365kW×2 co/ctr-ECCDs with 270kW ECH power from 5.5-U> ne_ave~0.45×1019 m−3

> Right-hand circular polarization for ECCDs> Based on previous calculations using TRAVIS, N// were set at ~±0.2> Direction of Ip agrees with the Fisch-Boozer theory> Ip reaches ~±26kA by ~6s> Pulse duration times were not enough long: the time constant of Ip evolution is ~6s, and saturated |Ip| could be ~47kA

47.4−71.5*exp(−t/5.5)

−46.8+57.6*exp(−t/6.6)

Evaluation of ECCD Efficiency

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> Applying the experimental values of ne = 0.45×1019 m−3, Rax = 3.75m, IECCD = 26kA at t = 6s, and PECCD = 730kW, the ECCD efficiency η defined as

η = ne*Rax*IECCD/PECCD

in the dual-ECCD experiment using 2-OLR and new UR antennas is evaluated as η = 6.0×1017AW−1m−2 at t = 6s in both the co and counter directions

> It is comparable to the previously obtained efficiency of the 2-OLR antenna,η = 5.0×1017AW−1m−2 at t = 6s

> Thus both the experimental result and TRAVIS calculation show the nearly equivalent ECCD availability of the new 2-OUR antenna as the existing LR antenna --> EC-driven current can be twice

Conclusions

> ECH system on LHD has been upgraded for recent years> A second 154 GHz gyrotron was installed> A 77 GHz injection port was relocated from top to horizontal> Two new ECH antenna systems were installed in 2-O port

> The upgraded ECH system significantly contributes to LHD exp.> Plasma param. region is extended to high-Te and high-ne side> High-Te0 with high-Ti0 is simultaneously achieved> Stable plasma is sustained by ECH only for up to 39 min> High-ne plasma heating is available by 154 GHz EC-waves> High current drive is available by combination of ECCDs

Future Plans

> One more 154 GHz gyrotron and related components> Further extension of plasma parameters: Te, ne, Ip, Tp, Ti, ...> Applying ECCDs for exp., especially 77G 1st-O and 154G 2nd-X

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Improvements in ECH and ECCD Properties by Upgrade of ECH...

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