second harmonic ech preionization with 7 pairs pf coil scenario...

Pl Sh th L b & F i A l t L b

Second Harmonic ECH preionization with 7 pairs PF coil scenario

for KSTAR

E.M. Choi, Y.S. Bae, C.H. Paek, W. Namkung, M.H. ChoPOSTECHPOSTECH

2001 2001 KPSKPSOctober 19-20, 2001

Chonnam univ.


AbstractAbstract

In the initial phase of KSTAR operations, the toroidal magnetic field is planned to be 1.5 T at the tokamak center. In this case, the electron cyclotron frequency is 42 GHz., and the operating frequency of the ECH pre-ionization system is 84 GHz, corresponding to the second harmonics. We modified the pre-ionization code with 7 pairs of poloidal coils. Through the pre-ionization simulation, we obtained the dependence of the loop voltage, electron temperature, and plasma currents for several input parameters in the second harmonic ECH pre-ionization. It is compared to the results of the fundamental harmonic ECH pre-ionization.


KSTAR Target Operation Modes

Bo = 3.5 T, Ip = 2 MA

PNBI = 16 MW, PRF = 12MWPLH = 3MW, PECH = 3 MW

4.0 Low-beta Reverse-shear mode4.1 Low-beta High-li mode4.2 Low-beta H-mode4.3 High-beta Reverse-shear mode4.4 High-beta High-li mode4.5 High-beta H-mode4.6 Full performance mode

Upgrade Plasma

Bo = 3.5T, Ip = 2 MA

PNBI = 8 MW, PRF = 6 MWPMW = 1.5 MW

3.0 Ohmic + NBI mode3.1 Ohmic + NBI + RF mode3.2 Ohmic + NBI + RF + MW mode3.3 Extended mode

Baseline Plasma

Bo = 3.5T, Ip = 2 MA2.0 ECH-assisted 6 V-outer start-up modeOhmic Plasma

Bo = 1.5 T, Ip = 100 kA1.0 ECH-assisted 5 V-inner start-up modeFirst Plasma Target Operation ModesOperation Phase


PF coil structure

(Unit : mH)

PF1 PF2 PF3 PF4 PF5 PF6 PF7 PLAPF1 85.6 26.55 5.96 5.28 7.45 7.13 8.3 0.11PF2 26.55 44.98 12.56 9.18 7.85 5.81 6.47 0.073PF3 5.96 12.56 13.43 10.38 5.3 2.96 3.13 0.037PF4 5.29 9.18 10.38 26.93 10.96 4.48 4.52 0.031PF5 7.45 7.85 5.3 10.96 327.4 37.32 31.21 0.135PF6 7.13 5.81 2.95 4.48 37.31 199.36 99.1 0.219PF7 8.3 6.47 3.13 4.52 31.2 99.1 316.45 0.284PLA 0.11 0.073 0.037 0.031 0.135 0.219 0.284 0.003


KSTAR Operation Scenario(First Plasma Phase)

(-0.6)

(-0.9)

Flux-linkage(V-s)

t (s)

0

0 10

14.055 14.255 15.255

14

Zero crossing

Ip=100 kA

(1.0)

ECH heating

(0.0)

17.0

PF Coil Current (kA) vs. time (sec)

-25

-20

-15-10

-5

0

5

1015

20

25

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

TIme (sec)

PF C

oil C

urre

nt (k

A)

PF-1PF-2PF-3PF-4PF-5PF-6PF-7FECCIVCIRC

Start EndInitial Current Charge


Input parametersInput parameters

1. A major radius; R = 180 cm.2. A minor radius; a = 50 cm.3. An error field range; Berr = 0.1 ~ 4 (mT)4. An initial neutral density; no = 0.2¥1013 ~ 3¥1013 (cm-3).5. RF pulse duration; TRF = 0.2s.6. A magnetic field; Bo = 1.5 T.7. A carbon impurity fraction; fci = 0.018. An oxygen impurity fraction foi is always set to 2 times fci.9. All wave propagates X-mode.


Pre-ionization code modelPre-ionization code model

Continuity equation

diffusion.the todue rate lossthe is v and drift toroidalthe todue rate lossthe is v

field, error todue rate lossthe is v rate, ionizationthe is v where

diff

dr

err

ion

)( diffdrerreionee vvvnvndtdn

++−=Particle balance

dtdn

dtdn eo −=

none

Circuit equation

plasma. and coils PF between sinductance mutualthe is Mthe and resistenceplasma teh is R

plasma,the for 8n and coilPF of pairs 7the for 7~1nwhere voltage) (resistive

voltage) (loop

n8

p

==

−=

−=

×−−

=⇒=−−

∑

∑∑

=

=

=

presis

n

nnloop

np

nn

pn

nn

RIVdtdIMV

dtM

RIdtdIM

dIRIdtdIM

8

7

18

88

8

188

88

8

18 0Energy balance

EiCXEQUi

IRADBREMEQUEdrerreRADOHECHe

vUPPVdt

dU

PPPV

vvvUV

PPPdtdU

−−=

++−++−−+

=

)(1

)(1)(

Ue, Ui, TeVloop, Vresis, Ip


Results of the code calculation Results of the code calculation

1. Temporal behaviorSecond harmonic case

FIG. 1-1. Plots of the plasma current Ip and the electron temperature Teas a function of time.The RF power 500 kW is applied for 0.2 sec, and the Ohmic heating is applied at 50 msec. The parameters are PRF = 500 kW, Berr=1 mT, f=84 GHz, no = 1.0¥1013 cm-3, ne(0) = 1.0â109 cm-3

0.0 0.5 1.0 1.5 2.0-200

0

200

400

600

800

1000

1200

1400

1600

Ip Te

tim e(sec)

I p(A

)

1.0

1.2

1.4

1.6

1.8

2.0

Te (eV

)

0.0 0.5 1.0 1.5-200

0

200

400

600

800

1000

1200

1400

Ip Te

tim e(sec)

I p(A

)

RF power = 500 kW No RF power

1.0

1.2

1.4

1.6

1.8

2.0

Te (eV

)


Fundamental harmonic case

0 1 2 3

0

50000

100000

150000

200000

250000

Ip Te

time(sec)

I p(A

)

-50

0

50

100

150

200

250

300

350

Te (eV

)

0 1 2 3-200

0

200

400

600

800

1000

1200

1400

Ip Te

time(sec)

I p(A

)

1.0

1.2

1.4

1.6

1.8

2.0

Te (eV

)

RF power = 500 kW No RF power

FIG. 1-2. Plots of the plasma current Ip and the electron temperature Teas a function of time. The RF power 500 kW is applied for 0.2 sec, and the Ohmic heating is applied at 50 msec. The parameters are PRF = 500 kW, Berr=1 mT, f=84 GHz, no = 1.0¥1013 cm-3, ne(0) = 1.0â109 cm-3


2. Error field scanSecond harmonic case

0 1 2 3 4

1.45

1.50

1.55

1.60

1.65

Berr(mT)

T e(e

V)

Te(No impurity) Te(fci=0.01) 0.0

0.2

0.4

0.6

0.8

1.0

ne (x10

12/cm3) ne(No impurity)

ne(fci=0.01)

FIG. 2-1. (a) The electron temperature Te and electron density neat 60 ms, plotted as a function of the error field Berr.

FIG. 2-1. (b) The plasma current Ip and resistive voltage Vresis at 60 ms, plotted as a function of Berr.

0 1 2 3 4

400

600

800

1000

1200

1400

Berr(mT)

I p(A

)

Ip(A) Ip(A)_im

-5.70

-5.65

-5.60

-5.55

-5.50

Vresis (V

)

Vresis Vresis_im



FIG. 2-2. (a) The electron temperature Te and the electron density ne at 60 ms,

plotted as a function of the error field Berr.

FIG. 2-2. (b) The plasma current Ip and resistive voltage Vresis at 60 ms, plotted as a function of Berr.

0 1 2 3 40

50

100

150

200

250

Berr(mT)

T e(e

V)

Te(No impurity) Te(fci=0.01)

-1.0

-0.5

0.0

0.5

1.0

ne (x10

14/cm3)

ne(No impurity) ne(fci=0.01)

0 1 2 3 40

5000

10000

15000

20000

Berr(mT)

I p(A

) Ip(No impurity) Ip(fci=0.01)

-6

-5

-4

-3

-2

-1

0

Vresis (V

) Vresis(No impurity) Vresis(fci=0.01)


3. Neutral density scan

Second harmonic case

FIG. 3-1.(a) The electron temperature Te and electron density ne at 60 ms, plotted as a

function of initial neutral density no.

FIG. 3-1.(b) The plasma current Ip and resistive voltage Vresis at 60 ms, plotted as a function of initial neutral density no.

0 1 2 30

2

4

6

8

10

No(x1013/cm3)

T e(e

V)


0.00

0.05

0.10

0.15

0.20

ne (x10

13/cm3)


0 1 2 3

1000

2000

3000

4000

5000

No(x1013/cm3)

I p(A

)

Ip(No impurity) Ip(fci=0.01)

-6

-5

-4

-3

-2

-1

Vresis (V

)

Vresis(No impurity) Vresis(fci=0.01)



FIG. 3-2. (a) The electron temperature Te and electron density ne at 60 ms, plotted as a function of initial neutral density no.

FIG. 3-2. (b) The plasma current Ip and resistive voltage Vresis at 60 ms, plotted as a function of initial neutral density no.

0 1 2 3

0

100

200

300

No(x1013/cm3)

T e(e

V)


0

5

10

15

20

25

ne (x10

13/cm3)


0 1 2 30

5000

10000

15000

20000

No(x1013/cm3)

I p(A

)

Ip(A) Ip(A)_im

-6

-5

-4

-3

-2

-1

0

Vresis (V

)

Vresis(V) Vresis(V)_im


4. RF power scanSecond harmonic case

FIG. 4-1. (a) The electron temperature Te and electron density ne at 60 ms, plottedas a function of the RF power PRF

FIG. 4-1. (b) The plasma current Ip and resistive voltage Vresis at 60 ms, plotted as a function of the RF power PRF.

0 500 1000 1500 2000

1.2

1.3

1.4

1.5

1.6

PRF(kW)

T e(e

V)


0.0

0.1

0.2

0.3

0.4

0.5

ne (x10

13/cm3)


0 500 1000 1500 2000

1000

1100

1200

1300

1400

1500

1600

PRF(kW)

I p(A

)


-5.8

-5.7

-5.6

-5.5

Vresis (V

)




FIG. 4-2. (a) The electron temperature Te and electron density ne at 60 ms, plotted as a function of the RF power PRF.

FIG. 4-2. (b) The plasma current Ip and resistive voltage Vresis at 60 ms, plotted as a function of the RF power PRF.

0 500 1000 1500 20000

200

400

600

800

PRF(kW)

T e(e

V)


0.0

0.5

1.0

1.5

2.0

ne (x10

13/cm3)


0 500 1000 1500 20000

5000

10000

15000

20000

PRF(kW)I p(

A)


-6

-5

-4

-3

-2

-1

0

Vresis (V

)



ConclusionConclusion

1. For the second harmonic case, ECH pre-ionization is not effective for initiating plasma. To make plasma initially, we must modify the central magnetic field to make fundamental harmonic magnetic field (3T) in tokamak or use mode conversion. For the fundamental harmonic case, ECH pre-ionization is very outstanding effect.

2. For the second harmonic ECH heating, the impurity effects are not significant and Te and Ip maximized near 500 ~ 1000 kW RF power.


ReferencesReferences

1. B. Lloyd, et al., Nuclear Fusion 31, 2031 (1991)

2. A. G. Kulchar, et al., Phys. Fluid 27, 1869 (1984)

3. Y-K. M. Peng, et al., Nuclear Fusion 18, 1489 (1978)

second harmonic ech preionization with 7 pairs pf coil scenario...

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