Optimization of the magnetic field configuration for … 1 (27) 7th Workshop on Fusion Data Processing Validation and Analysis. Frascati 26 - 28 March 2012 Optimization of the magnetic

F.Maviglia 1 (27) 7th Workshop on Fusion Data Processing Validation and Analysis. Frascati 26 - 28 March 2012

Optimization of the magnetic field Optimization of the magnetic field configuration for JET breakdownconfiguration for JET breakdown

F. MavigliaF. Maviglia

with contribution from

R. Albanese, P.J. R. Albanese, P.J. LomasLomas, A. , A. ManzanaresManzanares, M. , M. MatteiMattei, A. , A. NetoNeto, F.G. , F.G. RiminiRimini, P.C. de , P.C. de VriesVries

and JET EFDA Contributorsand JET EFDA Contributors

http://www.create.unina.it/index.php


Introduction

Modelling activity

Static and dynamic simulations

Intensified Visible Fast Camera KL8A

Experimental results

Conclusions

OutlineOutline


filling pressure;

toroidal electric field (E0

≈1V/m in present Tokamaks, E0

≈0.33V/m ITER);

magnetic field configuration (null position and extension of the low field region);

Breakdown optimization parameters:

1 2 3 4 5 6

−4

−3

−2

−1

0

1

2

3

4

ΔΨ = 0.01 Vs

R (m)

Z (m

)

IPRIM −15 (kA)IP4T 180 (A) IERFA 0(A)

1

2

3

4

5

6 7

8 9 10 11 12 13

14

15

16

17

18

P3ML

P3MU

P1

P2RU

P2RL

P3RU

P3RL

P4U

P4L

Static simulation

IPRIM transformer (open loop):• mode D,C initial value(=premag)[-7,-40] kA, iron fully saturated;• mode B premag ≈

0, iron with residual magnetization;

IP4 Vertical field (open loop)IERFA radial field (feedback)

Circuits used for breakdown at JET:

IntroductionIntroduction

Hexapolar field



;41

z

nullc B

BaL

z

null

BBa

= size of the field min.

P = pressure;

E = electric field;

= avg. stray field over the null;

;103.1exp102 43

EP

Pi

Avalanche

successful

if

Lc

/λi

>> 1minimize

<δBz

>, maximize

anull

•Connection length Lc

[1]:

•Ionization length

λi

:

= toroidal field;

1 2 3 4 5

−3

−2

−1

0

1

2

3

R [m]

Z [m

] ΔΨ = 0.01 Vs iso B= [0.5;1;1.5;2;2.5] mT

IP1 −15 [kA]IP4 180 [A]

with:

with:

Magnetic field configuration

[1] B. LLoyd, et al., Nucl. Fus. 31 (1991) 2031.


JET poloidal field (PF) coils JET iron

8 Coil sets, named P1 to P4,D1 to D4 (D not shown).

P4

P3

LimbsP1

P2

Central column

Collar(Shoes not

shown)



•CREATE Model [1] based on 2D FEM:•Passive structures: MS, VV, RR, MK2. Resistivity value of MS has been refined via best fit of the simulations with the experimental data. Resistivity of VV, RR, MK2 in agreement with [2-3].

References:[1] R. Albanese et

al., Nucl. Fusion, 38, 1998, pp. 723–738.[2] R. Albanese, et.al. Nucl. Fusion 44 (2004) 999–1007.[3] S.Gerasimov, ‘

JET_PassiveSimpleModel.pdf ‘.

Passive structures

#78021 (Ipre = -15kA)

Dyn. Sim. v.s. exp. estimations of mk2 current

ModellingModelling


0 2 4 6−6

−4

−2

0

2

4

6

CREATE−NL/CREATE−L model

R [m]Z

[m

]

JET Iron Model

Centre limb pad

Outer limb pad3 mm gap present in the magnetic circuit at z=4.5m, and not at z=-4.5m, present at JET and considered in the model: up-down asymmetry.

-Outer limb pad: thickness 3mm

-Centre limb pad: thickness 3mm

CREATE iron model

ModellingModelling


E

Mode D breakdownStatic simulation using as input primary and vertical field current (other noisy curr. set to 0).

-Hexapole null splits in two quadrupole nulls in the direction of the radial field given by the upper iron gaps.

-Inboard-low null expected to be preferred for plasma formation for the higher electrical field.

|Br|≈0.35mT

Critical points for JET breakdown magnetic reconstruction: Residual iron magnetization, not included in present exp. measurements; Perturbing effect of vessel and in-vessel passive currents.

StaticStatic simulationssimulations


Configurations used for breakdown:Configuration 1 Configuration 2 Improved

2 2.5 3 3.5

−1.5

−1

−0.5

0

0.5

1

1.5

2

R [m]

Z [m

]

Z [m

]

IntensifiedIntensified

VisibleVisible

Fast Camera KL8AFast Camera KL8A

Specifications

Region of interest

272 x 384 px

Freq. 1.0 kHz

Exposur e Time

142.9 s

Filter none

Intensifi er Gain 700 v

Specifications

Region of interest

176 x 256 px

Freq. 7.5 kHz

Exposur e Time

125.0 s

Filter none

Intensifi er Gain 750 v


Comparison between dynamic simulation

and fast camera [1] (carbon wall):-Inner field null preferred for plasma formation.-Plasma pushed against the inboard and included in the region between the two lines where Btg

= 0. -The ionization cloud appears to be pushed down in the divertor region. -For a successful breakdown the plasma is pushed up toward the outer wall.

-0.5

0

0.5

1.0

1.5

2.0

Pulse No: 78369t = 0.006028s

Pulse No: 78369CREATE L flux-map

2.5

-1.0

-1.5

-2.0

-2.5 2.01.5 2.5 3.0 3.5 4.0 4.5

Z (m

)

IPRIM = -19.4(kA)IP4T = 123(A)IFRFA = 138(A)Other 0(A)

6ms

Force

Δψ = 0.02Vs

R (m)

JG10

.248

-4c

1.5

2.0

1.0

0.5

0

-0.5

-1.0

-1.5

2.52.0 3.0 3.5

Z (m

)

R (m)

1.5

2.0

1.0

0.5

0

-0.5

-1.0

-1.5

2.52.0 3.0 3.5

Z (m

)

R (m)

1.5

2.0

1.0

0.5

0

-0.5

-1.0

-1.5

2.52.0 3.0 3.5

Z (m

)

R (m)

JG10

.248

-5c

Pulse No: 78369t = 0.014028s

Pulse No: 78369t = 0.028028s

Pulse No: 78369t = 0.038028s

time increasing

[1] F.Mavilgia et al.,Fus. Eng. and Des. 86 (2011) 675–679.

Standard non optimized breakdown dynamic evolution

H

L


Multi-pole field (2D plane geometry):

Hexapole

splits in 2 quadrupole nulls

in the direction of the perturbation field with vertical and radial components.

-

Hexapole

null.

Perturbed hexapolar field, represents iron-gapsSymmetric multipolar field: np=6

filaments added represent JET irongaps



Radial field added to rotate perturbed field: Zoom in

The two quadrupole nulls are rotated in the direction

given by the correction radial field.

* filaments added represent radial field correction

*

*



Optimization of field null position during breakdown Aims:

Place the null field position far from the inner divertor region.

Solution:

Rotate the 2 quadrupole field nulls by applying an offset radial field bias.

2 3 4−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.50 ms

R [m]

Z [m

]

IP1 −20.0 [kA]IP4 258 [A]IFRFA −2 [A]Other PF 0 [A]

ΔΨ = 0.01 Vs iso B= [0.5;1;1.5;2;2.5;] mT

Flu

x

2 3 4−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.50 ms

R [m]

IP1 −20.0 [kA]IP4 258 [A]IFRFA 118 [A]Other PF 0 [A]

ΔΨ = 0.01 Vs iso B= [0.5;1;1.5;2;2.5;] mT

Flu

x

2 3 4−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.50 ms

R [m]


ΔΨ = 0.01 Vs iso B= [0.5;1;1.5;2;2.5;] mT

Flu

x

2 3 4−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.50 ms

R [m]


ΔΨ = 0.01 Vs iso B= [0.5;1;1.5;2;2.5;] mT

Flu

x

Standard radial bias =0A radial bias =+120A radial bias =+240A radial bias =+360A

-In the cases with radial

bias

≠0 the upper inner field null expected to be preferred for plasma formation due to higher electrical field.

Static sim

all at 40s: Increasing radial field bias

→ quadrupoles

rotation



kl1-o4wb-raw @40.04:

Pulse #80400, std. radial bias =0

kl1-o4wb slow camera (40ms) first visible frame: plasma starts in an upper inner wall position with radial bias correction, far from divertor region.

kl1-o4wb-raw @40.03:

Pulse #80402, radial bias =+240A

ExperimentalExperimental

resultsresults

mode D mode D --20kA 20kA premagpremag


-20.0 -19.0

-18.0

-17.0

103

A

0.2 0.4 0.6 0.8 1.0 1.2

103

A

0.0

1.0

2.0

103 A

-4.0 -3.0 -2.0 -1.0 0.0

105V

0.00.51.01.52.0

2.5

a.u.

40.00 40.02 40.04 40.06SEC.

-2.0 -1.5 -1.0 -0.5 0.0

105

A

80400 80401 80402 80404

IP1 (primary)

IP4 (vertical)IERFA (radial)

VFB (vertical velocity control request)

HALPHA

Plasma current

0,std120A240A*360A

•Higher velocity loop control for st. pulses

•Higher radial field current peak for standard pulse.

•Plasma curr.>47kA, velocity loop “ON”

Radial bias:

*radial bias =+240A optimum predicted by sim.: exp. verified.


resultsresults



0.0

1.0

2.0

103

A

-4.0

-3.0

-2.0

-1.0

0.0

105

A

40.00 40.02 40.04 40.06SEC.

-1.0

-0.5

0.0

0.5

1.0

1.5

104

A

80400 80401 80402 80404

IERFA (radial)


std pulse


optimized

Radial bias:0,std120A240A360A

Velocity loop control peaks (≈105V) when plasma pulled up from divertor region for std pulses.

Moderate control action for optimized pulses. ∆IERFA in time interval of interest decrease form 3.2kA to 0.7kA: factor ≈4.

2.5kA peak std. pulse: amplifier limit =5kA

standard(radial bias=0)

optimized (radial bias=+240A)

time interval of interestExperimentalExperimental

resultsresults


VV


-20.0 -19.0

-18.0

-17.0

103

A

0.2 0.4 0.6 0.8 1.0 1.2

103

A

-1.0 0.0 1.0 2.0 3.0 4.0 5.0

103

A

-1.5

-1.0

-0.5

0.0

106

V

-2.5 -2.0 -1.5 -1.0 -0.5 0.0

105

A

40.00 40.02 40.04 40.06SEC.

0.00.20.40.60.81.01.21.4

a.u.

81755 81756 81757 81758

IERFA (radial)

IP4 (vertical)IP1 (primary)


plasma current

HALPHA

Radial bias (A):0,marginal0,NSB0,NSB+360, ok

•∆IERFA (≈4kA) for 0 bias pulses, limits (±5kA)

upper lim.

•Larger vertical velocity request for zero radial bias pulses

NSB

I0Z limit scan

for -20kA breakdown

•Non

Sustained Breakdown

(NSB) or

marginal for radial bias=0.


resultsresults



−100 0 100 200 300 400 5000

1

2

3

4

5Mode D: Premag −20kA

IERFA @40s (A) (radial field bias)ΔIER

FAm

ax (

kA) i

n ra

nge

of in

tere

st

radial bias =0

(std.)

min

Statistic all mode D breakdown.

ΔIERFA reduction factor ≈4 from std.

Statistic on all successful mode D breakdown with new VS system (named V5) measurements tuned with a precision lower then ±50A.

radial bias scan

figure of merit:

min (min (∆∆IERFA)IERFA)for t

time interval:•

|Plasma current| > 47 kA (velocity loop on) up to •40.065s (plasma in outer limiter).


resultsresults



0

1000

2000

40 40.01 40.02 40.03 40.04 40.05 40.06

−4

−3

−2

−1

0

x 10

5a.

u.

sec

IERFA

VFB (velocity loop control request)

A

1) 40.018s

time

increase

Fast visible camera for mode D Fast visible camera for mode D --10kA premag10kA premag

1 #824

01no

radi

albi

as#8

2400

radi

albi

as= +

150A

(radial)

Larger bdarea


0

1000

2000

40 40.01 40.02 40.03 40.04 40.05 40.06

−4

−3

−2

−1

0

x 10

5a.

u.

sec

IERFA


A

1) 40.018s

time

increase

deeper

in divertor

2) 40.045s


1 #824

01no

radi

albi

as#8

2400

radi

albi

as= +

150A

2

(radial)

Larger bdarea


0

1000

2000

40 40.01 40.02 40.03 40.04 40.05 40.06

−4

−3

−2

−1

0

x 10

5a.

u.

sec

IERFA


A

3

1) 40.018s

time

increase

Plasma touches upper wall

deeper

in divertor

2) 40.045s 3) 40.058s


1 #824

01no

radi

albi

as#8

2400

radi

albi

as= +

150A

2

(radial)

Larger bdarea


40.445s1.5 2 2.5 3 3.5 4 4.5

−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

R [m]

Z [m

]

1.5 2 2.5 3 3.5 4 4.5−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

R [m]

Z [m

]

1.5 2 2.5 3 3.5 4 4.5−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

R [m]

Z [m

]

1.5 2 2.5 3 3.5 4 4.5−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

R [m]

Z [m

]

P4 (vertical field) bias

0.400.420.440.460.480.50

0.0 0.2 0.4 0.6 0.8 1.0

10

3

A

200300400500600

0.0

0.5

1.0

1.5

a.u

.

40.40 40.45 40.50 40.55SEC.

-1.5

-1.0

-0.5 0.0

10

5

A

81627 low IP4 bias 81628 high IP4 bias

VLOOP (primary)

IP4 (vertical)

IERFA (radial)

HALPHA

IPLA

A

V/m

Different IP4

(vertical field) dynamic induces different eddy currents dynamics: magnetic null enters in the chamber*

later -> delayed breakdown.

8162

7 81

628

*dynamic simulations

E @ r = 2.95mE0 ≈0.48V/m


resultsresults

forfor

mode B high Emode B high E00

40.475s

*


40.512 s

Mode B low Electric field Mode B low Electric field ““ITER likeITER like””82076 radial bias= -50A

82074 radial bias= 0

82077 radial bias= +50A


82076820748207782078

Radial

bias: -50A

0A+50A

+100A

centered

Same initial iron magnetization as

mode D

E0 ≈0.3V/m


40.512 s

40.566 s

divertor





82076820748207782078

Radial

bias: -50A

0A+50A

+100A

centered

E0 ≈0.3V/m


40.512 s

40.566 s

40.574s

failed

E0 ≈0.3V/m

divertor

•E0 <0.3V/m not achievable without error field optimization (i.e. radial bias).•Min. electric field E0 ≈0.25V/m (pulse #82081),with radial bias = +100A.





centered


Up-down asymmetric iron gap modelling activity. Radial field ≈0.5mT at r=2.95m, for fully saturated iron.

This leads to split the ideal hexapolar null in two

quadrupolar

nulls.

Static and dynamic optimization to optimize the plasma formation region in the upper inner wall, far from divertor zone.

Accurate model, with a precision of a fraction of mT, has been employed for magnetic null position scan.

Fast visible camera

used to validate optimized plasma starting position

and dynamic evolution.

ConclusionsConclusions


Optimized breakdown avoids the plasma to be pushed in the divertor region as for the past pulses. Non optimized breakdowns are more fragile with a number of NSB.

VS system

improved

behavior, with smaller radial field current excursion (factor ~4), farther from amplifier limits.

Re-established at JET low electric field “ITER like” breakdown using I0Z bias:

mode D min E0

≈0.27V/m with premag

= -7kA;

mode B min E0

≈0.25V/m.

Low electric field pulses breakdown success particularly sensitive to error field optimization: ITER E0

= 0,33V/m.

ConclusionsConclusions

Documents

Optimization of the magnetic field configuration for … 1 (27) 7th Workshop on Fusion Data Processing Validation and Analysis. Frascati 26 - 28 March 2012 Optimization of the magnetic