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Status of the JET Faraday cup lost Status of the JET Faraday cup lost alpha particle diagnostic KAalpha particle diagnostic KA--22

F.E. CecilF.E. Cecil11 , V. Kiptily, V. Kiptily22 , D. Darrow, D. Darrow33, A. Murari, A. Murari22, and JET, and JET--EFDA contributors*EFDA contributors*JETJET--EFDA, EFDA, CulhamCulham Science Centre, Abingdon, OX14 3DB, UKScience Centre, Abingdon, OX14 3DB, UK1 Colorado School of Mines, Golden Colorado, USA1 Colorado School of Mines, Golden Colorado, USA2 JET2 JET--EFDA, Abingdon, UKEFDA, Abingdon, UK3 Princeton Plasma Physics Lab, Princeton, New Jersey, USA3 Princeton Plasma Physics Lab, Princeton, New Jersey, USA**Appendix of F. Appendix of F. RomanelliRomanelli et al., Proceedings of the 23rd IAEA Fusion et al., Proceedings of the 23rd IAEA Fusion

Energy Conf. 2010, Energy Conf. 2010, DaejeonDaejeon, Korea, Korea

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The JET lost alpha particle diagnostic KA-2 was installed in JET in 2005 to

investigate lost energetic ions in general and lost alpha particles from possible future

d-t plasmas in particular. We will summarize our operational experience with this

diagnostic over the past six years. In particular we will describe the response of KA-

2 to ICRH, scattered UV, Langmuir type behavior and various machine magnetic

fields. We will also summarize the measurement of lost energetic ions during ICRH

heated deuterium/helium plasmas during the 2009 JET campaign. Finally we will

discuss the theoretical and experimental evidence for the insensitivity of this

diagnostic to intense fluxes of fast neutrons as the basis for the consideration of such

a device as a lost alpha diagnostic for ITER and other future burning plasma

experiments.

This work supported in part by PPPL subcontract S010140-F and the U.S. Department of Energy and by

EURATOM and carried out within the framework of the European Fusion Development Agreement. The

views and opinions expressed herein do not necessarily reflect those of the European Commission.

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(1) Conceptual design of KA2 Faraday Foil lost alpha diagnostic

(2) Measured and calculated responses of a set of thin Faraday foils as a lost

alpha particle diagnostic for high yield d-t plasmas to:

(a) Fast neutrons(b) Energetic gamma rays(c) UV radiation/Langmuir (d) ICRH (e) Time varying magnetic fields

(3) Recent observations on JET

(a) Lost α’s / d’s with energies up to 7 MeV during ICRH 4He plasmas

(b) Energetic 3He/d’s during mode conversion plasmas

(c) Rough calibration of KA3 PMT current during ICRH 4He plasmas

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Amp Amp Amp Amp

0.5 MeV p, d, t0-1.6 MeV alphas

4.2- 5.9 MeV alphas

0.7-1.2 MeV p, d, t

2.5 um x 25 mm x 75 mm Ni foil

(1) Conceptual design JET Lost Alpha Diagnostic KA-2; 2005

2.5 um x 25 mm x 75 mm mica foil

Darrow et al.;Fus. Eng. and Design, 74, 853, (2005)

58Ni(n,p)

2.3-3.8 MeV alphas

1.1- 2.2 MeV p, d, t

6.3-7.2 MeV alphas1.7- 2.5 MeV p, d, t

5

Plasma

Beam

Pylon

Faraday cup modules

9°

15°

21°27°

33°

Schematic diagram of poloidal distribution of 5 sets of foils

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φ = Neutron flux = 6 E13 /cm2 - s;σ = Cross section = 6 E-25 cm2;n = Target density = 2.1 E 19 /cm2;reaction rate density = φ * σ * n = 7.4 E 8 /cm2-s predicted current = - 0.12 nA/cm2

Cross sections for 58Ni + n

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20

Energy (MeV)

Cro

ss s

ectio

n (b

)

(n,p)

(n,a)

Calculation of fast neutron induced currents

Measurements of fast neutron induced currents (per cm2 target)

• Machine Flux(n/cm2/s) Msd current Pred current

• TFTR(95) a 1E12 < 100 nA 0.1 nA• JET(97) b 3E12

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Attenuation coefficient at 5 MeV = 0.03 cm2/gm

Thickness of 2.5 micron Ni foil = .002 gm/cm2

Gamma ray flux= 6 1013 /cm2 - s;

Number absorbed= 6 1013 (1 – e- Atten * Thk )

= 4 10 13/cm2-s= 0.6 nA/cm2

Induced charge from 2.5 micron foil ~ 2.5 10-23 Coulomb/ (γ/cm2) a

Measured current for γ flux of 6 1013 /cm2 - s ~ 1.2 nA/cm2

a X. Ouyang et al. IEEE Trans Nucl Sci vol 54, p 1239 (2007)

Measurement of gamma ray induced currents (per cm2 target)

Calculation of gamma ray induced currents (per cm2 target)

Response (b): Energetic gamma rays

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Combined observed neutron/gamma insensitivityExample: KA-1 on JET for 16 MW d-t pulse

Total neutron yield JPN42976

0

2E+18

4E+18

6E+18

8E+18

10 11 12 13 14 15Time (sec)

Neu

tron

s/se

c

KA1 f2-f4 JPN42976

-10

-5

0

5

10

15

20

10 11 12 13 14 15

Time (sec)

Net

foil

curr

ent (

nA)

9

Observation of significant (µA) current during Ohmic heating

Response (c): Scattered UV/Langmuir

10 20 30 s

5

uA

0

1.0

MW

0.0

5.0

105

cps

0.0

69608 KA2 foil 411

69608 dd/N1CME5

69608 NBI/PTOT

10

Observed strong correlation with bolometer which is good measure of UV/Langmuir

10 20 30 s

1.0

MW

0.0

5

uA

0

69608 KA2 foil 411

69608 BOLO/TOPI

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Comparison of front foil current and bolometric power

Conclusion ~ 6 µA front foil current per MW total bolometric power:

Solution: 1) Install very thin (0.1 µm) Ni foil to suppress UV/low energy ions2) Measure BOLO and subtract using 6 µA /MW

1

10

100

1000

0.1 1 10 100 1000

Radiated power (MW).

Fo

il C

urre

nt (u

A)..

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Response (d): >100 µA of noise during high power (6 MW) ICRH

Comparison of foil currents for JPN 75699 (with 4.5 MW of RF power) where filters have been installed on KA2-415, 416 and 417 and JPN 74285 with no filters. Note that the currents in these three foils are at the 100 nA level whereas the currents in the unfiltered foils exceed 100 µA.

Solution: reduce noise by >100 with passive filters at amps

Comparison of 74285 (RED - no filters) at 68.0 sec and 75699 (Green - filters on 415, 416 and 417) at 57.4 sec

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

411 412 413 414 415 416 417 418

KA2 foil

KA

2 cu

rren

t (A

mpe

res)

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Response (e): Correlation between KA2 total current density and time derivative of Toroidal magnetic field (but NOT other magnetics)

I t (A

mps

)dI

t/dt

(Am

ps/s

ec)

J Tot(A

/m2)

-1.E+04

0.E+00

1.E+04

-8.E+04

-4.E+04

0.E+00

0 10 20 s

-2.E-04

0.E+00

2.E-04

4.E-04

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Toroidal field current derivative

-6.E+03

-4.E+03

-2.E+03

0.E+00

2.E+03

4.E+03

6.E+03

-30 -20 -10 0 10 20 30 40

KA2 (x 1E-5) A/m2

dIt/dt (A/s)79176

79209

79429

79265

Solution: subtract induced current by measuring dIt/dt and using approximate

correlation coefficient JTot (A/m2) ~ 4.5 10-8 (s/m2) dI t/dt (A/s)

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Observation (a):Lost alpha particles (or deuterons) with energies up to about 7 MeV (4 MeV) generated during ICRH (up to 6 MW) 4He/d plasmas

JPN 79171

KA2 112 and 114

KA2 132 and 134

KA2 142 and 144

ICRH

NBI

2.3-3.7 MeV

6.3- 7.2 MeV

2.3-3.7 MeV6.3- 7.2 MeV

2.3-3.7 MeV

6.3- 7.2 MeV

Recent observation of energetic charged particles

10 14 18 s

5

MW

0

20

nA 0

-10

20

nA0

60

nA0

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KA2 112,113 and 114

Just 114 (6.3 to 7.2 MeV)

JPN 79171

Alphas ?

2.3-3.7 MeV

4.2- 5.9 MeV

6.3- 7.2 MeV

deuterons ?

2 -2.3 MeV

5

MW

0

ICRH

NBI

11

nA

6

60

nA

0

10 14 18 s

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Foil currents at increasing RF power

0

10

20

30

40

50

60

0 1 2 3 4 5 6RF power (MW)

Ne

t F

oil

Cu

rre

nt

(nA

)

k112

k113

k114 x 2

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Energy spectra at top detector for different RF powers

0

10

20

30

40

50

60

2 3 4 5 6 7 8Average energy (MeV)

Ne

t F

oil

Cu

rre

nt

(nA

)

RF 5.7 MW

RF4.4 MW

RF3.7 MW

RF 2.9 MW

Alphas

19

0

20

40

60

3.5 4 4.5 5Electron Temperatute (keV)

Fo

il cu

rren

t (n

A)

Foil 114 x 10

Foil 113

Foil 112

Correlation between foil current and electron temperature

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2.24 MeV tail temperature good fit to foil current vs depth

• Pylon 3, first stack; Data averaged over RF pulse duration

0

5

10

15

20

2 3 4 5 6 7 8

Foi

l cur

rent

(nA

)

Energy (MeV)

Teff

=2.24 MeV

JET 79171, foils 31x

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Radial scrape off length ~4 cm• Data from top pylon (near midplane)

• Both energy ranges show similar scrape off length

0

10

20

30

40

50

4 5 6 7 8 9 10

Cur

rent

(nA

)

detector distance behind limiter (cm)

JET 79171

λ =4.1 cmE=2.3–3.7 MeV

λ =4.3 cmE=4.2–5.9 MeV

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Observation (b):Poloidal distribution of lost energetic 3He during

JPN 79341mode conversion plasma.

Note very weak correlation between front foil currents and bolometer (recall slide 10 above)

KA2 Foil 111

KA2 Foil 211

KA2 Foil 311

KA2 Foil 411

KA2 Foil 511

ICRH/PTOT

BOLO/TOPI

6 8 10 s

2MW

0

6MW

0

Foi

l cur

rent

s(s

ee n

ext f

ig fo

r ab

solu

te v

alue

s)

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Poloidal distribution front foil currents JPN 79341

1.E-07

1.E-06

1.E-05

1.E-04

-15 -10 -5 0 5 10 15 20 25 30Angle below machine midplane

Foi

l cur

rent

(A

)

t = 47.19

t = 50.69

t = 50.93t = 47.69

24JPN79352: Note that peak current occurs at later times for foils closer to machine midplane; rising at about 9o / sec.

JPN 79352

8 9 10 11 s

KA2 Foil 111

KA2 Foil 211

KA2 Foil 311

KA2 Foil 411

KA2 Foil 511

ICRH/PTOT

Foi

l cur

rent

nA

0

100

0

50

0

20

0

10

-50

0

0

50

02

MW

3

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Focal plane image of KA3 Scintillator Probe of αααα’s up to 3.7 MeV or d’s up to 1.9 MeV

Observation (c):Calibration of KA3 PMT during ICRH 4He plasmas

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Comparison of KA3 total PMT current and

KA2 foil 312 during JPN 79168 ICRH 4He plasmas

10 14 18 s

KA2 Foil 312

KA3 PMT Current

ICRH/PTOT

0

MW

3

2

nA

60

n

A8

0

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Conclusion: 8 nA of KA3 total PMT current corresponds to about 1E-4 A/m2 of KA2 312

current density (same poloidal height as KA3) during ICRH 4He plasmas

Comparison of KA2 and KA3

0

2

4

6

8

10

0.E+00 5.E-05 1.E-04 2.E-04 2.E-04KA2 Foil 312 Current density (A/m2)

KA

3 T

ota

l PM

T C

urr

en

t (n

A)

JPN79168

JPN79171

JPN79172

JPN79174

JPN79175

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Conclusions

• Faraday cup lost ion detector capable of operating in ITER like conditions for alpha currents > 10 nA/cm2

• Lost alpha/deuteron signals measured on JET for ICRH 4He d-t simulation plasmas

• Poloidal distributions measured during 3He mode conversion experiment

• KA2 data (KA2-312 at same height as KA3) will allow absolute calibration of KA3 scintillator losses