s. popovichev 10th meeting of itpa topical group on diagnostics, moscow, 10-14 april 2006 1 neutron...

S. Popovichev 10th Meeting of ITPA Topical Group on Diagnostics, Moscow, 10-14 April 2006 1

Neutron yield measurements and Neutron yield measurements and absolute calibration issues in JET absolute calibration issues in JET

towards ITER requirementstowards ITER requirements

S. PopovichevS. Popovichev

UKAEA Fusion, Culham Science Centre, Abingdon, UKin collaboration with A. Murari, L. Bertalot, G. Bonheure,

S.Conroy, M.J. Loughlinand contributors to the EFDA-JET workprogramme


Outline:

Introduction: ITER & JETIntroduction: ITER & JET JET Neutron Yield Monitors:JET Neutron Yield Monitors:

Time-Resolved Time-Integrated (Activation system)

Calibrations issues, results, challengesCalibrations issues, results, challenges Summary Summary


• Requirements, needs, potential solutions and status Requirements, needs, potential solutions and status of ITER NFM of ITER NFM has been already reported and published repeatedly, has been already reported and published repeatedly, e.g. see:G.J.Sadler, J.M.Adams et al., Varenna, 1997M. Sasao, A.V. Krasilnikov, T. Nishitani et. al., Plasma Phys.Control.Fusion, 46 (2004), S107K. Asai, T. Iguchi, K. Watanabe et. al., RSI, vol.75 (10), 2004A.V. Krasilnikov, M. Sasao, Yu. A. Kaschuck et. al., NF, 45 (2005), 1503 (see also materials of 9th ITPA)

• The definition, design, developments, integration of neutron The definition, design, developments, integration of neutron systems into ITER is already under way to a large extent. systems into ITER is already under way to a large extent.

Introduction: ITER & JETIntroduction: ITER & JET


Ii is very difficult to satisfy all requirements for neutron flux detectors using Ii is very difficult to satisfy all requirements for neutron flux detectors using one type of detector.one type of detector.

****************

Possible solution is to have several detectors and Possible solution is to have several detectors and independent independent different techniquesdifferent techniques which will complement each other. which will complement each other.

JET is a good example of this!JET is a good example of this!

• The complexity of choice and design of neutron yield detectors in ITER The complexity of choice and design of neutron yield detectors in ITER comes from very wide range of machine operation comes from very wide range of machine operation ((in situ in situ calibrationcalibration; ; H, DD, Trace T and full DT (50:50) plasmaH, DD, Trace T and full DT (50:50) plasma))

• The use of different fuels leads to:The use of different fuels leads to: large variation large variation in neutron fluxin neutron flux (about 10 orders!) (about 10 orders!) changeschanges in neutron energy in neutron energy spectra, spectra, e.g.e.g. as does the use of different as does the use of different

plasma heating techniquesplasma heating techniques..



The JET tokamak is the most suitable test bed for the development of The JET tokamak is the most suitable test bed for the development of neutron systems due to:neutron systems due to:

its plasma parameters (and it is its plasma parameters (and it is a ITER-likea ITER-like, ~, ~1/3 of ITER1/3 of ITER) ) uniqueunique capability to operate with capability to operate with DTDT fuel. fuel. JET has a comprehensive set of JET has a comprehensive set of absolutelyabsolutely calibrated neutron calibrated neutron

diagnostics making possible the cross check between “new” and JET diagnostics making possible the cross check between “new” and JET systems.systems.

Neutron systems proposed and designed for ITER could be tested at JET. Neutron systems proposed and designed for ITER could be tested at JET.

JET has already started a number of interesting developments/tests,JET has already started a number of interesting developments/tests,

e.g. testing and successful operation of e.g. testing and successful operation of NDD & Stilbene detectorsNDD & Stilbene detectors (RF)(RF) and and NE213 & CVD (ENEA, Italy)NE213 & CVD (ENEA, Italy) detectors during TTE-2003 and coming detectors during TTE-2003 and coming campaigns).campaigns).



JET Neutron Yield Monitors:JET Neutron Yield Monitors:Time-Resolved:

• Total (2.5 MeV + 14 MeV) Neutron Yield

• 14 MeV Neutron Yield

Time-Integrated (Activation system):• 2.5 MeV and 14 MeV Neutron Yield


JET Time-resolved Total Neutron Yield MonitorJET Time-resolved Total Neutron Yield Monitor

Detectors : 3 pairs of fission chambers - U235&U238

Operate in both pulse counting and current modes Usable for neutron emissions from 1010 to 1020 n/s Relatively insensitive to the neutron energyAbsolutely calibrated to 10% (in-situ using 252Cf source and by activation technique)DAC system consists of: 12 “slow” data-channels (typically t ~ 5-10 ms) which suitably merged to single time-trace 3 “fast” windows (typically t ~ 150 s, could be down to 20 s)


14 MeV Neutron Yield Monitors14 MeV Neutron Yield Monitors• The Si diode detectors are employed at JET for this purpose since 1987. • Several Si diodes with different surface area are installed in different

locations at JET allowing the 14 MeV neutron rates from 1013 n/s up to 1018 n/s to be measured.

• The detection sensitivities of such kind of system is ~ 1 count per 1010_1012 JET 14 MeV neutron (depends on an area of diode, location in the machine, energy threshold used)

• The Natural Diamond (NDD) and Chemical Vapor Deposited Diamond detectors have been successfully tested at JET during TTE campaign in 2003.

• At present three CVD (to measure total and 14 MeV neutron yield) and one NDD are installed at JET.


Three CVD diamonds are installed in 2005: A 2.5 MeV neutron monitor is built using a Polycrystalline CVD covered

with a 6LiF film detecting the alphas emitted by thermal neutron capture in 6Li. A neutron moderator surrounds the detector. CVD is located at the level of the torus midline, approximately 7.8 m from the plasma centre.

A 14 MeV neutron spectrometer is built using a single crystal diamond. It is sitting near Main Vertical Port, approximately 4 m from the centre of plasma.

A 14 MeV neutron monitor built using a high efficiency Polycrystalline CVD which is connected to a fast electronic chain. Location is near Main Horizontal port at the level of plasma midplane, approximately 6 m from the plasma centre.

One NDD is installed in the Torus Hall close to Main Horizontal port (the same detector box as for CVD3).

14 MeV Neutron Yield Monitors14 MeV Neutron Yield Monitors


Activation TechniqueActivation Technique It is based on the analysis of the radioactivity induced by the

plasma neutrons in selected samples.

Primary purposes: a reliable calibration of fission chambers to measure the 14 MeV neutron emission.

Careful neutron transport calculations are needed to relate the total neutron yield from the plasma to the neutron fluence at the sample position.

At JET, two codes have been used for transport calculations. Only after several iterations and extended investigations the

agreement between them was achieved.

To simplify the neutron transport problem is beneficial to choose irradiation ends as close as possible to the plasma (e.g. JET 3Upper irradiation end)


JET Activation SystemJET Activation System conventional gamma-radiation measurements >>> most widely used reactions at JET: DD neutrons - 115In(n,n’)115mIn, DT neutrons - 28Si (n,p)28AL, 63Cu(n,2n)62Cu, 56Fe(n,p)56Mn >>> detectors : 3 NaI, HPGe (absolutely calibrated)

The accuracy of the yields measurements is typically ~ 8-10% for both DD and DT neutrons (7% as best for delayed neutrons)

delayed neutron counting of beta-delayed neutrons from fission events (235U,238U,232Th)

>>> usually used to measure DD neutron yield on conditions that YDD>> YDT

>>> detector system: 2 stations with six 3He counters

At JET - 88 Irradiation ends located: in 5 octants ---> test of toroidal symmetry of neutron emissionwith inboard and outboard positions -> radial plasma positionand upper and lower positions --> vertical plasma displacement


• Introduction: ITER & JETIntroduction: ITER & JET

• JET Neutron Yield Monitors:JET Neutron Yield Monitors:– Time-Resolved

– Time-Integrated (Activation system)

• Calibrations issues, results, challengesCalibrations issues, results, challenges

• SummarySummary


Calibration issues Calibration issues (1)(1)•The absolute calibration of FCs was first obtained in 1984 in situ using

252Cf source. •Angular distribution of FC response were measured for 4 radii R values (ttotal meas > 10h).

•The overall accuracy of the calibration ±10%.

• Second in situ run of calibration was performed in 1985 after some changes were made to the diagnostic disposition.

• The insensitivity to the neutron energy spectrum was also demonstrated using other sources (241Am-Be and 14 MeV neutron generator).

Although this results was recognized to be appropriate only for those machine conditions at the calibration time.

• Later, activation measurements were used to deliver the absolute calibration with an improved accuracy ~ ±7%.

• Those measurements indicated that with the installation of new heavy equipment near JET main access ports, the response of individual FC is changing considerably over the time and had become dependent on the neutron energy spectrum.


•Fission chambers are checked against each other on the shot by shot basis and an alarm is raised if the response of one of the detectors by more than ~5% from their average.

•The FC monitor data are always cross checked against the data from other available independent neutron yield measurements

(e.g. Neutron Profile Monitor , MPR )

•Comparison with code predictions (e.g. TRANSP) and in-vessel dose rate calculations and measurements also confirms the adequacy of neutron calibration procedure.

Calibrations issues Calibrations issues (2)(2)


Calibration results Calibration results (1)(1)KN1 calibration check, Restart TTE

Yn(KN1) = 1.013 Yn KN4(Th)

R2 = 0.9982

Yn (KN1) = 0.982 Yn KN2(In)

R 2 = 0.9863

1.0E+14

5.1E+15

1.0E+16

1.5E+16

2.0E+16

2.5E+16

3.0E+16

1.0E+14 5.1E+15 1.0E+16 1.5E+16 2.0E+16 2.5E+16 3.0E+16 3.5E+16

Yn tot (KN4+Si), neutron/shot

KN

1 t

ot,

ne

utr

on

s/s

ho

t

KN4(Th) + KN2 (Si)

KN2 (In) + KN2 (Si)

Linear (KN4(Th) + KN2(Si))Linear (KN2 (In) + KN2(Si))

FCs calibration check during JET TTE campaign 2003

Yn total (DD+DT) from activation, neutron/shot

Yn

tota

l (D

D+

DT

) F

Cs,

neu

tro

n/sh

ot


Calibration results Calibration results (2)(2) TTE Calibration of KM7 detectors against KN2 activation system

y = 9.742E+10x

R2 = 9.977E-01

y = 7.654E+10x

R2 = 9.552E-01

y = 1.257E+12x

R2 = 9.973E-01

y = 2.732E+11x

R2 = 9.987E-01

y = 5.008E+11x

R2 = 9.972E-01

y = 1.098E+11x

R2 = 9.991E-01

1.0E+14

1.0E+15

1.0E+16

1.0E+17

1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06

KM7 diodes, counts/shot

KN

2, n

eu

tro

n/s

ho

t

Hdiode1214- DTHdiode1214 - DDMdiode0710 - DTHdiode0508Hdiode0608Mdiode0305Linear (Hdiode1214 - DD)Linear (Hdiode1214- DT)Linear (Mdiode0710 - DT)Linear (Hdiode0608)Linear (Mdiode0305)Linear (Hdiode0508)

Si diodes calibration for JET TTE campaign 2003

Si diode, counts/shot

Act

ivat

ion

Y14

, n

eutr

on/s

hot


Calibration results Calibration results (3)(3)NDD and CVD Diamond detectors

response to Tritium JET shots ## 61084-61236


Calibration results Calibration results (4)(4)Comparison of 14 MeV Yn measured by Neutron Profile Monitor (Bicron detectors) and MPR with Si diodes data (~450 TTE shots)

y = 1.0747xR2 = 0.9962

1.E+14

1.E+15

1.E+16

1.E+17

1.E+14 1.E+15 1.E+16 1.E+17

Yn(14 MeV), Si diodes, n/shot

Yn(1

4),

Neu

tron

Pro

file

Mon

itor

, n/s

hot

Yn 14 (Si diodes), neutrons/shot

Yn

14 N

eutr

on P

rofil

e m

onito

r, n

/sho

t

Neutron Profile MonitorNeutron Profile Monitor Magnetic Proton Recoil SpectrometerMagnetic Proton Recoil Spectrometer


Calibration results Calibration results (5)(5)

Two shots with T gas puff and different DD/DT ratios:

61097: large T influx

61374: small T influx

Comparison between FC(red) and TRANSP (blue)

Yn

tota

l (D

D+

DT

) F

Cs,

10^

16 n

/sho

t

Time


Challenges…Challenges…FCs HardwareFCs Hardware - Did not have serious - Did not have serious

technical/hardware problemstechnical/hardware problems so far. so far.

14 MeV neutron monitors.14 MeV neutron monitors. There are two most serious problemsserious problems:

radiation damageradiation damage of Si diodes (fluence limit of ~ 1012 n/cm2), the detectors have to be replaced periodically; can be used only in pulse-counting mode so the dynamic range is dynamic range is

restrictedrestricted (so saturation issues arise).

ThereforeTherefore JET TTE solution JET TTE solution of this problem was to install : of this problem was to install : several (4)several (4) Si Si diodesdiodes with different sensitivities and CVD & NDDCVD & NDD detectors with high radiation hardness.


Challenges…Challenges…FCs CalibrationsFCs Calibrations :

fission chamber calibration can change fission chamber calibration can change considerably with installation of the new considerably with installation of the new equipment near to FC equipment near to FC (e.g. ~17.5% change because of installation of EFCC in 2002)

the individualthe individual fission chamber calibration factor fission chamber calibration factor are quite sensitive to the neutron energy are quite sensitive to the neutron energy spectrum (e.g. different response to DD and DT spectrum (e.g. different response to DD and DT neutrons). neutrons).

It has been noticed during PTE1 (1991), DTE1 (1997) and TTE (2003).

Extensive MCNP calculations are needed to quantify these effects.


KN1 total (Rn<2e16 neutrons/sec)

y = 0.9968x

R2 = 0.9997

y = 0.999x

R2 = 0.9999y = 1.0018x

R2 = 0.9993

0.E+00

1.E+16

2.E+16

3.E+16

4.E+16

5.E+16

6.E+16

7.E+16

0.E+00 1.E+16 2.E+16 3.E+16 4.E+16 5.E+16 6.E+16 7.E+16

KN1 average

YR

NT

x

Yrnt1 - Oct. 8 (low Rn)



Linear (Yrnt5 - Oct. 6 (lowRn))Linear (Yrnt3 - Oct. 2 (lowRn))Linear (Yrnt1 - Oct. 8 (lowRn))

JET FCs TTE 2003 JET FCs TTE 2003 CalibrationsCalibrations

Total neutron yield, (FCs average = Activation), n/shot

Tot

al n

eutr

on y

ield

, in

divi

dual

FC

s,

n/sh

ot

FCs Total neutron yield, (Rn< 1016 n/s i.e. mostly DD neutrons)


KN1 YRNTs total (Rn>2e16 neutrons/sec)

y = 0.9532x

R2 = 0.999

y = 0.9814x

R2 = 0.9998

y = 1.0803x

R2 = 0.9987

0.0E+00

1.0E+16

2.0E+16

3.0E+16

4.0E+16

5.0E+16

6.0E+16

7.0E+16

8.0E+16

9.0E+16

0.0E+00 1.0E+16 2.0E+16 3.0E+16 4.0E+16 5.0E+16 6.0E+16 7.0E+16 8.0E+16 9.0E+16

KN1 average, (n/shot)

YR

NTx

, (n/

shot

)

Yrnt1 - Oct. 8 (high Rn)



Linear (Yrnt5 - Oct. 6 (highRn))Linear (Yrnt3 - Oct. 2 (highRn))Linear (Yrnt1 - Oct. 8 (highRn))

JET FCs TTE 2003 JET FCs TTE 2003 CalibrationsCalibrations

Total neutron yield (FCs average = Activation), n/shot

Tot

al n

eutr

on y

ield

, in

divi

dual

FC

s,

n/sh

ot

FCs Total neutron yield, (Rn> 1016 n/s) i.e ~50-50% DD & DT neutrons)


JET Fission Chambers responseJET Fission Chambers response

235U counter response – linear energy scale 238U counter response – 19.4 cm Pb shield


SummarySummary• The neutron emission from JET is reliably measured by a

comprehensive set of neutron yield monitors available.

• These monitors can operate usefully over a wide range of neutron intensities (FCs are covering 10 decades).

• The absolute calibration relies on activation measurements and is performed to an accuracy of ~ 10%.

• Monte Carlo transport calculations have to be always performed in support (and understanding) of the calibration data.


Issued to be addressed:Issued to be addressed:• It will need to perform the Monte Carlo Neutron transport It will need to perform the Monte Carlo Neutron transport

calculations with detailed ITER model will be needed calculations with detailed ITER model will be needed (especially for activation measurements).(especially for activation measurements).

• Particular attention has to be given to the calibration Particular attention has to be given to the calibration methods/procedures of ITER neutron diagnostic (several methods/procedures of ITER neutron diagnostic (several different methods should be used)different methods should be used)

>> >> Direct calibration by neutron generator is practical only before start-up Direct calibration by neutron generator is practical only before start-up when the ITER vessel will be cold. Will be this calibration valid forwhen the ITER vessel will be cold. Will be this calibration valid for hot vessel?hot vessel?

>> An activation system for >> An activation system for in situin situ and for and for routine cross calibrationroutine cross calibration is strongly is strongly recommended. recommended.

What else? Time for discussion!What else? Time for discussion!

s. popovichev 10th meeting of itpa topical group on diagnostics, moscow, 10-14 april 2006 1 neutron...

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