Association EURATOM - MEdC - IFA

Association EURATOM - MEdC 

SHFD neutron diagnostics 

Tokamak neutron diagnostics based 

on the superheated fluid detector 

(SHFD) 

Vasile (Liviu) Zoita 

National Institute for Laser, Plasma and Radiation Physics 

(NILPRP) 

Plasma Physics and Nuclear Fusion Department 

Dense Magnetised Plasmas Laboratory 

Magurele - Bucharest 

1st Association Day, Institute of Atomic Physics, Magurele - Bucharest, 11 November 2004



Outline 

• The superheated fluid detectors (SHFD’s) 

- principle of operation 

- characteristics 

- applications 

• Use of the SHFD’s in fusion neutron diagnostics 

• Proposals for SHFD application for neutron diagnostics 

on EU tokamaks 

• Proposals for SHFD neutron measurements on JET 

• Proposals for SHFD neutron measurements on FTU 

• Neutron diagnostics for dense magnetised plasmas 




Superheated fluid detectors (SHFD’s) 

Suspensions of metastable droplets which readily vaporise into bubbles 

when they are nucleated by radiation interactions. 

SHFD’s: 

• Superheated drop detectors (1979) 

• Superheated emulsion detectors 

• Bubble detectors (1984) 

Mixture of 

• Nuclear interactions 

• Thermodynamic behaviour 

• Mechanical response 

Neutron dosemeters: SHFD’s with volumetric, optical and acoustical 

counting 

The characteristics and advantages of SHFD’s neutron dosemeters: 

• Immediate, real time, visible response to neutrons 

• High neutron sensitivity 

• (Practically) Zero gamma sensitivity 

• Lightweight, rugged and compact 




[1] 




Characteristics of the neutron detection process 

• SHFD’s –microscopic bubble chambers 

- Energy transfer 

- Recoil nucleus range 

• Threshold energies depending on: 

- droplet composition 

- operating temperature 

- operating pressure 




Bubble formation in SHFD’s 

[2] 




Table 1 SHFD’s characteristics 

(Commercially available bubble detectors) 

Shape and 

dimensions of 

detector 

Energy range of 

detector 

Energy thresholds 

Detector sensitivity 

(n/cm 2 )/count 

Standard SHFD Spectrometer 

SHFD 

Cylinder, 

Cylinder, 

length/diameter length/diameter 

(mm): (approx.) (mm): (approx.) 

150/20 

80/15 

200 keV – 15 MeV 10 keV, 100 keV, 

600 keV, 1.0 MeV, 

2.5 MeV, 10.0 

MeV 

10 3 - 10 5 10 4 

Advanced SHFD (*) Remarks 

Disc, 

diameter/thickness 

(mm): (approx.) 

100/10 

100 keV – 20 MeV 

(**) Detectors with 

(**) 

10 2 - 10 3 

various customerselected 

energy 

thresholds can be 

constructed 

(*) All parameters represent design data 




[1] 




Control of the response function of the SHFD’s 

>continuously variable energy threshold 

[3] 

Effective neutron thresholds for various superheated emulsions 




[1] 




[1] 




[2] 

Energy thresholds for a two-fluid SHFD spectrometer 




[2] 

Reconstructed AmBe neutron spectrum 




Bubble detector calibration [1] 

(PND detector type) 

Am-Be neutron source 

-Strength = 1.13 x 10 7 n/s 

-Fluence weighted average energy = 4.15 MeV 

>Compare with D-D fusion spectrum: ~2.5 MeV 

A conversion factor of 3.70 x 10 -5 mrem/n cm -2 for the Am-Be source 

is used (as calculated from dose equivalent defined in NCRP Report 

No. 38). 

The conversion factor can be used to convert sensitivities in 

bubbles/mrem to bubbles/ n cm -2 if desired. 




SHFD’s for fusion neutron measurements 

1992, Kurchatov Institute, Moscow 

- Superheated Dispersed System (SDS) 

JET 

- T10 and T15 tokamaks 

- Plasma focus device 

> personal dosimetry on fusion devices 

Inertial confinement fusion 

- neutron imaging 

Knock-on tail energy spectrum 

DMPLab, NILPRP, Bucharest, on DMP devices in 

-Romania 

- Germany 

- Poland 




JET: Knock on tail diagnostics (R. Fisher et all, 2001) 

[4] 




[4] 




The “Knock-on tail diagnostics”: analysis of Fisher’s measurements 

- Used Standard type BD’s (though improved selected) 

- Obtained ~100s counts 

- statistical error ~10% at best 

- With new SHFD’s: ~1000s counts 

- Statistical error in the few % range 

> simply from new, higher quality, customer-built detectors 




Proposals for SHFD application on EU tokamaks 

(A stage-by-stage approach) 

Stage 1 

Neutron fluence measurements at a specific location on the tokamak 

Location: near or at the place of the activation detectors 

Expected results 

- Time-integrated (over one tokamak shot, or a series of JET discharges), 

energy-integrated (above the detector threshold) value of the neutron 

fluence (n/cm2) at that location. 

- Comparison of the two methods based on very different neutron 

interaction processes. 

- Improvement in the accuracy of the measurement of the neutron yield 

per discharge. 

>A first step towards a new calibration technique => ITER 




Stage 2 

Spatial distribution of the neutron fluence around the tokamak 

(Stage 1 done simultaneously, on one discharge, at various locations 

around tokamak installation) 


- Evaluation of the neutron dose around the tokamak machine 

- Analysis of the effects of non-thermal components of the reacting 

deuteron population in a tokamak plasma 

- Comparison with neutron transport calculations. Code validation. 

Stage 3 

Determination of the neutron energy spectrum (time-integrated over 

one or a few tokamak shots) 


-Information about the spectral characteristics of the neutron field 

around the tokamak (i.e., including scattered neutrons and non-fusion 

neutrons). 




Neutron spectrum at 

a tokamak machine 

Fusion and non-fusion neutrons 

Neutron producing reactions 

[5] 

• Nuclear fusion 

•Deuteron disintegration by high energy 

electrons 

- Direct reaction: D(e, e’n)H 

- Indirect reaction (photo-disintegration): 

D(γ, n)H 

•Photonuclear reactions within the walls of 

the fusion device 

W(γ, n)W 




Proposal for JET diagnostics 

Time-integrated enhanced resolution threshold 

spectrometer (TIER-TS) 

Rationale 

•The non-fusion neutron emission associated with disruption dominated 

tokamak discharges can be successfully addressed. 

•The SHFD technique is able to measure directly the neutron dose around 

the machine. No other fast neutron detection technique is capable of 

providing such information. 

•SHFD neutron diagnostics techniques have been evaluated and found to 

be of particular interest for the characterisation of the fast neutron field of 

the JET tokamak machine. 







General Proposal 

It is proposed to: 

•Develop a time-integrated enhanced (energy) resolution threshold 

spectrometer (TIER-TS) by modifying a commercially available dosespectrum 

detector set 

•Increase the number of energy thresholds and improve the spectrum 

unfolding technique in order to increase the accuracy of the spectrum 

reconstruction 

•Perform neutron spectrum measurements in the range 10 keV –1 MeV 

using the TIER-TS device on JET during Campaigns C16 and C17 







Acceptance criteria 

•High scientific importance: it addresses by means of a new approach a key 

issue related to the neutron field of the JET machine: the spectral 

characteristics of the non-fusion neutron component. 

•TIER-TS device is a stand-alone equipment, implementation on JET with 

no interference with other machine components. 

•No impact on the shutdown, preliminary tests can be accommodated within 

planned neutron diagnostics tests during JET restart operations. 







Technical details: TIER-TS structure & characteristics 

-36 detectors (4 detectors for each energy threshold) 

-Very broad energy range: 10 keV – 10 MeV 

-Nine energy thresholds: 10 keV, 50 keV, 100 keV, 300 keV, 600 keV, 

1MeV, 1.8 MeV, 3.7 MeV, 10 MeV 

-Energy resolution in the range 40-65% for the energy range 10 keV –1 MeV 

-Overall dimensions: approximately 500x 250x100 mm3 

Initial configuration (2005): integrate the one-day JET neutron emission 

Upgrade: (data acquisition components) integrate the neutron emission on 

a single JET discharge 







Work plan 

-Technical specification and launch of order: February 2005 

-Purchase of the TIER-TS detectors and accessories: April 2005 

-Operational tests of TIER-TS on JET: May-June 2005 

-Development of data acquisition and processing techniques: August 2005 

-Neutron spectrum measurements on JET: campaigns C16 or C17 

(September 2005) 

-Analysis and interpretation of the TIER-TS data: November 2005 





Threshold SHFD Stacks (TSS) 

Aim 

Cross-calibration of foil activation neutron diagnostics 

Use foil activation capsules at four out of six irradiation ends 

Workplan for 2005 

Develop diagnostics method (including neutron transport 

calculations) 

Perform a benchmark experiment 

Carry out measurements on JET (campaign C16 or C17) 




Proposal for FTU diagnostics 

High sensitivity SHFD set (four new detectors) and standard SHFD 

set (4-6 detectors) 

Time-integrated Enhanced Resolution Threshold Spectrometer 

(TIER-TS) 

Aims 

Neutron fluence measurements (on single shot FTU discharges) 

-at former foil activation locations 

-at various locations around the machine 

Neutron spectrum measurements (on single shot FTU discharges) 




Proposal for FTU diagnostics 

Workplan 

Experimental setup evaluation: February 2005 

Neutron fluence measurements (I): March 2005 

Neutron fluence measurements (II): June-July 2005 

Neutron spectrum measurements: August/December 2005 

Install TSS at former foil activation irradiation ends? 

Re-activate pneumatic system? 




Neutron diagnostics: methods and techniques for dense 

magnetised plasmas (plasma focus) 

Developed by the DMP Laboratory, NILPRP, Bucharest, in 

collaboration with: 

Institute for Physics and Nuclear Engineering (IFIN-HH), 

Magurele, Bucharest 

Institute for Nuclear Reactor Engineering, Colibasi, Pitesti 

Faculty of Physics, University of Bucharest 




Neutron diagnostics developed for the Plasma Focus 

Devices at NILPRP, Bucharest 

Multichannel silver activation system 

- Neutron yield 

- Time integrated neutron anisotropy 

Multichannel fast scintillator-photomultiplier 

- Modified time of flight 

-Time resolved neutron spectrum 

- Time resolved neutron anisotropy 

Solid state track detectors 


- Time integrated neutron spectrum 

- Anisotropy (fluence, spectrum) 

Nuclear emulsions 


- Time integrated neutron spectrum 

- Anisotropy (fluence, spectrum) 




Neutron diagnostics methods developed and devices constructed for 

• standard, capacitive driven plasma focus devices (three machines with stored 

energies between 4 and 50 kJ) 

• unconventional (single-shot) inductive storage devices 

Examples: 

•Six-channel silver activation system for time-integrated fluence anisotropy and 

a single channel indium activation detector for neutron yield measurement 

•Five-channel fast scintillator-photomultiplier system used mainly for timeresolved 

neutron spectroscopy (modified time-of-flight technique), but also for 

time-resolved neutron fluence anisotropy 

•Solid state track recorders (fissionable deposits: Al alloys (containing 20% or 

10% U235 and 10% or 5% Pu239) and pure metal disks of depleted uranium) 

and nuclear emulsions mainly used for time-integrated neutron spectrum 

absolute measurements, as well as for time-integrated fluence and spectrum 

anisotropy investigations 

Particular attention was paid to absolute measurements (e.g., neutron yield) 

and the associated calibration techniques 




SHFD neutron diagnostics on the PF-1000 DMP facility 

at IPPLM, Warsaw 

Fluence measurements 

Measurements of the neutron fluence spatial distribution 

Neutron detector calibration 




Detector locations on the PF-1000 machine 

Ag 

In 

BD 









Cross-calibration 


250 

225 

200 

shot 2530 (all detectors) new 

average: 128 

st. dev: 21% 

normal (33) bubbles 

175 

150 

125 

100 

75 

50 

25 

0 

0 1 2 3 4 5 6 7 8 9 

detector number 




shot 2530 (no det 6) new 

200 

175 

average: 120 

st. dev: 15% 

150 

normal (33) bubbles 

125 

100 

75 

50 

25 

0 

0 1 2 3 4 5 6 7 8 9 

detector number 




Bubble detector vs. Ag activation (90 0 ) 




Bubble detector vs. Ag activation (90 0 ) 




Other DMP neutron diagnostics 

• BD neutron collimator for PF-1000 

• Neutron pinhole camera for PF-1000 

• Neutron detection and analysis for explosive 

detection 




Conclusions 

SHFD’s provide new posibilities for tokamak neutron 

diagnostics 

SHFD’s can be used during next year (2005) 

experimental campaigns on JET and FTU 

SHFD’s have been successfuly used on pulsed fusion 

plasmas 

A R&D programme during the next 3 years could lead 

to the development of a complex, versatile neutron 

diagnostics system with applications to EU tokamaks 

and ITER 




References 

(Only references to non-NILPRP, Bucharest work are included in this list) 

[1] Bubble Technology Industries, Chalk River, Ontario, Canada, 

(2002) 

[2] F. d’Errico and M. Matzke, Rad. Prot. Dosimetry, Vol. 107, pp. 

111-124 (2003) 

[3] F. d’Errico, Rad. Prot. Dosimetry, Vol. 84, pp. 55-62 (1999) 

[4] R.K. Fisher et all., Rev.Sci.Instrum., Vol. 72, pp. 796-800 

(2001) 

[5] J. Strachan and D. Jassby, Trans. Am. Nucl. Soc., Vol. 26, p. 

509 (1977)

Association EURATOM - MEdC - IFA

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?