ESI 2009, CERN, GENEVAG. BonheureMay. 15, 2009 1 Neutron diagnostics for fusion experiments Georges...
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Transcript of ESI 2009, CERN, GENEVAG. BonheureMay. 15, 2009 1 Neutron diagnostics for fusion experiments Georges...
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 1
Neutron diagnostics for fusion experiments
Georges Bonheure
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 2
Outline• Introduction• Time-resolved neutron emission• Time-integrated neutron emission• Neutron profiles• Neutron spectra• Summary
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 3
Neutrons produced in fusion reactions:
D + T -> (4He + 3.56 MeV) + (n + 14.03 MeV) Q = 17.59 MeV D + D -> (3He + 0.82 MeV) + (n + 2.45 MeV) Q = 4.03 MeV T + T -> 4He + 2n Q = 11.33 MeV
What do neutrons do?
Introduction: fusion neutrons
D
T n
4He
fusion reactions cross sections
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1 10 100 1000
kT (keV)
cro
ss s
ection (
barn
)
D-D D-TD-3HeT-T
10
1
10-1
10-2
10-3
10-4
Fusion energy: Neutron energy transferred to the
reactor coolant
Fuel generation: Breeding T from Li:nslow + 6Li -> 4He + Tnfast + 7Li -> 4He + T + nslow
To minimize: activation, radiation damage
D
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 4
The largest tokamak: JET (Joint European Torus: www.jet.efda.org)
JET: outside view
Record: Q = 0.8
Steady state: Q = 0.3
total output : max 16 MW
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 5
www.iter.org
The future
ITER site now!
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 6
Neutron source: progress in parameters
The jump to ITER
Biggest increase in neutron fluence!> Radiation hardness
Plasma volume
100 m3
850 m3
Neutron source strength
1010 – 5.7 1018 n s-1
1014 – 1020 n s-1
Neutron flux at first wallITER ~ 10x JET
Neutron fluenceITER ~ 104 x JET(1025 n m-2)
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 7
The plasma as a neutron source
BABABABBAAAB
BA ddtftftntn
tY vvvvvvrvrvrr
r
)(),,(),,(1
),(),(),(
D-D : )(5.82 keVTEin
D-T : )(180 keVTEin
))(1()()(
)()()(
,,
,, rrr
rrr k
vY
vY
n
n
btDTbtDD
btDDbtDT
D
T
Ion temperature:
Ion density ratio:
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 8
Access: ITER diagnostics are port-based where possible
Each diagnostic port-plug contains an integrated instrumentation package
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 9
Introduction: fast neutron diagnostic systems
• The variety of measurements that are possible are generally restricted due to:– Limited access to plasma
– Harsh radiation environment X,
– Strong magnetic fields, powerful high frequency wave generators and power supply
– Heat loads, mechanical stress– Timescale of measurements– Activation, tritium, beryllium
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 10
Neutron diagnostic systems: 4 types of systems
Time-resolved total emission(non-collimated flux)
Time-integrated emission(fluence)
2D-cameras (collimated flux along camera viewing lines)
Spectrometers (collimated flux along radial and tangential viewing lines)
Fusion power
Absolute emissionCalibration of time-resolved emission
Spatial distribution of emissiontomography
Plasma temperature and velocity
Combination of these measurements characterizes the plasma as a neutron source
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 11
• Short range of interactions: characteristic scale is the nucleus size: 1 fermi (fm) 10-13 cm!
• Elastic scattering: A(n,n)A• Inelastic scattering: A(n,n’)A*• Radiative capture: n + (Z,A) -> + (Z,A+1)• Fission: (n,f)• Other nucl.reactions: (n,p),(n,),…• High energy particle production (En > 100 MeV)
Interaction of neutrons
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 12
1. Time-resolved neutron emission
• Fission counters:
• 238U and 235U counters embedded in moderator and led shield
• Operate both in counting and current mode• Dynamic range: 10 orders of magnitude• 3 pairs installed at different positions around JET• Low sensitivity to X and radiation• No discrimination between 2.5 and 14 MeV neutron
emission• Calibrated originally in situ with californium 252Cf neutron
source, periodically cross-calibrated using activation techniqueU235 U238
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 13
Calibration with JET Remote Handling System
252Cf source strength: 109 n/sDuration : 3 days
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 14
1. Time-resolved neutron emission
• For mixed 14 MeV and 2.5 MeV neutron fields:– Silicon diode
• Fluence limit ~ 1012 cm-2
– Natural diamond detectors (NDD)
– Chemical vapor deposited (CVD) diamond detectors
• Radiation hardness >3.1015 cm-2
New radiation hard detectors are tested in JET
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 15
1. Time-resolved neutron emission
GEM based neutron detection
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 16
2. Time-integrated neutron emission
• Neutron activation method
Sample activity measurements:Sample activity measurements: 1) gamma spectroscopy 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)2) delayed neutron counting (235U,238U,232Th)
>>>detectors: 2 stations with six 3He counters
Calibration: accuracy of the time-resolved measurements is typically ~ 8-10% for both DD and DT neutrons (7% at best using delayed neutron method) – after several years of work !!
Samples used as flux monitors are automatically
transferred to 88 Irradiation ends
Neutron transport calculations with MCNPto obtain the response coefficient for the samples
•MIX composition:
•Se-16%, Fe-20%, Al-16%, Y-48%
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 17
PRINCIPLE• Escaping light charged particles p, t, d, 3He
or hit selected targets and produce nuclear reactions of type A(z, n)B*, A(z,γ)B*,…
• B* radioactive decay (gamma photons) are measured using high purity germanium detectors
Activation techniqueActivation technique
Activation probe (targets holder)
Example of JET results: Gamma spectrometry of a natural Titanium target
HpGe detector
48Ti(p,n)48V Ep > 4.9 MeV
A measurement challenge: Escaping alpha particles
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 18
3. Neutron profiles: 2D cameras
• Two multi-collimator arrays (60tons each) with 19 channels available in total , 10 horizontal and 9 vertical
• Adjustable collimators: Ø10 and 21 mm
• Detectors: – Liquid organic scintillators
NE213 with pulse shape discrimination
– BC 418 plastic scintillators– CsI scintillators for γ rays
• Calibration: embedded sodium (22Na) sources
• γ / n separation control: movable americium beryllium 241Am/Be source
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 19
Digital pulse shape discrimination technique
n
n/γ separation obtained with a 14 bits- 200 MegaS/s DPSD prototype
One NE213 detector of neutron camera is exposed to a plasma pulse
• Benefits – Detailed post
processing possible (events identification, pile-up,…)
– Deconvolution of spectrum information
– Increase dynamic range in both energy and count-rate
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 20
Study of tritium diffusion
vnr
nD
trrrt
n
)(1
Pulse 61161: ne0 = 1.9 1019m-3Pulse 61372: ne0 = 4.5 1019m-3
Theoretical predictions for D, v can be verified against measurements
Time (s) Time (s)
R (
m)
R (
m)
nT/nD
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 21
4. Neutron spectroscopy
• Time of flight• Proton recoil
– 1) ‘thick hydrogenous target’ (high efficiency)
• No information on recoil angle : energy spectrum recovered by unfolding
– 2) ‘thin hydrogenous target’ (low efficiency)
• Analysis of recoil proton momentum
Trade off: energy resolution vs detection efficiency
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 22
Neutron spectroscopy: time of flight (TOFOR)
Energy resolution for DD neutrons: ~5%Detection efficiency: 8 10-2 cm2
Count rate: < 500 kHzSimulated with GEANT code
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 23
23
TANDEM
TOFOR
NE213
MPR
TG DiagnosticsGarching
April, 2009
23
4. Neutron spectroscopy
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 24
Neutron spectroscopy: spectral unfolding techniques
Comparison between different unfolding techniques:
• Maximum entropy (MAXED)
• Minimum fisher regularisation (MFR)
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 25
Summary: neutron diagnostic systems
Systems JET ITER
Time-resolved total emission
Total: fission counters14 MeV: Silicon diodes
fission counters Diamond detectors
Time-integrated emission
Foil activation Foil activation
2D-cameras Liquid scintillators NE213 Plastic scintillators BC418
Diamond detectors Stilbene, NE213,U238 fission counter, fast plastic
Spectrometers Time of flight Proton recoil systems:1) NE213 and stilbene2) Magnetic proton
recoil
To be defined
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 26
Final remarks
• With the move towards ITER– role of fast neutron diagnostics will increase– Capabilities of those systems need to accommodate an increase in
fluence by 4 orders of magnitude and in flux by 1 order of magnitude
• JET has an extensive set of fast neutron diagnostics, more than 2 decades of accumulated experience, and it will continue to play a leading role in development of fast neutron measurements for fusion applications
• Active research areas include new radiation hard detectors, new electronics and acquisition systems, spectrometers, tomography and unfolding techniques
• Neutron measurements contribute to advanced physics studies e.g in the field of plasma particle transport
• For references see in: http://pos.sissa.it/ ‘Neutron diagnostics for reactor scale fusion experiments’
ESI 2009, CERN, GENEVA G. Bonheure May. 15, 2009 27
Thanks…