study of advanced neutron diagnostics for mast
TRANSCRIPT
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1EURATOM/VR Association, Department of Physics and AstronomyDivision of Applied Nuclear Physics, Ångström Laboratory, Uppsala University, Sweden
2EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, UK
M Cecconello1, S Conroy1, G Ericsson1, M Weiszflog1,R Akers2 and M Turnyanskiy2
Study of advanced neutron diagnostics for MAST
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Outline
TRANSP neutron sources used in MCNP
MCNP modelling and some results
Collimators, detectors, DAQs and magnetic compatibility
An appetizer from JT60U
Fast ions, neutron emission and neutron diagnostic in MAST
Proposed neutron camera for MAST and MAST Upgrade
A look at the near future and conclusions
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Redistribution of fast ions due to TAE in JT60U
M Ishikawa et al Nucl. Fusion 47 (2007) 849–855
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Most of the fusion neutron production is due to beam-thermal reactionsthe beam-beam term accounts for 10 -20 % of the total while the thermal-thermal is negligible.
Neutron emission on MAST
∫ ><= dVvnS DDDn σ2
21
Neutron rate
BBBTTHDD vvvv ><+><+>=<>< σσσσ
Sn = 1 – 10 x 1013 s-1
reduction in the beam-plasma interaction energy (due to the relative velocity of beam-thermal), leading to a reduced fusion reactivity.
Energy shift of the neutron spectra.
Effect of NBI heating and induced toroidal rotation:
D + D ⇒ 3He (0.82 MeV) + n (2.45MeV), Q = 3.27MeV
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Fast Ions and Neutron EmissivityThe neutron emissivity profile is strongly dependent on the fast ion spatial and energy distribution.
TRANSP simulated poloidal projections of co passing fast ion distributions with V||/V~0.7-1 with and w/o
anomalous fast ion diffusion
TRANSP simulated neutron source
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Fast Particles Studies on MAST
Study of fast ions driven modes is important to understand the redistribution and/or losses of fast ions that can affect the heating efficiency, the stored energy and cause damage to the PFCs.
Document fast particle driven collective instabilitiesAE: TAE, EAE, BAE, Alfvén cascades, high frequency CAEEnergetic Particle modes: chirping modes, long-lived modes
Effects of fast ions upon core instabilitiesTypically n = 1 internal kink: sawteeth, fishbones, infernal modeUse on/off axis beams as source of fast ions
Exploit specific capabilities of MASTSuper-Alfvénic beams, VNBI ~ 2.5 VA
Large fast ion fraction with high β (above ITER values)Externally driven modes (TAE antenna), n = 1 – 3
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Example of instabilities and neutron yield on MAST
“The LLM does not seem to cause notable plasma energy degradation in MAST discharges. However […] changes in the LLM frequency, possibly indicat[e] an enhancement of fast particle losses.” [1]
Long Lasting Modes during NBI and current ramp-up
0 . 0 5 0 . 1 0 0 . 1 5 0 . 2 0 0 . 2 5 0 . 3 0 0 . 3 50
1
2
3
4
5
t (s)
Sn (x 10
13s-1)
[1] M.P. Gryaznevich et al Nucl. Fusion 48 (2008) 084003
P NB
I=
1.5
MW
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MAST Present Neutron Diagnostic
235U Fission Chamber (from PPPL)1
- pulse (5 ms) and current (10 μs) modes- Campbelling mode (0.5 ms)- calibrated with a 252Cf neutron source and
backed up by activation foil measurement- no saturation expected with the increased
neutron rate from NBI upgrades
1(Planned installation of a spare 235U and a 238U for neutrons with En > 1 MeV.)
Used for total emission strengthmeasurements (fusion reaction rate)
relative emissivity profile ⇒ transport properties & MHD study
the energy spectra ⇒ reacting ions energy distribution
What have studied the possibility of:
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Proposed neutron diagnostic for MAST and MAST U
Horizontal fan of 14 lines of sight
Vertical fan of 9 lines of sight
Camera system consisting of:
Collimator with liquid scintillator detectors
Radial position of the detectors between 3 and 4 m
Preferred location: MAST NPA location
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PORT 6
MAST VACUUM VESSEL
PORT 5
PORT 4
43 USING THE EXISTINGFIXING SCREWS
A A
ELECTRICALCUBICLE
PROPOSED
POSITION
B K.HAMMONDP.R.JONESA.WHITEHEAD27/10/99
D.O. I. 9
ITEM 35 AND 69 ADDED, ITEMS 78 WAS 168 OFF( GRID REF G27, N27, S25 )
( GRID REF R28 )ITEMS 89 - 93 INCL. _ ADDED
D.O.I. 25
1234567891011121314
Horizontal lines of sight
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MAST SOUTHPINI Injector (2.5MW/5s)
MAST SWInjector
(2.2MW/0.4s)
MAST Vessel CFC Beam
Dumps
MAST S-WESTPINI Injector (2.5MW/5s)
Horizontal lines of sight and PINI injectors
R = 4 m
neutroncamera
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Vertical lines of sight
MAST MAST Upgrade
Massive PF coils in the way of a vertical stack of lines of sight.
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TRANSP Simulation of MAST Neutron Source
90 100 110 120 130 140 1500
1x107
2x107
3x107
4x107
5x107
6x107
r (cm)
(cm
-3s-1
)
PNBI = 3.2 MW (co-NBI)
Ip = 0.6 MA
Te ≈ Ti ≈ 0.8 keV
Pulse 18821 @ 0.25 sQuasi-stationary H-mode plasma:
Neutron emissivity radial profile
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90 100 110 120 130 140 1500
1x107
2x107
3x107
4x107
5x107
6x107
r (cm)
Synthetic MAST Neutron Source
(cm
-3s-1
)
Neutron emissivity radial profile
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TRANSP Simulation of MAST U Neutron Source
90 100 110 120 130 140 1500
1x108
2x108
3x108
4x108
5x108
r (cm)
(cm
-3s-1
)
PNBI = 10 MW (1 PINI co, 1 PINI counter, 2 PINIs off-axis co)
Ip = 1.2 MA
Te ≈ 2.4 keV
Neutron emissivity radial profile
Scenario C (long pulse operation)
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MCNP Model of MAST and of the Neutron Source
Volume sampled for neutron spectra.
Vertical section Horizontal section
Neutron Source
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MCNP Neutron Flux and Spectrum Calculations
MCNP calculates:
n
n
SΦΓ =MCNP the flux of neutrons per MAST neutron
nEdd MCNPΓ the energy spectrum of the
flux of neutrons per MAST neutron
nΦ neutron flux (cm-2s-1)
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Source Neutron Energy Spectrum
For Maxwellian distributions, the energy distribution of the neutrons is very nearly Gaussian
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎠⎞
⎜⎝⎛ ><−
−=2
exp1)(W
EEW
Ef nnn π
21
He3
4⎟⎟⎠
⎞⎜⎜⎝
⎛
+><
=mm
TEmWn
nn
0.5 1.0 1.5 2.0 2.5 3.0 3.50.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
neutron energy (MeV)
MCNP f(En)
<En> = 2.49 MeVW = 0.32 MeV
dΓM
CN
P/d
En (×
10-9 c
m-2 M
eV-1)
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Neutron Flux throughout MAST Area (midplane)
log 1
0(Γ M
CN
P)
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Horizontal Lines of Sight & Neutron Emissivity MAST
1413121110
9876
54
32 1
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Horiz. Lines of Sight & Neutron Emissivity MAST U
1413121110
9876
54
32
1
For MAST Upgrade the same lines of sight are used.
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Neutron Collimator and Shielding for MCNP
Polyethylene sphere:
L = 50, 70 and 90 cm LD
D = 11.24 and 35.68 mm
A = 1 and 10 cm2
Detector located at the sphere centre
Detector area defined by the collimator diameter
Collimator cross-section is circular
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Horizontal Lines of Sight: Field of View @ R = 3 m
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2-2
-1.5
-1
-0.5
0
0.5
1
1.5
2MAST Field of View - SETUP G
x (m)
y (m
)L = 50 cm, A = 10 cm2 L = 90 cm, A = 1 cm2
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2-2
-1.5
-1
-0.5
0
0.5
1
1.5
2MAST Field of View - SETUP I
x (m)
y (m
)
radial field of view width ≈ 40 cm radial field of view width ≈ 8 cm
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0.5 1.0 1.5 2.0 2.5 3.0 3.510-13
10-12
10-11
10-10
10-9
10-8
dΓM
CN
P/dE
n (cm
-2M
eV-1)
neutron energy (MeV)
Collimated Neutron Energy Spectrum @ R ≈ 3.2 m
L = 50 cm, A = 10 cm2
L = 90 cm, A = 1 cm2
MCNP Line of sight # 6
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Horizontal Collimated Neutron Fluxes @ R ≈ 3.2 m
L = 90 cm, A = 1 cm2
1 2 3 4 5 6 7 8 9 10 11 12 130.0
0.5
1.0
1.5
2.0
Γ MC
NP (×
10-1
0 cm
-2)
line of sight
centralcolumnshadowing
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MCNP Direct Fluxes and Line Integrated Emissivity
1 2 3 4 5 6 7 8 9 10 11 12 130.0
0.5
1.0
1.5
2.0Γ M
CN
P (×
10-1
0 cm
-2)
line of sight
Line integrated emissivity along the line of sight
Direct neutron flux (no neutron scattering)
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1 2 3 4 5 6 7 8 9 10 11 12 1310-14
10-13
10-12
10-11
10-10
10-9Γ M
CN
P (c
m-2)
line of sight
Horizontal Collimated Neutron Fluxes @ R ≈ 3.2 m
totaldirect
backscattered
shieldscattered
Neutron flux components
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MAST Vertical Lines of Sight and Field of View
0 0.5 1 1.5 2-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1MAST Field of View - SETUP H
L = 90 cm, A = 1 cm2, R = 3 m
vertical field of view width ≈ 4 cm
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0 5 10 15 200
1
2
3
4
5Γ M
CN
P (c
m-2)
angle (deg)
Vertical Collimated Neutron Fluxes @ R ≈ 3.2 m
L = 90 cm, A = 1 cm2
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Expected Count Rates on MAST
nn
n dEE
ASC ∫=d
d MCNPΓε ε detector efficiency
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14100
101
102
103
104
105
Collimator: L = 90 cm, ε = 5 %
line of sight
C
ount
Rat
e (H
z) 10 x A , 10 x Sn
A = 1 cm2, Sn = 1013 s-1
10 x A , Sn
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Count Rate and Time Resolution on MAST
Assuming a complete camera system, the count rate required fora neutron emissivity profile measurement with a Poissonian statistical uncertainty δ = N-1/2 and a time resolution Δt is:
2
1δΔt
C ≥ Δt = 1 ms, δ = 0.1 ⇒ C ≥ 0.1 MHz
With the present system (≈ 3 MW NBI power)we can push the time resolution to 10 ms with a statistical uncertainty of 10 % (central channels), by using a vertically elongated collimator.
For MAST Upgrade a the time resolution of less than 10 ms, with δ = 0.1, might be achievable due to the much higher expected NBI power.
This is NOT as an uncertainty of 10 % on the emissivity profile!
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Different Collimator Cross-Sections
circular elongated
L = 90 cm, A = 1 cm2 L = 90 cm, A = 4 cm2
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Neutron Collimator and Shielding
Need of neutron collimation, shield against scattered neutrons and against γ rays emission associated with capture of thermal neutrons by surrounding materials (neutron shield, magnetic shield, support structure).
Boron loaded Polyethylene 0.48 MeV γ are produced by 10B(n,α)7Lireduction of the 2.23 MeV γs
Polyethylene (CH2) 2.23 MeV γ are produced by H(n,γ)D
Both give rise to significant γ-background in the scintillator.
MCNP estimate of γ-background not yet performed.
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Neutron Detector
Liquid scintillators BC-501A (NE213) from Saint-Gobain Crystals
Good PSD capabilities for n/γ discrimination
Hamamatsu R762 PMT
Requires temperature control for stability and flash point (< 25 °C)
Response function for neutron spectroscopy (energy calibration)Good contact with Physikalisch-Technische Bundesanstalt(2.5 MeV monoenergetic neutron sources, γ sources).
Calibration for absolute neutron yield measurements
High efficiency (5 %) and high count rate capabilities
Neutron ⇒ Recoil protons ⇒ photons
LED Gain stabilization
Temperature monitor
SiPM (SensL)Insensitive to B field
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Data Acquisition
PMT FastAmplifier
FlashADC
Flash ADC with 1Gsamples memory, 10 bit resolution
Sampling rate of 200 MHz (Δt = 5 ns), 8 GHz maximum
Raw data transfer in PC connected to flash ADCs after acquisition is finished
Individual pulses are recorded (Δt = 350 ns)
Neutron/γ discrimination and post processing is carried out via software on the PC
Count rate of analog PSD systems is restricted by the gate integration time of the electronic circuit to 105 kHz.
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Magnetic Field at Detector Location in MAST
R (m) B (mT) B (mT)3 32
22
46
4 32
Poloidal field is mainly perpendicular to the PMT side
R (m) B (mT)3 136
4 100
MAST
Bφ < 1 mT
MAST Upgrade
Bφ < 2 mT
B (T)
Magnetic shielding not too difficult.
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What happens next ?
2008 - 2009 Proof-of-principle at MAST
Single line of sight for radial and vertical scans
Test of different collimator geometries
Neutron emissivity profiles measurements
2009 Finalize design of neutron camera for MAST
2009 Application for partial funding to the Swedish Research Council (VR)
Application in April, answer in November
2010/2011 ? Installation and Operation
Extensive MCNP simulationsShielding and support, DAQS development
Emissivity profiles from inversion of neutron camera data
EFDA Priority Support: 0.33 ppy and 156 k€ for development
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Neutron Camera on MAST and MAST U
Reduced time resolution but spatially resolved neutron emissivity profiles
0 . 0 5 0 . 1 0 0 . 1 5 0 . 2 0 0 . 2 5 0 . 3 0 0 . 3 50
1
2
3
4
5
t (s)
Sn (x 10
13s-1)
Fast ions spatial distribution
Reacting ions energy distribution function
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Conclusions
AcknowledgmentsSpecial thanks to B Lloyd, G Cunningham, N Conway, M Dunstan, R Scanell, M Walsh and the MAST team.
Single line of sight proof-of-principle for MAST is doable and can provide and indication of the neutron emissivity profiles in a reasonable amount of pulses.
Neutron camera with L = 90 cm, A = 10 cm2 is required for achieving in MAST high performing plasmas a time resolution of 10 ms with enough spatial resolution (at least 10 horizontal LoS, 9 vertical LoS) and sufficient statistic (10 % uncertainty).
In MAST Upgrade, depending on the total NBI power available, the time resolution can be pushed below 10 ms (10 % uncertainty).
In principle the same collimator structure can be used for both MAST and MAST Upgrade
Liquid scintillators with DPSD seem ok
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MAST Vertical Stack
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.010-11
10-10
10-9
10-8
dΓM
CN
P/d
En (×
10-9 c
m-2 M
eV-1)
neutron energy (MeV)
Z = 0 cm Z = 10 cm Z = 20 cm Z = 30 cm
Not a viable solution due to PF coils presence.
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1 2 3 4 5 6 7 8 9 10 11 12 13 140.0
0.2
0.4
0.6
0.8
1.0
line of sight
Γ MC
NP (a
.u.)
Different Neutron Emissivity Profiles compared
Line integrated neutron emissivity
MAST 18821MAST Synthetic
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Post-experiment data processingpile-up reprocessing,
dedicated n/γ separation
simultaneous n/γ discrimination and PHA
correction for PMT gain variations
Digital Pulse Shape Discrimination
n
γ
Y. Kaschuck, Nuclear Instruments and Methods in Physics Research A 551 (2005) 420–428
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Liquid Scintillator as Neutron Spectrometer
0 1 2 3 4 5 6 7 8 9 10
ϕ E / (
MeV
-1s-1
cm-2
)
En / MeV pulse height
coun
ts
source measured
Courtesy of A. Zimbal Physikalisch-Technische Bundesanstalt
The energy spectrum of neutrons provides information on their production mechanisms and the energy distributions of the reacting ions.
recoil proton edge
Compton electron edge
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Liquid Scintillator Energy Calibration
Low Z material: γ interactions are Compton only
L(Eγ) = L (En) but Eγ ≈ 2-3 En
En : L(En) = L(Eγ) electron energy equivalent
L(E) is linear in Ee non linear in Ep
Compton electron
recoil proton
eeeMeV
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MAST U Vertical Lines of Sight and Field of View
0 0.5 1 1.5 2-1.5
-1
-0.5
0
0.5
1
1.5MAST Upgrade Field of View - SETUP H
R (m)Z
(m)
L = 90 cm, A = 1 cm2, R = 3 m
vertical resolution ≈ 4 cm
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Magnetic Field at Detector Location in MAST Upgrade
B (T)
R (m) B (mT)3 136
4 100
The poloidal field is mainly perpendicular to the PMT side
The toroidal field is negligible (< 2 mT)
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Photo-multiplier Magnetic Shielding
Outer shield: soft iron (1 mm thick, rin = 23 mm)
Inner shield: μ-metal (0.8 mm thick, rin = 21 mm)
150 mT
Shielding factor up to 104
0.2 mT
B(T)
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Neutron Energy Spectrum outside MAST Vessel
0.5 1.0 1.5 2.0 2.5 3.0 3.50.0
0.5
1.0
1.5
2.0
2.5
dΓM
CN
P/d
En (×
10-9 c
m-2 M
eV-1)
neutron energy (MeV)
<En> = 2.50 MeVW = 0.35 MeV
MCNP f(En)
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TRANSP Simulation of MAST Neutron Source - 3
PNBI = 3.5 MW (co-NBI)
Ip = 0.6 MA
Te ≈ Ti ≈ 1.1 keV
Pulse 18808 @ 0.28 s
90 100 110 120 130 140 1500
1x107
2x107
3x107
4x107
5x107
6x107
r (cm)
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Counting modes
Pulse Mode
Current Mode
Campbelling Mode