Escaping alpha-particle monitor for burning plasmas · Escaping alpha-particle monitor for burning...

Escaping alpha-particle

monitor for burning plasmas

V G Kiptily et al

CCFE is the fusion research arm of the United Kingdom Atomic Energy Authority

V. Kiptily et al | 15th IAEA TM on Energetic Particles| Princeton, NJ, USA | 5th - 8th September 2017 |

Contributors

A. E. Shevelev1, V. Goloborod’ko2,3, M. Kocan4, K. Schöpf2, E.

Veshchev4, V. Yavorskij2,3

1 A.F. Ioffe Institute, St. Petersburg, Russia2 Institute for Theoretical Physics, University of Innsbruck, Innsbruck, Austria3 Institute for Nuclear Research, Ukrainian Academy of Sciences, Kiev, Ukraine4 ITER Organisation, St Paul Lez Durance, France


Aim of the talk

To present a concept for continuous monitoring of

anomalous fluxes of the MeV alphas lost to the

ITER wall


Introduction

ITER diagnostic requirements for escaping alphas and fast ions


In ITER, all escaping alphas and fast ion measurements are planned to be madeby supplementary diagnostics, i.e. IR cameras viewing the first wall


(M. Garcia-Munoz et al)


Proposed novel technique

1.5 2.0 2.5 3.0 3.5 4.0

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

V.K

iptily

Z(m

)

R(m)

Be

❖ Escaped alphas strike Be-target*

❖ Measurements of gammas from the 9Be(,n)12C reaction

❖ -particles with E > 1.7 MeV give

rise to 4.44-MeV gammas;

-particles with E > 4 MeV give rise

to 3.21-MeV & 4.44-MeV gammas

❖ A thick Be-target is placed in the

field of view of a -ray detector

❖ An identical blind detector for the

background monitoring is needed

Kiptily et al Fusion Technology 22 (1992) 454

Lost α-particle

-ray detector

_________________________________________________* 10B(,p )13C is an option


2005-proposal for ITER


Upper Radial Neutron Camera in-port cassette

Exit of the Upper RNC In-Port collimator

EPP#1


A generic location of the escaped alphas monitor

Exits of collimators for 2 monitors : a blind monitor and Be-target viewer

Collimator with a pure-water neutron attenuator

Detector


Exits of collimators for 2 monitors : a blind monitor and Be-target viewer.

The blind monitor is needed to control the background emission.

Collimator with a pure-water neutron attenuator, which has an variable length, 0 - 150 cm, depending on fusion power

collimatorDetector

A generic location of the escaped alphas monitor

Collimatorwith H2O attenuator


A generic location of the Be-target (#1)

4.44-MeV gammas produced by alphas are passing through the Be-tile with minor attenuation to a detector inside the Port Plug


A generic location of the Be-target (#2)

FoV spots : background monitor and Be-target viewer


Alpha monitor field-of-view

Detector

In-portcassettes


GRITER – Gamma Ray detector for ITER

A new architecture of gamma-ray detectors for ITER:a stack of thin isolated high-Z scintillatorswith independent signal readout

ADVANTAGES:

❖ n-fold increase of the available count rate relative to a single-crystal architecture of the same volume

❖ reduction of high-energy background

❖ Radiation resistance (CeBr3): fluence of 1012

protons/cm2 (>1 Mrad SI-equivalent dose).

DRAWBACKS:

❖ a reduced detection efficiency

❖ more expensive than single crystal

STATE-OF-ART COMPONENTS

Scintillators: LaBr3, CeBr3 etc.

Readout: APD, SiPM etc.

DAQ: Field Programmable Gate Array (FPGA)


2 4 6 8 10

10-4

10-3

10-2

1-cm LaBr3 detector

4.44 MeV 6.8 MeV 9.0 MeV

dN

/ N

dE

E(MeV)

MCNP calculations: gamma-ray spectra

0 2 4 6 8 10

10-4

10-3

10-2

10-1

8-cm LaBr3 detector

4.44 MeV 6.8 MeV 9.0 MeV

dN

/ N

dE

E(MeV)

A comparison of gamma-ray spectra calculated for the LaBr3 detectors with cross section 4 x 4 cm2

Where FEP – full energy peak; SEP – single escape peak related to the escape from the detector of the 511-keV photon; DEP – double escape peak related to the escape from the detector of both 511-keV photons produced due to annihilation of positron (gammas with E> 1022 keV generate e-e+ pairs in the detectors

DEPSEP

FEP

DEP

SEP FEP


MCNP calculations: GRITER size optimization

0.5 1.0 1.5 2.0-0.005

0.000

0.005

0.010

0.015

4.44-MeV gammas

DE

P -

FE

P

Layer thickness, cm

0.5 1.0 1.5 2.0

0.00

0.01

0.02

4.44-MeV gammas

FEP

SEP

DEP

Eff

icie

ncy

Layer thickness, cm

0.5 1.0 1.5 2.0

0.02

0.03

0.04

0.05

Ba

ckg

roun

d /

4.4

4-M

eV

DE

P

Layer thickness, cm

Calculations made for the LaBr3 scintillator:• Energy resolution, E/E ≈ 3%• Decay times ~ 20 ns• DAQ allows up to 5 MHz Pulse Height Analysis

Chugunov et al. Nucl. Fusion 51 (2011) 083010Nocente M et al. IEEE Trans. Nucl. Sci. 60 (2013)

1 cm thick section is chosen


MCNP calculations: background and signal

MCNP model and input data

• Port-plug: Ø300 cm (80% SS + 20% H2O)

• Collimator: Ø4 cm, L=125-150 cm (alignment ≈ #7 RNC in-port detector)

• Neutron attenuator*: pure H2O (variable length, depending on fusion power)

• Neutron source: 1.5x1020 s-1

• Neutron flux to the FW: 2.2x1013 cm-2 s-1

➢ Background calculation: neutron and gamma-ray fluxes at the detector position

1) Parallel 14.1-MeV neutron flux, 2.2x1013 cm-2 s-1, normal to Port Plug

2) Parallel 14.1-MeV neutron flux, 1010 cm-2 s-1 (as in RNC report), along the collimator

3) Parallel 14.1-MeV neutron flux, 2.2x1013 cm-2 s-1, normal to divertor, which seen by GRITER (5-cm spot )

➢ Signal calculation: the 4.44-MeV gammas from Be-target (isotropic source)

__________________________________________________________________________________* for 150-cm case of 14-MeV neutron attenuation factor ~5x10-7 and 4.44-MeV -attenuation ~7x10-3


GRITER line of sight: spot on the W-divertor

Be

GRITER

Divertor


GRITER: background spectrum

Side gamma-ray background and the divertor emission will dominate.Background count-rate in the 1st section of the GRITER ~ 4.75x105 s-1.


GRITER efficiency

DEP

FEP

Rate per source photon

1 2 3 4 5 6 7 8

➢ DEP and FEP efficiency calculated for the Ø4 cm and 150 cm long collimator filled with pure water attenuator.

➢ Reduction of the water attenuator to 125 cm could increase the efficiency by factor ~ 2.2


Modelling of escaping alphas

NC radial diffusion modelling (FIDIT and DOLFI codes ) made by V. Yavorskij et al shows that with non-monoenergetic source of DT alphas :

o Loss enhancement from E≈1MeV and decrease for E<1MeV

o ≈ 1.5-fold enlargement of the NC loss for alphas with E>E*, i.e. of those contributing to –Be reactions


Flux of escaping alphas & 9Be(,n1)12C gammas

In ITER scenario 2

o FO + cone loss : FO << D

o NC radial diffusion losses (E > 1.7 MeV): D ~ 5x1013 cm-2 s-1

(PD ~ 350 kW/m2 ,E > 0.1MeV)

In the case of 1 MW/m2 loss flux (used for FILD assessments): ≈1.5x1014 cm-2 s-1

Gamma-ray emission rate: R4.44MeV ~ 2x1011 cm-2 s-1


GRITER: signal-to-background ratio @ 1 MW/m2

Due to the forward scattering and attenuation the S/B ratios are decreasing from the front to the rare individual sections. Overall GRITER S/B ratio ~ 1/3,taking in account that E/E = 5%

The time resolution for the individual sections calculated as

For GRITER with 125-cm neutron attenuator :t ~ 30 ms at = 10% (see ITER Requirements!)

∆𝑡 =𝐵 + 𝑆 + 𝐵

2

𝑆2 𝜀2


Gamma Ray Alpha Monitor

Diagnostic Heat loads range

(MW/m2) or flux

range

(particles/m2/s)

Accuracy

of heat

loads/flux

Spatial

Range,

Poloidal

and

Toroidal

coverage,

Resolution

Energy

Range,

MeV

Energy

Resolution,

MeV

Pitch angle

range and

resolution

Time range and

resolution,

ms

S/N Sensitive elements Life time (number of 400s

DT shots)

n-

fl

u

e

nc

e

Particle fluence

Gamma-Ray

Alpha Monitor

>5 1013

cm-2s-1

>350kW m-2 ,

E>0.1 MeV

10% or

better

1 point Alphas:

>1.7

H, D, T:

>0.5

3He:

>0.8

N/A Integral dt<100 for

10 cm2

Be-target

>1/3 detector,

SiPM/MPPC

Detector >1012

protons/cm2 or

>1 Mrad

>5000 shots


GRAM vs IR


Tests during non-DT operation

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.210

-6

1x10-5

1x10-4

10-3

10-2

10-1

9Be(p,

)

6Li

(b

)

Ep (MeV)

R6

Threshold EH≈1.7 MeV

0.0 0.4 0.8 1.2 1.6 2.010

-6

1x10-5

1x10-4

10-3

10-2

R5

R4

R2 & 3

R1

9Be(p,)

10B

(

b)

Ep (MeV)

Most intensive6.84 MeV &7.48 MeV 3.56 MeV

H-ions & DD-protons (~3 MeV)

D-ions: 3He-ions:9Be(D,p )10Be9Be(D,n )10B

9Be(3He,p )11B9Be(3He,n )11C


Summary

❖ The use of the 9Be(,n )12C reaction is proposed for continuous monitoring of the escaped MeV alpha-particles by measuring 4.44-MeV gamma-rate

❖ GRITER, high performance gamma-ray detector, is proposed for GRAM (it could be useful for other applications as well)

❖ GRITER could operate at count-rate >5x106 s-1 in every section, substantially exceeding capabilities of a single crystal detector of the same size.

❖ The port occupied by the In-Port RNC detectors, equipped with 2 GRITERS (alphas and background measurements) is a generic for GRAM

❖ The collimators are filled with neutron attenuator based on pure water; length of the attenuator is variable depending on the expected fusion power

❖ Fokker-Planck FIDIT and DOLFI codes show that the radial diffusive loss mechanism is dominant in the MeV-range near equatorial plane.

❖ Signals and S/B ratios in all GRITER sections have been assessed at different alpha loss-rates, attenuators and field-of-view with MCNP

❖ The system can be used/tested during the non-DT operation: monitoring escaped DD-protons, H-, D- and 3He-ions


Thank you

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