G. Croci 1,2, C. Cazzaniga 3, G. Claps 4, M. Cavenago 5, G. Grosso 1, F. Murtas 4,6, S. Puddu 6, A....
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- Slide 1
- G. Croci 1,2, C. Cazzaniga 3, G. Claps 4, M. Cavenago 5, G.
Grosso 1, F. Murtas 4,6, S. Puddu 6, A. Muraro 1, E. Perelli Cippo
1, M. Rebai 2,3, R. Pasqualotto 7, M. Tardocchi 1 and G. Gorini 2,3
Development of GEM-based neutron beam monitors 1 Istituto di Fisica
del Plasma, IFP-CNR - Milano (IT) 2 INFN, Sezione di Milano-Bicocca
(IT) 3 Dipartimento di Fisica, Universit di Milano-Bicocca (IT) 4
INFN LNF - Frascati (IT) 5 INFN LNL - Legnaro(IT) 6 CERN Geneva
(CH) 7 Consorzio RFX Padova (IT)
- Slide 2
- OUTLINE Why and how to use GEM-based detectors to detect
neutrons FAST NEUTRON DETECTORS Mainframe projects Prototypes
construction Performances on neutron beams Large area detector (35
x 20 cm 2 ) THERMAL NEUTRON DETECTORS Mainframe projects Prototypes
construction Performances on neutron beams Conclusions and Future
Perspectives 2
- Slide 3
- WHY AND HOW TO USE GEMS TO DETECT NEUTRONS GEMs offer the
following advantages Very high rate capability (MHz/mm 2 ) suitable
for high flux neutron beams like at ESS Submillimetric space
resolution (suited to experiment requirements) Time resolution from
5 ns (gas mixture dependent) Possibility to be realized in large
areas and in different shapes Radiation hardness Low sensitivity to
gamma rays (with appropriate gain) GEM detectors born for tracking
and triggering applications (detection of charged particles) In
order to detect neutral particles you need a converter Fast
Neutrons: Polyethylene converter + Aluminium Neutrons are converted
in protons through elastic scattering on hydrogen Thermal Neutrons:
10 Boron converter Neutrons are detected using the productus
(alpha,Li) from nuclear reaction 10 B(n,alpha)7Li 3
- Slide 4
- FAST NEUTRON BEAM MONITORS Details about triple GEM detector,
HV-GEM Power Supply, CARIOCA chips and FPGA-Board have been already
shown by G. Claps talk 4
- Slide 5
- Complete GEM detector system HVGEM HV Filters 3 GEM detector
with padded anode 3 GEM detector with padded anode FPGA Board LNF
128 ch FPGA Board LNF 128 ch DAQ PC 12 V PS Charged particles X Ray
GammasNeutrons Current Monitor 2D monitor with pads readout
Possibility to set time slices from 5 ns up to 1 s 5
- Slide 6
- Mainframe Projects CNSEM (Close Contact Neutron Surface
Emission Mapping) diagnostic for ITER NBI Prototypes (SPIDER &
MITICA) Beam monitor for ChipIr @ ISIS and ESS E d =100keV nGEM
neutron Detector Aim: Reconstruct Deuterium beam profile from
neutron beam profile. Angular resolution and directionality
property needed ChipIr CAD model at ISIS-TS2 ESS Model Aim:
Construct large area, real-time and high rate beam monitors for
fast neutron lines Deuterium Beam (100 Kev) Neutron Flux 10 10 n/cm
2 s Deuterium Beam composition: 5x16 beamlets See G.Gorini Talk
6
- Slide 7
- nGEM (fast neutrons GEM) prototypes 1 Analogue Prototype
(nGEM-S-1) 100 cm 2 active area Cathode: Aluminium (40 m) +
Polyethylene (60 m) 2 Small area Digital Prototypes (10x10 cm 2
nGEM-S-2/3) nGEM-S-2 Cathode: Aluminium (40 m) + Polyethylene (60
m) Gas Ar/CO 2 & Ar/CO 2 /CF 4 nGEM-S-3 (same cathode as full
size prototype) Cathode: Aluminium (50 m) + Polyethylene (100 m) 1
Full-Size SPIDER prototype (nGEM-FS-1) Cathode: Aluminium (50 m) +
Polyethylene (100 m) 20 x 35 cm 2 active area 4 Prototypes of nGEM
have been built and tested so far with Gas Mixture Ar/CO 2 &
Ar/CO 2 /CF 4 7
- Slide 8
- Test @ Neutron Facilities Directionality Property nGEM-S-1
(Analogue) High Voltage Scan (efficiency scan) All prototypes
Linearity w.r.t neutron flux nGEM-S-2 Beam Profile Measurements All
Digital prototypes Gamma Background sensitivity All prototypes Fast
neutron time-line (ISIS beam time profile reconstruction) nGEM-S-2
Counting stability All digital prototypes Imaging nGEM-S-2/3 FNG
Enea Frascati (Italy) 2.5 MeV neutrons 14 Mev neutrons Max Flux: 10
11 n/s (14 MeV) 10 9 n/s (2.5 MeV) ISIS Rutherford Appleton
Laboratory Didcot (Uk) Spectrum from Thermal to 800 MeV Flux:
Thermal ( 1MeV): 6*10 5 n/cm 2 s nTOF CERN Geneva (Ch) Spectrum
from a few meV to several GeV Flux 10 5 n/cm 2 /pulse 8
- Slide 9
- 2.5 MeV neutron Test at FNG (Frascati Neutron Generator ENEA)
Deuterium beam Deuterium target nGEM detector Analog Prototype
nGEM-S-2 See P. Valente Talk 9
- Slide 10
- Directionality Property 10 Neutron Flux 10 8 n/cm 2 s (measured
by in-site NE213 scintillator). The optimized aluminium thickness
that allows to discard protons emitted at an angle > 45is 40 m
(determined by MCNP Simulations) Each pulse height spectrum was
normalized considering the total number of neutrons generated by
the neutron gun measured by the NE213 scintillator. n p p Al gas CH
2 n pp G. Croci et Al, JINST C03010 2012 Results confirm that nGEM
is fully able to discard protons emitted at >45. 10
- Slide 11
- Neutron flux Linearity nGEM-S-2 Very important feature for a
beam monitor Neutron Flux up to 10 8 n/cm 2 /s Counts over the full
area scales linearly with neutron flux Efficiency (@ 2.5 MeV) =
2*10 -5 V GEM = 1020 V 2.5 MeV neutrons (Ar/CO2/CF4 gas mixture)
Detector working point and gamma rays background rejection Counting
rate Vs chamber gain: up to 890 V the chamber is sensitive to fast
neutron but not to gamma rays (Ar/Co2 70%/30% gas mixture) ISIS FNG
11
- Slide 12
- Real-time 2D beam map measurements Monitor for a fast neutron
beam with energies ranging from a few meV to 800 MeV Tested at
neutron beam of the Vesuvio facility at RAL- ISIS 2D Beam profiles
and intensity in real time Neutron beam monitorig during the
shutter opening nGEM-S-2 12
- Slide 13
- Vesuvio Beam 2D Measurement Y direction cut X direction cut 2D
Fast Neutron Intensity Map FWHM = 34 mm FWHM = 36 mm G. Croci et
Al, NIM A 720, 144-48 OFFLINE Analysis 13
- Slide 14
- Detector Counting Rate Stability in time Counting stability
Neutron flux = 10 5 /n/cm2 nGEM counting rate exactly follows the
ISIS beam Measured% of counting rate variation with time = 4.7 %
Stability is a very important feature for a beam monitor G. Croci
et Al, NIM A 720, 144-48 14
- Slide 15
- Fast Neutron time line Rate measurement scan on time delay from
beam T 0 using GEM detector with 100 ns gate. Comparison with
proton ISIS current impinging on the target (double structure) nGEM
is able to see the double proton structure E n >2MeVE n
- n Low efficiency detector 1% is sufficient since the neutron
flux is very high (>10 6 n/cm 2 s) bGEM prototype of thermal
neutron beam monitor Triple GEM detector equipped with an aluminum
cathode coated with 1m of B 4 C: first bGEM prototype Exploit the
10 B(n,) 7 Li reaction in order to detect thermal neutrons B 4 C
coated aluminium cathode mounted on its support B 4 C coated
aluminium cathode assembled inside the bGEM chamber layout Detector
Schematics 22
- Slide 23
- e CN CH N CH 3 N2N2 CH 2 e Atoms, Radicals Molecules, Ions and
Electrons powered electrode grounded electrode Time-average voltage
profile across electrodes in rf discharge Plasma deposition area B
4 C target RF plasma sputtering system for B 4 C coating at IFP-CNR
(Milano,Italy) Gas Injection Courtesy of E. Vassallo (IFP-CNR )
23
- Slide 24
- Thermal neutron measurements as a function of detector gain (wp
and -rejec) at ISIS-Vesuvio A wide plateau is present for 820
V
- Future Perspectives A new larger area nGEM neutron detector for
MITICA (the evolution of SPIDER) is under design and will be
developed next year A new high efficiency (>50%) thermal
neutrons GEM- based detector - based on a 3D cathode of thin
lamellas - for future spallation neutron sources has been designed
and is currently been built. Results will be presented in the next
months. This detector can represent a valid alternative to 3 He
detectors We are working on a new GEMINI chip which will be able to
increase the number of channels. The new chip can manage 32
channels, in comparison to the 8 channels of CARIOCA. This new
GEMINI chip will be used to upgrade all these detectors 29
- Slide 30
- Relationship with the industry HVGEM : MPElettronica Rome
(Italy) CARIOCA Chips: Artel SRL Florence (Italy) MB-FPGA:
Athenatek Rome (Italy) GEM FRAMES: Meroni & Longoni Milan
(Italy) GEM Foils: CERN Detector construction: LNF-INFN (Frascati)
and IFP-CNR (Milano) 30
- Slide 31
- Spare Slides 31
- Slide 32
- Filters in the beam line: effect on nGEM counting rate
MaterialCountrate (Hz) %Expected if fast neutrons (6 MeV) Expected
if thermal neutrons Expected if gamma rays No Material1307100 //
Lead (5 cm) 4423437 %15 %7.3 % Cadmium (1 mm) 12089398%0%0%97%
Polyethylene (15 cm) 139109%9%0%29% Aluminium (2.5 cm)
8586573%79%75% Lead: the observed decrease is compatible with the
hypothesis that the fast neutron beam is scattered by the lead
block and that the detector is non sensitive to gammas Cd: the
observed decrease is compatible with the thesis that we are not
detecting thermal neutrons CH 2 : the observed decrease is
compatible with the fact that we are detecting fast neutrons G.
Croci et Al, NIM A 720, 144-48
- Slide 33
- Material Filters in the beam (Imaging with bGEM) CH 2 L- Shaped
Cd Neutrons are scattered Neutrons are absorbed 33