The BANDGEM detector G Croci 1 2 3

The BAND-GEM detector G. Croci 1, 2, 3, A. Muraro 1, G. Grosso 1, E. Perelli Cippo 1, G. Albani 3, C. Cazzaniga 3, G. Claps 4, , F. Murtas 4, M. Rebai 2, 4, M. Tardocchi 1, C. Höglund 5, 6, L. Hultman 6, J. Birch 6, R. Hall-Wilton 6, 7, Xiao-Xiao Cai 5, 8, I. Llamas Jansa 5, 8 and G. Gorini 3, 4 1 Istituto di Fisica del Plasma (IFP-CNR) – Via Cozzi 53, 20125 Milano, Italy – Sez. Di Milano-Bicocca – Piazza della Scienza 3, 20126 Milano, Italy 3 Dipartimento di Fisica, Università degli Studi di Milano-Bicocca – Piazza della Scienza 3, 20126 Milano, Italy 4 INFN – Laboratori Nazionali di Frascati –Via Fermi 40, 0044 Frascati, Italy Spallation Source ESS AB, P. O. Box 176, SE-221 00 Lund, Sweden 6 Department of Physics, Chemistry and Biology (IFM), Thin Film Physics Division, Linköping University, SE-581 83 Linköping, Sweden 7 Mid-Sweden University, SE-851 70 Sundsvall, Sweden Institute for Energy Technology, Box 40, 2027 Kjeller, Norway 2 INFN Financial support from CNR; ESS pre-construction in-kind contract 5 European GEM 8 IFE:

SHOULD WE DETECT THERMAL NEUTRONS WITH GEMS? GEM detectors born for tracking and triggering applications (detection of charged particles). . . but if coupled to a solid state converter they can detect Thermal Neutrons 10 Boron converter Neutrons are detected using the productus (alpha, Li) from nuclear reaction 10 B(n, alpha)7 Li Face 3 He world shortage GEMs offer the following advantages High rate capability (up to 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) G. Croci et Al JINST 7 C 03010; F. Murtas et Al, JINST 7 P 07021; G. Croci et Al, NIMA 720, 144; G. Croci et Al, NIMA, 712, 108; G. Croci et Al, JINST 8 P 04006; G. Croci et Al, NIMA 732, 217; G. Albani et Al, JINST 10 C 04040; G. Croci et Al, EPJP 130, 118 G. Croci et Al, EPL, 107 12001 G. Croci et Al, Prog. Theor. Exp. Phys. 083 H 01;

OUTLINE THE BANDGEM DETECTOR Principle of operation Detector Simulation Results APPLICATION @ LOKI-ESS LOKI Demonstrator

Boron Array Neutron Detector BANDGEM Thermal neutron detector

Scheme and Principle of operation n n θ Al 2 O 3 10 cm α Cathode 3 D Lamella System 6 cm α Ed e- 2 mm Triple GEM 5 10 B 4 C 10 B Al 2 O 3 Padded Anode Alumina Lamellas coated on both sides with 10 B 4 C Using low θ values (few degs) the path of the neutron inside the B 4 C is increased Higher efficiency when detector is inclined 4 C 4 C

The lamellas Material = Allumina (Al 2 O 3) 6 cm A lamella is composed by 15 strips 12 cm 2 mm 6 2 mm

10 B 4 C Coating on the lamellas Deposition done by Dr. Carina Hoglund The resulting coated lamellas A 1 μm 10 B 4 C coating has been deposited on both sides of the lamella and on all the 15 strips In total more than 50 lamellas have been coated 50 Lamellas are necessary to assembly the first detector prototype Coatings are slightly conductive ρ = 696 Ω*cm 7

Detector Assembly The full Lamella System. A total of 48 lamellas have been mounted. Their distance is 2 mm 8 Assembly with Triple GEM detector 128 Pads of area 6 x 12 mm 2 have been used as anode

BANDGEM simulation Numerical Simulation of Neutron conversion efficiency and electron extraction GAS=2 mm B 4 C=2 mm Volumetric Simulation (1000 e-) Diffusion ON Good Electron 1000, Out Electron 263 Percentage 26. 3 Volumetric Simulation (1000 e-) Diffusion OFF Good Electron 1000, Out Electron 486 Percentage 48. 6

Detector test at IFE (JEEP II Reactor, RD 2 D beamline) Ed = 230 V/cm Et 1=Et 2= 3 k. V/cm; Ei = 5 k. V/cm Mixture Ar/CO 2 70%/30% 230 cc/min Carioca chips FPGA-LNF Motherboard Angle = 7 degrees 10 VGEM = 980 V

High Voltage Scan – Working point Ed = 230 V/cm Et 1=Et 2= 3 k. V/cm; Ei = 5 k. V/cm Mixture Ar/CO 2 70%/30% 230 cc/min Need to understand the gamma ray background component. On-site measurment with a gamma source VGEM working point values are higher than usual one (870 V) Neutron energy En = 34. 5 me. V 11

Angular scan Neutron energy En = 34. 5 me. V Beam size = 9 mm x 9 mm The counting rate depends on the angle between the beam and the lamellas. There is about 0. 5 of systematic error settings due to the mechanics 12 The 3 He tube in front of the GEM is counting 14660 n/s with an efficiency of 87% at this neutron energy. It is fully in the beam

Comparison 3 He -GEM 3 He tube has a diameter of 2. 54 cm We see the same behaviuor (inverted in 3 He for the same angles). The GEM is absorbing neutrons. There are still some feautures to be understood n Slits 3 He Maxima and minima are due to the geometry of the GEM GEM is used as absorber 13 En = 34. 5 me. V

First efficiency estimation as a function of wavelenght ε(λ) = 1 – e-cσ(λ) Where σ(λ) = λ/ λ 0 If λ=λ 0=1. 54 A ε=0. 15 for 10 degrees and ε==0. 20 for 7 degrees (Angle with respect neutron direction) 14

BANDGEM detector for neutron diffraction measurements • First BANDGEM Prototype • Bronze sample • BANDGEM @ 90° • 3 He counts about 3. 4 times the BANDGEM • BANDGEM/3 He Solid Angle Ratio = 0. 45 Same Measurement Time BANDGEM INES (ISIS) sample pos. Transmitted neutron beam Incident neutron beam GEM position 3 He Tube

Application to the European Spallation Source (ESS)

The LOKI instrument @ ESS SANS Instrument

BANDGEM application @ LOKI. . Just an example of a possible LOKI vessel Configuration. . . BANDGEM Modules As rear detector panels Requirements for rear detector panel • Rate Capability = 40 k. Hz/cm 2 • Time resolution bettter than 1 ms • Efficiency of about 60% at 4 Å • X-Y Space resolution of about 4 mm Construction of BANDGEM demonstrator for LOKI as an upgrade of the first prototype

The BANDGEM umbrella for LOKI 337 mm 2 Lamellae system 96 Total active area: 647 cm 2 Cathode 8 6 GEM 1 2 GEM 2 2 400 mm Readout anode GEM 3

Detector Assembly – The cake Readout anode Triple GEM Lamellas system Aluminate mylar cathode

The Front End Electronics The first protoype electronics is based on Carioca Chip. Total dimension : 3 x 6 cm 2 Digital Chip with 8 channels Equips the LHCb GEM detectors Fast chip – used for triggering Adapted from MWPC A new chip is being tested: the GEMINI chip. Mixed analog and digital chip that Has 16 channels/chip. This is the chip that we would like to use at ESS for LOKI BANDGEM Especially developed for GEM detectors

Conclusions First BANDGEM prototype reached an efficiency of 20% at 1. 54 Å First BANDGEM prototype successfully tested as neutron diffractometer improvement w. r. t. single layer BAND-GEM demonstrator for LOKI New simulation Higher efficiency Being designed Small area prototype ready before end 2015 Geant 4 simulations on-going.

Thanks from. . . the BANDGEM team

Complete GEM detector system Charged particles X Ray Gammas Neutrons 12 V PS HVGEM LNF DAQ PC Current Monitor 24 HV Filters 3 GEM detector with padded anode (Carioca Chips) FPGA Board LNF 128 ch 2 D monitor with pads readout Possibility to set time slices from 5 ns up to 1 s

Resistivity measurements of the B 4 C coatings Measurement performed (using the 4 points method) on the first (preliminary) alumina sample coated by Carina with 1 μm of B 4 C Since thickness of the sample was 1 μm the measured resistivity ρ = 696 Ω*cm The coatings can be considered as partially conductive 25 In collaboration with CNR-IMIP

Detector Assembly (3) Assembly with Triple GEM detector 128 Pads of area 6 x 12 mm 2 have been used as anode 12 mm Lamella disposition on the pads 26 2 mm 6 mm

GEM Foil The GEM foils will be realized at CERN and they will be glued to their frames using the same technique used for the production of the cathode. Each GEM foil will be sectorized in 8 sectors, in order to reduce the possible damage caused by a spark. A total of 3 GEM (triple GEM) will be installed in the detector and the gap between each GEM (Transfer gaps) is equal to 2 mm. All the GEM foils will be sandwiched and glued on the upper trapezoidal frame.

Padded Anode y ϕ The anode will be composed by 1024 pads. The the size of the pads is between 7. 7 and 137 mm 2. The maximum pad size is similar to the one of the n. GEM for SPIDER, and we have already tested the low noise level. The PADs is divided into 10 ϕ sectors, while the dimension of the PADs is constant along the y-coordinate and equal to 4 mm. At the moment only the PADs were designed, while the position of the readout electronics is still under investigation. The design of the read-out electronic position will be decided after the test of the GEMINI Chip. The anode will be glued on the GEM 3 frame, and the gap between the GEM 3 and the PADs (induction gap) will be equal to 2 mm.

Small Area Prototype- for testing 107 mm In order to test the technology processes that will be used for the construction of the demonstrator and to validate the numerical simulation as soon as possible, it was decide to made a small scale prototype (active area=10 x 10 cm 2). 115 mm With this detector we can test the production method of the lamellae system (it is the same of the demonstrator) and we can validate the numerical simulations. It will be composed by 25 lamellae (all with the same dimensions) and the 10 x 10 triple GEM system with its cathode will be the same of the actual Band. GEM (and of the other 10 x 10 GEM detectors such as the b. GEM). This should allow the production and the test of the detector up to the end of this year.