Presentations for this session Anton – Detector concept and rate estimations Scott – Readout Jonathan – Data Management

Detectors for Direct Spectrometers: Principle, readout channels and Rates ESS Detector Group Anton Khaplanov IKON

Introduction ESS Detector Group contact persons for Sectroscopy Anton Khaplanov Direct Geometry Spectrometers Fatima Issa Indirect Geometry Spectrometers (this presentation on direct geometry instruments only)

Multi-Grid Concept and Design

Multi-Grid Detector - Principle B-10 film Al substrate n conversion gas fragment 1 fragment 2 gas n n Introduced at ILL, jointly developed by ILL and ESS under CRISP project

Efficiency Efficiency can be optimized depending on the wavelength range Efficiency for: 32 layers (16 cells) 0.75, 1.0 and 1.5 um B4C and optimized for 4Å (does not take into account the fill factor)

Detector: 2.4 m 2 active area Blade x18432: enriched B4C coating good adhesion, uniformity, Column x8: wire-frame coincident readout Grid x1024: low activity, minimal dead material Multi-Grid Detector – Large Area

Multi-Grid Detector – Instrument Concept

10 B 4 C layer production

MG grid test detector 2 columns of 12 grids 32 layers Individual channel readout Flow-through or sealed Under construction in Lund To be used at the ESS Source Facility, IFE beam line. Multi-Grid Detector Design and testing at ESS

MG.CNCS Size = half of “8-pack” module – 1m x 20cm Operation from autumn grids 2 columns of 48 grids 32 layers Adapted layer thickness Flow-through Test at spectrometer Operation for 6-12 months Side-by-side comparison to He3 User experiments Operation in Low Pressure Improved Position resolution Demonstrator test at TOFTOF Prototype for ESS Spectrometer Multi-Grid Detector – Instrument Demonstrators

Complete simulation in GEANT4 ESS Detector Group Framework Extension of GEANT4 including crystal structure and interactions of thermal neutrons Full simulation of performance scattering direct comparison to He3 Efficiency correction matrix Work of Eszter Dian Multi-Grid Detector – Simulations

Readout Scheme and Expected Rates

Number of channels

Multi-Grid readout principle Multiple layers – rate spread over ~16-20 voxels for each pixel  Wire rate reduced by x10 compared to pixel rate n Cell 1Cell Cell 16 Cell 15

Readout Scheme Grid-wire coincidences Signals in 1 grid and 1 wire define an event 3d-position localization grid # and wire #  unique voxel Voxel position in spherical coordinates Theta and phi  scattering angle Radial coordinate  energy determination rows n n E i, Q i n E f, Q f

Voxel identification – coincidences Beam hitting 1 pixel (15 voxels) Linear scaleLog scale

Rates Assumptions 1e6 n/s/cm2 per monochromatic pulse 10x monochromatic pulses per period 14x periods in a second Sample size – 1cm2 Sample scatters 10% of the beam (all modes combined) Sample scatters 0.1% of the beam in one Bragg reflection Typical scattering come (for powder) at ~90 deg Elastic peak width – 50us

Global Rates 1e6 n/s/cm2 per monochromatic pulse, about 10x pulses ~1e7 n/s/cm2 Assuming ~10% scattering (all modes)  1e6 scattered neutrons / s  ~20% coverage  2e5 neutrons in detector / s (approximately 100x100 pixels)  20 n/s/pixel (2 n/s/voxel)  2000 n/s/wire row (200 n/s wire)  80 n/s/grid Analogous analysis for diffractometers: Paper in preparation: I. Stefanescu, B-based detectors for the diffraction instruments at ESS

Worst Case Rates 1e6 n/s/cm2 per monochromatic pulse, about 10x pulses per period ~1e7 n/s/cm2 Assuming ~0.1% scattering in a single Bragg refection  1e4 n/s in a single reflection Powder: band into ~ pixels; 1/5 of 2pi in detector  (1/2 *1/5)* 1e4=1e3 in one wire row  1e2 per wire  Grids: (1/100)* 1e4  1e2 per grid Single crystal: peak into ~5 pixels  (1/2 )* 1e4 = 5e3 in one wire row  5e2 per wire  Grids: (1/2)* 1e4  5e3 per grid

Worst Case Instantaneous Rates 1e4 n/s/cm2 in a single reflection 14 pulses / s  1e3 n/pulse Assuming pulse ~50us elastic peak width  instantaneous rate 2e7 n/s Powder: band into ~ pixels; ~1/5 of 2pi in detector  (1/2 * 1/5) * 2e7 = 2e6 in one wire row  2e5 per wire  Grids: (1/5 * 1/100)* 2e7 = 4e5 per grid Single crystal: peak into ~5 pixels  (1/2) * 2e7 = 1e7 in one wire row  1e6 per wire  Grids: (1/2) * 2e7 = 1e7 per grid Counts will saturate, but this is only in the elastic peak, for the rest of ToF spectrum, time-average rates are worst case Global instantaneous: assume 10 peaks in detector  2e8

Rates Summary, in Hz B10 MGGlobalpixelvoxelwiregrid Average rate2e Worst-case average rate 2e Worst-case instant rate 2e84e64e51e61e7 He3Globaltube Average rate2e52000 Worst-case average rate 2e55000 Worst-case instant rate 2e81e7 To convert to rates in 1’’ He3: Same physical rates, but readout only by a single tube in place of a wire row  Rate (He3 tube) = rate (MG wire) *10 Readout: Average and peak rates OK Peaks will saturate, but information is not in peaks Detector: MG rate spread over ~10 tubes He3 – higher gain (needed for charge division)

Outlook To investigate performance further, full simulation is needed: Beam λ, t distribution at sample Scattering scenarios at sample Detector response With all 3 points included – possible to compare detector configurations with respect to quality of measured data. McStas Geant4