A characterization system for the monitoring of ELI-NP gamma beam University of Florence and INFN Rita Borgheresi July 5, 2018
Outline 0 Characterization System for ELI-NP γ beam 1 Compton Spectrometer 2 Nuclear Resonant Scattering System 3 Gamma Profile Imager 4 Gamma Calorimeter
Next Section 0 Characterization System for ELI-NP γ beam 1 Compton Spectrometer 2 Nuclear Resonant Scattering System 3 Gamma Profile Imager 4 Gamma Calorimeter 0 / 27
ELI: Extreme Light Infrastructure ELI-ALPS Hungary I nvestigation of ultrafast dynamics at attosecond and ELI-Beamlines nm spatiotemporal scales Czech Applications of high brightness sources of energetic particles and x-rays ELI-NP Romania Ultra-intense laser and gamma ray pulses enabling photonuclear studies 1 / 27
ELI-NP: Extreme Light Infrastructure - Nuclear Physics ELI-NP will study a wide range of research topics in fundamental physics, nuclear physics and astrophysics, and also applied research. 1 High Power Laser System: (HPLS) • 2x10 PW Laser System • Focused laser intensity can reach 10 23 W/cm 2 2 High Intensity Gamma Beam System: (GBS) • Production method: laser photons Compton inverse scattered on high energy electrons • Two energy lines 2 / 27
The source of ELI-NP γ beam Inverse Compton radiation is not intrinsically monochromatic 4 γ 2 e E γ ∼ E L · e θ 2 · (1 − ∆) 1 + a 2 0 / 2 + γ 2 • a 0 , laser parameter • ∆ ∼ (4 γ e E L )/mc 2 Collimation system • Stack of 14 slits with aperture Gamma beam energy distribution vs independently adjustable (0-25 mm) collimator aperture • Each slit composed of two 40 × 40 × 20mm Tungsten blocks. 3 / 27
The requirements of ELI-NP γ beam Photon energy [MeV] 0.2-19.5 Photon energy tunability steplessy Bandwidth ≤ 0.5 % ≤ 2.6 · 10 5 # photons per shot within the FWHM Average diameter of beam spot ≤ 1 mm 10 22 − 10 24 Peak brilliance [N ph /s · mm 2 · mrad 2 0.1%] Linear polarization > 90 % 4 / 27
The requirements of ELI-NP γ beam Photon energy [MeV] 0.2-19.5 Photon energy tunability steplessy Bandwidth ≤ 0.5 % ≤ 2.6 · 10 5 # photons per shot within the FWHM Average diameter of beam spot ≤ 1 mm 10 22 − 10 24 Peak brilliance [N ph /s · mm 2 · mrad 2 0.1%] Linear polarization > 90 % Gamma Beam Characterization System: Give a measurement of the gamma beam characteristics . 4 / 27
Two Characterization System : • low-energy line (E γ < 3.5 MeV) • high-energy line (E γ < 19.5 MeV) High energy characterization system Low energy characterization system This talk is about the low energy line characterization system. 5 / 27
Gamma Beam Characterization System A specific system equipped with four detectors has been developed to measure and monitor the beam parameters during the commissioning and the operational phase. Imager 3 Compton 1 INFN- Ferrara Spectrometer INFN- Firenze Gamma 4 Calorimeter INFN- Firenze 2 Nuclear Resonant Scattering System INFN- Catania 6 / 27
Next Section 0 Characterization System for ELI-NP γ beam 1 Compton Spectrometer 2 Nuclear Resonant Scattering System 3 Gamma Profile Imager 4 Gamma Calorimeter 6 / 27
Mylar foils Gamma Micrometric beam target Φ Electron detector e - Gamma detector γ HPGe Cu BaF 2 collimator Si-strip Compton Spectrometer (CSPEC) CSPEC is used for online energy spectrum monitor, using a non-destructive method. 7 / 27
Compton Spectrometer (CSPEC) CSPEC is used for online energy spectrum monitor, using a non-destructive method. Working Principle The basic idea is to measure the energy (T e ) and the scattering angle ( φ ) of electrons recoiling at small angles from Compton interaction of the beam on a micrometric target (1-100 µ m). m e · T e E beam = Mylar foils � cos( φ ) T e · (T e + 2m e ) − T e Gamma Micrometric beam target • T e : measured with HPGe Φ Electron detector detector e - Gamma detector γ HPGe • φ : determined by a double Cu BaF 2 collimator sided strip detector Si-strip • The scattered gamma is acquired for trigger purpose 7 / 27
Energy reconstruction: Expected performance Beam Peak energy E γ 2.5 [MeV] σ stat (E γ ) [%] 0.04 E γ σ syst (E γ ) [%] 0.11 E γ Beam bandwith (BW) Detector response E γ 2.5 [MeV] Simulated BW [keV] 6 Detector σ [keV] 12 Detector resolution on measurement of peak energy and bandwith ≤ 0 . 5%, then better than the beam bandwith . 8 / 27
Energy reconstruction: Expected performance Beam Peak energy E γ 2.5 [MeV] σ stat (E γ ) [%] 0.04 E γ σ syst (E γ ) [%] 0.11 E γ Beam bandwith (BW) Detector response E γ 2.5 [MeV] Simulated BW [keV] 6 Detector σ [keV] 12 Detector resolution on measurement of peak energy and bandwith ≤ 0 . 5%, then better than the beam bandwith . 8 / 27
CSPEC: the HPGe detector The HPGe detector , chosen for its excellent energy resolution, will measure the energy of the scattered electron. Detector design: • The HPGe crystal is built in a planar custom configuration by CANBERRA: - 80 mm, diameter - 20 mm, thickness - electrically cooled • To minimize the energy loss: - 100 µ m, cryostat Be-window thickness - ≤ 1 µ m, electrical contacts 9 / 27
Electron source test HPGe detector tests Verified the accuracy of Monte Carlo simulation using electrons of definite Energy resolution energy emitted by 207 Bi source. 2400 2200 2000 Simulated Energy Spectrum 1800 1600 Measured Energy Spectrum 1400 1200 1000 800 600 400 200 0 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 Deposited Energy [MeV] The measured peak positions are in Energy resolution at 1332 keV: agreement with the simulated ones with a precision better than 1 keV . R E = FWHM = 0.157 ± 0.002 % E 10 / 27
CSPEC: the Si-strip detector The angle of the Compton scattered electron is determined by double-sided silicon strip detector . • 1024 strips for each view Detector design: implanted along orthogonal • Silicon strip detector produced directions by Hamamatsu • readout by VA1 chip, with 128 - 5.33 × 7 cm 2 charge sensitive amplifiers - 300 µ m thickness • Impact point resolution: - 3 µ m on the junction side (x-view) - 11 µ m on the ohmic side (y-view) 11 / 27
Si-strip preliminary test with cosmic rays Cluster characteristic: Cluster Signal/Noise: • Cluster inclusion cuts ( S N ) cluster = � m S i seed: i =1 S/N > 10 σ i neighbours: 250 S/N > 3 Y side: <S/N> = 29.3 +- 0.3 200 -2 -1 0 1 2 Entries 150 • Cluster Multiplicity - y view 100 1000 X side: <S/N> = 44.2 +- 0.5 50 800 600 0 0 10 20 30 40 50 60 70 80 90 100 S/N 400 • Y-view: larger noise, due to a 200 greater capacitance 0 0 2 4 6 8 10 Nstrip 12 / 27
CSPEC: the BaF 2 detectors The scattered photon is detected, in coincidence with the electron, by BaF 2 crystals to provide a trigger for the CSPEC data acquisition. This coincidence is very effective in suppressing the background. • Small calorimeter made of Detector design: a matrix of 4 × 4 BaF 2 crystals (1.2 × 1.2 × 5 cm 3 ) • Read out by a multianode PMT manufactured by HAMAMATSU (H12700 model) • BaF 2 has two scintillation components: • fast: τ = 0 . 6 − 0 . 8ns • slow: τ = 630 ns 13 / 27
The BaF 2 detectors tests • Signal shape identification 3 10 × 900 1000 800 Energy [ADC channels] 700 800 acceptance region 600 1275 keV 600 500 400 511 keV 400 300 Dark emission 200 200 100 0 0 0 5 10 15 20 25 30 35 40 R [a.u.] • Typical detector signal 14 / 27
The BaF 2 detectors tests • Signal shape identification 3 10 × Detector self-calibration 900 1000 800 Energy [ADC channels] 700 800 acceptance region 600 1275 keV 600 500 400 511 keV 400 300 Dark emission 200 200 100 0 0 0 5 10 15 20 25 30 35 40 R [a.u.] • Typical detector signal The intrinsic radioactivity of BaF 2 , originated from natural 226 Ra impurities, can be used to self-calibrate the detector. 14 / 27
Next Section 0 Characterization System for ELI-NP γ beam 1 Compton Spectrometer 2 Nuclear Resonant Scattering System 3 Gamma Profile Imager 4 Gamma Calorimeter 14 / 27
Nuclear Resonant Scattering System (NRSS) NRSS has to provide an absolute energy calibration for GCAL and CSPEC. 15 / 27
Nuclear Resonant Scattering System (NRSS) NRSS has to provide an absolute energy calibration for GCAL and CSPEC. Working Principle Detect the resonant γ decays of properly chosen nuclear levels when the beam energy spectrum overlaps the selected level. Detector design Target nuclear levels A X E r (MeV) ∆ E r (MeV) 6 Li 1 . 0 · 10 − 4 3.56288 11 B 2 . 7 · 10 − 5 2.124693 12 C 3 . 1 · 10 − 4 4.43891 27 Al 10 · 10 − 5 2.21201 27 Al 5 · 10 − 5 2.98200 15 / 27
NRSS: The γ detector The NRSS γ detector is made of a screened array of four BaF 2 crystals (5 × 5 × 8 cm 3 ) surroundings a LYSO crystal (3 × 3 × 6 cm 3 ). Two operation modes • Fast Counting mode: Use the BaF 2 fast response to provide a prompt information on the established resonant condition. • Energy mode: Use LYSO crystal to perform a energy spectrum measurement. In this configuration the BaF 2 act as Compton shield. 16 / 27
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