Monitoring of stray magnetic fields near the PROSPECT detector

Transcription

1 Monitoring of stray magnetic fields near the PROSPECT detector Corey Gilbert On behalf of the PROSPECT Collaboration ORNL is managed by UT-Battelle, LLC for the US Department of Energy Next Talk G : Temperature Dependence studies of the 6Li-doped liquid scintillator used in PROSPECT Brennan T Hackett

2 Motivation PROSPECT is a high precision spectrum antineutrino experiment that requires a well characterized background environment because it is operating at surface level Overburden: ~1m.w.e. Challenge: Neutron scattering experiments conducted in high magnetic environments Backgrounds include: Cosmic Gammas Neutrons Magnetic fields Next Talk G : Temperature Dependence studies of the 6Li-doped liquid scintillator used in PROSPECT }Brennan T Hackett!2

3 High Flux Isotope Reactor (HFIR) Polarized Triple Axis Spectrometer Fixed-Incident- Energy Triple-Axis Spectrometer Inner/ Outer Core 85 MW Thermal Power Research Reactor ~93% enriched 235U fuel Very compact core (h=0.6m d=0.4m) ~42% duty cycle allows good background characterization Neutron Powder Diffractomete HB-1 HB-2 PROSPECT HB-3 HB-4 Cold Neutron Experiment Hall WAND Sample Environment Storage Polarized Neutron Development Neutron Residual Stress Mapping Triple axis spectrometer 4-circle Diffractomete!3

4 Magnets at HFIR Superconducting magnets ranging from 5-11 Tesla are used on various beamlines High field magnets (25-30Tesla) are being considered Mag E 8T Vertical Asymmetric Field Cryomagnet Temp Range: 1.7 to 300 K Used on beamlines : CG-2, CG-4C, HB-1, HB-1A, HB-3!4

5 PMT Configuration in PROSPECT Detector Each of the Li-loaded liquid scintillator filled optical segments holds 2 5 PMTs PMTs are known to be sensitive to magnetic fields. Relative magnetic field values over the range of the device need to be assessed Earth s magnetic field is G at ORNL - Declination: -5º 33 30, Inclination: 64º NOAA Magnetic Field Calculator!5

6 Recent Experimental Efforts to Test/Control Magnetic Environments The STEREO Experiment (Neutrino) - arxiv: v1 (2018) Magnetic shield of PMT used in a DAMPE electromagnetic calorimeter (Dark Matter) - arxiv: v4 (2013) Performances investigation and material selection of PMT magnetic shields for the space experiments with GRIS and PING-M instruments (Space) - R M Faradzhaev et al. J. Phys.675 (2016) First Observation of P-odd γ Asymmetry in Polarized Neutron Capture on Hydrogen (Fundamental Symmetries) - arxiv: v1 (2018) Magnetic field effects on the photocathode uniformity of Hamamatsu R7081 photomultiplier tubes (Industry) - NIMA 697(2013) 46!6

7 Helical Orbit Spectrometer (HeliOS) Studies of short lived isotopes Magnetic field needs to be parallel to beam within 1 mrad Monitoring magnetometers are crucial for this type of experiment!7 Wuosmaa, A. NIMA. 2007

8 PMT Sensitivity to Magnetic Field Backgrounds Low-energy electrons travel along a long path in a vacuum to reach the dynodes. Slight magnetic fields distort that trajectory, causing an anode sensitivity variation Hamamatsu PMT 127mm Hamamatsu, PMT Basics and Applications 2007!8 Boyle J., Master s SESAPS Thesis

9 PMT Module Configuration 240 Hamamatsu R6594 (127 mm ø Q.E. 25%) - 10 stage dynode of box & line configuration 68 ET9372B (130 mm ø Q.E. 28%) - 12 stage dynode of linear focused configuration PROSPECT PMTs are fitted with a Hitachi FINEMET magnetic shield - Amorphous metal composed of Nb, B, Fe, Cu!9

10 Magnetic Field Background Characterization Background B-field was measured using a Lakeshore hall probe (HMMT-6J18-VF) before placement of PROSPECT detector Results showed hotspots approaching 2 Gauss PROSPECT Gauss!10 Boyle J., Master s Thesis 2016

11 Current Magnetometer Technology GMN Earth 1fT 1pT 1nT 1µT 1mT Lenz J., Edelstein A., IEEE Sensors Journal 2006!11

12 Adafruit Triple-Axis Magnetometer Model: LSM303DLHC Selectable range: +/- 1.3 G to +/- 8.1 G Magnetic resolution: 2mG Read through Raspberry Pi I2C 20.3 mm 22.9 mm!12

13 Monitoring of Magnetic Field Rx Core triple axis magnetometers Compact LN2 TOP VIEW DAQ Rack Low cost Online monitoring Alert system 3 1 Remote control 2!13

14 Axes Shift Calibration Out of the box, sensors are not calibrated X and Y magnetic fields plotted as magnetometer is rotated about Z axis before and after axis shift is applied. Programmed in python, takes <1 minute Before After!14

15 Axis Magnitude Calibration Metrolab THM1176-LF hall probe used as known value - Range: 8.0 mt - Resolution: 2µT ± - Accuracy: 20µT or 0.2G Sensor s axes are compared to known and shifted to match!15

16 Magnetic Field Magnitude Around PROSPECT Reactor Core 0.6 Scan using Metrolab hall probe DAQ Rack Gauss Varying magnetic field from 0.15 G to 0.6 G Scanned at sensor height (16cm) Hot spot near DAQ 0.1!16

17 Operation of Sensors since Oct 31 Spike correlated to testing ramp up and down of Mag-E (8 T) on HB-2A!17

18 Magnets Used Since Deployment of PROSPECT Detector MAG-B (5T) MAG-A (5T) MAG-H (5T) MAG-E (8T) MAG-G (11T) MAG-D (11T) HB-1A HB-1 HB-2A HB-2C HB-3 CG-2 CG-4C 3/9/18 4/8/18 5/9/18 6/8/18 7/9/18 8/8/18 9/8/18 10/8/18 11/8/18 Reactor ON Reactor OFF!18

19 Conclusions A compact, low cost magnetic monitoring system has been deployed surrounding the PROSPECT detector at HFIR. Sensors show very good stability and sensitivity to background events Me!19

20 Backup Slides!20

21 Effects of various shielding positions!21 Leo, W.R. Techniques for Nuclear and Particle Physics Experiments. 1994

22 Calibration accuracy Metrolab probe average values plotted with sensor data Sensors values are within 0.2 G of Metrolab probe after calibration Solid lines: Adafruit Sensors Dashed lines: Metrolab probe!22