Optical Transmission/Absorption Measurements associated with the QA Procedures for the MICE Scintillating Fibre Tracker
MICE, the international Muon Ionization Cooling Experiment, is a project to design, construct, operate and test a cell of a muon ionisation cooling channel that may be used for a future Muon Collider or Neutrino Factory.
The object of the MICE experiment is to take a beam of muons created from protons from the ISIS accelerator hitting a titanium target and to show that it is possible to create a narrow intense beam, using detector techniques from particle physics.
Charged-particle tracking in MICE is provided by two solenoidal spectrometers, each a 4 T superconducting solenoid instrumented with a tracker composed of five planar scintillating-fibre stations[1]. Each station is in turn made up of three doublet layers of scintillating fibres. During the "Optical QA" step of construction, the fibres within a doublet layer were excited sequentially to confirm correct location and connectorisation. The "Station QA" step then checked the uniformity of response across the whole station.
Optical QA
During the Optical QA process, a violet LED (ETG ETG-5UV405-15, 405 nm) was used to excite fibres sequentially across a doublet layer[2], and the output connectors monitored to ensure correct channel assignment.
To allay concerns that this might affect the optical fibres, a sample (without mirror-coating) were formed into a bundle glued into a brass ferrule. They were then subjected to repeated exposures to light from the same LED, and also later to illumination from a broadband Mercury arc lamp (to partially reverse the damage).
Transmission through the optical fibre as a function of wavelength was measured using a Hitachi U-4100 Spectrophotometer. Since the coupling of light from the spectrophotometer's source to the fibres is very inefficient, an aperture was inserted into the spectrophotometer's reference path, and into the sample path during the background measurement, to avoid saturation.
Measurements were also made on samples of a plastic drinking straw coated with black paints (Humbrol no. 33 "Matt Black" enamel, and Games Workshop no. 61-51 "Chaos Black" water-based matte acrylic) used elsewhere on the project.
Results are provided in the SciFiDamage spreadsheet (last modified 15th December 2006).
Station QA and Assembly/Installation
The doublet and subsequent station assembly obviously required manipulation of the bare scintillating fibres.
During the Station QA process a radioactive source was scanned over the exposed station after completion (see [1], fig.10), and the selected stations then required assembly into Trackers, and subsequently the Trackers were inserted into the bores of the Spectrometer Solenoids.
To prevent damage to the scintillator from any UV component of the ambient illumination, all light sources were covered in (yellow) anti-UV film (EncapSulite G10 UV filtering film) during such work. Where this was not possible (such as the cosmic-ray tests and the insertion into the magnets in the MICE Hall, a light-tight tent was set up.
Measurements made on the black plastic material used for the tent and on the yellow foil are provided in the SciFiTent spreadsheet (last modified 7th November 2007).
Acknowledgements:
Henry Nebrensky made the measurements.
Peter Hobson advised on setting up the exposure rigs and spectrophotometer.
Cinzia da Viá suggested trying broadband illumination to undo the radiation damage.
Disclaimer
This data is provided in the form of spreadsheets, images and text files as saved to disk over a decade ago. Supporting information is mostly from memory.
References
1. "The design, construction and performance of the MICE scintillating fibre trackers", Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 659 pp.136-153 (2011) doi:10.1016/j.nima.2011.04.041
2. M. Takahashi, P.R. Hobson, P. Kyberd and J.J. Nebrensky: "Illumination System for the MICE Tracker Station Assembly QA" MICE Note MICE-NOTE-DET-167 (2007)
This material forms part of the MICE Miscellaneous data, DOI: 10.17633/rd.brunel.5024885 ( Construction/Tracker/OpticalTransmissionAbsorptionMeasurementsAssociatedWithTheQAProceduresForTheMICEScintillatingFibreTracker.zip ).
