Getting the green light

Aurora Popescu (CSU undergrad) and Justin Dokter (Research Associate) examine light-guide bar prototypes from Indiana University and Fermilab at Colorado State. Photo: D.Warner

Transparent acrylic bars are flying the friendly skies as the Photon Detector group purchases, prepares, tests and assembles the ProtoDUNE-SP light-readout system. From vendors on the east coast, to production and test sites in the Midwest, to assembly in the Rockies, they are destined for installation in the Pays de Gex.

ProtoDUNE-SP will implement photon detectors (PDs) of two different designs, one of which incorporates two wavelength shifts, and the other only one. The geometry and readout is the same for both. Each anode plane assembly in ProtoDUNE-SP will hold ten photon detectors, half of one design, half of the other, each instrumented with 12 silicon photomultipliers (SiPMs).

A team at Indiana University (IU) led by Stuart Mufson is working on PDs for which radiator plates mounted longitudinally along 2.1-m light bars perform an initial conversion of UV light to blue. The bars shift the incoming blue light to green, and act as light guides to the SiPM readout. About half the needed radiator plates have been manufactured and all meet quality specifications.  The team will ship the plates and bars off to Colorado State University (CSU) where a team led by Norm Buchanan and David Warner will perform the mounting and assembly.

At Fermilab, a production facility for the second type of light guide is turning on.  (See related article.) The bars for this single-wavelength-shifting design, purchased from a vendor in New Jersey, will get dip-coated and tested before shipment to CSU.

Mounting structure and other tooling at CSU. Photo: D.Warner

Meanwhile in Fort Collins, the CSU team has built most of the attachment parts and assembled mechanical prototype modules of both the IU and Fermilab designs. They have submerged these modules in a large cryogenic bath, tested them, and started production of components for the PD assemblies for ProtoDUNE-SP.

Back in the Midwest, a team at Northern Illinois University (NIU) led by Vishnu Zutshi is testing SiPMs. Tested SiPMs head to CSU, where they get mounted on readout boards, 12 to a board, then sent back to NIU for post-assembly tests.

The first four boards — 6% — needed for ProtoDUNE-SP are tested and ready.  Some of the parts delivered in the latest batch of SiPMs don’t quite meet ProtoDUNE’s quality specifications, but the team is confident that it can produce enough boards. Parts remaining from older shipments will be sufficient for most of the PDs needed for ProtoDUNE-SP, and the yield from newer production runs, although reduced, should make up the difference.

A few miles east, a team at Argonne National Lab (ANL) is developing the SiPM Signal Processor DC power input for the PDs. To minimize the risk of noise in the system, they have implemented optical interfaces.  Two of these modules are currently assembled and tested, one of which is headed to CERN for the vertical slice integration test this month.

All systems are go!