Quarknet Summer Research
Build fiber optic ribbons for light testing
The team prepared fibers to be tested at CERN by cleaving, cleaning and coating them. 220 fibers were cleaved to length and inspected for flat, clean ends so light would come straight out of them. The fibers were then burned and cleaned to remove the plastic cladding and sheath, exposing the quartz core. The fibers were then mounted in a frame to make a “ribbon” of fibers. These fibers were then deposited with p-terphenel (ptp) in vacuum chambers.
After deposition, the ends of the fibers were bundled and photomultiplier tubes at the end of light guides were mounted to detect any light coming out of the fibers. One ribbon was shipped to CERN for testing in the test beam and the other three were tested using cosmic rays at the lab at The University of Iowa.
Prepare a vacuum system for depositing ptp on fibers
The team brought the old Veeco vacuum system into service for deposition of ptp onto the quartz fibers. The system had a leak in its water cooling jacket and had filled with water. The entire system had to be dismantled, cleaned, repaired and flushed. After maintenance was performed, the system tested well so was brought into service. Objects placed in this system were cleaned and ptp was carefully measured so the thickness of the deposition was controlled. This system allowed us to do our own vapor deposition and gave us great flexibility in constructing various configurations of fibers for our tests.
Testing fibers with a spectrometer
The team prepared and tested individual fibers using a spectrometer. The fibers were placed in a two-channel spectrometer and had ultra-violet light shined perpendicular to the line of the fibers. Fibers with their cladding and sheathing passed none of the light to the ends of the fibers. Fibers that had the cladding and sheathing removed passed a small amount of light but not much. Fibers that had the ptp deposition on them showed sizeable increase in light at the end of the fibers from those without the ptp. Again, multiple configurations of fiber design were tested by this setup. The results of these tests were used to make configurations for the cosmic ray tests.
Build a cosmic ray test stand at The University of Iowa
The Team set up a lab to test the fibers using cosmic rays. With the help of Dr. Norbeck, the team constructed two cosmic ray counters and placed them on top of each other in a light-tight box. The size of the plastic scintillator blocks in the counters was matched to the size of the aforementioned ribbons. Photomultiplier tubes were mounted on the blocks to detect any light created in the plastic blocks. The blocks and tubes were wrapped in light-tight materials so only the invisible cosmic rays could penetrate the blocks. The counters were placed one on top of the other with the ribbon between them. After proper signal discrimination and coincidence processing, the counters triggered the presence of a cosmic ray between them passing through the ribbon. This trigger activated the charge accumulator and recorded the size of the pulse in the ribbon. This setup allowed us to use the cosmic rays as our own accelerator beam. Long accumulation times were necessary to make up for the lack of intensity of this natural beam. Three of the ribbons were tested at The University of Iowa; One with fibers that were not modified, one with fibers that had the center 20 cm of cladding/sheathing removed and replaced with ptp and one that had every other cm of the cladding/sheathing removed and deposited with ptp.
Other activities during the summer
The team also cleaved about 1500 fibers for use in a training calorimeter for CERN. These were sent to CERN for assembly by their team. Other activities included building two more 4-counter cosmic ray telescopes for teachers to use during the school year, re-arranging the lab workspaces during remodeling, machining frames for alternate detectors, modifying a polishing machine for quartz fiber polishing, setting up the lab for various tests and writing reports.