RIE pre-production VPT Brunel tests Peter R Hobson with Barbara Camanzi, Derek Imrie, Mark Osborne, Christopher Selby and Omar Sharif Department of Electronic and Computer Engineering, Brunel University, UK 6 February, 2001
Automated VPT test system • Superconducting (persistent current) 4. 0 T axial field magnet • VPT gain at 4. 0 T relative to 0. 0 T measured with tube at 15 degrees to field axis • DC gain at 0. 0 T measured using anode and cathode currents • Pulsed gain at 4. 0 T and 0. 0 T measured using fast blue LED at 1 k. Hz repetition rate • Data taken with Vanode = 1000 V, Vdynode = 800 V • Single tube torpedo in current use, 6 VPT torpedoes under construction 6 February, 2001
DAQ system A PC controls the anode & dynode HT and measures voltages and currents. This instrumentation is IEEE 488. 2 based 6 February, 2001 The same PC also controls a step motor via RS 232, and has a 32 channel differential 16 -bit ADC card for the anode signals (pulsed LED tests).
The production system at Brunel GPIB control system and DAQ 4 T magnet Single VPT in torpedo 6 February, 2001
Relative pulsed gain The ratio of the gain at 4. 0 T to that at 0. 0 T for a tube angle of 15° to the magnetic field is a critical parameter. All but 1 tube tested (86 in first batch, 60 in second batch) pass the acceptance criterion. 6 February, 2001
DC gain from automated system DC gain measured in the automated test system. Mean gain = 9. 3 6 February, 2001
Repeatability A number of tubes (18) from batch 1 were measured twice, usually after about a 12 hour delay. Repeatability of the system is good. 6 February, 2001
Photocathode Uniformity • Photocathode response (VPT operated as a diode) measured with stable blue-violet LED (spectrum a good match to Pb. WO 4 emission) • Repeat scans show repeatability is reasonable. Positioning errors are ± 0. 5 mm and ± 3°. • Three diameter scans at 120 degree intervals. • System is now semi-automated, results are preliminary. Scanning of tubes with visual photocathode defects is underway. 6 February, 2001
Photocathode uniformity 6 February, 2001
Future work • Complete testing of the pre-production batch of 500 tubes • Complete construction and commissioning of the 6 -VPT torpedoes • Complete the construction of the step-motor automated VPT feed system • Prepare for the production run later in 2001 6 February, 2001
Conclusions • System is working • Approximately 25 tubes per working day can be tested at present, this should rise to 50 with completion of the final system (new 6 VPT torpedoes plus automated feed) • Repeatability of the relative gain at high field is very good • Photocathode scan work looks promising • So far so good, but a great deal of work to do in the next four years! 6 February, 2001
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