Peter Hobson - Brunel University, UK3 July 2003 VPT 4 Tesla testing  An automated characterisation facility based at Brunel has been commissioned to handle VPT devices.  Samples (about 10%) from the production batch (of total) are now being tested at Brunel.  Currently processing about 60 tubes per month.  Small improvements over the last 6 months to improve stability of pulsed and DC LED and to minimise the effect of humidity on DC leakage currents.  Developing a new VPT carrier which could allow us to test around 200 per month or more.

Peter Hobson - Brunel University, UK3 July T System at Brunel DAQ Card NI 6033E Step Motor Maclennan PCI bus RS 232 Automated VPT tester at Brunel. Mainly uses IEEE488.2 instruments. ADC is multiplexed and PCI based. VPT and Pre-amp Anode current Cathode current

Peter Hobson - Brunel University, UK3 July T System at Brunel 4.0T Superconducting solenoid at Brunel Persistent current, no power supply “Zero” field region is actually about 0.5 mT All tubes operated at 1000V on anode and 800 V on dynode. The photocathode is held at 0V.

Peter Hobson - Brunel University, UK3 July 2003 DC illumination data ~ 180 nA (at 0T) 30 seconds

Peter Hobson - Brunel University, UK3 July 2003 Pulsed LED data LED pulsed at 500 Hz 10 seconds

Peter Hobson - Brunel University, UK3 July 2003 Measurement correlations Different illuminated areas Problem of DC leakage current correction Encouraging! DC gain = (I anode – I dark )/ (I cathode – I dark )

Peter Hobson - Brunel University, UK3 July 2003 Batch acceptance test at 4T Arrows indicate angular regions of end caps VPT Axis at 15 o to Magnetic Field Central illumination

Peter Hobson - Brunel University, UK3 July 2003 VPT Summary  About 10% of all delivered tubes have been measured at 4T, only one working tube failed to pass the acceptance criterion.  Some tubes noisy at 1.8T are also noisy at 4T. All tubes noisy at 4T were found to be noisy at 1.8T (or at 0T).  Almost all tubes at Brunel are measured by the same skilled technician  consistency.  Problems with tubes (or system) are found rapidly due to on-line display of measured DC and pulsed data.  All raw measurement data is archived at Brunel, processed (summary) data is archived in a database at RAL.