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Status of VPT measurements at RAL

Status of VPT measurements at RAL. Bruce Kennedy RAL, 3 July 2003. Outline. VPT delivery schedule Reminder of RAL VPT test rig Summary of standard measurements Discussion of anomalous VPTs. VPT deliveries. RAL 1.8T test rig. Details of RAL test rig.

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Status of VPT measurements at RAL

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  1. Status of VPT measurements at RAL Bruce Kennedy RAL, 3 July 2003 B W Kennedy, RAL PPD

  2. Outline • VPT delivery schedule • Reminder of RAL VPT test rig • Summary of standard measurements • Discussion of anomalous VPTs B W Kennedy, RAL PPD

  3. VPT deliveries B W Kennedy, RAL PPD

  4. RAL 1.8T test rig B W Kennedy, RAL PPD

  5. Details of RAL test rig Diffuser plate to ensure uniform illumination VPT holder B W Kennedy, RAL PPD

  6. VPT statistics • Delivered: 5500 (inc 500 pre-production) • Visual inspection: 5000 • Tested at 1.8T: ~4800 • ~10 not tested – could not take high voltage B W Kennedy, RAL PPD

  7. Test procedure • Yield measurements • Response v angle at 1.8T • Response v field at 15 B W Kennedy, RAL PPD

  8. VPT yield measurements Mean response at 1.8T over range 8-25 B W Kennedy, RAL PPD

  9. Comparison with RIE data Gain, qe measured byRIE at 0T Compared with RALmeasurement at 1.8T B W Kennedy, RAL PPD

  10. Anomalous VPT behaviour • Majority of VPTs perform well at 1.8T • Small fraction (~5%) show “discharges” • Indicated by increase in signal width B W Kennedy, RAL PPD

  11. Example of discharge VPT 790, 9 VPT 790, 11 B W Kennedy, RAL PPD

  12. Characteristics of discharges • Repeatable • Appear in same range of angles for given VPT • Persist over weeks / months • Most common at 9 to magnetic field • Not seen at zero field • Incidence reduced at lower voltage • Tests at Va/Vd = 800/600 show fewer spikes • Fraction of anomalous tubes constant in • Delivery date • VPT serial number B W Kennedy, RAL PPD

  13. Tests on anomalous VPTs 1 • Modification of applied voltage • Standard is Va/Vd = 1000V/800V • Test runs at: • 1000/850 • 800/600 • 750/600 • Define peak width >10 as “noisy” B W Kennedy, RAL PPD

  14. Noisy VPTs v Voltage B W Kennedy, RAL PPD

  15. Noisy points v voltage B W Kennedy, RAL PPD

  16. Tests on anomalous VPTs 2 • Long runs at reduced voltage • 24-hour exposure at 800/600 • Hoped to reduce discharges • No obvious effect seen (3 long runs) B W Kennedy, RAL PPD

  17. Tests on anomalous VPTs 3 • Gradual voltage ramping • Successive test runs at fixed angle at • 0/0, 600/400, 800/600, 1000/800 • “Gentle” treatment could reduce noise • Tests over limited range of angles so far • Noise low at low volts, but returns at 1000/800 B W Kennedy, RAL PPD

  18. Example of slow V ramping B W Kennedy, RAL PPD

  19. Tests on anomalous VPTs 4 • Cutting open of one noisy VPT • Resin “socle” carefully removed • No indication of corrosion of pins or other abnormality • VPT envelope pierced (to allow air in) and carefully cut away • No visible defects in anode or dynode B W Kennedy, RAL PPD

  20. Comparison of prod & pre-prod VPTs • 389 pre-production VPTs recently re-measured • Noisy tubes: • 18 (4.6%) show spikes • Size of spikes differs from production VPTs Spike Height B W Kennedy, RAL PPD

  21. Spike heights - prod & pre-prod B W Kennedy, RAL PPD

  22. Anomalous VPTs in latest batch • Bar codes 4701-5100 • 208 VPTs tested in detail so far • 191 (91.8%) OK • 7 (3.4%) show spikes • 10 (4.8%) need retesting – possible noise, but data ambiguous • Fraction of noisy VPTs consistent with previous batches • Bar-codes of noisy tubes: • 4908, 4924, 5013, 5015, 5038, 5047, 5070 B W Kennedy, RAL PPD

  23. Summary and conclusions • VPT deliveries are ~ on schedule • 500 pre-prod + 5000 production VPTs delivered • Magnetic field tests are progressing well • 4800 measured at 1.8T in RAL variable-angle rig • Small proportion (~5%) anomalous at 1.8T • Further tests continuing B W Kennedy, RAL PPD

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