Murphy's law the return…

The day of yesterday has been very good until, I decided to switched off the system. High dark count rate occured just then. Today, the background pressure is arround 4.10-e7 mbar (in 3 days), slightly better then yesterday. The polarisation scheme is as followed:

• front MCP : -1000 V -> -14000 V
• rear MCP : +1000 V
• anode : +1350 V

V	100	200	300	400	500	600	700	800	900	1000	1100	1200	1300	1400	1500	1600	1700	1800	1900	2000	2100	2200	2300
micro A	2	4	7	9.5	11.5	14	16	18	20.5	23	25.5	28	30	32	34.5	37	39	41.5	44	46.5

With respect to yesterday, I can notice that there is 1-2 micro A more above 500 V. Courant leak ?… A first pulse with a repetition rate of 1Hz is detected with 1600 V and the anode at 1300V. The pulse width is about 10 ns and the amplitude around 15-35 mV and is independant of the gage status (on / off). It repetition rate seems to be less with the votlage on the anode around 1100 V. A second pulse with a width <5 ns and and amplitude of 5-10 mV is present for a voltage of 1900 V. At 2000V the darkcount is around 30 Hz while yesterday it around a few Hz !

The system had a strange comportement during the morning and finally the reference channel (D16) died during lunch ! In the afternoon, something had changed, the pictures where much better and we could start to increase the DS16 threshold. The detector was still noisy around 500Hz (+/-300Hz) , and we let it run the whole night at 2100V.

posted by Mathieu Gisselbrecht at Sep 5, 2006 10:14 AM