MCPs 80mm-I

The set-up used in order to callibrate MCPs is given by the figure below. Monitoring the voltage and the current (see table), one can determinate the MCPs internal resistance and the actual MCP difference of potential. Table : Applied voltage vs current

V	100	200	300	400	500	600	700	800	900	1000	1100	1200	1300	1400	1500	1600	1700	1800	1900	2000	2100
micro A	2.5	4.5	7	9.5	11.5	14	16.5	19	21	23.5	26	28.5	31	33	35.5	38	40.5	43	45.5	48	50

In the configuration where the arrow is set the typical voltage through the plates is 1850 V. When the gage is on the count rate is about a 5kHz. A first test of imaging shows that the pulse height is two weak (small) to trigger the DS16s. In the figure below we can see that only a few card from the rear-side anode is answering (cards: E-F & G-H). Only the cards A & B from the front-side anode are present, and they have a little amount of counts. The hit distribtion is only 2 pixels: 1x +1y with an anode @800V. Since the discriminator levels are set to the minimum it means that there is not enough gain !!!… Concerning the localization of the hits on the detector it seems, that the charged particles emitted by the ion gage are localized almost in the center of the detector : image of the 35mm diameter of the flange with lens effect due to strange electrosatic fields inside the vacuum chamber, lost of gain on the edge of the MCPs ....

posted by Mathieu Gisselbrecht at Aug 1, 2006 12:00 AM