Faraday Cup Measurment Notes » History » Revision 9
Revision 8 (John Crum, 08/27/2012 04:29 PM) → Revision 9/11 (John Crum, 08/27/2012 04:54 PM)
h1. Faraday Cup Measurment Notes Picoammeter setup: * plug in * wait 1 hour * activate ZCHK (maybe already when turned on) (should say ZC on screen) * plug into faraday holder * set to lowest range (2nA) * activate ZCOR to set zero (should say ZZ on screen) * set auto range if desired * deactivate ZCHK to begin measuring * focus beam to a spot * pull out holder until spot hits the faraday cup (max current) ** 200keV *** 1.01 nA ** 120 keV *** 2.53 nA h1. Exposure Time to Screen Current measurment * refer to Tecnai Help for "Exposure Time, Plate Camera CP" * formula: beam current (nA) = 2.15 * emulsion / measured_exposure_time ** exp time is between 3.1 and 3.5 depending on size of beam ** emulsion = 1 ** beam current is between 0.61 and 0.69 nA h1. Leginon screen scale factor measurement * adjust scale factor until beam current is same as faraday cup ** 200 keV *** 0.725 ** 120 keV h1. Camera sensitivity ** 200 keV *** 45-50 count/e ** 120 keV *** 107 count/e h1. 2011-02-02 calibration on Tecnai 2: * faraday measurement: 1.52 nA * Tecnai main screen measurement (emulsion = 1): 2.15 / 2.6 = 0.83 nA * Leginon scale factor to match faraday current: 0.793 * Legion measures Tietz sensitivity: 68.7 counts/e- h1. Finding the Faraday Cup * See picture below * Center to cup is 4mm * Use a 6mm or 7mm Allen (hex) wrench as a wedge (spacer) between the holder end cap and stage. Use the wrench as a lever to fine tune the position