Faraday Cup Measurment Notes » History » Revision 10
Revision 9 (John Crum, 08/27/2012 04:54 PM) → Revision 10/11 (John Crum, 02/28/2013 12:21 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. 2013-02-28 Calibration on T12 Spirit
* 120kV, Filament Heat= 29, step 1, Spot 3, mag 46K, Beam Current = 5.5-7.5 µA, LaB6 installed 2013-02-22
* TVIPS F416 camera
* Technai main screen measurement (emulsion = 1): 2.15 / 0.11 = 19.54 nA
* Leginon scale factor to match Faraday current: 0.991 (was 0.80)
* Leginon measure Tietz sensitivity: 38.8294 counts/e- (was 32.5211)
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