Procedure to align the double slits
LAST VALUES:
February 2021 (I.P.)
All Optical encoder values at zeros (due to black out in december 2017- january 2018)
L=0.000 R= 0.000 U=0.000 D=0.000 This initial positions should corresponded to (2x1) mm opening (horizontal x vertical), as deduced from the procedure in point 1) (see below)
(Potentiometers readings: L=2.1 R=0.7 U=1.4 D=-4.1)
Final positions of the doublelsit after the alignment (2x1 mm horizontal x vertical):
L = -0.857 R = +0.8105 U = -0.198 D=+0.1975 (Optical encoders)
(Petentiometers: L=1.2 R=1.5 U=1.1 D=-4.1)
30/11/2015 (folder BACHI/Alignement/Dec2015):
(2X1) L=L=2.19 R=0.56----U=1.4 D=-1.8 ZEROUP=0.887;ZERODOWN=-2.33;ZEROLEFT=1.18;ZERORIGHT=-0.44
(1X1) L=1.69 R=0.06----U=1.4 D=-1.8
(2X2) L=2.19 R=0.56----U=1.9 D=-1.3
Jan2014 (folder BACH/Jan2014):....
29/7/2014
(5X1) L=3.486,R=2.182;U=1.462,D=-1.987
(2X2) L=1.9,R=0.8;U=1.75,D=-1.3 ZEROUP=0.7;ZERODOWN=-2.3;ZEROLEFT=0.9;ZERORIGHT=-0.2 (29/7/2014)
NOTE: Move UP from high to low values...
1) Set Entrance slit fully open. Determine the zero by moving one of the slits and monitoring Io and finding the position where the counts are half.
2) Once the zero position is found for UP, DOWN, LEFT and RIGHT, open all of them of 0.5mm in order to have a 1x1 opening.
3) Move this 1x1 double slit on a grid of values and measure the ratio of the First to Second harmonic and the intensity of teh First harmonic.
4) Once the best position (highest 1/2 ratio) is found, optimize the pitch of SM1 and SM2, and then x and z.
5) Open the horizontal slit to 5 mm if you want to have high flux (but with higher 2nd harm contamination) or to 1x1 in order to have a better suppression of 2nd harmonics.
NOTE: For the HE undulator a good setting is 2X1 (see files 30/11/2015)
For LE und the beam is broader, so, in order to have the same flux probably it is better a 3x2 configuration.
Note: The ratios and Io values in the tables are not typical values.
In the end, the position was chosen as compromise between first/second harmonic ratio and Io intensity. The final position was not far from the beam center determined by Io half intensities.
L
<---------------|
R
|---------------->
UP
^
|
DOWN
|
V
