APS Undulator-A Tapered spectrum quick simulation
Calculations by Toshi Tanabe, May 13, 2008.
Page author: Bruce Ravel
Undulator A in tapered action at APS 10ID
Shelly Kelly prepared a plot showing the incident intensity at APS 10ID with the undulator set up to measure the uranium LIII edge using the third (red trace) and second (green) harmonics. It looks like this:
You see a couple of persistent mono glitches in both spectra. The tapering parameters are something similar to this:
|
3rd harmonic |
2nd harmonic |
||
units |
gap |
taper |
gap |
taper |
keV |
18.4 |
2.3 |
18.2 |
0.5 |
mm |
15.658 |
1.104 |
20.169 |
0.412 |
With such a large taper on the 3rd harmonic, the 2nd is only down by about a factor of 2 in flux. In practice, Shelly and I often find that the beamline seems better behaved (linearity, stability, better data, etc) using the 2nd, if the samples are not too dilute.
Computing the tapered Undulator A spectrum
SPECTRA calculation results to match the curve above gives slightly different undulator settings (see below Spectra screen)
Magnified in the interested region
Screenshots of SPECTRA
Parameter Setting in SPECTRA (APS ring parameters may not be the latest)
Toshi have found a tables for tapered Undulator-A at APS site
