January test plan for BESSY
prepared by Brad Wargelin
(last update: 1998 Jan 14)

================= Table of contents =================

============= 1. General notes =============

============ 2. Position nomenclature =============

(x22z and hn2z are the default data collection positions)

x2cen central windowlet of fpc_x2 hncen central windowlet of fpc_hn x22z +2 mm in z from x2cen (1 windowlet offcenter, to avoid anode) hn2z +2 mm in z from hncen (1 windowlet offcenter, to avoid anode) hn16z +16 mm in z from hncen (last full windowlet nearest edge) hn18z +18 mm in z from hncen (partial windowlet nearest edge) hn48y +48 mm in y, +2 mm in z from hncen (last full windowlet along long axis)

============== 3. KMC beam ==============

a. Setup stuff

Select *** TBD *** beamline aperture. Start with Si crystal. Remember that crystals can only be changed while BESSY personnel are there, roughly 7 am - 3 pm. Edit $DB/ly.rdb and lz.rdb for x2cen, x22z, hncen, hn2z, hn16z, hn18z, hn48y. SAO chamber must pump overnight before beginning of tests on Monday.

b. Find window(let) centers of FPCs

Finding our bearings should be a little faster because we can use the results from last time to get close. Positioning accuracy is less important because we are not doing fine-scale windowlet scans. All we'd like to do is hit the center of each windowlet, accurate to +/- 100 um, preferably with a beam less than about 1-mm in diameter. The edge scans (BP = Beam Profile tests) will tell us where the blocking plate aperture edges are, and also provide info on the beam profile. The wire scans (WS tests) will tell us where the central windowlet is.

Use ratemeter to find approximate edge positions, then do edge (BP) scans. Move to central windowlet. Refine stage positions for "x2cen", "hncen", etc. in $DB, keeping in mind that the blocking plate(s) may not be exactly centered. Do four 1dscans (15- points, 100- um, 10 sec) about each wire. Refine stage positions for "x2cen", "hncen", etc. in $DB.

c. Spectral Response Functions/Energy Linearity

Spectra will be collected from monochromatic beams at several energies ranging from 800 eV to 5.9 keV. Particular attention will be paid to the Ar-K and Si-K absorption edges. (We would like to check the Si edge because there may be residual Si in the Al coating on the FPC windows.) These tests also give us info on the QE of the FPC as a function of energy so we would like good beam intensity calibration, which includes regular recording of the ring current. At least, we would like to get good data on the Si and Ar edges. We will study how the escape peak fraction varies with position (near the edges of the gas volume vs. in the center) by collecting spectra at several positions for a few energies (marked by **). We also expect differences in spectra if the x-rays directly hit the FPC anode wire. All measurements will be made 2-mm offcenter (perpendicular to the anode wire) to avoid this effect, but we will also collect spectra on-center at a few energies (marked by *). We will measure the Energy Linearity of the FPCs by collecting spectra over a wide range of energies using the same FPC voltage setting. It is best to collect these spectra contiguously in time (with intervening voltage changes). These tests give us info on pileup, too---be sure to adjust the pulser amplitude so you can see the x-ray/pulser pileup peak at a representative sample of energies. If time permits, measure the pileup fraction and compare with the expected fraction of (~0.4 usec)x(rate). The pileup processing time should be independent of energy.

Adjust detuning and pulser amp to get pulser/x-ray pileup

Crystal FPCset Energies
Beryl 852 852
Beryl 930 930
Beryl 1012 1012
Beryl 1254 1254
Beryl 1487 1487
InSb 1740 1740, 1800-1880/10-eV steps
Si 2165 1900,2042*,2165*,2293*,2984*,4000,5000,5900
Si 2984 1900,2042,2165,2457,2984, 3100, 3150-3250/10eV steps
3444,4000,4511,5000,5415,5900
Si 3444 3444
Si 4511 1900,2042,2457,2984,3444**,4000**,4511**,5000**,5415**,5900**
Si 5415 5415
(add peak and pulser channels in testlist....)
xx voltage settings
xx energies
xx total voltage/energy/position measurements

d. Gas Opacity

Spectra will be collected at full (400 torr) and half (200 torr) pressure, at 4 energies, and the counting rates (and thus detector QE) compared. Since window transmission is nearly 100% at these high energies, differences in QE arise almost entirely from differences in gas density (and a very small amount from differences in window bowing at the different pressures).

Relative beam intensity on the KMC cannot be determined as accurately as on the SX700, so measurement uncertainty will be of the order of one or two percent, even after correcting for ring current.

e. Filter Transmission

Transmission has already been measured below 1700 eV on the SX700 beam, except for the Be filter. As before, these measurements will be run by PTB with their photodiode. Don't forget to make the measurements with beryl when the beryl crystal is installed for the SRF msmsts!

================== 4. Whte Beam (12.20) ==================

a. Absolute QE

Since FPC energy resolution is so poor, we use various filters to select out different energy bands from the continuum synchrotron spectrum. Filter transmission will have been measured on the SX700 and KMC beams.

Before pumpdown, new plates with 1.5-mm-diameter apertures will be fastened on top of the blocking plates. The aps must be centered one windowlet above the central windowlet (+2 mm in z). The exact sizes of these apertures will be measured at SAO.

Before making measurements, the apertures must be centered on the beam. (What criterion do we use for this?)

The FPC voltage will probably need to adjusted to fit the spectrum more or less completely in the 512 channels. (Don't worry about the last percent or two if it's a problem---we can model and correct for it).

Adjust pulser amplitude for each filter??

b. Counting rate linearity. With TBR filters, data will be collected for each energy at several widely varying counting rates to determine the accuracy of the pulser deadtime correction method and equations (to ~0.2%). The setup is the same as for Absolute QE, but at several different rates.

c. Relative aperture sizes (with photodiode)

Measure the relative sizes of the Aperture Plate apertures (mounted in 2 holders in the PTB crosses on the beamline) by inserting them into the beam in front of a photodiode.

The apertures must be centered on the same part of the beam.

d. Relative aperture sizes (with FPC)

The apertures 3-20 um in diameter are made from 12-um-thick gold foil, which becomes annoyingly transparent above about 5 keV. Larger apertures are made from 40-um-thick foil, which is completely opaque. Although the PTB photodiode has much more dynamic range than the FPCs, it has no energy resolution, so its signal will include some of the high-energy punch-thru. This can be estimated fairly well, but we'd also like to measure the thin apertures with an FPC, which can discriminate between the apertured and punched-thru photons.

=================5. Beamline configurations ================

a. KMC

b. Whte beam (12.20)