MHATT-CAT HHL Mono Detuning Studies

Eric Dufresne, Don Walko
MHATT-CAT
Started April 3, 2002
(www.xor.aps.anl.gov/~dufresne/optics/HHL_detune/)

• MHATT-CAT optic's page.
• Introduction
• Experimental method and results found on 4/3/02.

Introduction.

The work shown below is an account of what was learned on a beamline study 
period from 04/03/2002 to 04/05/2002. During some 7ID-D beamtime, David Reis's
group found that two beams were present when one detune the HHL mono. They 
found that one of the beam was not attenuated by 0.002 inch of Cu foil which
was thus identified as the 3rd harmonic. The two beams were separated by as much
as 2 mm in the 7ID-D hucth which was quite surprising. The main beam itself
was attenuated by Cu. A pool was started on a proper theory for the phenomena!
We were all pretty surprised that the two beams would be separated.
It seemed that one could use this physical separation to dutune the mono. 
Thus, some beam time was used following this report to document and investigate
this further. Below is an account of our findings.

Summary of findings for 04/03/2002.

Today, we set the 1:1 YAG viewing screen just after the X-ray BPM in 7ID-C.
The YAG:Ce fluorescence at 550nm is imaged by two identical F/4 acromats
each with its focal plane either on the CCD or the front of the YAG screen.
This jig has been described in an Activity Report last year by ED.
Between the lens, a ND filter can be placed to reduce the light intensity on the
TV camera. The image below were all taken without ND filter, but by filtering
with a 0.002" thick Cu foil and a 1/8" Al plate. 

It is important to mention that with the ND filter in and no X-ray filter in the
beam, we find only one beam, the fundamental of the monochromator. Thus the 3rd
harmonics is much weaker than the fundamental.

The figures below show the third harmonic beam as we detuned the beam with the 
second crystal picomotor called pth clockwise (CW). The monochromator was 
first detune CCW so that the 3rd harmonic beam is above the main beam and is 
cut by a vertical edge. Fig 4-03.1 shows the two 
beams with the 3rd harmonic being above the fundamental (RHS in picture). Edge
diffraction we believe cause some diffraction fringes. The presence of an edge 
is consistent with our findings in February 2001 when we found out that a 
vertical edge cuts the beam after the first mirror filter tank, but before the
exit window of the micromonochromator. 

Fig. 04-03.1. Here the third harmonic was detuned CCW to climb up and be nearly
blocked by a vertical edge (up is right). The WinTV2000 digitizer board was set to a
brightness of 172 and contrast of 255 from its defaults parameters. These settings
were used for all other figures below except if stated otherwsie.

Fig 4-03.2 shows the two beams after tweaking pth 
CW by a few steps. The third harmonic beam moved down and now clears the 
vertical edge.

Fig. 04-03.2. Several stepped detuned CW from Fig. 04-03.1. Tweaking CW
moves the beam down.

Fig 4-03.3 shows the two beams after tweaking pth 
again CW by a few steps from Fig 4-03.2. The third 
harmonic beam now is within about a mm from the main beam.

Fig. 04-03.3. Several steps tweaked CW from Fig. 04-03.2.

Fig 4-03.4 shows the two beams after tweaking pth 
again CW by a few steps from Fig 4-03.3. The third 
harmonic beam now is overlapped with the main fundamental beam.

Fig. 04-03.4. Several steps tweaked CW from Fig. 04-03.3. The default settings
of the digitizer are used here (Brightness=128, contrast = 128).

Fig 4-03.5 shows the image of the fluorescence after
tweaking pth to peak up the flux on the 7ID-C diode sum. 

Fig. 04-03.5. Here we tweaked the BPM diode sum to peak up the 10 keV X-ray signal.
The default settings of the digitizer are used here (Brightness=128, contrast = 128).

Fig 4-03.6 shows the image of the fluorescence after
tweaking pth CW from Fig 4-03.5 to decrese the maximum
flux on the 7ID-C diode sum by 5%. Note that if one goes CW, only one beam is 
present! Thus it is pretty clear that the right direction to detune is CW since
the third harmonics is more significantly suppressed. This is a very useful 
conclusion for this study. 

Fig. 04-03.6. Here we detuned the second crystal pth CW by cutting the BPM diode sum signal
by 5%.

Thursday, Jan. 24, 2002. Time series with a 0.5 mm (H) by 0.5 mm (V)
white beam, with the mono at 10.0 keV.

The data was started on 01/24 at 00h23 and lasts for more than 14.5 hours. Two
figures are shown below. Fig. 01-24.1 shows a time 
series of the intensity not normalized to beam current decay. the data was taken
every 3 seconds.  The diode signal tracks the ring current decay as expected.
One glitch occur in the data because of access to 7ID-B after 10 hours in the
time series. The LN2 fills occur every 2 hours or so. The 7ID-B and C ion
chamber were disabled for this tseries. 

Fig. 01-24.2 shows a time serie of the 7ID-C Beam 
Position. The beam motion peak to peak is about 110 and 50 microns in the
vertical and horizontal direction respectively. 

Fig 01-24.1 . Time series of the beam intensity in 7ID-C, starting at 00h23 on 01/24
and lasting 14.5 hours. The 7ID-C diode sum, the ring current decay, and LN2 level
are the only valid data because both ion chamber in B and C were disabled.

Fig 01-24.2 . The beam position, 49 m from the source, or 19 m from the High Heat Load mono
in 7ID-C during the same time series as Fig. 01-24.1. The time series is started on 01/24 at 00h23,
and lasts for 14.5 hours. The beam is stable to about 110 and 50 microns in the vertical and horizontal
directions respectively, likely due to thermal drifts.

Wednesday, Mar. 20, 2002. Beamline vacuum investigations and major EPS
water flow sensor failure.

Today, I spent the morning doing maintenance on the cryocooler vacuum jackets 
and I investigated the EPS Vacuum situation. I first outgassed all the ion 
gauges, hoping it may prevent pressure spikes, particularly on the in-vacuum
Huber chamber. 

One problem the MHATT-CAT staff should fix is to slow down the reponse of the 
goniometer ion gauge controller, the Granville Phillips 307. It can be set to 
respond in 3s rather than the default 0.5s response. It is well known that 
when the Huber circle suddenly moves, the motor shaft seal leaks and often 
will close the FEV and trip the beamline EPS. This occur when the mono has not 
been changed energy for several weeks. The beamline staff should repair this
problem before II's join in.

The other less known problem is that the L5-20 controller display may sometime 
with beam display 0 instead of the actual pressure. This is beam related, and
only occurs when X-rays are in 7ID-A. It is believed that the solution is the 
shield the outside of the ion gauge from the white beam.

At night, I investigated the X-ray BPM and now suspect a broken foil. Around 
midnight, another Proteus water flow sensor broke, but for the first time on
the L5-23 fixed mask. The beamline vacuum screen said mask flow trip. So I 
swapped the electronics module again with our spare and the unit now reads again
2.5 gpm. It took a while to reste the beamline because the APS Front End Photon
Shutter 1 (PS1) was closed and needed to be reset. Note that this is the second
such failure this month. Dohn Arms swapped the L5-20 Proteus flow sensor on
3/14/2002. This flow sensor is brand new since it replaced the broken flow
sensor we repaired in Sept. 2001. Why did it flake out so fast? Could it have
something to do with the fact that in the past two runs, we've closed the gap 
more than in the last several years, in particular pushing the mono to higher 
energies such as 20-25 keV?

Thursday, Mar. 21, 2002. Repair of the X-ray BPM and
mono energy calibration near the Zn edge.

Today, I recalibrated the mono energy with the Zn edge. The absorption 
coefficient is shown in Fig. 03-21.1. This time the scans were performed
with 0.5 eV steps, consistent with the EXAFS data taken in the elemental foil
set. Fig. 03-21.2 shows the derivative of the previous scan. The edge 
had moved by 2 eV from 9.659 to 9.661 keV.  This change may have occured
following the realignment from white beam operations to monochromatic beam
operation.

Next, the X-ray beam position monitor in 7ID-C was repaired. During the UofM 
Geology experiment, the fluorescence signal was lost. The diodes were tested 
and were still working. I also tried to read the signal from one diode with a 
SRS 570 without  success. The problem seemed to point to a broken foil. 

Don Walko and I opened the X-ray BPM vacuum T and found indeed that the foil
was shattered (see Fig. 03-21.3). We had one last spare, thus replaced it with 
a wrinkly foil (see Fig. 03-21.4). I retested it tonight and it works again!

Fig. 03-21.1. The near edge absorption coefficient of a Zn foil performed on 3/21/2002.
The edge closely resembles EXAFS data provided by the foil set vendor.

Fig. 03-21.2. The derivative spectrum of the Zn absorption edge performed on 3/21/2002.
In the foil cabinet, the edges (here 9.659 keV) is defined as the peak of the derivative spectrum.
The calibration was off by 2 eV.

Fig. 03-21.3. The broken Cr foil inside the 7ID-C X-ray BPM was repaired on 3/21/2002
by Don Walko and Eric Dufresne. They also replaced the Be window with a thicker one (0.01").

Fig. 03-21.4. The new Cr foil inside the 7ID-C X-ray BPM. Note the wrinkles.