[Ifeffit] Capillaries

[Matt Newville]

Hi Paul, 

I probably have as much experience with micro-XAFS as anyone on this
list, and am willing to make a few comments.

First, Steve Heald and Dale Brewe at APS/PNC-CAT have extensive
experience making and using single capillaries for focussing --
probably more than anyone else.   They're really the people to ask.

Second, I believe there is not a commercial supplier of suitable
capillaries, and that Heald and Brewe made essentially all of their
own capillaries. After a few years of experience, I believe they
could get 1 micron spots fairly routinely.

Third, I think the consensus is that capillaries don't work too well
for EXAFS.  I wouldn't be willing to say that PNC-CAT has abandoned
them, but I haven't seen capillaries used for this purpose in a long
time.  Without going into the details of the problems here, I can
say that we at GSECARS and Heald etal at PNC-CAT regularly use 10cm
long KB mirrors to focus APS undulator A to 2-3 microns for
micro-XAFS, and that other beamlines at APS and other sources use
such mirrors for micro-beam work as well.

Fourth, Micro-EXAFS with a 1 micron beam and a 1 micron sample is
challenging because of sample vibrations.  But as the sample and
spot size get to 5 to 10 microns, it works reasonably well.  Many
problems that appear to need 1 micron can get by with 5 microns,
especially when the penetration depth is considered.

Fifth, getting below 10 microns is heavily dependent on source
characteristics, especially divergence.  A 4m in vacuum undulator is
an excellent start, but you might need to remove the larger beamline
mirrors and slit down the source to get to 1 micron.  

Finally, It might be worth considering taking your experiment to an
existing micro-EXAFS beamline, or visiting one ahead of time. ;).

--Matt

On Thu, 29 Apr 2004, Paul Fons wrote:

> Continuing in the vein of marginally relevant questions (you need to 
> take data before you can analyze it with horae!), I have yet another 
> question.  To make life more exciting, I would like to take a 4 m in 
> vacuum undulator beamline that has a focussing mirror with a 250x600 
> micron spot size and focus down as much of the beam as I can to 
> dimensions on the order of a micron (or a little bit bigger) using a 
> monocapillary.  I would then like to do microexafs with this setup.  
> The brilliance of the undulator is about 5x10^15 in the range I am 
> interested in (about 11-12 keV).  Has anyone had any experience with 
> this sort of focussing and might you recommend a company or spec to 
> try?  Thanks in advance.
> 
> 						Paul