RE: Coherent Brem using SOS configurations

["James Kellie" <j.kellie@physics.gla.ac.uk>]

Dear Elton,

When I was in Jlab recently for the CLAS meeting, Bernhard gave me a copy of
the draft paper from Harut, and as you say the degree of linear polarisation
from the SOS radiation was measured to be only around 5%.

However, the most interesting aspect of the paper is I think the way in
which the authors use a second diamond crystal mounted in its own goniometer
downstream of the radiator to act as an alalyser to measure the degree of
linear polarisation of the photon flux. Furthermore the analyser is tunable,
since by changing the crystal orientation, the photon energy for which its
analysing power is maximum can be changed. I think this could be potentially
very advantageous for hall B and certainly for Gluex.

I am going to follow up the idea at Glasgow, and I think your suggestion
that a workshop is organised at JLab, to which experts in the field are
invited is an excellent one.

Regards,

Jim.



-----Original Message-----
From: Elton Smith [mailto:elton@jlab.org]
Sent: 11 March 2004 16:39
To: Richard Jones; mecking@jlab.org; sober@cua.edu; Jim Kellie
Cc: halld-jlab@jlab.org
Subject: Coherent Brem using SOS configurations



Hi Richard and Jim,

I wanted to make sure you were aware of some recent developments in
producing photon beams with crystal radiators.

You have probably already heard about recent work/measurements which
produce high-energy beams using a special case of coherent bremstrahlung
using the so-called String-or-Strings (SOS) configuration. Harut Avakian
has made a draft paper available to Bernhard Mecking describing recent
measurements at CERN. The draft indicates that coherent-like peaks at say
80% of the electron beam energy can be achieved with enhancements over
Bethe-Heitler of around 18. For comparison, our coherent peaks (after
collimation) show enhancements of approximately 4-5. The drawback of this
system, if it is proven is that measurements of the polarization are quite
small, i.e. less than 5%.

Let me know if you have any information and/or opinions on this work. We
should think about whether to pursue this as a collaboration. Bernhard is
interested in developing some of these ideas here at JLab. The Yerevan
Physics Institute is involved in the measurements (A. Apyan and R.O.
Avakian are authors). Richard: Are these some of the contacts you have in
Armenia, and has any of this work been discussed for further study?

Generally, JLab clearly has an interest in developing special photon beams
at high energy and/or polarization. Therefore, it might be useful to
consider a workshop and/or meeting at JLab to invite some of the experts
and pursue this further.

Any comments/suggestions?

--
Elton Smith
Jefferson Lab
elton@jlab.org
(757) 269-7625