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CHESS East
Source Size
Horizontal and Vertical Beam Size
Jeff White - Current as of
2/16/2005
Horizontal Beam Size:
The beam size may vary from the design value either due to beta errors in CESR's
conditions or by emittance errors from changing the pretzels or changing of the wigglers
conditions. Otherwise the horizontal beam size is not likely to change during HEP
operation
This has the form:
 h(station)
= (
 h(station) *
 h
+
 h2(station) *
 2)1/2
where:
h(station) is the horizontal beta at that location
h
is the horizontal emittance which is a constant
for a given lattice
h
(station) is the dispersion function
is the energy resolution i.e.. =
E
/ E where:
E is the energy spread in GeV E is the
beam energy in GeV.
Vertical Beam Size
The design vertical beam size is zero. During HEP operation the vertical beam size
observed is due to emittance growth from both the beam - beam interaction and from
horizontal to vertical coupling adjustments used to control the beam - beam interaction.
Rather than trying to predict the vertical beam size, we measure it at an observation
point for the visible light (500nm) for each beam during HEP operation. Under the assumptions that
the beam - beam interaction produces a certain vertical emittance and the local variations
in coupling and vertical dispersion around the ring make small contributions to the
vertical beam size, the beam size at any point in the ring may be simply scaled from the
observation at some point in the ring. The observation point for the
electrons is located at 15West on CESR. There is a grid associated with
the electron image that has a spacing of 5mms. The observation point for
the positrons is located at 24East on CESR. There is a grid associated
with the electron image that has a spacing of ~4.7mms.
This has the form:
v(station)
= (
v(station) /
v(observation
point))1/2 *
v(observation point)
Last Update:
2006-09-21
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