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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)

2012 X-ray Runs

Feb. 22nd - March 26th
May 30th - July 2nd

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