CAT Chat Minutes

September 29, 1995


Issues that require action and/or follow-up
What will be the influence of lower values of the beam coupling parameter in the vertical direction on the following?

a. Particle beam lifetime

b. Photon beam power density distribution in the vertical direction

c. Design of the optics

d. There is a reduction in the lifetime of the stored beam when the coupling is reduced. This is primarily due to the Touschek effect (intrabeam scattering). The reduction of vertical coupling to 1% from 10% decreases the Touschek lifetime roughly by a factor of 3, and the overall lifetime only by about 30% when the vacuum of the storage ring is 1 nanoTorr and 1 mA is stored per bunch (100 bunches to deliver 100 mA). If the current per bunch is increased, the Touschek lifetime proportionally decreases due to an increase in the bunch density.

e. The photon power density distribution does not change much with reduced vertical coupling. In the attached figures calculated for true parameters of the APS, Roger Dejus of the XFD has shown these distributions for two undulator configurations and for vertical coupling values of 10%, 1%, and zero percent. It is apparent that cooling schemes for the optics can be implemented without any consideration to the value of the beam coupling.

f. Since the particle source size and divergence are proportional to the square-root of vertical emittance, a reduction of coupling from 10% to 1% will decrease the particle beam size and divergence in the vertical direction by a factor of about 3. While this will enhance the vertical brilliance delivered by the APS, the optics technology may not be able to match the photon beam requirements to transfer such brilliance to the sample.

Is the space on the top of the storage ring available to users for installing electronics racks, pumps, exhaust systems, etc.?

No. This space is currently reserved for the future needs of the accelerator systems, insertion devices, and beamline front ends. Hence, users must optimize the space available to them on the Experiment Hall floor for all their needs. If there is a hardship case, that will be addressed by the APS on a case by case basis.

Can one use the roof top of a FOE for installing electronics racks, pumps, exhaust systems, etc.?

There is some limitation on permitted installations on the roof top of FOEs. The installations should not produce vibrations; the installation should not require constant attendance; the installation should meet all the safety requirements; the installation should not exceed a height of about 30" above the storage-ring roof level. It should be realized by the user that such area above the FOE can only be accessed from the top of the storage ring, which is a controlled area. To access to the roof of the FOE requires a work-permit (even if the work involved is minor), which must be arranged through the Floor Coordinator.

Information items
Update on planned beamline commissioning time during October 95 operation of the storage ring:  There are no planned beamline commissioning activities during the entire month of October 1995. The beamline commissioning plans for November will be developed shortly.