RF cavity R&D at LBNL for the NLC Damping Rings,FY2000/2001 Page: 3 of 93
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In order to provide the required accelerating voltage,
momentum acceptance and stable beam at high currents the cavities
for the NLC damping rings must have strong HOM damping, a high
gradient and accomodate heavy beam loading. Table 1 shows some
parameters of the damping ring and pre-damping ring RF systems,
some of which have changed significantly since the previous report.
The total voltage and beam power can be delivered by three copper
cavities in each of the main damping rings but seven cavities are
now required to produce the desired voltage in the positron pre-
damping ring. The maximum bunch frequency is now the same as
the RF frequency of 714 MHz, previously only every other bucket
was filled giving a 357 MHz bunch rate. The power density and
stresses in the NLC cavity are comparable to the current PEP-fl
operating conditions (taking the scaled PEP-fl design as the
baseline). Means of reducing the stress without sacrificing the good
HOM damping properties and accelerating mode efficiency have been
implemented. Simplifications of the mechanical design and
fabrication have also been adopted.
The PEP-fl RF cavity is among the first designs with strong
damping of the higher order modes (HOMs), which are now seeing
operation in the high-current e+ e- factories around the world [2,3].
This design has already proven to be very successful in the reduction
of coupled-bunch instability growth rates, contributing to the rapid
commissioning of the rings and the early attainment of high
luminosity. The technology developed for PEP-fl has already been
put to further use for the 1.5 GHz ALS third harmonic cavity upgrade
, and is a natural candidate for future projects such as light
sources, storage ring based colliders and linear collider damping
rings . Many lessons learned during the design, manufacture and
commissioning of these cavities were applied to the new design. The
availability of better analysis tools and faster computers also now
allows more detailed study of some aspects of the design.
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Rimmer, R.A.; Atkinson, D.; Corlett, J.N.; Koehler, G.; Li, D.; Hartman, N. et al. RF cavity R&D at LBNL for the NLC Damping Rings,FY2000/2001, report, June 1, 2001; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc885353/m1/3/: accessed September 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.