Recent Progress on High-Current SRF Cavities at Jlab Page: 3 of 3
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Proceedings of IPAC'10, Kyoto, Japan
frame design to provide support and alignment of the cold
mass similar to that used for the SNS and 12 GeV upgrade
cryomodules, see figure 8. A test of this design with beam
would validate the HOM damping properties of the
cavities and demonstrate operability in a configuration
that is very close to a production-ready environment.
Plans for such a test are presently under discussion. This
design could be used for a fourth generation light source.
Fig. 7. Concept for a high-current test cryounit.
Fig.8. Cross section of high-current test cryounit showing
helium circuit, space frame and support rods.
There is increasing interest in high-current capable
cavities and cryomodules for hadron machines such as
proton drivers (e.g. for neutrino physics), spallation
neutron sources, and accelerator driven subcritical
reactors. Many of these machines are proposed to be CW
or high duty factor with high average currents. Prospects
are good that such machines could be built in the near
future . The JLab high current cavity concept could be
a good candidate for such machines. It has a large bore,
which is beneficial for minimizing beam halo interception
as well as providing good cell-to-cell coupling. This tends
to minimize distortion of the field flatness due to
manufacturing tolerances or other detuning effects.
However a smaller bore could yield greater efficiency,
which is very important for CW applications, and there is
potential for a tradeoff in these respects.
The concept can easily be scaled to different
frequencies and this exercise has been performed for
several potential applications from 650 MHz to 2.45 GHz.
However it is not always optimal to simply do a
geometric scaling as the resulting iris diameter may be
unnecessarily large at the low end and unreasonably small
at the high end. Also the number of cells and strength of
HOM coupling are strongly application dependent.
The high current cell shape has been scaled to a number
of different beta values from 0.65 to 1 . In this scaling
it is important to preserve the flat outer profile of the cell
that gives low tendency for multipacting. One example is
shown in figure 9, using an SNS-style helium vessel and
coupler for illustration.
Fig. 9. High-current 650 MHz 3=0.9 cavity concept
Although the original high-current FEL application at
JLab has gone away there is still interest in this concept
for other applications from high brightness electron
injectors to high power CW proton drivers. The designs
can be easily scaled to different frequencies and beta
values and adapted to specific HOM damping
requirements. A beam test of this concept would be very
useful in validating the impedance characteristics,
especially above the beam pipe cut-off frequency.
 F. Marhauser et.al., "JLab High-Current Cryomodule
Development", Proc. ERL09, Cornell University,
 R.A. Rimmer, F. Marhauser, "A Family of L-Band
SRF Cavities for High Power Proton Driver
Applications", Proceedings of PAC09, Vancouver,
BC, Canada 2009.
 R.A. Rimmer, "Prospects for a Very High Power CW
SRF Linac", Proceedings of the Workshop on
Applications of High Intensity Proton Accelerators,
October 19-21, 2009 Fermi National Accelerator
Laboratory, Batavia, IL, USA, published by World
07 Accelerator Technology
T07 Superconducting RF
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Robert Rimmer, William Clemens, James Henry, Peter Kneisel, Kurt Macha, Frank Marhauser, Larry Turlington, Haipeng Wang, Daniel Forehand. Recent Progress on High-Current SRF Cavities at Jlab, article, May 1, 2010; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc845278/m1/3/: accessed December 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.