RF Breakdown Studies Using a 1.3 GHZ Test Cell Page: 3 of 3
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Figure 4 shows the scope traces of the forward power,
cavity pickup, and reflected power. Measurements of the
RF parameters were analyzed, and the power in the test
cell was found to be 221 kW, corresponding to a gradient
of 71 MV/m.
The process of requesting ANL safety approval for
high-pressure operation of this test cell has already begun.
After this approval is granted, we plan to conduct a
detailed series of experiments using this 1.3-GHz test cell.
Among the many experimental variables we hope to study
are different electrode metals, different surface
preparation, different gases, and different magnetic fields.
402.5 MHz Test Cell
In order to study the effect of the radiofrequency on RF
Breakdown in gas-filled cavities, we plan to conduct a
follow-up series of experiments at a lower frequency.
Because of the availability of a 402.5-MHz test stand at
LBNL, it is likely that we shall choose this frequency.
The plan is to bring this test stand to operational
condition, design and build a 402.5-MHz test cell, and to
conduct a similarly-detailed series of experiments at this
lower frequency. Earlier, a 500-MHz test cell had already
been designed as shown in figure 5, so we anticipate that
a modification of the existing design will be used for the
402.5-MHz test cell.
Type, SaFety Factor - Top/Bottom
1 6/2009 3:51 PM
Figure 5: Axi-symmetric ANSYS calculations for the 500
MHz cavity with safety factor calculations at 1600 psi
Separate computer simulations are being carried out for
the gas breakdown region and the surface breakdown
Gas Discharge Simulations
Muons, Inc. is presently working with Dr. Dave Rose of
Voss Scientific on physical models of RF breakdown in
hydrogen gas as part of our program to develop RF
cavities for muon cooling . This effort is directed
toward understanding and mitigating breakdown in the
conditions of a muon cooling channel, where there are
large magnetic and radiation fields. This modeling effort
is focused on the breakdown of the pressurized gas itself,
but we now know that the nature of the gas also plays a
role in the breakdown of the metallic surfaces of the
cavity, even in the surface-breakdown region.
Metal Surface Simulations
ANSYS modeling will be used to study the heating of
small areas of the metal surface. We shall examine the
effects of current flow at asperities and at low-work-
function areas, in order to understand the characteristic
behaviors of different physical models. We expect these
simple simulations to give us useful insights into the
physics at the metal surface.
 M. BastaniNejad et al., EPAC08, Genoa Italy
 P.M. Hanlet et al., "High pressure RF cavities in
magnetic fields," EPAC06, Edinburgh, Scotland.
 R.H. Fowler and L. Nordheim, "Electron emission in
intense electric fields," in Proc. Roy. Soc. (London),
A119, pp. 173-181, 1928
 S.G. Tantawi, "Progress in High Gradient Accelerator
Structure Research for Future Linear Accelerators,"
 D.V. Rose et al., Proc. 16th International Pulsed
Power Conference, Albuquerque, NM, 2007
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Sah, R.; Johnson, R.P.; Neubauer, M.; /Muons Inc., Batavia; Conde, M.; Gai, W. et al. RF Breakdown Studies Using a 1.3 GHZ Test Cell, article, May 1, 2009; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc926971/m1/3/: accessed November 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.