Pump Out Port Impedance Page: 2 of 6
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The mode in Figure 2 is at frequency 1.52 GHz and has a shunt impedance
R = 7100 ohm, Q = 3400 and R/Q = 2. Several other modes of the port
(not shown in the figures) couple with the beam. This is unacceptable, and
therefore requires shielding.
A standard fine mesh shield reduces the pumping capacity of the port
by 17%. Therefore, a simpler shield which would not reduce the pumping
capacity as much, is investigated. The properties of the required shielding
are given below:
" Shield must consist of wires, both parallel and perpendicular to the
* Center to center spacing between the wires must be less than or equal
to 3 cm.
* The size of the wire is determined by mechanical reasons, and dissi-
With the above mentioned specifications, a shield with 3 cross wires in
each direction, as shown in Figure 3, removes all of the impedance contribu-
tion from these ports. If the diameter of each cross wire is taken to be 1 mm,
the pumping capacity reduces only by 5%. Figures 1 and 2 (bottom) show
that the eigenmodes of the shielded port are decoupled from the beampipe.
Figure 4 gives a 3-dimensional plot of the port with the cross wire shield.
The small aperture pump out ports at the interconnects between the arc
dipole and the CQS package, and at the warm to cold pipe transition make
a total broadband contribution IZ/nj of less than .002 ohm and therefore do
not require shielding.
The large aperture pump out ports have a pipe ID of about 12 cm, which
is comparable to the beampipe ID of 12.28 cm. The resonances of these ports
will couple with the beam, and hence they require shielding.
 G. McIntyre, Private Communication.
 T. Weiland, Particle Accelerators 15 (1984), pp. 245-292.
 Collective Instabilities in RHIC, Eds. S. Peggs, W.W. Mackay
 D. Weiss, Private Communication.
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V., Mane & Peggs, S. Pump Out Port Impedance, report, October 1, 1994; United States. (https://digital.library.unt.edu/ark:/67531/metadc871848/m1/2/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.