Pump Out Port Impedance Page: 1 of 6
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Pump Out Port Impedance
Vibha Mane and Steve Peggs
There are broadly two kinds of vacuum pump out ports in RHIC. The
port with aperture smaller than the beampipe aperture (Small Aperture
Ports) make a small inductive contribution upto the pipe cutoff frequency
and therefore do not require shielding. The port with aperture comparable
to the beampipe aperture (Large Aperture Ports) have resonances, which
couple with the beam. Therefore these require shielding, and an appropriate
shield design is presented.
II. Small Aperture Ports
The vacuum ports at the interconnect between the arc dipole and the
CQS package have a port ID of 2.2 cm and a beampipe ID of 6.91 cm .
There is one such port at every other interconnect, with a total of approxi-
mately 233 ports. The inductance of each port, as determined numerically
using MAFIA  is 1.4 x 10-11 henry.
The vacuum ports at the warm to cold transition have a port ID of 2.5
cm and beampipe ID of 12.28 cm. There are a total of 16 such ports. The
inductance of each port as determined from MAFIA is 5.5 x 10-12 henry.
The total contribution to broadband impedance IZ/nl from the above
mentioned ports is less than 0.002 ohm. This is very small compared to the
broadband impedance threshold of 1.5 ohm, due to microwave instability
III. Large Aperture Ports
The vacuum port in the warm pipe have a port ID of 12 cm and beampipe
ID of 12.28 cm, with a total of 36 such ports . The unshielded port has sev-
eral resonances below the cutoff frequency of the beampipe. The eigenmodes
of the geometry were determined using MAFIA . Figures 1 and 2 (top)
show that the transverse electric modes of the port couple with the beam.
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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/m1/1/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.