Measurement of HOMs in the RHIC RF Cavities Page: 2 of 10
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C-AD/ AP /320
Measurement of HOM in the RHIC RF cavities
. P. Abrei and E. M. Choi
January 7 2009
Whe present results of Higher Order Modes (HOMs) mensuremnent in the RHIC accelerating (28
MHz system) and storage (197 MHz system) cavities. The power of the excited HOMs deposited into
the HOM damper is ineasured and compared with an analytical calcuation of the HOMs power. The
quality factors (Q) are also measured and compared to previous mneasurements.
The Relativistic Heavy Ion Collider (RHIC) consists of two counter rotating beams which
collide at two different experiments (PHENIX at IP8 and STAR at IP6). The particles
that are accelerated range from protons to gold ions and each accelerator ring has the
capability to accelerate a different specie. Table 1 summarizes the main machine param-
eters. The RF system on both rings has to be able to capture, accelerate and store up to
120 bunches with an average total bunch intensity of 1.0 x 10' particles/bunch for gold
ions and 2 x 10" for protons. In the case of heavy ions the RF system must capture the
particles at injection, accelerate them through transition and transfer the bunches from
the 28 MHz system to the 197 MHz system. The 28 MHz accelerating cavities operate
with 300 kV before transition and 150 kV throughout the rest of the energy ramp for ions
and the 197 MHz system operates with 4 MV total gap voltage. In the case of protons
since the particles are injected above transition, only acceleration and storage is needed
and the 28 MHz RF cavity is used with a voltage of 300 kV while the. 197 MHz system
uses a much smaller voltage of 50 kV only to increase the synchrotron frequecy spread
and improve Landau damping. The harmonic numbers of the 28 MHz system and the
Table 1: Machine parameters.
gold ions protons
Energy 100 GeV/n
Circumference 3833.852 in
Revolution Frequency 78.2 kHz
Beam Frequency (120 bunches) 9.831 MHz
rms bunch length (o) 5 11s
Ganmn Transition ( t,) 22.8 25
28 MHz System Voltage 300 - 150 kV 300 kV
197 MHz System Voltage 4 MV 50 kV
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Abreu,N.P. & Choi, E. M. Measurement of HOMs in the RHIC RF Cavities, report, January 7, 2009; United States. (digital.library.unt.edu/ark:/67531/metadc894726/m1/2/: accessed July 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.