LHC beam-beam compensation studies at RHIC Page: 2 of 5
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Proceedings of PAC09, Vancouver, BC, Canada
Table 1: Main RHIC parameters relevant for beam-beam
effects, for polarized protons. Note that the polarized pro-
ton bunch intensity is also limited by intensity dependent
depolarization effects in the AGS.
quantity unit achieved goal
beam energy E GeV 250 250
bunch intensity Nb 1011 1.1 2.0
rms emittance e mm mrad 1.85 3.3
rms bunch length m 0.7 0.30
beam-beam parameter /IP ... 0.0078 0.0074
no of IPs ... 2 2
3* at IP6, IP8 m 0.7 0.5
(Ab., AOy)IP6-rP10 7 (19.1, 19.6)
(b., Ay)IP8-ipio (8.4, 10.9)
This article is an abridged and
updated version of
To investigate strong long-range interactions, test com-
pensation schemes, and benchmark simulations, experi-
mental data are needed. In the SPS wires were installed
for this purpose [14-17]. The wire experiments in RHIC
complement these studies. The beam lifetime in RHIC is
typical for a collider and better than in the SPS wire exper-
iments. In addition, head-on effects can be included, and
with properly placed long-range interactions and wires, the
compensation of a single long-range interaction is possible.
Wires in RHIC
The wire parameters are shown in Table 2 
Location in the ring. For a successful compensation
the phase advance between the long-range interaction and
the compensator should be no larger than about 10 de-
grees . It is possible to place a wire after Q3 to compen-
sate for a vertical long-range beam-beam interaction near
the DX magnet (Fig. 3). In the Blue ring the wire is in-
stalled above the beam axis, in the Yellow ring below the
beam axis (see Fig. 4).
u copnE RHIC Sector 5
I -6d ( -lm) DSI
02] (28.5mr) 0 1 is
01 0 06
9.8m MOm " V
-14.3m O (35mr)
Figure 3: Location of wires in RHIC and location of long-
range beam-beam interaction for compensation.
Integrated strength. To compensate a single long-range
interaction, the compensator's integrated strength (IL)
Table 2: Parameters for RHIC Wires. The wire material is
Cu at 20 C. The nominal wire strength is for a single long-
range interaction with a proton bunch intensity of 2 x 1011.
strength (IL), nominal
max. strength (IL),a
length of wire L
radius of wire r
number of heat sinks n
electrical resistivity pc
heat conductivity A Wi
thermal expansion coeff.
radius of existing pipe r,
current I, nominal
max. current in wire Imays
current ripple AI/I (at 50 A)
electric resistance R
max. voltage Umax
max. power Pma x
max. temp. change AiTmay
max. length change ALmax
vertical position range
Q m 1.72x10-8
n m-K-- 384
Figure 4: The two long-range beam-beam wires in the
RHIC tunnel during installation.
must be the same as the opposing bunch's current inte-
grated over its length (IL) Nbec, where I is the cur-
rent in the wire, L its length, Nb the bunch intensity, e the
elementary charge, and c the speed of light (see Table 2).
In the LHC, (IL) 80 A m is required for the 16 long-
range interactions on either side of an IR . Such a
strength is also expected to lead to enhanced diffusion at
amplitudes larger than 6 o- . To study the enhanced dif-
fusion, the RHIC wire is designed for (IL)max 125 A m.
Wire temperature. The wire's temperature should not ex-
ceed 100 C. We use n= 3 heat sinks cooled with forced
air, spaced apart by L/(n - 1). The maximum temperature
increase in the center between 2 heat sinks is
1 pc (IL)2
Tmax = 872 A (n 1)2r4
where pc is the electrical resistivity, A the heat conductivity,
and r the wire radius. To move the wire compensator close
to the beam, its radius should not be much larger than an
rms transverse beam size. We have ATm ax < 15 K.
Beam Dynamics and Electromagnetic Fields D02 - Non-Linear Dynamics - Resonances, Tracking, Higher Order
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Fischer, W.; Luo, Y.; Abreu, N.; DeMaria, R.; Calaga, R.; Montag, C. et al. LHC beam-beam compensation studies at RHIC, article, May 1, 2009; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc1012170/m1/2/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.