Magnets for RHIC Page: 4 of 6
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tion of this superconductor in its cabled form.
Prestress is applied to the coil directly by the
iron yoke through a 5 mm thick insulator-spacer
surrounding the coil. The relatively close iron
leads to some iron saturation field effects at
high field that must be corrected with the lumped
corrector magnets located at each quadrupole. ,
There are no internal trim coils in these magnets.
The 10 m long magnets are assembled in fixtures
that introduce the required 47 mm sagitta during
the construction process. The sagitta is locked
in place via the outer stainless steel weldment,
which also serves as the helium pressure vessel.
The cold mass is supported in a cryostat with
folded, insulating posts (originally designed by
FNAL for the SSC) (2), as shown in Fig. 6. The
SUPPLY HEADER 240 A
\ \ ELI I TILITY NEAIDER
He RETURN HEADER
Figure 6. Cross Section of RHIC Dipole in Cryostat.
primary design parameters for the dipole magnet
and the superconductor used in its construction
are given in Table 3.
Table 3. Basic Arc Dipole and Superconductor
B, minimum operation
B, 100 GeV/amu
Current for 100 GeV/amu
Stored energy at 100 GeV/amu
Coil, number of super-
Coil inner radius
Iron outer radius
Critical current density
@ 5T, 4.2 K
Number of wires in cable
Width of cable
Mid-thickness of cable
The performance of the half-length model
constructed and tested during the past year was
excellent. Figure 7 shows the training history of
" " " (2.6K)
~* Short-sample prediction
- RHIC operating field
Figure 7. Training History of Prototype RHIC
the magnet. The first quench was above the
required operating field and after several addi-
tional quenches, the magnet's field reached a
level near its short sample limit. It is expected
that future magnets will reach a somewhat higher
field because of continuing improvements in the
current capacity of the superconductor and
improved cable fabrication.
The measured transfer function, sextupole har-
monic and decapole harmonic are shown in Fig. 8.
The large magnetization evident in the harmonics
at low field is due to the large filament size (20
11m) in the superconductor used for this magnet.
Future magnets are expected to benefit from the
reduced filament size (<5 tim) that is being
developed in the very active superconductor R&D
program (3) currently underway. Table 4 lists the
measured mean values of the various harmonics,
including also the expected mean value and the
expected magnet-to-magnet variation extrapolated
from CBA experience. It is seen that the har-
monics in this prototype are well within the
expected error distribution.
The design for the arc quadrupoles is shown
in Fig. 9. It too is a single layer magnet using
the same conductor as in the dipole. Again the
use of copper wedges provides the needed degrees
of freedom to achieve good field quality over the
aperture of the magnet. The single layer design
is particularly welcome in a quadrupole magnet to
reduce the number of coils that must be built
and assembled. The main parameters for the
quadrupole are given in Table 5.
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H., Willen E. Magnets for RHIC, report, May 1, 1986; United States. (https://digital.library.unt.edu/ark:/67531/metadc870325/m1/4/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.