ISABELLE: superconducting storage accelerator Page: 2 of 9
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The iron shield is closely coupled to the coils within the cryogenic envelope
providing magnetic field enhancement and mechaiical support. These mag-
nets have achieved fields in excess of 4 T, show virtually no training and
have field uniformity approaching the B ~ 10- required for storage ring
applications. Two such models have undergone extensive tests including
life tests which include more pulses than the expected total life of
ISABELLE. Based on these models a typical ring magnet pair would look like
Fig. 1 and a half cell of the bending sections would look like Fig. 2.
The insertions are designed for maximum flexibility based on an exten-
sive study by experimental physicists including conceptual design of numer-
ous experiments. The requirement which most dramatically affects the apear-
ance of the machine is the 40 m long free space around the low beta inter-
action regions. The overall facility takes on the appearance of Fig. 3.
We have chosen four long insertions to make a large number of experimental
setups possible and to make the periodicity large to reduce the problems
with structure resonances. Hopefully, the identity of the insertions can be
relaxed after some experience with the machine. There are also four service
insertions in each ring used for beam dumps, injection, rf, etc.
The luminosity of the machine has been set at 10 /cm sec. Such per-
formance seems to be required by several experiments. Higher luminosities
seem to be difficult to achieve and the overall interaction rate might be
difficult for experiments to cope with.
Keil3 has shown that if currents are limited by he beam-beam interac-
tion, the luminosity, L, is given by L = cv ("I x where X is the
3 \vEfv /
line density of particles in each beam, AQ is the permissible beam-beam
tune shift, Et the normalized transverse emittance, - the free space in the
interaction region, and v is the classical proton radius. Using ISABELLE
parameters, and tune shift limit AQ = 0.005, we find a current of six am-
peres is required to achieve design luminosity. We have chosen a design
current of 10 A giving some margin for later parameter adjustment or even
higher luminosity. The low beta values and small crossing angles are com-
patible with Keil's formulae.
We have chosen a warm vacuum. We believe there are numerous engineer-
ing simplifications from this choice. Furthermore, in a cold vacuum if a
monolayer or more of gas were cryo-pumped on the surface, the beam current
would probably be limited to about an ampere by the pressure bump phenomena.
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Barton, M.Q. ISABELLE: superconducting storage accelerator, article, January 1, 1974; Upton, New York. (digital.library.unt.edu/ark:/67531/metadc1024398/m1/2/: accessed December 15, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.