Several options for layout and magnet technology were considered.
Only the (vertically focussing) quad nearest the interaction point was studied,
since the next (horizontally focussing) quad was located outside of the CLEO
magnet pole tip and the present iron/copper quads are adequate for most
configurations. For each option, optics were computed at 5.3 GeV which
provided cm and
m.
Apertures were designed to accommodate
a 12
beam stay clear and a
2.5 mrad horizontal crossing angle.
A double-walled, cooled beam pipe was assumed.
For each configuration three parameters were calculated: 1) the long range
tune shift for 10 mA bunches and fixed crossing angle at a point 2.1 m
from the interaction point (corresponding to bunches spaced by 14 ns); 2)
the chromaticity from the IR quads (on one side only); and 3) the total
horizontal aperture required for 2.5 mrad crossing angle. The results
are summarized in Table
.
NdFeB and SmCo refer to high permanent magnet material. The NdFeB
material has
Tesla, giving a significant advantage
in gradient
over the SmCo, which was assumed to have
Tesla.
(The present CESR
permanent magnet quads are made from an older type of SmCo which has
Tesla.) The NdFeB material, however has a lower Curie
temperature
(
310 C compared to
480 C for SmCo) which causes the temperature
coefficient
to be 4 times larger, and requires special care to avoid exposing the
material to excessive temperatures.
The first four rows in Table are
design exercises that do not easily accommodate
the 4.7 to 5.6 GeV energy range.
The SmCo options which can accommodate this energy range (rows 5 to 7)
require unrealistically large gradients (k=0.8 m) in the
associated Fe/Cu quads.
The superconducting quad options (rows 8 and 9)
require placing the cryostat far inside
the drift chamber which places undesirable constraints on the cryostat and
the drift chamber design.
Hybrid options (rows 10 to 12) using SmCo and superconducting quads
satisfy all of the requirements discussed earlier.
The SmCo is most
effective when high fields are required in small volumes. It also is a
very effective mask against high energy particle background.
The superconducting quads provide a controllable high-gradient field
and offer the capability to
include additional magnet coils in the same cryostat.
We plan to install in the cryostat horizontal and vertical dipole
correction coils
and skew quad coils for detector solenoid compensation.
The option in row 11 of Table was chosen because it
provides the best set of machine parameters while providing sufficient
space for mounting detector and accelerator hardware.
A drawing of the proposed quads is given in Fig. .
Current densities for the quadrupole windings are modest-less than 300
A/mm. Peak magnetic fields at conductors are approximately 3.5 Tesla,
not including the solenoid field.