Design Description
The beryllium vertex beam pipe we have in the current version of CLEO, called
CLEO II.V, has performed very well.
The vertex beam pipe described here closely follows the design of the CLEO II.V
vertex beam pipe.
The new vertex pipe consists of two sub-assemblies: the
beryllium sub-assembly and the copper sub-assembly.
The beryllium sub-assembly design has a double wall made of
two concentric tubes of beryllium. The
inner tube bears the vacuum load and has eight ribs.
The outer tube is as thin as possible
and serves to contain the coolant that will flow between the two tubes.
The CLEO II.V pipe uses water as a coolant. These tubes were joined
with a braze joint in CLEO II.V, but they may be left unjoined for CLEO III.
This joint
helps to react the force caused by the pressure in the coolant channels
but increases the difficulty of the project and the radiation thickness of
the beam pipe. The coolant as it passes
through the CLEO II.V pipe is below atmospheric pressure. For CLEO III
we are considering moving to a hydrocarbon coolant which will be
pumped through the pipe in the more usual manner.
This new design avoids coolant-to-vacuum joints which were a
complicating feature of the old design.
Joined to the ends of the beryllium tubes is a manifold that joins
the cooling channels of the beryllium to external cooling lines.
Coolant to air joints join one side of the manifold to the outer
beryllium tube and the other side to the inner beryllium tube. On the
CLEO II.V beam pipe the cooling lines were brazed in place. This proved to
be a problem in other assembly work. For the CLEO III beam pipe the coolant
connection is made with an O-ring sealed block attached with small fasteners.
Finally, the beryllium sub-assembly ends in stainless steel extensions that
are brazed to the ends of the inner beryllium tube. These form
the beryllium sub-assembly.
The stainless steel extensions of the inner
beryllium tube are welded to the
copper sub-assemblies via the stainless steel side
of a copper-stainless steel explosion bonded ring.
The joints on both sides of the
stainless extensions are between atmosphere and UHV at less than
10-9 torr and
must be leak tight to less than 2 x 10-10 ATM CC/sec of Helium.
The copper sub-assembly and the non-beryllium parts of the beryllium
sub-assembly will be manufactured at Wayne
State University and Cornell University.
The completed copper sub-assembly and the other non-beryllium parts
will be supplied for joining to the beryllium sub-assembly.
The completed beryllium sub-assembly will be shipped to Cornell
University where its inner vacuum surface will be coated with gold
in a sputtering process. This assembly can be shipped back to the
vendor for joining to the copper sub-assembly,
measurements for tolerances and
testing for structural integrity and vacuum tightness.
The tested final assembly will have its exposed beryllium
surfaces coated, for example with an epoxy sealer,
such as BR127 (Cytek), to guard against corrosion.
Two such assemblies are required.
Last modified: Wed Jan 17 17:15:58 EST 2001