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