To minimize the shut down (“dark”) time, we are placing all new magnets on girders. Then, when CESR operation is stopped for the upgrade, the girders will be moved to the tunnel and fitted into the storage ring. Each of the twelve girders contains two horizontal focusing quadrupole magnets, one large combined function magnet (bends the beam trajectory and focuses the beam vertically), and four small correcting magnets. Prior to installation, all magnets must go through a magnetic field measurement procedure and be accurately aligned in respect to each other and in respect to the girder.
The production strategy of CHESS-U magnets is similar to what was used in the past during CESR construction. All design, assembly of a magnets and girders, magnetic field measurement and magnet alignment is being done “in-house”, and for components fabrication, we contracted local vendors.
In the beginning of the project, we explored technologies available from local vendors (EMT, Camron) and realized that they can provide extremely reliable and precise machining at the scale required for CHESS-U magnets fabrication. Considering those, we decided to make the CHESS-U magnet with solid cores. The solid cores fabrication is more cost efficient, requires less labor and time than fabrication with laminates. The latter technique was used for construction of old CESR magnets.
We spent significant efforts and resources to develop magnetic field measurement systems. For quadrupole magnet characterization, we built a rotating coil bench. For the field mapping of the combined function magnet, we adopted the bench used for tuning undulators.
To align magnets on the girder in respect to each other and to girder fiducials, we used a combination of a Vibrating Wire magnetic field measurement technique and magnetic field mapping by a 3-axis Hall sensor. This allows us to find the location of the magnetic axis of the magnets and align them directly, avoiding the use of the magnet’s fiducials. This type of alignment should reduce the probability of the misalignment errors and improve performance of the magnetic optics.
There are two areas designated to the CHESS-U Magnet Program. In the “Annex” area, we temporarily store components delivered from vendors and do all the assembly and magnetic field measurement work. Part of this area is shown in Figure 1. Here, one can see three girders in various assembly stages. The first (closest) is in the beginning of the process; they are just girder stands connected by couplers. The next girder is in a more advanced stage. It has the supporting beam on stands and a 2.3m long combined function magnet (red) on the beam. The third girder has two quadrupole magnets (blue), a combined function magnet (red) and a few correcting (black) magnets on it. It is ready to be moved in the magnetic field measurement facility for the field mapping and final alignment. To move the girders in “Annex”, we use air-pads. After assembly and magnet testing in the Annex, we transport girders into the L0E area in Wilson Laboratory. See Figure 2 for the girders "dressed" with power supplies, cooling lines, etc. So far, eight girders out of a total of twelve have been assembled and transported to L0E. Four more are in the process of assembly and testing in Annex.
The projection date for completion of the assembly work in Annex is the end of April 2018.