Bending magnet for SESAME storage ring
by Attilio Milanese (CERN)
The first SESAME dipole on the magnetic measurement bench at ALBA
Image credit: CERN
The CESSAMag project has reached an important milestone with the first unit tests of the bending magnets.
The bending units (dipoles) are the largest magnets of the SESAME storage ring – each dipole weighs 6.5 tons and is 2.5 m long. These massive components need precise mechanical construction – down to a few tens of microns – to meet the requirements on magnetic field quality and alignment. In addition, the design involves a superposition of dipolar and quadrupolar fields, and an excitation range going into a saturated nonlinear regime. All this made the characterization of the first magnet a critical milestone in the overall project.
CERN is responsible for the design, procurement and test of these 17 dipoles, within the CESSAMag project, largely funded by the EU. Within this framework, CERN has placed a contract with TESLA (UK) for manufacturing the magnets, and is collaborating with ALBA synchrotron (Spain) who provides in kind contribution for carrying out the magnetic measurements.
The test campaign on the first dipole last December fully confirmed the design: the measured magnetic field was in all cases very consistent with the simulations, and in particular the field in the aperture – where eventually the electron beam will circulate - was uniform down to 1∙10-4. This challenging target could only be met with both careful design and proper mechanical assembly by the manufacturer.
The production of the rest of the series is now progressing well in the UK, and 4 more magnets are already in Spain for measurements. In the meantime, the first dipole has been shipped to CERN, where it was used for a full integration check of a SESAME cell, including quadrupoles, sextupoles, the girder support structure and the vacuum chamber.
