INSTALLATION OF SKEW SEXTUPOLE MAGNETS AT KEKB

A new set of magnets, the skew sextupole magnets, were designed, manufactured and installed in the KEKB tunnel during the three month shutdown of January, February and March, 2009. Twenty magnets were installed in the HER and eight magnets were installed in the LER, respectively. The skew sextupole magnets are used to correct for the chromatic X-Y coupling at the interaction point (IP). A significant luminosity boost was achieved. The skew magnet parameters and the field measurement results are described in this report. MAGNET DESIGN Recently, from the results of computer simulation with beam-beam interactions[1,2], it was found that large chromatic X-Y coupling at the IP deteriorates the luminosity. A correction scheme of chromatic X-Y coupling at the IP using skew sextupole magnets was proposed. Since the request for installing a new set of magnets was made just before the shutdown, the entire process of the magnet design and production needed to be simplified and optimized. The magnet parameters were optimized so that the magnets can be operated using spare power supplies. Polyester enamelled copper (PEW) wires, which were used for the KEKB solenoid magnets for mitigating the electron cloud instability in the LER, were used. The number of turns was determined by the specifications of the available bipolar power supplies. The magnet bore needed to be large enough so that the cooling channel of the existing vacuum chamber fits. The length of the magnet was determined by the space available in the beam line. The pole has the basic sextupole equi-potential curve without any modification to the pole shape. Spare magnet supports for the corrector magnets were recycled as magnet supports for the skew sextupole magnets with some modifications. Table 1 summarizes the basic magnet parameters. Table 1: Magnet Parameters Magnet bore diameter 160 mm Magnet length 200 mm