8th corrector per section for Elettra

Introduction:

To control both position and angle of the electron beam in the photon source point one needs four steerers, in pairs before and after the source point. This is fully satisfied in controlling both position and angle in the insertion devices source points but not for the dipole ones. This handicap however is not due to any design mistake but simply due to the fact that according to the initial requests Elettra was not supposed to have any dipole magnet beam lines. After Elettra came into operation in 1994 dipole beam lines started being built and functioning well although at the source point only the position or the angle could be controlled but not both due to the fact that a steerer after the dipole was missing. In general most dipole beam lines have a large acceptance and just fixing the vertical angle is enough, however some beam lines like SYRMEP and MCX are very sensitive to both angle and position and therefore a better control of their source point is necessary for increased reproducibility. In that case an additional steerer had to be added after the bending magnet so that the steerers before and after the dipole source point are in pairs. This however proved to be not so simple due to the lack of space, there was only a maximum of 140 mm between Q2 and S1 where a NEG pump was positioned, so the magnet had to be <140 mm thick but providing about 130 Gm or a kick of about 2 mrad at 2 GeV in both planes while the NEG pump had to be installed somewhere nearby resulting in changing that part of the vacuum chamber. Note that an alternative solution adopted by other storage rings namely using additional coils in the sextupoles cannot be realised in the case of Elettra because the sextupole poles do not create a closed magnetic circuit.

Magnet installation and measurements:

At the moment one prototype is installed in section 6 for the usage of the Syrmep Beamline. In order to change the NEG pump location, the installation of the magnet was done after changing a part of the vacuum chamber with a new one designed at ST and realized by Cinel.
Preliminary tests with the e-beam confirmed the correct power supply polarity, the symmetry of the magnet on horizontal and vertical plane and the magnetic simulations. The offset between the mechanical and the magnetic centre was also checked by the preliminary measurements. The rms orbit distortion introduced by the corrector was calculated for different current settings. The average rms distortion confirmed the mechanical symmetry; a rms of 0.39 (0.15) mm in the horizontal (vertical) plane was measured with the power supply set at ±0.5A. Doubling the power supply settings also the distortion doubled. As expected no noticeable tune shift was observed.