Agenda: New injection layout proposal to reduce optics pertubations.
A recent Presentation by M. Aiba has indentified perturbations of the lattice due to the injection chicane, in particular Beta-Beating of ~45%. (see minutes of the PSB Beam Dynamics working group meeting on 24th September). BG presented some ideas to optimise the PSB injection chicane. In order to reduce this effect, the following parameters were considered:
Offset of Injected beam (~10mm)
Increased Injected Beam Angle (max 80mrad)
Reduced BS angles
Increase Magnet Length (250 – 400mm)
Increased Painting Bump
Most effectibve measures are an increased KSW bump combined with an offset of the injected beam of ~10mm resulting in a Beta-Beating of ~15%. A 35 mm KSW bump can be accepted in case the adjacent main dipole aperture can be ±60 mm. MC confirmed that the vacuum chambers of the 1B1 and 16B1 are ±66 mm with ±64 mm and ±61 mm scrapers installed respectively. Simulations also showed that an increased injected beam angle will only be useful if an offset of the injected beam of ~10mm is not possible. (combined measures decreases the BS1-BS2 distance too much). In order to validate a new injection layout proposal the following issues need to be studied/confirmed:
Aperture available for 35mm KSW bump,
Possibility of offsetting the injected beam ~10mm,
Influence of BS magnets on closed orbit,
Optimise layout to increase space for foil handling device,
Max. value of acceptable Beta-Beating.
Furthermore, CC proposed to study the use of Q-strips
on the main quadrupoles in order to correct the Beta Beating effect.
JB presented 1st order quantifications of the
eddy current effects in the PSB injection area. Assuming a pulse with a
rise, fall time and flat top of 1 ms each, 0.35 mm thick laminations, and
constant average field (1 T) in yoke result in an acceptable 0.48mm skin
depth. The choice of a relatively thick lamination will thus be
acceptable, having a positive influence on the vacuum load as well as on the
filling factor of the magnet. Concerning the eddy currents in the vacuum
chamber, calculations of a vacuum chamber 190 x 70mm internally, made of corrugated inconel,
sitting inside 80 mm magnet gap results in an acceptable 62.6μs field delay.
JB also presented a proposal for a double aperture septum to increase the
injected beam angle. The proposed geometry uses a multiple turn coil around
the orbiting beam aperture in series with a single turn coil around the
injected beam aperture. Alternatively these apertures could be powered
independently, but the effect of the magnetic coupling between the resulting
two circuits would have to be studied more carefully.