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Paul Scherrer Institut PSI Accelerator Development and Operation Support

Paul Scherrer Institut
5232 Villigen PSI, Schweiz/Switzerland
Tel. +41 56 310 21 11
Fax. +41 56 310 21 99

E-Mail: andreas.streun@psi.ch

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Parameter list for the booster

injection energy 100 MeV
extraction energy 2.4 GeV
circumference 270 m
straights (3) 8.68 m
lattice FODO
RF frequency 500 MHz
cycling rate 3.125 Hz
tunes Qx , Qy 12.41 , 8.38
momentum compaction 0.005
final emittance 7 nm

The Booster synchrotron is located in the same tunnel as the storage ring and has thus with 270 m a very large circumference. This solution saves substantial costs on the building (e.g. shielding walls!) as well as costs for operation in the top-up injection mode. The power consumption is less than 200 kW to run the booster continuously.

The booster lattice has a 3-fold symmetry (like the storage ring) and is based on a modified FODO structure with many small combined function bending magnets (after an idea from G.Mülhaupt). This leads to an exceptionally good emittance for such an injector and makes injection into the storage ring relatively easy.

The booster has 3 dispersionless straight sections: the first one is used for injection from the Linac, the RF cavity is located in the second one and the third one houses some diagnostic equipment.

There are two types of combined function bending magnets: the F-type provides horizontal focusing, whereas the D-type defocuses the beam horizontally. All combined function bending magnets of both types are connected in series to a single power supply, which controls its time dependent current with pulse width modulation.

The cycling rate of the booster is 50 Hz/16 = 3.125 Hz.
During acceleration the magnetic fields increase by a factor of 24, corresponding to the energy increase from 100 MeV to 2.4 GeV. At this energy the magnetic field has a maximum of 0.72 T in the D-type bending magnet, requiring a maximum current of 840 A.

Due to the low value for the stored magnetic energy we do not need a resonant circuit to provide the necessary periodic wave form for the magnet current. Instead an electrolytic capacitor bank is periodically charged and discharged .

The maximum induced voltage during the ramping of the magnets is less than 500V against ground, avoiding thus the problems of a high voltage installation.

The combined function bends are responsible for the overall focusing properties. But the addition of 18 separate quadrupoles (arranged in 3 families) allows a variation of the tunes within an integer range.
The situation is similar for the chromaticities of the lattice: The main chromaticity correction is built into the bends as well. A set of 18 separate sextupoles (connected into 2 families) is used to optimize the chromaticity during the magnet ramp, taking eddy current effects of the vacuum chamber (which has dimensions of only 30x20 mm) into account.

The beam coming from the Linac is injected into the booster by a fast kicker magnet, with a rise time of 200ns, followed by a septum magnet. A similar system of kicker and septum is responsible for extracting the beam at the final energy of 2.4 GeV.

Standard FODO cell