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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 storage ring

reference energy 2.4 GeV
circumference 288 m
current 400 mA
emittance 5 nm
tunes Qx , Qy 20.42 , 8.18
momentum compaction 0.6 10-3
main RF frequency 500 MHz
peak RF voltage 2.6 MV
third harmonic RF cavity 1500 MHz
radiation loss/turn 500 keV
energy spread 0.09%
damping times (x, y, E) 9 , 9 , 4.5 ms

The circumference of the storage ring is partioned into 12 triple bend achromats (TBA).
The lattice has a 3-fold symmetry and a total of:

3 long straight sections 11.7 m
3 medium long straight sections 7 m
6 short straight sections 4 m.

To minimize the emittance of the stored beam, the 3 bend angles of a TBA cell have values of 8, 14 and 8 with a bending radius of 5.73 m. All 36 bending magnets have a common power supply. The corresponding magnetic field is 1.4 T at 2.4 GeV or 1.57 T for future operation at 2.7 GeV.

The generous space of a 11 m long straight section is used for a very efficient injection process. 4 kicker magnets displace the stored beam by about 15 mm towards a septum magnet (injection bump). At the same time a new bunch coming from the booster passes through the septum and - after a damping time of a few ms - is finally absorbed by the stored beam.
Two short straight sections 4 m are housing the 500 MHz RF system with a total of 4 cavities. In 2002 a superconducting third harmonic cavity (1.5 GHz) was installed in a medium long section. It is used to increase the bunch length, thus reducing the electron density in a bunch. This in turn enhances the lifetime and the stability of the beam.
The other straight sections are or will be used for installing a variety of undulators, tailored to the needs of a particular beamline.

A total of 174 quadrupoles are used to optimize the optical parameters of the beam, giving a beam emittance of only 5 nm. In addition 120 sextupoles correct the chromatic properties, giving a large momentum acceptance (about 4%) and a large dynamic aperture. All these multipoles have individual digital power supplies to give a large flexibility for the optimization process.

A total of 72 digital beam position monitors (DBPM) are installed in the storage ring. They are mounted directly on the steel girders and serve as fix points for the vacuum chamber.
This DBPM system is a unique development and covers the operation modes, which are relevant at a modern facility like SLS:
1. high bandwidth, medium resolution for turn to turn measurements
2. medium bandwidth, high resolution for closed orbit measurements
The complete integration of the DBPM electronics into the EPICS based SLS controlsystem allows for an instant switching between the two modes.

The BPMs are used to keep the orbit in the storage ring stable to better than 1 m, with a fast feedback system.