The PS in the LEP injector chain - 50th anniversary of the CERN ...

Fig. 12: Possible PS–SPS transfer of eight bunches into eight buckets. The three SPS accelerating systems work
with the following harmonic numbers: h = 2312 at 100 MHz, h = 4616 at 200 MHz, and h = 8120 at 352 MHz.
No re-phasing was needed in the PS
Tests of electrons and later of positrons were done on 1.2 s cycles while the PS was delivering
beams of different particles to its other users, in a 14.4 s supercycle (later in a 19.2 s supercycle). It
required only two injection cycles, one positron and one electron. Acceleration of leptons was
achieved on these two consecutive 1.2 s cycles in the nominal supercycle for LEP filling (see Fig. 13)
[10]. During lepton acceleration in the ‘bunch expansion’ mode, the HF ferrite cavities and the
resonant 200 MHz cavities, normally used for proton acceleration, were respectively short-circuited
and damped.
Fig. 13: Distinctive 19.2 s PS supercycle. Positrons and electrons were accelerated on the antepenultimate and
penultimate cycles
The slow cycling, combined-function PS accelerator was used as an electron accelerator besides
its other uses as proton, antiproton, and ion synchrotron. After initial commissioning tests it was ready
to deliver electron bunches of design characteristics with better than 90% overall transmission
efficiency to the SPS. Bunch length and energy spread could also be reduced by a factor of four from
the nominal values by simply decreasing the wiggler current. Although at high intensity (greater than
2 × 10 11 electrons) transverse blow-ups were observed due to the presence of ions, the beam quality
was not affected by collective effects at nominal intensity.
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