Beam extraction - 50th anniversary of the CERN Proton Synchrotron

A certain amount of ‘Q-gymnastics’ is necessary to prepare the ejection. The beam is first brought
to the inside half of the vacuum chamber, then the horizontal tune is increased from its normal value of
about 6.25 to about 6.36 by means of an auxiliary quadrupole. Finally the semi-quadrupole is switched on
and, after de-bunching, the particles are spilt by a negative slope on the main field flat-top. The reason for
this is that the negative chromaticity requires that the resonance be approached from higher Q values so
that the beam is pushed into the extraction toward the outside.
Fig. 8: The semi-quadrupole and its magnetic field
The phase space plots in Fig. 9 show the way the beam flowing out in the separatrices is split at the
electrostatic septum and how it behaves at the entrance of the thin septum magnet.
Fig. 9: Left: phase space plot at ES83. Right: phase space plot at TSM85.
Sharing was used essentially with internal target 1 until all physics experiments disappeared from
the South Hall in 1981. All internal targets were thus suppressed to avoid excessive irradiation of the
machine components. Efficiency for extraction 62 alone reached 93%, losses being shared on the
electrostatic and first magnetic septum.
De-bunching was and still is performed before extraction. It has several advantages: it eliminates
the accelerating frequency structure, precludes any interaction with beam controls loops, and allows the
enlargement of Δp/p which decreases the sensitivity to low-frequency ripples. In 1987, the maintenance of
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