438
F. Bordry et al.
operate and improve the accelerators and their associated transfer lines. This chapter
will give an overview of the instrumentation in use in modern accelerators, although
the choice available today is so vast that inevitably it will not be possible to cover
them all.
8.6.1 Beam Position Measurement
A beam position monitoring system can be found in every accelerator. Its role is to
provide information on the position of the beam in the vacuum chamber. In linacs
and transfer lines Beam Position Monitors (BPMs) are used to measure and correct
beam trajectories, while in synchrotrons such monitors are distributed around the
ring, providing the global orbit. Their location is usually chosen to be close to
the main quadrupole magnets where the β-functions are largest and so any orbit
distortion a maximum.
8.6.1.1 Pick-Ups
The measurement of beam position relies on processing information from pick-up
electrodes located in the beam pipe.
Four pick-up families are commonly employed (see e.g. [118]):
• Electrostatic
These consist of two electrodes insulated from and located on opposite sides
of the vacuum chamber (either left & right for the measurement of horizontal
position and/or up & down for the measurement of vertical position). As the beam
passes inside the pick-up it charges up the electrodes, which act as capacitors. The
amount of charge collected by each electrode will depend on the position of the
beam. Hence, by comparing the charge on opposite electrodes, a beam position
can be calculated. A so called “shoe-box” design (Fig. 8.58) is often used for
linearity, while a button design (Fig. 8.59a, b) is favored for short bunches and its
low cost, but needs correction for its non-linear response [119].
• Electromagnetic
Fig. 8.58 Example of a horizontal shoe box pick-up from the CERN SPS showing right electrode,
left electrode and the full assembly in its vacuum chamber
F. Bordry et al.
operate and improve the accelerators and their associated transfer lines. This chapter
will give an overview of the instrumentation in use in modern accelerators, although
the choice available today is so vast that inevitably it will not be possible to cover
them all.
8.6.1 Beam Position Measurement
A beam position monitoring system can be found in every accelerator. Its role is to
provide information on the position of the beam in the vacuum chamber. In linacs
and transfer lines Beam Position Monitors (BPMs) are used to measure and correct
beam trajectories, while in synchrotrons such monitors are distributed around the
ring, providing the global orbit. Their location is usually chosen to be close to
the main quadrupole magnets where the β-functions are largest and so any orbit
distortion a maximum.
8.6.1.1 Pick-Ups
The measurement of beam position relies on processing information from pick-up
electrodes located in the beam pipe.
Four pick-up families are commonly employed (see e.g. [118]):
• Electrostatic
These consist of two electrodes insulated from and located on opposite sides
of the vacuum chamber (either left & right for the measurement of horizontal
position and/or up & down for the measurement of vertical position). As the beam
passes inside the pick-up it charges up the electrodes, which act as capacitors. The
amount of charge collected by each electrode will depend on the position of the
beam. Hence, by comparing the charge on opposite electrodes, a beam position
can be calculated. A so called “shoe-box” design (Fig. 8.58) is often used for
linearity, while a button design (Fig. 8.59a, b) is favored for short bunches and its
low cost, but needs correction for its non-linear response [119].
• Electromagnetic
Fig. 8.58 Example of a horizontal shoe box pick-up from the CERN SPS showing right electrode,
left electrode and the full assembly in its vacuum chamber