9 Accelerator Operations
549
chapter we focus on the performance and operational use of a collimation system.
We quickly introduce a few central definitions:
• A collimation system is an ensemble of collimators that is integrated into the
accelerator layout to intercept stray particles and to protect the accelerator.
• Collimation is acting in the normalized phase space. With z = x or z = y,
the Twiss functions β z and α z , and the emittance z we define the normalized
coordinates z n and z
n as:
z n =
z
√
z β z
, z
n =
α z z + β z z
√
z β z
.
(9.59)
It is noted that the transverse beam size (Gaussian rms) is given by σ z =
√
z β z .
• An unperturbed particle describes a circle in normalized phase space with
amplitude:
a z =
z 2
n + z
2
n .
(9.60)
• Collimator settings from the beam are defined in normalized coordinates (numbers of beam size σ z ) with n 1 being the collimator family setting closest to the
beam, n 2 the second closest setting, and so on. Several families usually define a
hierarchy that must be respected. Often this results in stringent tolerances on the
positioning of collimators.
9.7.2 Definition of Cleaning Efficiency and Performance
A collimation system is designed to intercept stray particles with maximum
efficiency and thus to protect critical regions of the accelerator. Critical regions
can be experiments that must be protected against background from beam halo,
super-conducting magnets that must be protected against quenches or hands-on
maintenance equipment that must be protected against activation from beam losses.
A system with 100% efficiency would absorb all impacting particles and power
with zero leakage into critical zones. However, the various nuclear processes in the
collimator jaw materials will always cause some particles to escape the system.
The creation of secondary and tertiary halo in a two-stage collimation system is
illustrated in Fig. 9.10.
9.7.2.1 Local Cleaning Inefficiency
For collimation it is convenient to define inefficiency or leakage [76]. We first
introduce inefficiency and then connect it to efficiency. The inefficiency η c of a
collimation system with a primary collimation cut at n 1 is defined as the ratio
549
chapter we focus on the performance and operational use of a collimation system.
We quickly introduce a few central definitions:
• A collimation system is an ensemble of collimators that is integrated into the
accelerator layout to intercept stray particles and to protect the accelerator.
• Collimation is acting in the normalized phase space. With z = x or z = y,
the Twiss functions β z and α z , and the emittance z we define the normalized
coordinates z n and z
n as:
z n =
z
√
z β z
, z
n =
α z z + β z z
√
z β z
.
(9.59)
It is noted that the transverse beam size (Gaussian rms) is given by σ z =
√
z β z .
• An unperturbed particle describes a circle in normalized phase space with
amplitude:
a z =
z 2
n + z
2
n .
(9.60)
• Collimator settings from the beam are defined in normalized coordinates (numbers of beam size σ z ) with n 1 being the collimator family setting closest to the
beam, n 2 the second closest setting, and so on. Several families usually define a
hierarchy that must be respected. Often this results in stringent tolerances on the
positioning of collimators.
9.7.2 Definition of Cleaning Efficiency and Performance
A collimation system is designed to intercept stray particles with maximum
efficiency and thus to protect critical regions of the accelerator. Critical regions
can be experiments that must be protected against background from beam halo,
super-conducting magnets that must be protected against quenches or hands-on
maintenance equipment that must be protected against activation from beam losses.
A system with 100% efficiency would absorb all impacting particles and power
with zero leakage into critical zones. However, the various nuclear processes in the
collimator jaw materials will always cause some particles to escape the system.
The creation of secondary and tertiary halo in a two-stage collimation system is
illustrated in Fig. 9.10.
9.7.2.1 Local Cleaning Inefficiency
For collimation it is convenient to define inefficiency or leakage [76]. We first
introduce inefficiency and then connect it to efficiency. The inefficiency η c of a
collimation system with a primary collimation cut at n 1 is defined as the ratio