192
M. Brugger et al.
Fig. 5.1 Schematic view of
beam collisions with the
nuclei (N) of the rest-gas
γ
N
b ea m
be am pi pe
design path
A constant lifetime corresponds to an exponential decay of the intensity with
time t proportional to exp(−t/τ ).
The intensity and beam lifetime can be monitored by measuring the beam current
I which is directly proportional to the intensity, I = Nef , where e is the charge of
the particle and f the revolution frequency in a ring [11].
We can distinguish between several types of collision processes.
• Beam-gas scattering: collisions of beam particles with particles from the residual
gas in the evacuated beam pipe, sketched in Fig. 5.1.
• Thermal photon scattering: inverse Compton scattering of electrons or positrons
with photons from black-body radiation in the beam pipe; relevant for beam
energies > 10 GeV
• Intra-beam scattering: collisions or close encounters with other particles in the
same beam; most relevant at lower energies and for very dense beams
• Quantum lifetime: particles leaving the acceptance by quantum fluctuations in
synchrotron radiation
• Colliding beams: particle collisions or close encounters when beams cross in
colliders
Estimates for the first two types which involve collisions with particles outside the
beam will be given below.
The losses from the different loss mechanism have to be added. This implies, that
the corresponding lifetime contributions add reciprocally
1
τ
=
i
1
τ i
An example of observed lifetimes in LEP is listed in Table 5.1, where losses from
intrabeam scattering were negligible.
The single beam lifetime is observed before beams are brought into collisions.
In LEP this was dominated by the thermal photon scattering. LEP was generally
operated with sufficient aperture and over-voltage from the RF-acceleration system,
so that losses from the quantum lifetime were negligible. More details on lifetimes
observed in LEP with a discussion of quantum lifetime and small, but non-negligible
effects which made lifetimes longer than originally anticipated can be found in [12].
M. Brugger et al.
Fig. 5.1 Schematic view of
beam collisions with the
nuclei (N) of the rest-gas
γ
N
b ea m
be am pi pe
design path
A constant lifetime corresponds to an exponential decay of the intensity with
time t proportional to exp(−t/τ ).
The intensity and beam lifetime can be monitored by measuring the beam current
I which is directly proportional to the intensity, I = Nef , where e is the charge of
the particle and f the revolution frequency in a ring [11].
We can distinguish between several types of collision processes.
• Beam-gas scattering: collisions of beam particles with particles from the residual
gas in the evacuated beam pipe, sketched in Fig. 5.1.
• Thermal photon scattering: inverse Compton scattering of electrons or positrons
with photons from black-body radiation in the beam pipe; relevant for beam
energies > 10 GeV
• Intra-beam scattering: collisions or close encounters with other particles in the
same beam; most relevant at lower energies and for very dense beams
• Quantum lifetime: particles leaving the acceptance by quantum fluctuations in
synchrotron radiation
• Colliding beams: particle collisions or close encounters when beams cross in
colliders
Estimates for the first two types which involve collisions with particles outside the
beam will be given below.
The losses from the different loss mechanism have to be added. This implies, that
the corresponding lifetime contributions add reciprocally
1
τ
=
i
1
τ i
An example of observed lifetimes in LEP is listed in Table 5.1, where losses from
intrabeam scattering were negligible.
The single beam lifetime is observed before beams are brought into collisions.
In LEP this was dominated by the thermal photon scattering. LEP was generally
operated with sufficient aperture and over-voltage from the RF-acceleration system,
so that losses from the quantum lifetime were negligible. More details on lifetimes
observed in LEP with a discussion of quantum lifetime and small, but non-negligible
effects which made lifetimes longer than originally anticipated can be found in [12].