636
K. Hübner et al.
The experience gained at HERA with high luminosity lepton proton collisions,
beam dynamics, various enabling technologies, the electron storage ring spin
dynamics, and the control of collective effects have a tremendous impact on the
design of these machines, in particular, the layout of the interaction regions.
HERA beam dynamics performance is used to benchmark computer codes
needed to develop the EIC designs. HERA operational experience is extremely
important for designing the complex interaction regions with unprecedented detector acceptance, assessing detector backgrounds induced by the beams and their
mitigation. The design of the magnets which were developed for the HERA
interaction regions have been carried over for the design of other colliders, such
as BEPC-II, KEKB, ILC, LHeC, and eRHIC. Some beam dynamic phenomena
observed in HERA directed the attention of the EIC designers to specific aspects
of electron ion collisions.
The examples in the following sections illustrate the positive impact of the HERA
design and operational experience on other colliders and in particular to the Electron
Ion collider eRHIC.
10.5.2.1 Lepton-Hadron Beam-Beam Interactions
The concept of lepton proton collisions in HERA was to adjust the the strength of
the beam-beam force for each beam such as this beam would collide with a beam of
its own species. A typical beam-beam strength in terms of incoherent beam-beam
tuneshift for e + − e − collisions was x e
x,y 0.03. For Hadron, the strengths of
beam beam interactions was typically below x
p
x,y 0.01. This succesful concept
was used successfully in other colliders such as KEKB and is also adapted at the
EIC design.
Occasionally, when the HERA beams were brought into collisions. an observation was made which is a concern for the electron ion collider. Under the influence
of strong beam-beam interaction, the electron beam can develop coherent transverse
oscillations. If this happens, the unstable motion of the electrons affects in turn the
hadron beam via the beam-beam coupling. The hadrons will start to oscillate as
well driven by the beam beam field of the unstable electron beam and the hadron
beam emittance will then filament in phase space and become diluted that way. The
effective beam size grows considerably and practically irreversely in the process
which quickly renders the beam unusable.
This phenomenon was observed only occasionally at HERA and its rare occurrence made it impossible to perform systematic studies. Furthermore the impact on
operations was very small and therefore, no resources have been invested to study
the effect in detail.
The experience with lepton proton collisions in HERA, raised a concern that
this effect would occur regularly in the EIC, because of significantly enhanced
beam-beam parameters per collision in the EIC. This triggered realistic beam-beam
interaction simulations for eRHIC. The beam-beam study was performed using the
K. Hübner et al.
The experience gained at HERA with high luminosity lepton proton collisions,
beam dynamics, various enabling technologies, the electron storage ring spin
dynamics, and the control of collective effects have a tremendous impact on the
design of these machines, in particular, the layout of the interaction regions.
HERA beam dynamics performance is used to benchmark computer codes
needed to develop the EIC designs. HERA operational experience is extremely
important for designing the complex interaction regions with unprecedented detector acceptance, assessing detector backgrounds induced by the beams and their
mitigation. The design of the magnets which were developed for the HERA
interaction regions have been carried over for the design of other colliders, such
as BEPC-II, KEKB, ILC, LHeC, and eRHIC. Some beam dynamic phenomena
observed in HERA directed the attention of the EIC designers to specific aspects
of electron ion collisions.
The examples in the following sections illustrate the positive impact of the HERA
design and operational experience on other colliders and in particular to the Electron
Ion collider eRHIC.
10.5.2.1 Lepton-Hadron Beam-Beam Interactions
The concept of lepton proton collisions in HERA was to adjust the the strength of
the beam-beam force for each beam such as this beam would collide with a beam of
its own species. A typical beam-beam strength in terms of incoherent beam-beam
tuneshift for e + − e − collisions was x e
x,y 0.03. For Hadron, the strengths of
beam beam interactions was typically below x
p
x,y 0.01. This succesful concept
was used successfully in other colliders such as KEKB and is also adapted at the
EIC design.
Occasionally, when the HERA beams were brought into collisions. an observation was made which is a concern for the electron ion collider. Under the influence
of strong beam-beam interaction, the electron beam can develop coherent transverse
oscillations. If this happens, the unstable motion of the electrons affects in turn the
hadron beam via the beam-beam coupling. The hadrons will start to oscillate as
well driven by the beam beam field of the unstable electron beam and the hadron
beam emittance will then filament in phase space and become diluted that way. The
effective beam size grows considerably and practically irreversely in the process
which quickly renders the beam unusable.
This phenomenon was observed only occasionally at HERA and its rare occurrence made it impossible to perform systematic studies. Furthermore the impact on
operations was very small and therefore, no resources have been invested to study
the effect in detail.
The experience with lepton proton collisions in HERA, raised a concern that
this effect would occur regularly in the EIC, because of significantly enhanced
beam-beam parameters per collision in the EIC. This triggered realistic beam-beam
interaction simulations for eRHIC. The beam-beam study was performed using the