Accelerator studies
Accelerator studies
This area is tentatively covered by 12 working groups:
WG1: Optics, low-beta IR design, alignment and feedbacks for the collider ring
WG2: Beam-beam interaction & collective effects
WG6: Pre-injector complex & e+/e-sources
WG7: Integration issues & electrical network
WG8: Machine detector interface, collimation and masking
WG9: Vacuum & shielding & heat extraction
WG10: Polarization & energy calibration
WG11: Civil engineering & services
WG12: Elements of costing & power estimates & heat management
Details on each WG is provided below:
The arc optics needs to vary with beam energy so as to achieve the target horizontal emittance required (from beam-beam effects). The two beams will be transported through separate arcs. Cost & power optimization (number, field, and length of quadrupole magnets) should be taken into account in the optics design. The final focus system and its chromatic correction should provide a large momentum acceptance of 2% for optimum beam lifetime in the presence of beamstrahlung and radiative Bhabha scattering. Alignment tolerances, BPM specifications and tuning schemes for achieving low vertical emittance need to be determined. A related item is orbit & other feedback systems. The ring configuration for low energy, up to 240 GeV, could be different from the one at 350 GeV, e.g. with separate RF sections at 45 GeV (perhaps up to 120 GeV beam energy) and joint RF sections at highest energy. Aspects of the control system architecture may also be discussed in connection with emittance control, tuning, and feedback. Special optics requirements and elements, including wigglers and spin rotators may be proposed for polarization purposes.
The optics of the fast cycling injector ring may also be designed in this WG.
The beam-beam effect enters a new regime with large hourglass effect and large Qs. The consequences should be explored and parameters optimized. resulting luminosity can be simulated in strong-strong and weak-strong approximations. The effect of the beam-beam at large tune shift on polarization needs to be explored for beam energies up to 80 GeV.
An important effect is beamstrahlung, the resulting steady state distribution, and beam lifetime need to be modeled. The possible effect of beamstrahlung on polarization should also be investigated.
A TLEP impedance budget & model will be set up.
Collective effects include resistive wall, cavity impedance, detuning wake fields, impedance contributions from photon stops, vacuum chamber. This WG should define the minimum aperture and guide the design of the vacuum system and arc magnets. An overall impedance budget should be set up.
Single-bunch instability thresholds and mitigation schemes should be explored. The interplay of TMCI with impedance, beam-beam Landau damping, and detuning wake fields should be investigated. Transverse and longitudinal coupled-bunch instabilities need to be addressed in particular for running at the Z pole.
For possible upgrade, more exotic schemes like charge compensation may also be considered.
This WG should design the collider ring arc magnets – dipoles, quadrupoles and sextupoles - (which may or may not be the same as needed for the VHE-LHC proton injector ring), the magnets for the fast cycling injector, the magnets for the low-beta interaction region, kicker and septa for top up injection, kicker and septa for beam dumps, emittance and polarization wigglers, Siberian snakes and spin rotators.
This WG will design the SRF cavities and cryomodules, including high-power couplers, HOM couplers, and cryo load, the RF power sources, the RF distribution, the cryoplants and cryogenic distribution. The WG study will include a cost optimization with respect to optimum RF gradient & RF-section length. Crab cavities for Tera-Z operation will also be considered.
This WG will develop the top-up injection systems for the collider and accelerator rings, and examine top-up related detector issues.
This WG will design the electron injector, the positron source & positron system, the preinjector complex, the modifications of the PS & SPS or an alternative new injector system, polarization aspects, and assess the prospects for using Siberian snakes in the injector chain combined with a polarized positron source. Concepts for an intense positron source will be investigated and a maximum production rates be determined.
This WG will take into account requirements for VHE-LHC, e.g. concerning the length of the straight section. It will examine the cohabitation of the lepton and proton injector and accelerator rings in the same tunnel as well as some integration issues with the experiments in the interaction region. Impact of different ring diameters will also be considered, as well as integration issues with existing tunnels, e.g. for a “LEP3”.
This WG will consider the final-quadrupole integration inside the experiments, develop a solution for the injector-ring bypass, study the decries from radiative Bhabha, beamstrahlung, gas scattering and thermal photon scattering and its efficient collimation, masking of synchrotron radiation in front of the detectors, and simulate the expected background.
This WG will develop a solution for synchrotron radiation handling, which may include photon stops, shielding, and cooling; the TLEP vacuum system, which may feature localized of uniform NEG coating, pumps, and clearing electrodes, ensuring vacuum stability for target beam parameters. Activation issues will also be addressed, e.g. through FLUKA simulations, and effects of radiation to electronics be analyzed.
This WG will study self-polarization w/o & with wigglers, including the optimum parameters of polarization wigglers, spin matching strategies, and possible use of snakes. It will explore the requirements for achieving longitudinal polarization at the Z pole, including the design of spin rotators. It will study energy calibration methods, such as resonant depolarization and a bending-magnet spectrometer and determine the expected resolution. The (perhaps exotic) possibility of accelerating & injecting polarized lepton beams using Siberian snakes in injector(s) and collider will also be examined.
This WG will describe the state of the engineering studies for an 80 or 100-km tunnel including experimental caverns & access shafts, as well as cooling & ventilation issues. Different ring diameters will also be considered, as well as integration issues with existing tunnels, e.g. for a “LEP3”, and perhaps the possibility of relocating CMS or ATLAS.
This WG will develop a cost-optimized design and the power budget of TLEP. Options for recovering and reusing 200MW of waste heat will also be studied.
