Katsunobu Oide

Ground motion studies for large future linear colliders

A future large accelerator, such as a TeV linear collider, should have an extremely small emittance to give the required luminosity. Precise alignment of machine components is essential to prevent emittance dilution. The ground motion spoils alignment of the accelerator elements and results in emittance growth. This paper discusses ground motion and its effect on the main linac. The ground motion in the frequency range of seismic vibration is mostly coherent in the related accelerator. However the incoherent diffusive or Brownian like motion may become dominant for a frequency region less than seismic vibration. This paper starts from the power spectrum of the ATL model then shows typical parameters of main linacs and considers measured data including excavated effects.

Quantum Excitation due to Classical Beamstrahlung in Circular Colliders

In the collisions at proposed future circular colliders, like FCC-ee and CEPC, a classical description of beamstrahlung is adequate, since the critical photon energy is much smaller than the particle energy. In the classical regime, for a constant electromagnetic field a simple relation exists between the average photon energy u and the average squared photon energy u2, which is the same as for standard synchrotron radiation in storage rings. This simple relation only holds if the electromagnetic field is constant and uniform. This is not the case for a beam-beam collision. We here derive an analytical expression for the ratio 〈u2〉/〈u〉2 considering the case of Gaussian-bunch collisions. We compare our result with the photon energies obtained in beam-beam simulation for FCC-ee at beam energies of 45.6 GeV and 182.5 GeV, using the two independent codes BBWS and GuineaPig. Finally, we re-optimize the FCC-ee parameters of a possible monochromatization scheme for direct Higgs production at a centre-of-mass energy of 125 GeV, derived previously, by applying the refined expression for the rms photon energy.

JACoW : Extraction Line and Beam Dump for the Future Electron Positron Circular Collider

The conceptual design of an extraction line and beam dump for the future electron positron circular collider is presented. The proposed extraction line, consisting of abort kicker system, spoilers and beam diagnostics apparatus transports the electron and positron beams to the main beam dumps. The beam must be spread over a large surface in order not to damage the beam dump and the window, which separates the ring from the dump. The extraction line redistributes bunches at different location on the face of beam dump. Monte Carlo simulations using FLUKA have been performed to estimate the distribution of energy deposition on the window and beam dump to find the optimal absorber and its dimensions.

JACoW : Vertical Dispersion and Betatron Coupling Correction for FCC-ee

The FCC-ee project foresees to build a 100 km e+/ecircular collider for precision studies and rare decay observations in the range of 90 to 350 GeV center of mass energy with luminosities in the order of 1035cm−2s−1. To reach such performances, an extreme focusing of the beam is required in the interaction regions with a low vertical beta function of 2 mm at the IPs. Moreover, the FCC-ee physics program requires very low emittances never achieved in a collider with 1 nm for x and 2 pm for y , bringing down the coupling ratio to 2/1000. Thus, coupling and vertical dispersion sources have to be controlled carefully. This paper describes the tolerance of the machine to magnet alignment errors as well as the optics correction methods that were implemented, such as the Orbit Dispersion Free Steering, in order to bring the vertical dispersion to reasonable values. The correction of the betatron coupling, being also a very important source of emittance growth, has been integrated to a challenging correction scheme to keep the vertical emittance as low as possible.

Projects for ultra-high-energy circular colliders at CERN

Within the Future Circular Collider (FCC) design study launched at CERN in 2014, it is envisaged to construct hadron (FCC-hh) and lepton (FCC-ee) ultra-high-energy machines aimed to replace the LHC upon the conclusion of its research program. The Budker Institute of Nuclear Physics is actively involved in the development of the FCC-ee electron–positron collider. The Crab Waist (CR) scheme of the collision region that has been proposed by INP and will be implemented at FCC-ee is expected to provide high luminosity over a broad energy range. The status and development of the FCC project are described, and its parameters and limitations are discussed for the lepton collider in particular.

Status of 1.54 GeV ATF linac

Accelerator Test Facility (ATF) consists of a 1.54 GeV S-band linac, a beam transport line, a damping ring and an extraction beam line. A beam commissioning of the linac was performed in November 1995. A single bunch and multi-bunch beam were accelerated up to 1.43 GeV at the end of the beam transport line. The beam experiments on high-gradient acceleration, structure BPM and multi-bunch energy compensation were performed after the beam commissioning. The operation of the linac was suspended from April 1996 for the construction of the damping ring. The operation of the linac was restarted from December 1996, and the beam commissioning of the damping ring was carried out in January 1997.