Generation Of Linear Colliders Research Articles

Emittance growth due to wake fields on curved bunch trajectories

Very short bunches with high peak currents are required in linac based X-ray Free Electron Lasers (SASE-FELs) and in the next generation of linear colliders. In most designs, short bunches are produced by lingitudinal compression in magnet chicanes, where particles with different energies have different path lengths so that a bunch with an energy distribution correlated with longitudinal particle position can shrink in length. However, care has to be taken that the low emittance beams are not blown up by wake field effects. Especially the wake field calculation for very short bunches on curved trajectories with relatively small bending radii (of the order of meters) requires consideration of “overtaking effects”. “Overtaking” means, that on a curved trajectory the wake of the bunch tail may reach the head because the field travels on a shorter straight path. We present a treatment to calculate these fields considering transient regimes and shielding effects as well as calculations on the emittance growth for the case of the TTF-FEL bunch compression system.

An FEL scheme for generating high-power optical beams for gamma-gamma colliders based on chirped pulse amplification techniques

A method to produce high-power optical beams for converting high-energy electron beams to TeV gamma rays via Compton backscattering in the next generation linear colliders is proposed. The scheme is an application of the chirped pulse amplification technique to a single pass, high-gain free-electron laser.

Majorana neutrino versus Dirac neutrino in e +e − → W +W − through radiative corrections

Radiative corrections to e +e − → W +W − from Majorana neutrinos are studied in the context of the see-saw mechanism. Focusing on the effects of the fourth generation neutrinos, we calculate W-pair form factor, the differential cross sections and the forward-backward asymmetries for the polarized electrons at one-loop level. The behaviour of the form factors at the threshold of Majorana particle pair production is found to differ from that of Dirac particle pair production. In the cross section for unpolarized electrons, the radiative corrections, depending on the mass parameters of the see-saw mechanism, are found to be ∼ 0.5% at the energy range of the LEP200 and the next generation linear colliders.

Measurement of wake-field suppression in a detuned X-band accelerator structure.

Research is under way at SLAC to develop accelerator structure for a next generation linear collider. A full-scale prototype {ital X}-band structure has been built in which the dipole mode frequencies were detuned to suppress the long-range transverse wake field by about 2 orders of magnitude. To verify that the detuning works as expected, a facility, the Accelerator Structure Setup, was constructed in the SLAC Linear Collider to measure the long-range wake field. This Letter presents the results from the measurement of the prototype {ital X}-band structure with this facility.

VLEPP based photon linear collider 100 × 100 GeV with ultimate luminosity

The possible parameters of a photon linear collider at its ultimate luminosity, based on the VLEPP physics and technology [V.E. Balakin et al., Proc. 6th Nat. Conf. on Accelerators, Dubna, 1978; V.E. Balakin, Proc. 4th Int. Workshop on Next Generation Linear Colliders, Garmisch, 1992], are presented. At a photon energy of 100 × 100 GeV the maximum achievable luminosity is about 1 × 10 36 cm −2 s −1. Beam parameters, luminosity characteristics, and ways to reduce the background are considered as well.

Controls for the Tesla test facility status and future plans

The Tesla Test Facility (TTF) is designed to perform intensive testing of the superconducting cavities foreseen for the next generation of linear colliders. In the first step the TTF will be equipped with all the components necessary to build and test the superconducting cavities. In the second step a linear accelerator will be build using the previously tested cavities. Finally, all the components of a linear accelerator will be installed and have to be controlled. Since the Tesla collaboration is internationally supported, there will be a variety of different subsystems which may be installed with their own controls. This will lead to several problems which have to be solved in the final design of the overall control system. This paper describes the different subsystems and how these systems may interact.

Cryogenic controls for the TESLA test facility

The TESLA Test Facility (TTF) is designed to perform intensive testing of the superconducting cavities foreseen for the next generation of linear colliders. The cryogenic system is one part of this facility. The controls for this system will initially use the existing software and hardware to be able to cool down the first cavities fabricated in the TTF workshop. Later the control system will be modified to meet the current standards in process and accelerator controls. The hardware will be changed to use the VME system as the major platform. The operating system and the communication will be based on de-facto standards such as UNIX for the workstations and the front-end computers and TCP/IP for network communication. The application software (EPICS) will be part of a collaboration with several other institutes. The final goal is to port all the software to the POSIX standard and to use Object-Oriented tools wherever possible. The first part of this paper describes the migration from the existing control system to the future design. Special decisions on hardware and software solutions are highlighted. Nonproprietary field busses for remote process I/O are becoming usual for slow control. A suitable bus for our future basic I/O system had to be selected. Finally a new temperature monitor module working on the CAN-bus and its measurement procedure will be explained.

Supersymmetric left-right model and its tests in linear colliders

We investigate phenomenological implications of a supersymmetric left-right model based on SU(2) L × SU(2) R × U(1) B– L gauge symmetry testable in the next generation linear colliders. We concentrate in particular on the doubly charged SU(2) R triplet higgsino Δ , which we find very suitable for experimental search. We estimate its production rate in e +e −, e −e −, e −γ and γγ collisions and consider its subsequent decays. These processes have a clear discovery signature with a very low background from other processes.

Initial longitudinal polarization in e+e− → W+W− as a tool to probe trilinear gauge boson couplings

We discuss the potential of initial longitudinal polarization in testing the values of trilinear gauge boson couplings from the reaction e + e − → W + W − at next generation linear collider energies. The combination of e + L e − R and e + R e − L cross sections should have a significant role in reducing the range of values of anomalous couplings allowed by the unpolarized cross section. We explicitly apply this approach to models with reduced number of free parameters, inspired by symmetry requirements, and determine the order of magnitude of expected sensitivities.

Prospects for generating polarized electron beams for a linear collider using an rf gun

The next generation of linear colliders — represented by the Japanese Linear Collider (JLC) and the Next Linear Collider (NLC) — will probably utilize polarized electrons generated by a photocathode gun. A photocathode gun with high polarization ( P e) photocathodes (up to P e ∼ 80% achieved to date) is currently providing polarized electrons for the SLC. The SLC source requires subharmonic bunching at low energy to reduce the bunch length prior to S-band bunching and a damping ring at high energy to reduce the transverse emittance. The use of an rf gun can eliminate the former and possibly simplify the latter. However, rf guns as presently developed have serious problems with vacuum contamination, which would quickly lower the quantum efficiency (QE) of a semiconductor photocathode. In addition, the “charge limit” previously reported for high peak current pulses puts a limit on the laser power usable for photoexciting a low QE cathode near the bandgap threshold. These problems have so far precluded any serious attempt to design an rf gun for polarized electrons. Several technical advances that now improve the prospects for a practical polarized electron rf gun are described. Finally, new ideas for high polarization photocathodes that permit operation in a relatively poor vacuum and techniques being explored to mitigate the low QE “charge limit” are discussed.

Higgs contribution to theW pair production in left-right electroweak model

We investigate the neutral Higgs contributions to the pair production of light (W1) and heavy (W2) charged gauge bosons of the left-right symmetric electroweak model in electron-positron annihilations. The Higgs contributions are shown to be of the same order of magnitude as the chirality flip part of the Majorana neutrino exchange channel (they cancel each other at high energies). Our numerical examples concern with the processe+e−→W1W2 where the contribution of the Higgses is more important than in the pair production of equal mass weak bosons. It turns out that the Higgs contributions are negligibly small in the energy range of the next generation linear colliders if the gauge coupling constants of the left-handed and right-handed interactions are equal and the see-saw relation between the neutrino mixing angle and neutrino masses is strictly valid as we have assumed.