P. Chen

Beam-beam phenomena in linear colliders

The beam-beam interaction in electron-positron linear colliders shows very di erent aspects from that in storage rings. The single-pass nature of the linear colliders allows drastic deformation of the bunch shape during one collision. Also, under the very strong electro-magnetic eld together with the high beam energy, phenomena which are not important in storage rings come into play, namely the phenomena involving the quantum eld theory. The synchrotron radiation in the beam-beam eld, called beamstrahlung, becomes extremely energetic. The strong eld can even create electronpositron pairs from the beamstrahlung photons. In the present lecture note both the classical and quantum phenomena are described. KEK Preprint 91-2, April 1991 Lecture at 1990 US-CERN School on Particle Accelerators, Nov.7-14, 1990, Hilton Head Island, So. Carolina, USA. Lecture Notes in Physics 400. Frontiers of Particle Beams: Intensity Limitations, Springer Verlag, pp. 415-445. Revised Nov. 1992. Printed. April 7, 1995 BEAM-BEAM PHENOMENA IN LINEAR COLLIDERS Kaoru Yokoya and Pisin Cheny Natinal Laboratory for High Energy Physics, Oho, Tsukuba-shi, Ibaraki, 305, Japan yStanford Linear Accelerator Center, Stanford University, Stanford, CA94309, USA

Observations of microwave continuum emission from air shower plasmas

We investigate a possible new technique for microwave detection of cosmic-ray extensive air showers which relies on detection of expected continuum radiation in the microwave range, caused by free-electron collisions with neutrals in the tenuous plasma left after the passage of the shower. We performed an initial experiment at the Argonne Wakefield Accelerator laboratory in 2003 and measured broadband microwave emission from air ionized via high-energy electrons and photons. A follow-up experiment at the Stanford Linear Accelerator Center in the summer of 2004 confirmed the major features of the previous Argonne Wakefield Accelerator observations with better precision. Prompted by these results we built a prototype detector using satellite television technology and have made measurements suggestive of the detection of cosmic-ray extensive air showers. The method, if confirmed by experiments now in progress, could provide a high-duty cycle complement to current nitrogen fluorescence observations.

Parameters of the SLAC Next Linear Collider

In this paper, we present the parameters and layout of the Next Linear Collider (NLC). The NLC is the SLAC design of a future linear collider using X-band RF technology in the main linacs. The collider would have an initial center-of-mass energy of 0.5 TeV which would be upgraded to 1 TeV and then 1.5 TeV in two stages. The design luminosity is >5/spl times/10/sup 33/ cm/sup -2/ sec/sup -1/ at 0.5 TeV and >10/sup 34/ cm/sup -2/ sec/sup -1/ at 1.0 and 1.5 TeV. We will briefly describe the components of the collider and the proposed energy upgrade scenario.

Electron energy spectrum and maximum disruption angle under multiphoton beamstrahlung

The final electron energy spectrum under a multiphoton beamstrahlung process is derived analytically in the classical and the intermediate regimes. The maximum disruption angle from the low energy tail of the spectrum is also estimated. The results are then applied to the TLC (TeV Linear Collider) and the CLIC (CERN Linear Collider) parameters.<<ETX>>

Disruption effects on the beam size measurement

At the SLC Final Focus with higher currents and smaller beam sizes, the disruption parameter D/sub y/ is close to one and so the pinch effect should produce a luminosity enhancement. Since a flat beam-beam function is fit to deflection scan data to measure the beam size, disruption can affect the measurement. Here we discuss the quantitative effects of disruption for typical SLC beam parameters. With 3.5/spl times/10/sup 10/ particles per pulse, bunch length of 0.8 mm and beam sizes of 2.1 /spl mu/m horizontally and 0.55 /spl mu/m vertically, the measured vertical size can be as much as 25% bigger than the real one. Furthermore during the collision the spot size actually decrease, producing an enhancement factor H/sub D/ of about 1.25. This would yield to a true luminosity which is 1.6 times that which is estimated from the beam-beam deflection fit.

Simulations on pair creation from beam-beam interaction in linear colliders

The authors modify the computer code ABEL (analysis of beam-beam effects in linear colliders) to include the pair creation processes, using the equivalent photon approximation. Special care has been taken on the nonlocal nature of the virtual photon exchanges. The simulation results are compared with analytic formulas, and are applied to the next-generation colliders such as JLC.<<ETX>>

Simulation of high energy beam focusing by a plasma

A study is made of the focusing of a high-energy electron beam and a positron beam by means of a plasma. The simulation is done using the code CONDOR. Results are presented of simulation and simple model calculations. The authors demonstrate the focusing of the beams.<<ETX>>

Depolarization due to beam‐beam interaction in electron‐positron linear colliders

We investigate two major mechanisms which induce depolarization of electron beams during beam‐beam interaction in linear colliders. These are the classical spin precession under the collective field of the oncoming beam, and the spin‐flip effect from beamstrahlung. Analytic formulas are derived for estimating these depolarization effects. As examples, we estimate the depolarization in the Stanford Linear Collider (SLC) and a possible future TeV linear collider (TLC). The effects are found to be negligibly small for SLC and not very large for TLC.

Applications of a plasma lens with bootstrap disruption

The authors examine the viability of employing the mechanism of bootstrap disruption with an underdense plasma lens to enhance the luminosity in linear colliders. They discuss the optics of an underdense plasma lens for electrons and positrons. They present results of such a scheme for the SLC (Standford Linear Collider) and heteroenergetic B-factory designs.<<ETX>>