Design Studies for a High Current Bunching System for CLIC Test Facility (CTF3) Drive Beam

A bunching system is proposed for the initial stage of CTF3 which consists of one (two) 3 GHz prebunchers and one 3 GHz travelling wave (TW) buncher with variable phase velocities. The electron beam is emitted from a 140 KV DC gun. Since the macropulse beam current (3.5 A) at the exit of the TW buncher is rather high, inside the TW buncher one has to take the beam loading effect into consideration. By using PARMELA, it is shown numerically that the bunching system can provide the bunches whose properties satisfy the design requirement of CTF3. The 0.8 m long TW buncher working at 2pi/3 mode has two phase velocities, 0.75 and 1. The dimensions of the caities in the two phase velocity regions are proposed considering the beam loading effect. The transient beam loading effect and the multibunch transverse instabilities are studied numerically, and it is concluded that higher order mode couplers should be installed in the TW buncher with the loaded quality factor of the dipole mode lower than 80.Comment: 5 figures, presented at the Linear Accelerator Conference 2000, August 2000, US

Density narrowing effect in the collisional cluster scattering of the light by gases

The spectral intensities of a collisional cluster scattering band in CF4 gas have been computed using molecular dynamics. Several densities from 20 to 269 Amagat as well as several models of interaction induced polarizability and of intermolecular potential have been studied. A qualitative agreement with experimental results has been obtained showing the narrowing effect of the gas density on the two-body line shape of the collisional cluster Raman band

Collision induced light scattering in the far Rayleigh wing of gaseous nitrogen

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Isotropic and anisotropic interaction induced scattering in liquid argon

The collision induced scattering (CIS) spectra have been studied for liquid argon at 130 K and 615 amagat. For the first time, isotropic CIS intensities are measured and the depolarized CIS spectrum is obtained up to 370 cm−1. Molecular dynamics simulations are performed for several models of polarizabilities and intermolecular potentials. They show that theoretical polarizabilities deduced from self consistent field calculations are in agreement with both depolarized and isotropic CIS experimental spectral shape

Multipolar polarizabilities from interaction-induced Raman scattering

In this chapter the authors first give a general presentation of collision-induced scattering (CIS), also named interaction induced scattering. The different types of molecular interaction are mentioned, with a special emphasis on the multipolar polarizabilities contributions studied in the authors\u27 laboratories since the beginning of 1990s. The authors describe the setup and the experimental procedure used for the measurement of the scattering on an absolute scale. They also discuss the multipolar contributions to depolarized and isotropic CIS for specific molecular symmetries. Studies in the Rayleigh wings of isotropic molecules such as CF4 and SF6 and of linear molecules such as N2 and CO2 are presented. The authors also report on observations made in the wings of vibrational Raman bands of CF4 and SF6

Collection Angle Dependence of the Depolarization Ratio in Light Scattering Experiments

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High order polarizabilities from optical interaction-induced Spectroscopy

Multipolar polarizability contributions to the collision-induced light scattering spectra of optically isotropic molecules may be put in evidence in the Rayleigh wings and in the vicinities of the v1 Raman vibrational lines. Experiments on CH4 or CF4 (tetrahedral symmetry) and SF6 (octahedral symmetry) make possible evaluations of the multipolar polarizabilities provided that isotropic Rayleigh spectra and anisotropic Raman bands are obtained in some relatively large frequency ranges. These evaluations — in particular those based on set inversion analysis — constitute experimental references for quantum chemistry computations of the multipolar polarizabilities. In the case of CH4, CF4 and SF6, the agreement between experimental and ab initio values is quite good

Collision-induced scattering in CO2 gas

Carbon‐dioxide gas rototranslational scattering has been measured at 294.5 K in the frequency range 10–1000 cm−1 at 23 amagat. The depolarization ratio of scattered intensities in the frequency range 10–1000 cm−1 is recorded. The theoretical and experimental spectra in the frequency range 10–470 cm−1 are compared. The anisotropic double differential cross section for scattered light is calculated theoretically considering first‐ and second‐order dipole‐induced dipole, first‐order dipole–induced octopole, and first‐order dipole–dipole–quadrupole light scattering mechanisms as well as their cross contributions