M. R. Masullo

Preliminary results on dielectric mirror damage due to the radiation of a high K undulator

Abstract Due to the high K value (4.8) of the LELA undulator, we expect a significant UV induced damage of TiO2SiO2 dielectric mirrors. Preliminary tests on commercial grade mirrors exhibit a great loss of reflectivity, due to two distinct processes of induced degradation. One of them is surface absorption of carbon in the upper SiO2-air interface. It is not affected by annealing. The other corresponds to a volume damage induced by the high energy radiation present during injection into the accelerator or during the runs at 1.5 GeV for synchrotron radiation production.

Final report on the LELA experiment

Abstract Progress in the LELA (free electron laser on ADONE) experiment from September 1986 to July 1987 is described. Improvements in machine lattice and control, and automation in cavity alignment allowed for a maximum Q factor of ≈ 103.

Optical cavity alignment and mirror damage in the LELA FEL experiment

Abstract The alignment of the LELA optical cavity, 17.5 m long, is described. The procedure to attain a close alignment of the undulator radiation axis and the cavity axis using an external laser is reported. Measurements of Q from stored light spectra are presented. Mirror degradation at increasing integrated electron currents is considered.

Progress report on the LELA experiment

Abstract After the installation of the optical cavity of the LELA experiment, a series of tests of the cavity alignment relative to the electron beam direction has been performed, showing the problems due to the peculiarity of this cavity. The use of piezoelectric translators in ultrahigh vacuum has permitted a smooth and precise control of the cavity optical axis. Preliminary results on mirror damage due to UV radiation have also been obtained.

Optical cavity of the Adone FEL experiment

Abstract A detailed description of the parameter choice for the LELA optical cavity is presented. Particular attention has been devoted to the alignement problems solved by means of a remote control system. First results on mirror damage due to UV radiation will be also reported.

Beam steering and orbit control at DAFNE

The commissioning phase without experiments of DAFNE, the Frascati double ring F-factory, has been completed. Single bunch luminosity exceeding cm -2 sec -1 has been obtained. Accurate beam position control is mandatory for luminosity achievement. Each ring, 100 m long, is equipped with 45 Beam Position Monitors and 31 correctors per plane. The integer part of both betatron tunes is 5. The closed orbit of the two Main Rings of DAFNE is essentially dominated by the magnetic cross-talk between the two rings due to fringing fields of dipoles and wigglers, the cross-talk between some of the transfer line magnets and the rings, and the effect of the ion clearing electrodes in the electron ring, since the residual misalignments of the magnets are much better than the required tolerances. The horizontal reference for the closed orbit is complex because of the off-axis trajectories in the interaction regions (IR), the splitters which separate the two beams at the IR ends, the presence of wigglers, and finally the four different types of dipoles. The line along which quadrupoles and sextupoles have been aligned corresponds to the line defined by the nominal bending radius of the dipoles, and this line is taken as reference for the closed orbit. The aim of the closed orbit correction is the optimization of the coupling and the exact overlap of the two beams at the interaction points (IPs). Several closed orbit correction methods have been implemented and used: best corrector method, harmonic method, orbit decomposition by eigenvalue of the measured Response Matrix. Coupling of the order of few , well below the 1% design value, has been achieved in both rings, by correcting the vertical orbit within mm and the horizontal one within mm with respect to the reference line. Coupling tuning over a large range is easily obtained using the skew quadrupoles. The vertical overlap of both beams at the IP, critical since the vertical dimension of the interacting bunches is 20 mm, is obtained with localized steering bumps with 5 mm accuracy.