The transformation of the Saclay electron linac (ALS) into an injector for a 2 GeV stretcher ring is under study. One of the problems associated with this transformation is the use of the existing sections in a new mode of operation. The sections were ontimized for low current operation (high attenuation, high internal resistance), they will be used in a high current, short pulse(1?s) mode resulting in a prohibitive transient beam loading energy spectrum broadening. The compensation method used at SLAC, wich consists in delaying the turn-on of some klystrons, has been studied theoretically and an experiment has been performed with a 1?s pulse, at the same beam loadinq level as for the future plans.

Transient Beam Loading Calculations and Experiment at the Saclay Electron Linac

The interaction of a beam with the deflecting modes of the cavities can make it unstable when the energy transferred to the mode is greater than the power lost in the walls. In a single cavity, the mechanism of the regenerative beam breakup has been clearly described. In the case of multiple passes the instability appears at a level of current in general much lower and is indeed the most severe limitation. The current threshold was evaluated earlier either in the impulse approximation or considering only one cavity where the mode is supposed to be excited ignoring the other cavities. The purpose of this paper is to take into account the effects of all the cavities whose deflecting mode frequencies coincide or overlap. The analysis is based upon the theory of the stability of the feedback systems and a simulation code in the time domain confirms the results. The only restrictive assumptions are the following: the displacement of the beam is supposed not to vary inside a cavity and the structure of bunched beams is neglected. A similar feedback analysis involving discrete-time systems which takes into account the bunched structure of the beam showed that the values of the BBU currents are exactly the same if the frequency of the deflecting mode does not coincide with the harmonics of the repetition frequency of the bunches [14].

Analyse de la stabilite de faisceau dans un accelerateur lineaire avec passages multiples en prenant en compte les effets de toutes les cavites

A new control system for the Saclay Linear Accelerator is now being designed. The computer control architecture is based on 3 dedicated VME crates with MC68000 micro-processors : one crate with a disk-based operating system will run the high level application programs and the data base management facilities, another one will manage the man-machine communications and the third one will interface the system to the linac equipments. Communications between the VME microcomputers will be done through 16 bit parallel links. The software is modular and organized in specific layers, the data base is fully distributed. About 90% of the code is written in Fortran.

The New Control System of the Saclay Linear Accelerator

Calculations of bealn power losses and equilibrium temperatures of the wtres of an e1ectrostati.c septum have been carried out. The occurence of an electromagnetic shower has been examined in the case of a metal foil septum and the longitudinal profile of the beam power losses is given.

Electrostatic Septum in a High Intensity Electron Accelerator

The transformation of the Saclay electron linac facility (ALS) into a 2 GeV, 100 ?A CW electron facility is described. Polarized electrons will be available in the whole energy range. In order to reach the required performances, the linac is rebuilt with new klystrons and with the addition of a partial recirculation. The 100 % duty cycle is obtained with a stretcher ring.

M. Jablonka

Papers

ALS II: The Saclay Proposal for a 2-GeV, CW Electron Facility