Pre-injector

linac | transfer line 1

Linac
The ESRF Preinjector is a 200 MeV linear accelerator which was ordered as a turnkey system.

This linac essentially consists of a 100 keV triode gun, a short standing wave buncher section and two 6 meter long 2/3 accelerating sections. The two RF modulators, each equipped with a 35MW Thomson TH2100 klystron, are operated at 10 Hz, whereas the gun is triggered either at 10 Hz or at 1 Hz. An important parameter in the design of the linac was the high stored energy in the accelerating section in order to obtain the relatively high peak current without too much broadening of the energy spectrum due to beam loading.

There are two distinct modes of operation of the linac. The first mode corresponds to multibunch operation of the storage ring and in this mode the linac delivers a 1µs electron bunch to the booster, thus filling the whole booster circumference. In the second mode of operation a 2 ns beam pulse of the linac will fill only one RF bucket of the booster, to allow for single bunch operation of the storage ring. The corresponding beam characteristics of the linac are as follows :

The installation of the linac begun in January 1991, and the commissioning took place in June later that year.At that stage the contractual beam characteristics for long pulse operation were obtained by the contractor, so that the booster commissioning could start in August 1991. Commissioning was resumed in January 1992 to finish the 2 ns operation mode.

During the Booster commissioning and, especially during the initial phase of the storage ring commissioning, the linac proved to be insufficiently reliable in the state it was in as delivered by the manufacturer. The ESRF therefore carried out some modifications on the gun modulator, which was revealing thermal problems and on the modulators to get rid of the electromagnetic noise responsible for the random tripping of the local linac control. Some of the major work involved over the next two years was the replacement of the old fashioned CGR control system by a full ESRF standard interface system and replacement of the pulse forming network. This work resulted in a higher reliability of the linac and ease of control from the control room.

TL1 : Transfer Line 1

The Transfer Line between the Linac and the Booster is 16 meters long. It includes two 15 degree dipole magnets and seven quadrupoles. In the straight between the two dipoles energy selection slits are installed. Steering of the beam along the Transfer Line is done with two pairs of steerer magnets, with the position of the beam controlled using four fluorescent screen monitors. The individual Transfer Line elements were purchased from industry and the assembly of the line was entirely done by the ESRF. The Transfer Line was installed early 1991 so that it became fully operational for the Linac commissioning.

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