The new fourth-generation synchrotron light source SKIF is under development in Novosibirsk, Russia. It consists of a 3 GeV electron storage ring with extremely low emittance, a booster synchrotron, and a linear accelerator. The paper discusses essential aspects of the design of the 200 MeV linear accelerator for SKIF, its main characteristics, and parameters in different operation modes. Description of the linac systems is presented.

As the injector of the new fourth-generation SKIF synchrotron light source at the BINP SB RAS (Novosibirsk, Russia), the linear accelerator will provide a 200 MeV electron beam. A precise measurement of the beam is very important for the control of the linac and even the entire light source. A set of diagnostic instruments for tuning the linac and measuring the beam parameters starting from the electron RF gun to the output of accelerator has been designed. The instrumentation should cover the dynamic diagnostic range of 0.6 to 200 MeV and a beam duration from the initial 100 ps to 3 ps at the output of the accelerator. The set includes eight fluorescent screens to measure beam transverse size, two Cherenkov probes and RF-cavity sensors to record beam duration, a dipole magnetic spectrometer to measure energy and energy spread, a Faraday cup (FC) and fast current transformers (FCTs) to measure beam charge current, and beam position monitors (BPMs) to check the beam position. This paper aims to give an overview of the beam instrumentation and briefly describes the design and parameters of each diagnostic system. The results of numerical and dynamics simulations of some of the instruments are briefed. Possible scenarios of linac tuning are discussed.

High Order Modes (HOM) excited by the beam in a superconducting RF gun (SRF gun) could destroy the quality of the electron beam. This problem is studied on the base of frequency domain description by considering of the equivalent RLC circuit contour for each HOM, periodical excited by a pulsed current source [1]. Expression for the voltage, the field amplitude and the phase of the excited HOM has been obtained. The equations for the coupling impedances of monopole TMHOM and TE-HOM in the RF gun cavity has been derived. In this calculation the change of the particle velocity due to acceleration is taken into account. Resonance frequencies, coupling impedances, unloaded and external quality factors, excitation voltages and field distributions for each HOM including trapped HOM are calculated for Rossendorf SRF gun up to the frequency of 7.5 GHz, using the complex field solver CLANS. The dependence of the calculated parameters from a cavity deformation has been studied. The influence of the seven most dangerous HOM on the beam quality has been estimated by particle tracking using the ASTRA code.

A superconducting rf photo electron injector (SRF gun) is under development at the Forschungszentrum Rossendorf. The project aims at several issues: improvement of beam quality for the ELBE superconducting electron linac, demonstration of feasibility of this gun type, investigation of critical components, and parameter studies for future application . In 2005 - 2006, a substantial progress has been made. The two 3½-cell niobium cavities for the gun have been delivered from the company ACCEL. The main parts for gun cryostat like vacuum vessel, cryogenic and magnetic shields are ready. Test benches for the cathode cooling system and the cavity tuner are being assembled. The photo cathode preparation lab has been arranged, and the diagnostic beam line has been designed. After delivery of the gun cavities, their RF properties are being measured at room temperature and the warm tuning is being carried out.

The status of the Rossendorf superconducting RF gun is discussed. This gun allows continuous wave operation with an energy of 9.5 MeV and an average current of 1mA. The 31⁄2 cell niobium cavity contains a normal conducting photocathode. A special choke flange filter at the cathode side prevent the RF leakage of the cavity. The design of the cavity, the tuner, the RF coupler the LHevessel together with the cryostat is finished and now in manufacturing. In the paper three features are discussed, which follows from the special demands of the 31⁄2 cell superconducting RF gun. The first feature is the tuning system. For the cavity two different tuners are necessary, one for the half cell (gun cell) and one for the accelerating cells. The second feature is the tuning of the cathode. The beam properties depend very sensitive on the cathode position. Therefore a special cathode tuner has been developed, which allows to move and to adjust the cathode position inside the cavity. The third no conventional feature is the excitation of a second RF mode inside the cavity. This is a magnetic mode (TE mode) which replaces the static magnetic field in normal conducting RF guns and decreases the transverse emittance of the beam by more than a factor of two.