Jim Jan Botman

SRFEL dynamics investigated with a 1-D numerical code

Designing a Storage Ring Free Electron Laser or improving the performance of an existing one first requires investigation of its longitudinal dynamics. With this aim, a 1-dimensional model, including energy spread and Microwave Instability (MI) effects, has been implemented in a numerical code. The code solves the differential equations of the longitudinal complex amplitude of the intra-cavity electric field, coupled with the differential equations describing the evolution of the electron bunch energy spread and of the MI. The agreement with experimental results of the Super-ACO FEL is also discussed.

The "TEU-FEL" project

The free-electron laser of the TEU-FEL project will be based on a 6 MeV photo-cathode linac as injector, a 25 MeV race-track microtron as main accelerator and a hybrid, 25 mm period undulator. The project will be carried out in two phases. In phase one only the 6 MeV linac will be used, The FEL will then produce tunable radiation around 200 µm. In phase two the linac will be used as an injector for the microtron. The FEL will then produce tunable radiation around 10 µm. Technical information will be presented on the different subsystems.

Longitudinal detuning for an SRFEL

The interaction between laser pulse and electron beam of a storage ring free electron laser (SRFEL) can be described in the longitudinal phase space as a function of the longitudinal detuning, which we define as the delay per pass between the laser pulse and the electron bunch. SRFEL dynamics versus detuning is studied by comparison of measurements performed at Super ACO with a numerical code. Experimental phenomena regarding detuning have been properly predicted by simulations. Quantitative agreement for pulse duration, pulse repetition frequency, laser power, etc. has been found.

The Eindhoven linac-racetrack microtron combination

The Eindhoven linac–race track microtron (RTM) combination has been designed to serve as injector for an electron storage ring. The linac is a 10 MeV travelling-wave linac (type M.E.L. SL75/10). In the RTM a 5 MeV standing-wave cavity, which is synchronized with the linac, accelerates the electron beam 13 times, such that the extraction energy is 75 MeV. The RTM end magnets are two-sector magnets tilted in their median planes, to provide strong focusing forces for optimal electron-optical properties. Closed-orbit conditions are fulfilled with the help of small correction dipoles located in the RTM drift space; the magnetic-field strengths of these correction dipoles are adjusted on the basis of beam-position measurements. Isochronous acceleration is accomplished by position- and phase-measurements. A low-cost elaborate diagnostic system will be used for efficient commissioning of the combination of the 10 MeV linac and the 10–75 MeV RTM.

The 75 MeV racetrack microtron Eindhoven

The 10–75 MeV Racetrack Microtron Eindhoven (RTME) is designed to serve as injector for the electron storage ring EUTERPE. In RTME electrons are injected at 10 MeV by a travelling wave linac.

Matching the emittance of a linac to the acceptance of a racetrack microtron

A 10 MeV travelling wave linac will be used as injector for the 10-75 MeV racetrack microtron Eindhoven. The six dimensional emittance of the linac will be matched to the acceptance of the microtron. In longitudinal phase space the negative dispersive action of the first bend in the racetrack microtron is counteracted by the dispersive action of the doubly achromatic bending section in the transport line. The data for the longitudinal emittance are obtained from numerical simulations. The energy spread of the initial beam is larger than the energy acceptance of the racetrack microtron. It will be reduced with a slit system in a dispersive section of the transport line.

A tuning procedure for a racetrack microtron

The electron-optical system of the Eindhoven RTM has been designed and constructed with non-stringent alignment and machining tolerances in the order of 0.1-1 mm and 0.1-1 mrad. The alignment and machining errors that are present can and must be counteracted with slightly different settings of the seventeen adjustable parameters (i.e. the excitation currents of the two end magnets and of twelve correction magnets (one at every turn), the beam energy and phase at injection, and the energy gain per turn), otherwise the beam will not be accelerated properly. All the errors are unknown and consequently their effects are unknown. Therefore, twenty-five beam-position monitors (BPMs) have been installed in the RTM (two for each turn and one at the extraction point) in order to measure the effects of the errors on the electron beam. The responses of the beam-positions at the BPMs with varying values of the RTM parameters have been studied. Based on these studies a tuning procedure is proposed and its usability and performance has been investigated with numerical simulations of the accelerator.

Design and Construction of Standing Wave Accelerating Structures at TUE

Two standing wave accelerating structures have been built for the operation of two AVF racetrack microtrons (RTM). For the first RTM a 3 cell 1.3 GHz on axis coupled standing wave structure has been designed to accelerate a 50 A peak current beam in 9 steps from the injection energy of 6 MeV to a final energy of 25 MeV. The beam will be used as drive beam for the free electron laser TEUFEL. The second structure accelerates a 7.5 mA beam in 13 steps from the injection energy of 10 MeV, to a maximum energy of 75 MeV. This 9 cell on-axis coupled structure operates at 3 GHz and was designed with a relatively large aperture radius (8 mm) in order to avoid limitations on the RTM’s acceptance. Design, fabrication and testing of the structures have been done in house. For the design of the structures the combination of the codes Superfish and Mafia has been used. Low and high power tests proved that the structures live up to the demands. With the experiences gained a design for the accelerating structure of the H linac of the ESS project has been made. The design of the cells as well as a novel type of single cell bridge coupler will be presented.

The extraction orbit and extraction beam transport line for a 75 MeV racetrack microtron

A beam transport system providing dispersion matching of the beam from the cavity axis of a racetrack microtron to the injection position in an electron storage ring is described. For extraction the last bend in the 10-75 MeV racetrack microtron Eindhoven has been designed to be less than /spl pi/ rad. This is realised in a three sector dipole field for the last bend, as opposed to the normal two sector dipole held for the other orbits in the microtron. The combination of the last bend in the microtron and the first bending section in the beam transport line from the microtron to the 400 MeV storage ring EUTERPE forms a double achromat. The total transport line consists of two bending and two straight sections, with quadrupole doublets for transverse phase space matching between microtron and ring.