C.J. Timmermans

A linear accelerator as a tool for investigations into free radical polymerization kinetics and mechanisms by means of pulsed electron beam polymerization

Abstract The use of electron irradiation in polymer research for polymer modification is a well known method. Recently the technique of pulsed electron beam polymerization has been introduced as a tool for investigations into the kinetics and mechanisms of free radical polymerization. The technique can be applied to homogeneous and in particular to heterogeneous polymerization systems such as an emulsion polymerization. The major advantages are: (1) no limitation to optical transparency of the system; (2) no additional initiator is required. The 6 MeV linear accelerator (linac) at the Cyclotron Laboratory of the Eindhoven University of Technology is used for the present investigations. In this contribution, the accelerator set-up will be described and pulsed electron beam polymerization experiments will be used to illustrate the new technique. The irradiation set-up operates with pulse repetition rates between 1 and 50 Hz at a monitored dose per pulse adjustable between 0.1 and 3 Gy. The reaction temperature can be varied up to 100°C. Results of the current investigations in the polymerization of styrene in bulk and methyl methacrylate in emulsion will be presented.

Design study of the storage ring EUTERPE

Abstract At present the 400 MeV electron storage ring EUTERPE is being constructed at the Eindhoven University of Technology. It is a university project set up for studies of charged particle beam dynamics and applications of synchroton radiation, and for the education of students in these fields. The design of the ring is described in this paper. Considering the requirements of users in different fields, a lattice based on a so-called triple bend achromat structure with a high flexibility has been chosen. With this lattice, different optical options, including the HBSB (high brightness, small beam), the SBL (short bunch length) and the HLF (high light flux) modes can be realized. A small emittance of 7 nm rad and a short bunch length of the order of several mm can be achieved. In the first phase the synchrotron radiation in the UV and XUV region (the critical wavelength is 8.3 nm) will be provided from the regular dipole magnets. Later on, a 10 T wiggler magnet and other special inserters will be added, and other applications and beam dynamics studies will be feasible. Bending magnets are of the parallel faced C configuration. The effective aperture of the vacuum chamber is 2.3 cm (vertical) in the bending magnets and 4.7 cm elsewhere with a working vacuum condition of 10 −9 Torr. Collective effects have been studied initially. First calculations indicate that a lifetime of several hours, influenced by the Touschek effect and residual gas scattering will be achievable for a 200 mA beam in the HLF mode for the standard rf parameters. A 70 MeV racetrack microtron will serve as injector for the ring.

Modification of a medical linac to a polymer irradiation facility

A linear accelerator for X-ray therapy has been modified to generate a 5 MeV pulsed electron beam. The main objective is to irradiate polymeric materials in open air in order to alter their chemical and mechanical properties. To meet the radiation protection standards a shielding has been built round the target. Safety is guaranteed by a fail-safe secured programmable logic controller (PLC) monitored by a personal computer. The accelerator can be monitored and controlled by a graphics oriented and menu driven program running on the personal computer. In addition, a control panel has been designed and built to show warning signals and to set various linac parameters. A description of the accelerator modification and of the new control system is presented.

Fringe field calculations for the inhomogeneous Twente Eindhoven microtron magnets

Abstract The Twente Eindhoven microtron, a 25 MeV electron source for a 10 μm free electron laser has inhomogeneous magnetic fields to improve the focusing properties of the microtron. In order to design the shape of the magnets, the fringe field properties like the effective field boundary and the defocusing force in the vertical plane, have been determined. In this paper we compare these properties obtained by measurements, numerical calculation using the POISSON group of codes and by a theoretical treatment of the fringe field. We considered both a dipole configuration including a coil and a magnet configuration with a sudden change of the gap. For the analytical treatment of the fringe field we use t the geometry of the considered pole boundary to a simpler boundary where the Laplace equation can be solved easier. The magnetic field is calculated by the potential at the pole boundaries. The effect of the coil is simulated by choosing a linear potential change along the coil axis. Saturation effects are not included.

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.

Beam positioning and monitoring in the racetrack microtron Eindhoven

A scheme to compensate for the effect of misalignments in the racetrack microtron Eindhoven is presented. An array of small dipole magnets will be employed to obtain closed orbits. These dipoles are located at the symmetry axis of the microtron, in the drift space between the two bending magnets. For each orbit a radial stripline beam position monitor (BPM) will be installed in the field free region. The strength of the corrector dipole magnet in the nth orbit is adjusted with the BPM signal in the (n+1)/sup th/ orbit. The design of the BPMs is described. It will be shown that a rectangular geometry has a distinct advantage over a conventional circular geometry since it is less dependent on vertical displacements of the beam. Expressions for the difference-over-sum signal are given and compared with that for a circular geometry. Results of measurements performed in a test bench on prototype BPMs are discussed.

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.

Electron beam focusing in a racetrack microtron by means of rotated two-sector dipole magnets

Abstract We present an unconventional method of electron beam focusing in a racetrack microtron (RTM). The RTM bending magnets have a two-sector shape (valley and hill) and are slightly rotated in their median plane in order to guarantee closed orbits. Then, isochronism is automatically fulfilled. Comparison between this new arrangement and a previous three-sector design, inspired by Froelich [1], shows that the focusing properties are greatly improved, e.g. regarding beam acceptance and construction sensitivity. We will give a detailed description of the two-sector layout, make a comparison with the three-sector magnet (acceptance and sensitivity) and give magnet parameters for optimum performance.

Geodetic concept for the storage ring EUTERPE

At present a 400 MeV electron storage ring EUTERPE is being developed at the Eindhoven University of Technology (EUT). It is a University project, set up for studies of beam dynamics, applications of synchrotron radiation and for the education of students in this field. The circumference of the ring is approx. 40 m with 12 dipoles and 32 quadrupoles. The critical wavelength of the emitted photon spectrum is 8.3 nm for the regular dipoles. The major ring components are being constructed at the own University Central Design and Engineering Facilities. The concept of the geodetical system and the instrumentation are briefly described.<<ETX>>

Numerical design and model measurements for a 1.3 GHz microtron accelerating cavity

Abstract As part of the free electron laser project TEUFEL, a 25 MeV racetrack microtron is under construction at the Eindhoven University. The accelerating cavity of this microtron is a standing wave on axis coupled structure. It consists of three accelerating cells and two coupling cells. Numerical field calculations for this cavity were done with the computer codes SUPERFISH, URMEL-T and MAFIA. Not only the accelerating modes but also the dangerous beam breakup modes were calculated with MAFIA. An aluminium, scale 1:1 model of the structure was made in order to measure various cavity properties. Field profiles were measured with the perturbation ball method. An equivalent LC-circuit simulation of the accelerating structure was made, which serves as a model for the interpretation of the results.