Microtron Research Articles

On Beam Blowup in a Racetrack Microtron

This paper reports on a preliminary theoretical study of the interaction of electromagnetic fields in the accelerating structure of a racetrack microtron with the transverse motion of electrons circulating through the structure. Basic equations of the transverse beam dynamics and of buildup of the deflecting modes are derived with the help of idealized models of a microtron as well as of the beam-structure interaction process. The dependence of the starting current for beam blowup -(BBU) on the parameters of the accelerator has been studied and some features of the Microtron Using a Superconducting Electron Linac (MUSL-2) of the University of Illinois were taken into account to make numerical calculations. It was shown that the starting current is extremely sensitive to the phase correlation between the returning beams and under some conditions can be much lower than that for a linac. The use of the thin magnetic lenses on each orbit helps to achieve higher values of the starting current.

Performance of a Multicavity Racetrack Microtron

Measured characteristics of both the extracted beam and the beam within the accelerator are given for a racetrack microtron with a three-cavity accelerating structure. Final beam energies of 9 to 15 MeV with currents up to 30 mA have been achieved by passing the beam six times through the cavities and beam energies of 4.5 to 7.5 MeV with currents up to 60 mA have been obtained after three traversals of the cavities. An improved injection system and magnetic guide field design are described, and the suitability of this type of machine for radiation therapy is considered.

The Racetrack Microtron as a Negative Pion Source for Radiotherapy

The Racetrack Microtron as a Negative Pion Source for Radiotherapy

A Variable Energy Racetrack Microtron

A racetrack microtron whose energy may be varied continuously from 4.5 to 18 MeV has been built at the University of Western Ontario, and has been operated to full energy. Electrons from an external electron gun are injected with an electrostatic inflector, and accelerated in a short sidecoupled linac section. The RF power delivered to the linac section can be varied by means of a power splitter, thus allowing the energy gain in the section to be adjusted continuously from 1.5 to 3 MeV. The accelerator can be operated in three different modes: single traversal of the linac section with a final beam energy of 1.5 to 3 MeV, n = 2 with three traversals of the linac covering the final energy range from 4.5 to 9 MeV and n = 1 with six traversals of the linac and a corresponding energy range of 9 to 18 MeV. The magnetic guide field consists of two 180° magnets with alternating high and low field regions. To satisfy the resonance conditions the average induction can be varied up to 0.6 T and the lengths of the drift space between the magnets can be adjusted by moving the pole pieces of the magnets.

Experience in Recirculating Electrons through a Superconducting Linac

An electron beam of several microamperes has been accelerated by a 6 foot 1.3 GHz superconducting niobium linac to 3.5 MeV on its first pass. It has been returned to the linac for two additional passes with energy gains around 3 MeV per pass to a final energy of 9.5 MeV. The recirculation is accomplished by means of two uniform field magnets placed at each end of the accelerating section in a racetrack microtron geometry which will accommodate the return beams for six passes through the linac.

Stability conditions for the spatial focusing in a racetrack microtron

The free parameters available to obtain a beam of limited extension in a racetrack microtron are investigated and discussed. The obtained result may be thought as a generalization of the analogous synchrotron problem. First order transfer matrices will be used to approach the problem. The influence of possible approximations will also be discussed.

Design of a 600 MeV Superconducting Microtron

The design of a 600 MeV racetrack microtron proposed for the University of Illinois consists of a 30 MeV superconducting linac operating at 1.3 GHz between two uniform field bending magnets about 6.4 meters apart. There will be 19 parallel return paths separated by 14.7 cm. Vertical focusing is provided on each return orbit by a quadrupole pair close to each magnet. For quadrupoles 20 cm long and separated by 10 cm, the gradients required to advance the vertical oscillation phase by 90° per revolution increase monotonically from 150 to 350 gauss per centimeter. Only very weak horizontal focusing powers are needed to keep the return beams within 2 mm of linac axis. The linac itself provides some focusing but two weak quadrupole singlets on the linac axis, one near each magnet, provide additional focusing. Electron trajectories for all traversals through the linac and the magnets have been calculated in detail, by a step by step procedure where required, and are presented here. These results confirm earlier, less complete, calculations indicating that the microtron design parameters are not critical and that an output energy resolution of one part in 104 is easily obtainable.

879. Argon resonance line lamp for vacuum ultraviolet photochemistry: A L Lane and A Kuppermann, Rev sci instrum, 39 (1), 1968, 126–127.

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.

892. An electrron bombardment weak-field ionizer for polarized ion source: G A Vasilev and E A Glasov, Nucl Instrum Methods, 58 (2), 1968, 303–306

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.

A minimum volume microtron magnet

A description and equations are given for an analytically-based 180° racetrack microtron magnet of minimum volume with independent pole and yoke construction.

Design of a high energy, high duty cycle, racetrack microtron

The design of a split-magnet racetrack microtron with a maximum final energy between 400 and 600 MeV is considered. Detailed calculations of the beam optics are presented. It is shown that adequate focusing can be provided by quadrupoles placed on the individual orbits. The phase stability of the device is investigated. The phase stable region is sufficiently large so that the tolerances on the homogeneity of the magnetic field and stability of the accelerating voltage are reasonable. As the result of phase focusing, the energy resolution of the microtron is on the order of 10 −3. Design parameters for a conventional (non-superconducting) rf system are given. Depending on the choice of an rf power source, the proposed microtron can provide an average current at maximum energy of 50 to 100 μmA at a duty cycle of 3 to 6%. At 200 MeV the average current is 75 to 200 μmA and the duty cycle is 10 to 30%. In comparison with an electron linac using a comparable amount of average rf power, the energy homogeneity and duty cycle of the microtron are superior by an order of magnitude. In addition the microtron is considerably more compact and is less expensive to build.

A method for stabilizing particle orbits in the race-track microtron

Axial stability and synchronism of particle motion in the race-track microtron can be attained by a simple correction of the magnet fringing fields.

Four-Sector Racetrack Microtrons

Racetrack geometries of the guide field are capable of freeing the microtron type of electron accelerator from its inherent limitations. Two completed racetrack microtrons of 2.5 and 6.3 MeV energy are described. A possible application of the design features of these accelerators to microtrons of up to 50 MeV is discussed. Preliminary results of a design study for a 200 MeV racetrack microtron are presented.

Generation of submillimeter radiation by a racetrack microtron beam in a Fabry-Perot resonator

Submillimeter radiation from 0.5 mm to 1.0 mm wavelength has been generated by means of a 6 MeV electron beam exciting a Fabry-Perot resonator. With a beam current of 4 mA, power levels of 10/µW to 50 µW were obtained in each harmonic of the fundamental 2800 MHz accelerating frequency.

Proposal for a new high-intensity microtron

Proposal for a new high-intensity microtron

Generation of millimeter waves with a racetrack microtron

A 6-MeV racetrack microtron has been used to generate millimeter radiation with a Fabry-Perot radiator having no dielectric medium. The electron beam is injected at an angle to the axis of the Fabry-Perot in order to achieve interaction with the transverse electric field in the cavity. Radiation is coupled out of the cavity in the zero order of a reflection grating used as one end plate. Radiation resistances of the order of one kilohm are obtained at 4 mm. A corresponding submillimeter design is shown.

Energy Spectrum of the Electron Beam in a Racetrack Microtron

The energy spectrum of the beam of a four-sector racetrack microtron has been measured here, using a high-resolution double focusing beta-ray spectrometer. For an energy gain per orbit of 750 keV, it was found that 50% of the integrated current in the eighth orbit (6 MeV) was contained in an energy interval of 34 keV and 90% of the beam current in a 73-keV interval. This narrow energy spread (±0.3%) is of particular interest in the generation of submillimeter radiation and in the use of the microtron as an injector for high-energy synchrotrons.

The microtron and areas of its application

The microtron and areas of its application

On the possibility of producing and accelerating positrons in a microtron

On the possibility of producing and accelerating positrons in a microtron

On the possibility of producing and accelerating positrons in a microtron

On the possibility of producing and accelerating positrons in a microtron