MeV Microtron Research Articles

A High Power Low Cost S-Band Waveguide Load for Accelerator Applications

The design and constructional aspects of a dissipative wall waveguide load in S-band are described. The load is fabricated for the high power microwave transmission line of 20 MeV Microtron. A mixture of cement and graphite is used as an attenuating material. A low VSWR could be obtained by providing linear taper along the length of the waveguide. Power dissipation per unit length in the load is kept almost constant and the dissipated heat is removed by circulating water. The load can be operated up to peak power of 5 MW and average power of 500 W. The VSWR of the load is better than 1.1 at the operating frequency of 2.856 GHz.

Theoretical and experimental aspects of a waveguide FEL

The dispersion properties of a guiding structure give rise to new kinematic and dynamic properties of a waveguide FEL. These new features are discussed in the small-signal small-gain approximation both in the homogeneous and inhomogeneous broadening regime, together with the outputs of a simulation code. The design of a compact waveguide FEL in the millimeter spectral range to be tested on a 5 MeV microtron FEL facility is also presented.

A far-infrared quasi-optical resonator for a Cherenkov free electron laser

A Cherenkov free electron laser experiment (Ch-FEL) employing a 5 MeV microtron electron-beam source and providing coherent radiation in the spectral range from 100 to 1000 μm is under way in our laboratories. Recent tests of a quasi-optical resonator are reported.

Recent results of the ENEA-Frascati undulator FEL experiment

An undulator free-electron-laser experiment (U-FEL) is under way at the ENEA-Frascati Center. The U-FEL employs a 20 MeV microtron as electron-beam source and operates in the middle infrared region around 30 μm. Recent results on the spontaneous-emission measurements are discussed.

ASTRID - The Aarhus Storage Ring

A small heavy-ion storage ring is presently under construction in Aarhus. The ring will be injected with singly-charged low-energy ions from a 200 kV ion accelerator and at a later stage with multiply-charged high-energy ions from an EN tandem accelerator. Conversion of the ring into a synchrotron radiation source by the addition of a 100 MeV microtron electron injector is now in the planning stage.

A Cherenkov infrared laser

Successful production of microwave radiation by Cherenkov masers has prompted an investigation into their feasibility for submillimeter and far infrared wavelength generation. A theoretical examination of output parameters such as frequency and small signal gain has been conducted for an easily fabricated resonator geometry. The resonator consists of two parallel plates, each with a thin (0.5 to 3 μm) dielectric coating, separated by 2 mm. This waveguide will support TM modes which are coupled to a relativistic electron beam propagating between the plates. While the interaction of the electrons with the dielectric causes spontaneous Cherenkov emission, the difference between the beam velocity and the phase velocity of the mode causes a bunching of the electrons which is responsible for further stimulated emission. The frequency of the generated radiation is determined by the dispersion relation of the waveguide mode. Gain is calculated assuming the effects of space charge modes are negligible, i.e., operation is in the Compton regime. Our results indicate that such a “double-slab” resonator will provide detectable levels of infrared radiation from a midly relativistic (3–10 MeV) electron beam. The theoretical analysis is undertaken in preparation for a series of experiments to be conducted at the ENEA facility in Frascati, Italy, where a 5 MeV microtron accelerator will be used to produce radiation in the 10 to 100 μm range. A suitable choice for the dielectric material would be polyethylene, both because of its low dielectric constant (2.2) and its relatively low loss in the infrared. A detailed discussion of the design choices will be presented.

A 25 MeV microtron for the establishment of absorbed dose standards

In this paper, a 25 MeV microtron which is mainly used for the establishment of absorbed dose standards is described. Its main parameters, construction and beam adjustments are given.

Six years experience in the use of a 10 MeV microtron for radiation therapy.

The use of the first 10 MeV microtron for radiation therapy is described. After six years and about 2500 patient treatments, an evaluation of the performance and properties of this kind of treatment unit is presented. The number of patients with specified tumor sites and treatment modality, and the number of working days lost due to failure of the machine per year, are given and the quality control programme is presented.

Performance of the 800-MeV Injector for the Bessy Storage Ring

The injector for the BESSY storage ring is an 800 MeV synchrotron with a 20 MeV microtron as preinjector mainly manufactured by Scanditronix AB. The synchrotron was designed as a separated function machine. The bending magnets, the focussing and the defocussing quadrupoles are powered by three independent Whitecircuits. These circuits are phase-locked to each other via a microprocessor. The repetition rate of the synchrotron is 10 c/sec. The max. extracted current measured at 570 MeV was 12 mA/50 ns. The emittance was ?x 1.6 × 10-6 ?m rad, ?y = 0.25 × 10-6 ?m rad. The energy was changed to 776 MeV in August 1982. The extracted current was 7 mA/50 ns.

The Control System for the Dedicated Synchrotron Radiation Storage Ring Bessy

BESSY is a 800 MeV electron-storage ring dedicated to research with synchrotron radiation in the VUV and soft X-ray region. The storage ring is fed by a 800 MeV separated function synchrotron with a clasical 20 MeV microtron as preinjector. The machines are remotely controlled by four minicomputers which are linked by a local network. The computers are connected to a commercially available electronic interface system. The general philosophy for the system design was determined by boundary conditions such as reliable processor hardware, reliable and powerful multi-user multi-programming real-time operating systems, well developed software tools, a ready-to-use distributed network with high throughput, compatibility of the electronic interface system, locally available service shops, and, if possible, the avoidance of assembly coding. This paper describes in detail the system which ultimately met these criteria and was subsequently implemented at BESSY.

Progress in the FEL Project at the C. N. E. N. Frascati Center

We present the essential features of the 20 ÷ 30 MeV microtron single pass FEL (oscillator) project developed at the C. N. E. N. Frascati Center for high average power infrared radiation generation (? = 10 ÷ 30 ?m).

Status of the Aladdin Project

The first description of an electron storage ring designed specifically to be a source of synchrotron radiation appeared in the proceedings of an earlier meeting in this series.1 We now report on the status of the 1 GeV electron storage ring Aladdin which is a development of the earlier work cited. This machine, now nearing completion, will be an intense source of synchrotron radiation over the wavelength range extending from the far infrared (100?) to the Berylium window cut-off (~3A). The machine incorporates a number of novel design features: a 100 MeV microtron injector, a simple but powerful computer based control system and an extremely flexible lattice.

Initial experience with the first 22 MeV microtron for radiation therapy

Initial experience with the first 22 MeV microtron for radiation therapy

SURF's up at NBS: A Progress Report

The NBS Synchrotron UV Radiation Facility (SURF-II) is a 250 MeV single-magnet, weak-focusing electron storage ring, with 10 MeV microtron injector. Circulating beams of up to 35 mA at energies up to 250 MeV have been achieved. Beam lifetime, limited by Touschek effect, is extended to several hours by resonant vertical rf excitation. At low energies bunch shape oscillations occur, involving coherent synchrotron oscillations, negative-mass-type blowup and loss of beam. Effective avoidance and suppression techniques are discussed. A new set of high current gradient correction coils and power supplies, plus additional pancakes for the main field coils are being obtained. These are expected to extend SURF operation to 280 MeV and provide useful light output to 0.4 keV photon energies.

The 13.5 MeV microtron facility at Catania

The 13.5 MeV microtron facility at Catania

Radiation beam characteristics of a 22 MeV microtron.

The properties of the electron and photon beams from a 22 MeV clinical microton are presented. Favourable isodose distributions for radiation therapy are obtained for both modalities. For the electron beam this is accomplished using a dual scattering foil system in which the secondary foil is shaped to optimize uniformity and minimize energy loss and energy straggling. The photon beam is flattened by a composite filter to produce dose distributions of high uniformity over a wide depth interval.

Application of the 30 MeV microtron for gamma and neutron activation analysis

Based on studies of variable multiplicity electron acceleration, the power-current microtron, a cyclic electron accelerator up to energies of 30–35 MeV has been developed at the Institute on Physical Problems of the Academy of Sciences of the USSR. The 1–1.5 kW electron beam of the microtron is comparable to the power output of modern linear accelerators operating at similar energies. At the same time, the microtron has a number of significant advantages, due to the simplicity of design of both accelerator and ultrahigh-frequency tract, the high efficiency of ultrahigh-frequency power utilization, good operating characteristics, strictly monochromatic electron beams (variations not exceeding ±50 keV at 30 MeV) and the possibility of continuously changing particle energy as required by the given experimental task.

A current transformer and gated integrator for measurement of weak currents from pulsed accelerators

Abstract A non-intercepting beam current monitor and a gated integrator are described which allow to measure peak currents down to about 1 μA from the PTB 5.8 MeV microtron. The monitor differs from similar circuits by using only one winding on a mu-metal core and by a special current-voltage converter of 40 mΩ input impedance.

Performance of the Illinois Superconducting Linac

The first section of the 1.3 GHz superconducting linac, being constructed for the proposed 600 MeV microtron, was installed into the cryostat and operated as an accelerator for the first time. An electron beam of 270 keV, chopped to a select phase spread of 6 degrees, was injected into the 3?/2 niobium structure and accelerated to 1 MeV with an input of 30 watts of microwave power at 4.2°K. The accelerated beam was 2 mm in diameter 3 meters beyond the accelerating section. The energy spread was less than 1%. The niobium section had not been outgass d at high temperature and had a Q of 1.4 x 108. The energy gain seemed to be limited to about 1 MeV per foot by field emission, as indicated by the rapid rise of the x-ray yield as the microwave power was increased.

Experimentelle Untersuchung der direkten Elektron-Positron-Paarerzeugung in Kupfer durch Elektronen von 5,8 MeV kinetischer Energie

The direct production of positrons by electrons in copper was investigated using the 5.8 MeV electron beam from the 6 MeV microtron of the Physikalisch-Technische Bundesanstalt. Cross sections were derived from the measurements under the assumption that the positrons produced directly and those produced indirectly by bremsstrahlung photons have the same angular distribution. The values obtained are greater than those calculated numerically by Lons by a factor of 1.3 to 1.45. It is shown that there is an essential contribution of direct positron production to the electron positron conversion factor in thin foils consisting of elements with low atomic number.