Jean-Pierre Labrie

Power handling capability of water cooled cw linac structures

Abstract To determine the ultimate cw power handling capability of room temperature linac structures under different cooling conditions, a prototype 2450 MHz on-axis coupled linac structure has been operated at power levels up to 210 kW/m corresponding to an average energy gradient of 3.5 MeV/m. Mechanical behaviour and changes in the rf parameters during high power operation are described and compared with results from computer modeling of thermal stresses.

An intense radiation source

Abstract A 10 MeV linear accelerator operating at 100% duty factor has been designed for large radiation processing applications. A beam intensity of 50 mA has the capacity to irradiate up to 1.3 MGy-Mg/h (130 Mrad-tonne/h) making it suitable for emerging applications in bulk food irradiation and waste treatment. An ability to provide high dose rate makes on-line detoxification of industrial pollutants possible. The source can compete economically with steam-based processes, such as the degradation of cellulosic materials for the production of chemicals and liquid fuels, hence new industrial applications are expected. The paper describes the main machine components, the operating characteristics and a typical application.

AECL IMPELA electron beam industrial irradiators

Abstract A family of industrial irradiators is being developed by AECL to cover an electron-beam energy range from 5 to 18 MeV at beam powers between 20 and 250 kW. The IMPELA family of irradiators is designed for push button, reliable operation. The major irradiator components are modular, allowing for later upgrades to meet increased demands in either electron or X-ray mode. Interface between the control system, irradiator availability and dose quality assurance is in conformance with the most demanding specifications. The IMPELA irradiators use a klystron-driven, standing-wave, L-band accelerator structure with direct injection from a rugged, triode electron gun. Direct control of the accelerating field during the beam pulse ensures constant output beam energy, independent of beam power. The first member of the family, the IMPELA 10 50 (10 MeV, 50 kW), is in the final stages of assembly at Chalk River Nuclear Laboratories. The IMPELA 10 50 is constructed around a 3.25 m long, high-power-capacity accelerator structure operated at a duty factor of 5%. Beam loading exceeds 60%. The rf power is provided by a 2 MW/150 kW modulated-anode klystron protected from load mismatches by a circulator. This prototype will be used to demonstrate the reliability and dose uniformity targets of the IMPELA family. Full beam operation of the IMPELA 10 50 is scheduled for early 1989.

A standing-wave structure for a synchrotron ring injector

Abstract A stand-alone linear accelerator is the simplest injector for a synchrotron ring. It is the appropriate choice for the injection of high current at high duty factors. This paper examines design parameters of a single-structure standing-wave linac, made from on-axis coupled cavities, operated in stored-energy mode, as a simple high-current, high-duty-factor, synchrotron ring injector.

Three-dimensional finite element heat transfer and thermal stress analysis of rf structures

Thermal expansion and thermal stress induced strain cause the detuning and limit the power level of radiofrequency (rf) structures. Two-dimensional finite element modeling has been used to determine the operating power limits of coupled cavity systems[1], but for complex high power accelerator structures without axial symmetry, a three-dimensional analysis is necessary. This paper describes results of a three-dimensional finite element temperature and thermal stress analysis. The analysis was performed for a high power coupled cavity linac structure operating at 1350 MHz. The results of the analysis are used to determine changes in the structure rf parameters as a function of power level and cooling water velocity.

High Power Electron Linac Structure

An on-axis coupled continuous wave (cw) electron linac has been designed for operation under 63% beam loading conditions. A prototype 2450 MHz linac structure has been constructed to determine operational stability at power levels up to 200 kW/m, corresponding to an average energy gradient of 3.5 MeV/m. Heat transfer from the structure to the cooling water has been optimized by computer modeling. Mechanical behaviour and predicted changes in the rf parameters during high power operation are described.

Experimental Comparison of Beam Excited Modes in Biperiodic Structures

An experiment to study excitations of higher order modes in a coaxial coupled structure and an on-axis coupled structure is in progress. The tuning and assembly of these structures is complete. Calculations have shown that a coaxial coupled structure is 5% less sensitive to beam excitation of its axially symmetric modes than an on-axis coupled structure. Low power tests have identified mode frequencies above the accelerating mode passband showing that higher order modes propagate in an on-axis coupled structure and not in a coaxial coupled structure. High power beam tests are scheduled for later this year.

Energy control of the IMPELATM series of industrial accelerators

Electron accelerator sources of radiation for industrial processes must maintain constant and reproducible irradiation parameters in order to provide satisfactory dose quality assurance. The advanced control system used in AECLs IMPELATM series of accelerators ensures this by making it possible to decouple the primary accelerator variables, beam energy and beam current. Beam energy is made independent of current by controlling the field amplitude in the standing-wave structure during a relatively long pulse (50–500 μs) and an energy stability similar to that of dc machines is achieved. Experiments with the calibration linac facility at Chalk River show that the beam energy can be held constant to within ± 2% on an absolute basis. This eliminates the requirement for the complex beam analysis after acceleration used on short-pulse linacs. Methods for the measurement of energy at the users site and at the calibration facility are described.

High flux bremsstrahlung source

Abstract A continuous wave (cw) linear accelerator designed to accelerate electron beams up to 50 mA intensity to an energy of 10 MeV is described. The high power electron beam can be converted into a high flux, forward peaked, bremsstrahlung source. The paper reviews the physics and engineering design of the accelerator and discusses problems associated with the acceleration of high power beams and their transformation into X-rays. The choice of the accelerator structure parameters, such as frequency, beam loading and energy gradient is discussed. A bremsstrahlung radiator, dissipating up to 500 kW of electron beam power, is described. Applications for the high flux bremsstrahlung source are suggested.