Michel Abs

The Rhodotron, a New 10-mev, 100-kw, Cw Metric Wave Electron-accelerator

New applications for high energy, high current electron beam processing are continually expanding. Today, however, 10 MeV rf electron linacs are frequently limited to an average beam power of only 20 or 30 kW. To achieve higher beam power, CW operation and the use of lower frequencies are necessary. In the last years, the principle for a new kind of electron accelerator was developed by the Atomic Energy Agency (CEA) in France. This accelerator is based on the principle of recirculating a beam throughout a single coaxial cavity resonating in metric waves. A 3.3 MeV, 4 mA prototype has been built and successfully tested. The industrial accelerator developed by IBA in collaboration with the CEA is a 10 MeV, 100 kW beam power unit with an additional beam exit at 5 MeV. The cavity, made of copper-plated steel, will resonate at 107.5 MHz. A rf power of 100 kW is needed to produce an electric field allowing an energy gain of 1 MeV per crossing. In addition, 100 kW of power is needed for acceleration. The 200 kW output amplifier uses a 100 kW plate dissipation tetrode (TH 681 from Thomson-CSF) in a grounded grid configuration. In this paper, the design of the new model as well as the prototype manufacturing schedule are presented in more detail.

THE SELF-EXTRACTING CYCLOTRON

At IBA a compact 14 MeV H+ cyclotron has been constructed. A special feature of this cyclotron is that there is no electrical deflector installed, i.e. the beam is self-extracted. The goal is to obtain high beam currents with good extraction efficiency without the need of single turn extraction. This is achieved with two ingredients: i) a special shaping of the magnetic field, showing a very steep fall-off near the outer radius of the pole and ii) the creation of a large turn-separation on the last turn. The pole gap has a quasi-elliptical shape, allowing for the steep fall-off of the magnetic field by the machining of a groove in one of the poles at a radius where the gap is small. The large turn separation is obtained by either the use of harmonic coils or by permanent magnet field bumps placed in two opposite valleys. Both methods have been tested and give good results with an extraction efficiency of 80%. The concept and layout of the machine is explained. The status of the project is outlined. First ...

The proton therapy system for the NPTC: Equipment description and progress report

At the beginning of 1994, the Massachusetts General Hospital (MGH) of the Harvard Medical School in Boston (MA, USA) a pioneer in proton therapy since 1959, selected a team led by Ion Beam Applications SA (IBA) to supply the proton therapy equipment of its new Northeast Proton Therapy Centre (NPTC). The IBA integrated system includes a compact 235 MeV isochronous cyclotron, a short energy selection system transforming the fixed energy beam extracted from the cyclotron into a variable energy beam, one or more isocentric gantries fitted with a nozzle, a system consisting of one or more horizontal beam lines, a global control system including an accelerator control unit and several independent but networked therapy control stations, a global safety management system, and a robotic patient positioning system. The present paper presents the equipment being built for the NPTC.

Technical status of the first industrial unit of the 10 MeV, 100 kW Rhodotron

The Rhodotron is a new type of industrial electron accelerator developed by IBA, Belgium, on the basis of the pioneering work performed by a French team at CEA, Saclay. The operating principle of this new technology makes it possible to easily produce high energy and high power electron beams. The combination of high energy and high current allows high product throughputs and/or the irradiation of thick structures in the electron mode. An X-ray target is also developed in such a way that the Rhodotron can also be operated in the X-ray mode while maintaining high dose rates. The construction of the first industrial unit (10 MeV, 100 kW) began in January 1992 and the first beam was obtained on October 29, 1993. This machine has now been tested at its full specifications. Technical performance data are presented in this paper.

The Rhodotron, a New High-energy, High-power, Cw Electron-accelerator

Over the last years, a new kind of industrial electron accelerator has been conjointly developed by the French Atomic Energy Agency (CEA) and IBA (Ion Beam Applications) in Belgium. This accelerator, called the Rhodotron, is a recirculating accelerator, operated in CW. It uses low frequencies (metric waves), that make possible the generation of continuous high-energy high-power beams. The construction of the first industrial model of the Rhodotron began in January 1992. It is a 10 MeV, 100 kW beam power unit, with an additional beam exit at 5 MeV. A target is also being developed in order to allow an efficient conversion of the electrons into X-rays. The different subsystems of this machine are now being assembled and tested. The first beam tests are scheduled for the autumn of 1993. A complete report presenting the state of development of this prototype is included in this paper.

A new design of truly selfshielding baby-cyclotrons for positron emitter production

The successful design of the Cyclone 30, a 30-MeV H/sup -/ cyclotron, gave birth to an original design of truly selfshielding baby-cyclotrons dedicated to positron emitter production. This new negative ion cyclotron will deliver 10-MeV protons and 5-MeV deuterons. Up to eight targets are located inside the circular return yoke of the magnet, which serves as a primary neutron and gamma-ray shield. The cyclotron is embedded in an additional neutron shield made of borated-hydrogenated material. One of the main goals of the design is the ease of access to the targets and to the cyclotron inner parts without compromising the shielding efficiency. Any combination of two opposed targets can be irradiated simultaneously. The size and weight of the proposed system are considerably reduced compared to those of existing cyclotrons.<<ETX>>

Status report of the development of a multi-mA self-extracted H+-beam cyclotron

In 1992, IBA developed a high intensity cyclotron for the production of Pd-103. Up to now 16 internal-target machines have been installed and are delivering 1 mA on average. Unfortunately such configuration suffers from two major drawbacks: i-little flexibility on the shape and size of the beam on target limiting the total power that target can tolerate, ii-activation of cyclotron components due to neutron production and primary-beam scattering. In 1995 IBA proposed a new method for the extraction of multi-mA positive ions [1] without the need of a deflector or a similar device. The extraction is obtained by a sudden and substantial reduction of the Lorentz force at the radial pole edge allowing the beam to escape from the machine (self-extraction principle). It was decided in 1998 to construct a prototype to test that extraction technology. This paper presents the status of the development. Focus is put on the RF system, ion source, magnetic configuration, and final layout.

Realignment of a diverging electron beam: a new beam delivery system for rhodotrons

Industrially useful electron beams produced at 300 keV or more are typically generated by introducing an oscillating magnetic field near the apex of a triangular scanning horn, thus creating a diverging treatment field. Product dosing is then accomplished by conveying target material through this field. For many irradiation applications this diverging beam introduces inefficiencies in beam power utilization and dosing non-uniformity. This paper presents beam delivery systems developed by IBA for Rhodotron accelerators and, in particular, a new scan horn for delivery of a non-diverging beam.

Development of the Cyclone® Kiube: A Compact, High Performance and Self-Shielded Cyclotron for Radioisotope Production

About 15 months ago, at IBA, we have launched the design, construction, tests and industrialization of an innovative isochronous cyclotron for PET isotope production (patent applications pending). The design has been optimized for cost effectiveness, compactness, ease of maintenance, activation reduction and high performances, with a particular emphasis on its application on market. Multiple target stations can be placed around the vacuum chamber. An innovative extraction method (patent applications pending) has been designed which allows to obtain the same extracted beam sizes and properties on the target window independent of the target position. INTRODUCTION This isochronous cyclotron for PET radioisotope production produces fixed energy 18MeV proton beam and is called the Cyclone® KIUBE, Figure 1. Today, three versions are available producing 100μA, 150μA and 180μA on target and the option with selfshielding is also available. Figure 1: CYCLONE® KIUBE.