W. Kleeven

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.

Overview of the IBA accelerator-based BNCT system

During the last few years, IBA started the development of an accelerator-based BNCT system. The accelerator is a Dynamitron built by RDI in USA and will produce a 20 mA proton beam at 2.8 MeV. Neutrons will be produced by the (7)Li(p,n)(7)Be nuclear reaction using a thin lithium target. The neutron energy spectrum will be tailored using a beam shaping assembly. This overview presents the current status of the system: after a description of every component, some design issues, solutions and experimental tests will be discussed.

High-intensity cyclotrons for radioisotope production and accelerator driven systems

IBA recently proposed a new method to extract high-intensity positive ion beams from a cyclotron based on the concept of auto-extraction. We review the design of a 14 MeV, multi-milliampere cyclotron using this new technology. IBA is also involved in the design of the accelerator system foreseen to drive the MYRRHA facility, a multipurpose neutron source developed jointly by SCK-CEN and IBA

Current performance of the self‐extracting cyclotron

The self‐extracting cyclotron is a 14MeV multi‐mA H+ machine from which the beam extracts without a deflector. The development of this prototype has started in 1998, and has now reached a point such that IBA considers to use it as a production machine. It is now installed in an irradiation facility and is equipped with two beam lines and two high power target‐system. Beams of more than 1 mA have been extracted and transported to targets Further development is ongoing in order to increase the current on target to at least 2 mA in the coming months. Commercial isotope production will start at the end of this year. This paper will describe the current configuration of the cyclotron and the associated performances. Emphases will be put on reliability and associated problems, beam optics and performances of sub‐systems.

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.

Cyclotrons: Magnetic Design and Beam Dynamics

Classical, isochronous, and synchro-cyclotrons are introduced. Transverse and longitudinal beam dynamics in these accelerators are covered. The problem of vertical focusing and iscochronism in compact isochronous cyclotrons is treated in some detail. Different methods for isochronization of the cyclotron magnetic field are discussed. The limits of the classical cyclotron are explained. Typical features of the synchro-cyclotron, such as the beam capture problem, stable phase motion, and the extraction problem are discussed. The main design goals for beam injection are explained and special problems related to a central region with an internal ion source are considered. The principle of a Penning ion gauge source is addressed. The issue of vertical focusing in the cyclotron centre is briefly discussed. Several examples of numerical simulations are given. Different methods of (axial) injection are briefly outlined. Different solutions for beam extraction are described. These include the internal target, extraction by stripping, resonant extraction using a deflector, regenerative extraction, and self-extraction. Different methods of creating a turn separation are explained. Different types of extraction device, such as harmonic coils, deflectors, and gradient corrector channels, are outlined. Some general considerations for cyclotron magnetic design are given and the use of modern magnetic modelling tools is discussed, with a few illustrative examples. An approach is chosen where the accent is less on completeness and rigorousness (because this has already been done) and more on explaining and illustrating the main principles that are used in medical cyclotrons. Sometimes a more industrial viewpoint is taken. The use of complicated formulae is limited.