Fig. 3-5 Cocktail beams in the AVF cyclotron Accelerator A cocktail beam consisting of four kinds of ions, N, Ne, Ar, and Kr, is generated in an ECR ion source and injected into the cyclotron. Ar ions can then be accelerated and extracted by the frequency specifically adjusted to Ar ion (13.881 MHz).

Table 3-1 Relationships between the acceleration frequency and the energy of cocktail beams around M/Q = 5

Since four kinds of ions around M/Q = 5 have the specific acceleration frequencies close to each other, the RF frequency which specifies the ion can be adjusted in a short time, i.e., several different kinds of ion species can be successively provided to users in a short time.

An AVF cyclotron accelerator can accelerate a wide variety of ion species, from light ions such as hydrogen and helium, to heavy ions such as argon and xenon. At JAERI, extensive R&D is underway in the fields of materials science and biotechnology, using various kinds of ions accelerated by a cyclotron. A cyclotron has over 100 operation parameters such as the main coil magnetic field and the acceleration frequency, which have to be finely adjusted for the acceleration of a particular ion species. If the ion species needs to be changed, it takes about 2 hours to finely re-optimize the operation parameters, so it is inconvenient for an AVF cyclotron to successively accelerate many kinds of ion species. In Takasaki Ion Accelerators for Advanced Radiation Applications (TIARA), this disadvantage of the AVF cyclotron has been successfully overcome by the development of the "cocktail beam" acceleration technique, which is one of the most time-efficient methods for changing the ion species and/or the energy. Cocktail beams are composed of several ions having a very similar M/Q value (the ratio of mass to charge). They are generated by an electron cyclotron resonance (ECR) ion source, injected into the cyclotron at the same time, and then extracted separately by a fine tuning of the magnetic field or by a slight changing of the acceleration frequency (which is specific to each ion species). Since it is possible to slightly change the frequency in a very short time (less than 30 seconds), many kinds of ion species can be successively provided for the irradiations. The success in development of the cocktail beam acceleration technique has brought a great increase in the operation efficiency of the AVF cyclotron at TIARA.

Reference M. Fukuda et al., Development of Cocktail Beam Acceleration for a Fast Ion Species and Energy Change, JAERI-Review-96-017, 229 (1997).

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