Chopped Deflector Technique for Single-Bunch Extraction at the 88-in Cyclotron

Abstract

The first deflector circuitry at the extraction of the 88-in Cyclotron at the Lawrence Berkeley National Laboratory has been modified to enable switching within a few hundreds of nanoseconds. This modification, along with the pre-chopper, allows the cyclotron to achieve single-bunch extraction. The novel procedure involves adjusting the pre-chopper to control the number of ion bunches injected into the cyclotron, thus managing ion energy deposition. These bunches are then accelerated until they reach the electrostatic deflectors, which control their extraction. After the deflectors are adjusted to transport the beam, the first deflector voltage is decreased until no beam current is extracted. Finally, through switching and selective phase adjustment of the first deflector to match the transit time of a bunch, the cyclotron is capable of extracting a single bunch. This capability is crucial for time-sensitive experiments and allows control over dose distribution in previously inaccessible regimes. The straightforward and cost-efficient implementation of this technique makes it an attractive option for many cyclotron facilities and medical cyclotron manufacturers.