Development of a laser ion source for production of high-intensity heavy-ion beams

Abstract

A laser ion source has been developed as a high-intensity source for the ion implanter and the single pulsed beam of the azimuthally varying field cyclotron at TIARA. Highly charged beams of C5+ and C6+ ions and low-charged beams of heavy ions such as C, Al, Ti, Cu, Au, and Pt are required for the single-pulse acceleration in the cyclotron and for the ion implanter, respectively. In the vacuum chamber of the ion source, a target holder on a three-dimensional linear-motion stage provides a fresh surface for each laser shot. A large-sized target with a maximum size of 300mm×135mm is mounted on the holder for long-term operation. The ion current (ion charge flux) in the laser-produced plasma is measured by a Faraday cup and time-of-flight spectra of each charge state are measured using a 90° cylindrical electrostatic analyzer just behind the Faraday cup. Carbon-plasma-generation experiments indicate that the source produces intense high- and low-charged pulsed ion beams. At a laser energy of 483mJ (2.3×1013W/cm2), average C6+ current of 13mA and average C5+ current of 23mA were obtained over the required time duration for single-pulse acceleration in the cyclotron (49ns for C6+ and 80ns for C5+). Furthermore, at 45mJ (2.1×1012W/cm2), an average C2+ current of 1.6mA over 0.88μs is obtained.