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

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 300 mm × 135 mm 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 483 mJ (2.3 × 10¹³ W/cm²), average C⁶⁺ current of 13 mA and average C⁵⁺ current of 23 mA were obtained over the required time duration for single-pulse acceleration in the cyclotron (49 ns for C⁶⁺ and 80 ns for C⁵⁺). Furthermore, at 45 mJ (2.1 × 10¹² W/cm²), an average C²⁺ current of 1.6 mA over 0.88 μs is obtained.