Emittance characterization of ion beams provided by laser plasma

Laser ion sources offer the possibility to generate ion beams suitable for particle accelerators. Today many laboratories, as well as the LEAS, are involved in the development of compact accelerators, easy to be installed in little laboratories. Pulsed lasers at intensities of the order of 108 W/cm2 and of ns pulse duration, interacting with solid matter in vacuum, produce plasma of high energy, temperature and density. The charge state distribution of the plasma generates high electric fields which accelerate ions along the normal to the surface of the ablated target. The energy of the emitted ions is of the order of some hundreds of eV and these have got a shifted Maxwell-Boltzmann distribution which depends on the ion charge states. To increase the ion energy, a post-acceleration system can be employed by means of high voltage power supplies of about 100 kV. The post acceleration system results in a good method to obtain high ion currents using a not expensive system and the final ion beams find interesting applications in the field of ion implantations, scientific applications and industrial use. In this work we study the electromagnetic and geometric properties, like the emittance, of the beams delivered by pure Cu targets. Plasma’s characterization was performed using a Faraday cup for the electromagnetic characteristics, while for the geometric ones a pepper pot system has been applied. This technique consists of a pierced mask in order to measure the divergence of the ions that can pass through it. To impress the ions, radio-chromic films type GAFCHROMIC EBT-1 were used. We study the emittance for different values of accelerating voltage: 20, 30, 40, 50 and 60 kV. Applying a laser irradiance of 0.1 GW/cm2 and 60 kV of accelerating voltage, we obtain 5.5 mA of output current and a normalized beam emittance of 0.2 π mm mrad. The brightness of the beams was 137 mA( mm mrad)-2.