Review of laser ion sources developments in Prague and production of q over 50+ ions at Prague Asterix Laser System (invited)

Abstract

The high-power iodine laser systems PERUN and Prague Asterix Laser System, with a maximum attainable laser intensity IL of up to about 6×1016 W/cm2, were used to generate highly charged ions of various elements (Al,Co,Ni,Cu,Ag,Sn,Ta,W,Pt,Au,Pb,Bi). The properties of ions were investigated mainly on the basis of time-of-flight method using ion collectors, cylindrical electrostatic ion energy analyzer, Thomson parabola spectrometer, and track detectors. Simultaneous x-ray and interferometric measurements were also implemented. Maximum ion charge states of heavy ions above z=50+ were recorded and the maximum energy of emitted ions exceeded Ei=22 MeV. Using laser intensities of about 1×1016 W/cm2 can produce such ions. Due to the convenient pulse length of the iodine laser, part of the pulse may interact with the self-created expanding plasma. It was proved that in this case the conditions for an appearance of the relativistic self focusing may be fulfilled (position of minimum focus spot in front of the target surface and the threshold laser intensity about 3×1014 W/cm2) and the highest charge states above 50+ may be generated, too.

Laser-driven generation of fast particles

“…Studies of laser-driven generation of highly charged ions with the use of long-pulse (ns or subns) lasers have a much longer history and have been performed by several research groups [7][8][9][10][52][53][54][55][56][57][58]. Some results obtained by the Czech-Polish group with the use of subns high-energy iodine lasers are presented in Table 3 [10].…”

“…Some results obtained by the Czech-Polish group with the use of subns high-energy iodine lasers are presented in Table 3 [10]. It is worth noticing that heavy ions of z~50 and energies in the MeV range are emitted in the beams of ion current densities in a far zone of tens mA/cm 2 .…”

“…These ions form a fast ion group, as opposed to the thermal, slower ion group accelerated by thermokinetic forces. The mechanism of acceleration using the double-layer in plasma corona dominates in the case of long driving pulses [7][8][9][10], but it can be also efficient in the case of short pulses of relatively low contrast (producing sufficiently thick underdense preplasma layer) [44,45]. Both the double-layer and S-LPA mechanisms were demonstrated to be efficient in generation backward-emitted heavy ion beams.…”

“…The most commonly used one is the time-of-flight method employing various types of ion collectors and electrostatic or magnetic ion analyzers [10,16]. Thomson mass spectrometers, solid-state track detectors and some nuclear activation methods are applied for these purposes as well.…”

“…However, powers and intensities, I L , of the used lasers were low (I L < 10 12 W/cm 2 ), so energies of produced particles were low (~keV) as well. The high-intensity experiments began in the seventies and up to the middle of the nineties they were performed almost exclusively with long nanosecond and subnanosecond laser pulses of intensities up to 10 16 W/cm 2 [7][8][9][10]. A real breakthrough in the field, especially in laser-driven generation of fast ion beams, took place, however, on the turn of the century, when short picosecond and subpicosecond laser pulses of powers from TW to PW level were employed in the experiments.…”