Progress in plasma research at IPJ and IPPLM, Poland

The most important results of theoretical and experimental studies of plasmas, which have been achieved at the IPJ in Swierk and IPPLM in Warsaw recently, are presented. Studies of physical phenomena in PF discharges, development of diagnostic techniques and research on new plasma technologies, as performed at IPJ, have been summarized. Studies of dense magnetized plasmas, investigation of physics and applications of laser-produced plasmas; and research on the development of advanced diagnostic techniques for the EURATOM fusion program, as performed at IPPLM, are also described

Expansion of tungsten ions emitted from laser-produced plasma in axial magnetic and electric fields

The experimental results of the investigations on the influence of external magnetic and electric fields on the characteristics of a tungsten ion stream emitted from a plasma produced by the Nd:glass laser (1 J, 1 ns) performed at IPPLM, Warsaw are presented. A negatively biased target up to −15 kV and a magnetic field up to 0.45 T were used in the experiment. A set of ion collectors and an electrostatic cylindrical ion energy analyzer located at small angles with respect to the laser beam axis and at large distances from the target were applied for ion measurements. The effect of an external magnetic field is essential to plasma expansion, but the effect of the retarding potential of the target is very weak in our experimental conditions. The aim of the studies was to prove the possibility of the optimization of ion beam parameters from laser-produced plasma for the particular application as a laser ion source coupled with the electron cyclotron resonance ion source for particle accelerators

Self-focusing in processes of laser generation of highly-charged and high-energy heavy ions

Laser-beam interaction with expanding plasma was investigated using the PALS high-power iodine-laser system. The interaction conditions are significantly changing with the laser focus spot position. The decisive role of the laser-beam self-focusing, participating in the production of ions with the highest charge states, was proved

Angular distributions of ions emitted from laser plasma produced at various irradiation angles and laser intensities

AbstractAngular distributions of currents and velocities (energies) of ions produced at various target irradiation angles and laser intensities ranged from 1010 W/cm2 to 1017 W/cm2 were analyzed. It was confirmed that for low laser intensities the ion current distributions are always peaked along the target normal. However, at laser intensities comparable to or higher than 1014 W/cm2, the preferred direction of ion emission strongly depends on the irradiation geometry (laser focus setting, the irradiation angle), and can be off the target normal. This is very likely caused by the non-linear interaction of the laser beam with produced plasma, in particular, by the action of ponderomotive forces and the laser beam self-focusing

Factors influencing parameters of laser ion sources

Various applications demand various kinds of ions. Charge state, energy and the amount of laser produced ions depend, primary, on the wavelength, the energy, the pulse duration, and the focusing ability of the laser used. Angle of the target irradiation, angle of the ion extraction (recording), and mainly the focus setting may significantly influence especially the portion of ions with the highest charge states. The participation of non-linear processes on the generation of ions with extremely high parameters is demonstrated. The observed effects support the idea of a longitudinal structure of the self-focused laser beam with a space period of ∼200 µm

The influence of an intense laser beam interaction with preformed plasma on the characteristics of emitted ion streams

AbstractIntense laser-beam interactions with preformed plasma, preceding the laser-target interactions, significantly influence both the ion and X-ray generation. It is due to the laser pulse (its total length, the shape of the front edge, its background, the contrast, the radial homogeneity) as well as plasma (density, temperature) properties. Generation of the super fast (FF) ion groups is connected with a presence of non-linear processes. Saturated maximum of the charge states (independently on the laser intensity) is ascribed to the constant limit radius of the self-focused laser beam. Its longitudinal structure is considered as a possible explanation for the course of some experimental dependencies obtained

Computations for nonlinear force driven plasma blocks by picosecond laser pulses for fusion

The concept of the fast ignitor for laser fusion has led to some modifications in applying petawatt-picosecond (PW-ps) laser-produced high intensity particle beams to ignite deuterium-tritium (DT) fuel. Some very anomalous measurements of ion emission from targets irradiated by picosecond laser pulses led to the development of a skin depth interaction scheme where a defined control of prepulses is necessary. Based on these experimental facts, we have applied a one dimensional two-fluid hydrodynamic code to understand how the nonlinear ponderomotive force generates two plasma blocks, one moving against the laser light (ablation) and the other moving into the target. This compressed block produces an ion current density of above 10¹¹ A cm���² and an ion energy of about 100 keV. This may be a rather promising option to use PW-ps laser pulses for igniting fusion in solid density DT fuel, realizing very high gain controlled fusion reactions

Implantation and sputtering of ge and si ions into SiO2 substrates using electric fields for acceleration and optimisation of laser-produced Ion streams used for modification of semiconductor materials

Laser plasma has been proved to be a potential source of multiply charged ions which could support the growing demands for high-current ion beams. To optimize efficiency of the ion implantation technology selection of proper laser beam characteristics is very important and should be investigated. With LIS, several variables can and must be controlled. The properties of ions (current densities, the ion charge state, angular and energy distributions) depend on target material and the laser energy, pulse duration and intensity on the target surface. So, the characteristics of laser-produced ion streams should be determined with the use of precise ion diagnostic methods. Based on the preliminary results for acceleration of ions produced with the use of a repetitive laser system at IPPLM the special electrostatic-acceleration system has been designed and prepared. This device permits to accelerate ions having charge states of 1+ to energies up to ∼40 keV. The movable target holder was located inside the cylindrical box connected with a high-voltage source (up to 50 kV at 50 mA). The accelerated Ge and Si ions was implanted to SiO2/Si substrates and analyzed. This contribution is concerned mainly on the analysis and optimization of laser-produced Ge and Si ion streams as well as on investigation of the direct implantation of these ions into SiO2 substrates. Targets were irradiated with the use of repetitive (up to 10 Hz) laser with energy up to 700 mJ in one pulse, at radiation intensities of ∼1011 W/cm2. The ion stream parameters were measured using the time-of-fight method. The depth of ion implantation was determined by X-Ray Photoelectron Spectroscope (XPS). After the implantation the samples were annealed in different temperatures in range of to create nanocrystal structures and then analyzed by means of Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The work has been performed within SEMINANO project supported by EC (within 6FP)

Plasma block acceleration by ps-TW laser irradiation

Plasma emission or ablation from laser-irradiated targets shows very complicated properties. One novelty was observed at irradiation of neodymium glass laser pulses of ps duration and TW power if there was a very strong suppression of prepulses by a contrast ratio of about 108 until 100 ps before the main pulse arrived. The emitted ion maximum energy was more than 50 times below the values observed in all the comparable numerous experiments. The other anomaly is that the number of the fast ions did not change when the laser intensity varied by a factor 30. This permitted a separation of the usual effects of self-focusing and permitted an analysis fully based on simplified plane geometry as a skin layer interaction mechanism. The consequence is that plasma blocks are accelerated by the nonlinear (ponderomotive) force with ion current densities above 1010 A/cm2. This provides basically new aspects for laser fusion using uncompressed solid DT fuel and a new kind of x-ray laser process may be possible