Proton extraction from transition metals using PLATONE Velardi, L.; Delle Side, D.; Kràsa, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2014, Volume:
735
Journal Article
Peer reviewed
In this work we present a study on proton beams extraction from a plasma generated by pulsed laser ablation of titanium and tantalum disks. The device used was the PLATONE laser ion source operating ...at the LEAS Laboratory in Lecce, Italy. It is based on a KrF laser operating at low irradiance (109-1010 W/cm2) and ns pulse duration. The proton and ions emission was analyzed by the time-of-flight technique using a Faraday cup as ion collector and an electrostatic barrier to identify the particles. Studies on the produced protons and ions at different laser irradiance values were performed. The extracted beams showed high proton flux up to 1010 protons/cm2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► Ions emitted by laser-produced plasmas have shifted Maxwell–Boltzmann velocity distribution. ► Only almost monoenergetic fast ions have Gauss energy distribution. ► Linear relation between relative ...spreads in energy ΔE/E and time-of-flight Δt/t of fast ions is valid only for ΔE<0.2E. ► TOF energy-sensitive detector gives higher peak velocity than velocity- and density-sensitive ones. ► Bursts of fast ions emitted by laser-produced plasma consist of almost monoenergetic ion beams.
The analysis of ion collector signals with the use of a time-of-fight signal function derived from a shifted Maxwell–Boltzmann velocity distribution is used to quantify the ion characteristics as the ion temperature and velocity of centre-of-mass motion of groups of ionized species constituting the ablated plasma. The analysis is also focused on velocity and energy distributions derived from the signal of a time-of-flight detector taking into account the underlying principle of sensor operation. The energy Maxwell spectra of ions are compared with the Gauss distribution with respect to the ratio of the centre-of-mass energy of ions to their temperature. The difference threshold between the Gauss and energy Maxwell spectra is determined via the limited validity of the basic relationship between spreads in energy and time-of-flight spectra ½ΔE/E=Δt/t. The analysis of velocity spectrum of fast ions emitted by Ti plasma produced with 300ps, kJ-class iodine laser operating at PALS facility shows that ion bursts consist of almost monoenergetic ion beams.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Galvanic grounding and isolation of the target from the vacuum chamber have different effects on plasma properties.•Voltage generated on the isolated target can significantly affect the plasma phase ...after the laser interaction.•Target grounding can cause reduction in ion emissions, as observed for heavier elements.
We have used grounded and isolated targets to measure currents of electrons escaping the pulsed laser-produced plasma. Presented experiments show that the laser-produced plasma is dominated by three phases such as the ignition phase, active and afterglow phases. The last two phases occurring after laser-plasma interaction are influenced by whether the target is isolated from the vacuum chamber or grounded. The voltage arising on the isolated target, which acts as a capacitor, mainly affects the active phase, where collisions of particles still form the plasma. This can cause reduction in ion emissions, as observed for heavier elements. The target charging accompanying the laser ablation was driven by nanosecond laser radiation with fluence ranging between 1–4 J/cm2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
When high-energy and high-power lasers interact with matter, a significant part of the incoming laser energy is transformed into transient electromagnetic pulses (EMPs) in the range of ...radiofrequencies and microwaves. These fields can reach high intensities and can potentially represent a significative danger for the electronic devices placed near the interaction point. Thus, the comprehension of the origin of these electromagnetic fields and of their distribution is of primary importance for the safe operation of high-power and high-energy laser facilities, but also for the possible use of these high fields in several promising applications. A recognized main source of EMPs is the target positive charging caused by the fast-electron emission due to laser-plasma interactions. The fast charging induces high neutralization currents from the conductive walls of the vacuum chamber through the target holder. However, other mechanisms related to the laser-target interaction are also capable of generating intense electromagnetic fields. Several possible sources of EMPs are discussed here and compared for high-energy and high-intensity laser-matter interactions, typical for inertial confinement fusion and laser-plasma acceleration. The possible effects on the electromagnetic field distribution within the experimental chamber, due to particle beams and plasma emitted from the target, are also described. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.
Experimental results are obtained concerning the target polarization, which aptly characterizes the laser ablation. The charge separation in the laser-produced plasma, structure of the ion front, and ...the current of fast electrons expanding into the vacuum chamber ahead of ions are of crucial importance for the interpretation of multi-peak structure of target currents appearing much later than the laser pulse. Of particular interest is the correlation between the partial maxima in the time-resolved target current and the square root of mass number of ionized species. The late-time negative charging of targets provides evidence for production of very slow ions by ionization of neutrals ablated at the target crater by radiation from plasma produced by 23 ns excimer krypton fluoride laser.
We show that a spatially well-defined layer of boron dopants in a hydrogen-enriched silicon target allows the production of a high yield of alpha particles of around 109 per steradian using a ...nanosecond, low-contrast laser pulse with a nominal intensity of approximately 3×1016Wcm−2 . This result can be ascribed to the nature of the long laser-pulse interaction with the target and with the expanding plasma, as well as to the optimal target geometry and composition. The possibility of an impact on future applications such as nuclear fusion without production of neutron-induced radioactivity and compact ion accelerators is anticipated.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM, UPUK
Abstract
Measurements had been performed of strong electromagnetic pulses (EMPs) generated as a result of laser–target interaction at the sub-ns kJ-class Prague Asterix Laser System facility. Two ...conductive Prodyn FD5C D-dot pencil probes were used. Measurements were performed inside the experimental chamber and outside the chamber in a large chamber window 40 cm in diameter in a setup that guaranteed 6 GHz bandwidth. A very good signal-to-noise ratio (17:1) was obtained after some steps were taken to ensure proper EMP shielding of the data collection setup. The EMP signal in the time domain was found to have the form of a sharp initial spike followed by gradually decaying oscillations interspersed with some secondary spikes. The values of the vertical component of the electric field strength were estimated. The highest value recorded in this experiment was
620
−
180
+
260
kV m
−1
at a distance of 40 cm from the target. It was observed that plastic targets—particularly the 100s of
µ
m thick plastic foils—tend to generate stronger EMP fields than Cu and Au targets. A time-frequency analysis was performed for a typical shot, clearly showing some spectral features that appear only sometime after the start of the signal and hence indicate EMP generation from secondary sources. Electrons ejected from the target were recorded with the energies exceeding 1.5 MeV, which indicates that highly energetic processes are triggered as a result of the laser–target interaction.
The current balancing the target charging and the emission of transient electromagnetic pulses (EMP) driven by the interaction of a focused 1.315 m iodine 300 ps PALS laser with metallic and plastic ...targets were measured with the use of inductive probes. It is experimentally proven that the duration of return target currents and EMPs is much longer than the duration of laser-target interaction. The laser-produced plasma is active after the laser-target interaction. During this phase, the target acts as a virtual cathode and the plasma-target interface expands. A double exponential function is used in order to obtain the temporal characteristics of EMP. The rise time of EMPs fluctuates in the range up to a few tens of nanoseconds. Frequency spectra of EMP and target currents are modified by resonant frequencies of the interaction chamber.
Experiments were performed using the Prague Asterix Laser System to study the effect of expanding plasma on electromagnetic pulse propagation (EMP) in the interaction chamber in an intensity regime ...of 1016 W cm−2. Similar to the interaction that occurs between radio waves and the ionosphere, the expansion of laser-produced plasma causes the vacuum chamber to be gradually filled with inhomogeneous plasma that interacts with the emitted EMP. Combining the space-time analysis of a plasma density inside the interaction chamber and the fast Fourier transform filtering of antenna signals, we have resolved the influence of the expanding plasma on space-time characteristics of EMP.
A high-power pulsed laser is focused onto a solid-hydrogen target to accelerate forward a collimated stream of protons in the range 0.1–1 MeV, carrying a very high energy of about 30 J (∼5% laser-ion ...conversion efficiency) and extremely large charge of about ∼0.1mC per laser pulse. This result is achieved for the first time through the combination of a sophisticated target system (H2 thin ribbon) operating at cryogenic temperature (∼10K ) and a very hot H plasma (∼300keV “hot electron” temperature) generated by a subnanosecond laser with an intensity of ∼3×1016W/cm2 . Both the H plasma and the accelerated proton beam are fully characterized by in situ and ex situ diagnostics. Results obtained using the ELISE (experiments on laser interaction with solid hydrogen) H2 target delivery system at PALS (Prague) kJ-class laser facility are presented and discussed along with potential multidisciplinary applications.
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