1,721,061 research outputs found
Extraction of metal ions from laser-produced plasma
No full textExperimental results concerning the extraction of Cu ions from laser-produced plasma are reported in this work. An XeCl excimer laser was used, providing a power density on the target surface of about 3.5×108 W/cm2. Laser wavelength and pulse duration were 308 nm and 20 ns, respectively. The experimental apparatus consisted substantially of a plasma generation chamber and a drift tube. An expansion chamber was mounted on the target stem inside the generation chamber. Its end together with a bored electrode connected to ground formed the acceleration gap, which was 1.3 cm large. A Faraday cup was used to reveal ions. The highest accelerating voltage applied to the extraction gap was 18 kV, resulting in extraction of an ion bunch of about 4.2 nC, with a peak current of 220 A
Novel pulse amplifying circuits by different characteristic impedance transmission lines
No full textTwo novel circuits used to amplify electric pulses by the coupling of transmission lines of different characteristic impedance are described. The circuits are intended for doubling voltage pulses and for doubling current pulses. The former is composed by a R0 transmission line closed on a set of two 2R0 storage lines connected in parallel, while the latter is composed by a R0 transmission line closed on a set of two R0/2 storage lines connected in series. The length of every storage line is half of input-pulse length. In both circuits, one storage line is characterized by an open extremity and the other line by a closed extremity. Connecting opportunely the storage lines to suitable load resistors, 4R0 and R0/4, for the circuit having parallel and series connected lines, respectively, a twice of the pulse intensity is obtained. Such devices are very suitable to generate high intensity voltage and/or current peaks which are very interesting in the field of the accelerators. Both circuit behaviours have been theoretically studied and verified by computer simulation
On the dynamics of a non-equilibrium Cu plasma produced by an excimer laser interaction with a solid
No full textWe report here on the expansion dynamics of a non-equilibrium plasma
produced by an excimer laser interaction with a Cu solid target. Its characteristics
were investigated in the fast and slow time regime by two Faraday cups of different
diameter. The larger cup had an 8 cm diameter collector and was fixed along a drift
tube at a distance of 20 cm from the plasma source; the smaller cup had a 3.3 cm
diameter collector and was fixed transversally to the target at a distance of about
6 cm. During the experiments the target support signal was also recorded. The
laser beam was focused onto the target and the spot dimensions were analysed
by scanning it on the lens focal plane. An average power density on the target of
0.3 GW cm−2 was achieved with a 15 cm focal length lens. Using signals from the
Faraday cups we obtained information on the overall plasma evolution in the slow
and fast time regimes. Fitting the plasma current waveform by a ‘shifted’ Maxwell–
Boltzmann distribution, a Knudsen-layer temperature of 5.3×105 K (∼50 eV) and
a drift velocity of 5300 m s−1 resulted. The system efficiency in ablation yield and
ion production was 0.235 μg pulse−1 and 5 × 1013 ion pulse−1, respectively
Fixed energy voltage compressor:theory,simulation and experiments.
Full text linkIn this paper we illustrate the theoretical analysis, design, computer simulation, experimental realization and results
of a circuit able to compress a rectangular pulse and to increase its intensity. Utilizing a pulse forming line, l long, and a
halved storage line, l/2 long, both connected on the same load resistor by means of fast switches, a time compression
factor of 2 and a doubled output voltage were achieved. Charging the pulse forming line at VC, or applying, to the
circuit, a short pulse VC/2 large, 2tl long, with t the delay per unit length, a compressed output pulse of VC, tl, was
obtained, as expected by theoretical analysis and computer simulation
Pre- and post-extraction analyses of different charge state ion components produced in a laser ion source
No full textKnowledge of the relative abundance and the energy distributions of various ion species produced in laser ablation plasma is essential both in the fundamental physics ground, to understand the thermalization and expansion dynamics of the plasma plume, and in the applied physics ground, to get an efficient and versatile ion source. We present measurements and analyses related to such aspects, both for plasma in free expansion and for the extracted ion bunch. In particular, we characterized the former by means of ion current measurements, employing appropriate Faraday cups and electrostatic spectrometers; as regard as the latter, we performed time-of-flight spectrometry and depth profiling of implanted substrates. The extracted bunch signal showed modulation on time-of-flight due to the presence of multiply charged ions; depth profiling by X-ray photo-electron spectroscopy also showed a maximum penetration range and a profile modulation compatible with a multi-energetic beam. In these experiments we used UV excimer lasers, at irradiance values in the range 0.1 - 10 GW/cm2, to generate plasma from Cu and Al targets. The ion beams were extracted at voltages of tens of kV, DC
Photoemission studies from metal by UV lasers
No full textStudies of electron emission by photoelectric process from pure Zn cathodes by UV laser beams
were performed. As UV sources, two different wavelength excimer lasers were utilized in order to
investigate the photoemission as pure photoelectric process and multiphoton process. The Schottky
effect was also considered. The utilized laser sources were a KrF operating at 248 nm wavelength
5 eV, 23 ns full width at half maximum FWHM, and a XeCl operating at 308 nm wavelength
4.02 eV, 10 ns FWHM. The cathode work function was 4.33 eV, a value lower and higher than
the photon energies of KrF and XeCl lasers, respectively. The photocathodes were tested in a
vacuum photodiode cell at 10−7 mbar. The cathodes were irradiated at normal incidence and the
anode-cathode distance was set to 3.7 mm. Due to the electrical breakdown into the photodiode gap,
the maximum applied accelerating voltage was 20 kV. Under the above experimental conditions a
maximum of 5.4 MV/m electric field resulted. Under the space charge effect, the electron emission
was higher than the one expected by the Child-Langmuir law. In saturation regime the electron
emission increased with the accelerating voltage owing to the Schottky effect and plasma formation.
The highest output current was achieved with the KrF laser at 14 mJ laser energy. Its value was
about 12 A, corresponding to a global quantum efficiency of approximately 110−4, while the
temporal quantum efficiency presented a maximum value of 1.110−4 located at the tail of the laser
pulse. The estimated efficiencies with the XeCl laser were lower than the KrF ones as well as the
output current and the plasma formation, although higher energy values than the KrF ones were
utilized. By the results obtained, we conclude that the plasma generation is strongly due to the
extracted current but weakly to the used laser intensit
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