S. Gammino

Tantalum ions produced by 1064 nm pulsed laser irradiation

A Q-switched Nd:YAG (yttrium aluminum garnet) laser (1064 nm wavelength) with a 9 ns pulse width, 1–900 mJ pulse energy, and 0.5 mm2 target spot, is employed to irradiate tantalum targets in vacuum. The irradiation produces a strong etching of the metal and forms a plasma in front of the target. The plasma contains neutrals and ions with a high charge state and a wide energy distribution. Time-of-flight measurements are presented for the ionic production. A cylindrical electrostatic ion analyzer permits to measure the yield and the charge state of the emitted ions and to extrapolate the ion energy distribution as a function of the laser fluence in the range 10–100 J/cm2. The measurements indicate that at high laser fluence the tantalum charge state may reach 8+ and the maximum ion energy about 6 keV. The ion energy distribution is presented as a function of the charge state. It follows approximately a “shifted Maxwellian distribution.” A better theoretical approach has been further developed considering t...

Results and interpretation of high frequency experiments at 28 GHz in ECR ion sources, future prospects

For the needs of future heavy ion accelerators, electron cyclotron resonance ion sources (ECRISs) should be able to deliver higher intensities and higher charge states. The 1e mA level intensity has already been reached by room temperature ECRIS for medium charge states of light elements (O6+, Ar8+). However, such level of intensity for heavy elements (like Pb27+ for CERN/LHC and GSI) requires more powerful ECRIS with higher electron densities (up to 1013 cm−3). On the other hand, an optimized magnetic configuration system has to be used in order to obtain the suitable compromise between the electron confinement and the high flux ion losses. Before the design of the future “high intensity ECRIS,” experiments have been performed with the superconducting SERSE source both at 18 and 28 GHz. After an overview of major results recently obtained, some scaling laws will be presented. Our results show that much larger intensities and charges can be reached with ECRIS. Then, we will show how the next ECRIS generat...

Operation of the SERSE superconducting electron cyclotron resonance ion source at 28 GHz

The SERSE source [P. Ludwig et al., Rev. Sci. Instrum. 69, 4082 (1998), and references therein] is a superconducting electron cyclotron resonance (ECR) ion source, operating at the Laboratori Nazionali del Sud in Catania since 1998; it is currently used as the main injector for the K-800 superconducting cyclotron. Its high magnetic field provides a high plasma confinement and large currents of highly charged ions, as compared to conventional sources. It can efficiently operate at the microwave frequency of 14 and 18 GHz [S. Gammino and G. Ciavola, Rev. Sci. Instrum. 71, 631 (2000); S. Gammino et al., ibid.70, 3577 (1999)] and has been used as a test bench for injection at 28 GHz. High-frequency operation is expected to create a higher plasma density, thus resulting in larger currents of multiply charged ions. In this article, we report the first operation of an ECR ion source at 28 GHz by using a gyrotron. The gyrotron itself and the waveguide line are described, along with the operational results (in xen...

Metallic etching by high power Nd:yttrium–aluminum–garnet pulsed laser irradiation

A Nd:yttrium–aluminum–garnet pulsed laser, with 1064 nm wavelength, 9 ns pulse width, and 0.9 J maximum pulse energy, is employed to irradiate in vacuum different metal targets (Al, Ti, Ni, Cu, Ta, W, Au, and Pb). In order to measure the erosion thresholds, the etching rates, and the chemical yields, a mass quadrupole spectrometer is interfaced to the vacuum chamber. Etching process shows a threshold, which ranges between 0.1 and 1.6 J/cm2 for lead and tungsten, respectively. Etching rates range between 0.3 and 10 μg/pulse for copper and lead, respectively. The irradiation produces chemical yields ranging between 0.04 and 0.6 atoms/100 eV for copper and lead, respectively. A simple theoretical approach is presented to justify obtained results. The objective of collected data concerns the possibility to use ejected atoms, neutral and ionized, in an electron cyclotron resonance ion source, in order to provide high current, multiply charge ion beams.

Angular distribution of ejected atoms from Nd:YAG laser irradiating metals

A Nd:YAG pulsed laser is employed to irradiate different metals in vacuum at the ECLISSE facility of the Laboratorio Nazionale del Sud, Catania, INFN. Laser pulse energy, 9 ns in width, ranges between 100 and 900 mJ. The ejection of atoms by means of laser irradiation is studied in terms of angular distribution, laser etching yield and film thickness deposited on a substrate. Light elements (Ni, Cu) show an angular distribution that is larger than heavy ones (W, Pb). A theoretical approach, applied to fit experimental data, indicates that the distribution depends on the high power of cos θ and that the flow velocity of ejected atom ranges between 27 000 and 88 000 m/s and the kinetic energy of ejected species ranges between 0.7 and 4.4 keV.

Ion and neutral emission from pulsed laser irradiation of metals

Abstract An Nd:YAG pulsed laser at 1064 nm wavelength with 9 ns pulse width and a maximum pulse energy of 900 mJ is focused on different metallic targets (Al, Ti, Ni, Cu, Nb, Sn, Ta, W, Au and Pb) placed in vacuum. The interaction produces a high etching for a pulse energy higher than a threshold value typical of each metal. Near the threshold a strong neutral emission takes place; at high pulse energy a stronger ionic emission occurs. The experimental thresholds of the ion emission are very similar to the threshold of the neutral emission. The atomic neutral emission is monitored by a mass quadrupole spectrometer and by the vapor thin film deposition technique. The ionic emission is detected through ion collectors (IC) using Faraday cups and time-of-flight measurements. The energy thresholds, the emission yields, the angular distribution, the fractional ionization, the kinetics and characteristics of the plasma production and the ion charge state are presented and discussed.

Comparison of nanosecond laser ablation at 1064 and 308 nm wavelength

To study the solid Cu ablation in vacuum, two different laser sources operating at 1064 and 308 nm wavelength are employed at similar values of laser fluences. The infrared laser is a Q-switched Nd:Yag having 9 ns pulse width (INFN-LNS, Catania), while the ultraviolet one is a XeCl excimer having 20 ns pulse width (INFN-LEA, Lecce). Both experiments produced a narrow angular distribution of the ejected material along the normal to the target surface. The ablation showed a threshold laser power density, of about 7 and 3 J/cm 2 at 1064 and 308 nm, respectively, below which the ablation effect was negligible. The laser interaction produces a plasma at the target surface, which expands very fast in the vacuum chamber. Time-of-flight (TOF) measurements of the ion emission indicated an average ion velocity of the order of 4:7 � 10 4 and 2:3 � 10 4 m/s for the infrared and ultraviolet radiation, respectively. We also estimated approximately the corresponding temperature of the plasma from which ions originated, i.e. about 10 6 and 10 5 K for IR and UV wavelength, respectively. A discussion of the analysis of the ablation mechanism is presented. At the used laser power densities the produced Cu ions showed ionisation states between 1þ and 5þ in both cases. # 2003 Elsevier Science B.V. All rights reserved.

Observations of the frequency tuning effect in the 14 GHz CAPRICE ion source

A set of measurements with the CAPRICE ion source at the GSI test bench has been carried out to investigate its behavior in terms of intensity and shape of the extracted beam when the microwaves generating the plasma sweep in a narrow range of frequency (+/-40 MHz) around the klystron center frequency (14.5 GHz). Remarkable variations have been observed depending on the source and the beamline operating parameters, confirming that a frequency dependent electromagnetic distribution is preserved even in the presence of plasma inside the source. Moreover, these observations confirm that the frequency tuning is a powerful method to optimize the electron cyclotron resonance ion source performances. A description of the experimental setup and of the obtained results is given in the following.

A study of the parameters of particles ejected from a laser plasma

We report on the results concerning the characteristics and the behavior of expanding plasma generated by a Laser Ion Source ~LIS!. The LIS technique is an efficient means in producing of multi-charged ions utilizing pulsed laser beams. In order to extract Cu ions, in this experiment an XeCl excimer UV laser was employed, providing a power density on the target surface up to 5 3 10 8 W0cm 2 . Two typologies of diagnostic systems were developed in order to detect the plasma current and the ion energy. The time-of-flight ~TOF! measurements were performed exploiting either a Faraday cup or an Ion Energy Analyzer ~IEA!. This latter allowed getting quantitative information about the relative ion abundances, their kinetic energy and their charge state. To study the plasma characteristics we measured the total etched material per pulse at 70 mJ. It was 0.235 mg and the overall degree of ionization, 16%. The angular distribution of the ablated material was monitored by optical transmission analysis of the deposited film as a function of the angle with respect to the normal to the target surface. Applying a high voltage to an extraction gap a multi-charged ion beam was obtained; different peaks could be distinguished in the TOF spectrum, resulting from the separation of ions of hydrogen, adsorbed compounds in the target and copper.

Angular distribution of ions emitted from Nd:YAG laser-produced plasma

Angular distribution of ion currents emitted from laser-produced plasmas are reported for a Nd:YAG laser with intensities lower than 1×1010 W/cm2. This distributions are strongly peaked along the normal to the target surface for Cu, Sn, Ta, W, Au, and Pb ion streams, independent of the incidence angle of the irradiated target. For Al, Ni, and Nb the main axis tends to decline to about −10°. The comparison of fits of Gaussian function and cosP(α−α0)+y0 to the experimental data verified the formal equivalency of both the functions. Fitted values of the FWHM and of the exponent P are compared for all the elements used. The angular distribution of mean ion velocity 〈v〉 and ion kinetic energy 〈E〉 are presented.