A. E. Stepanov

Laser ion source for heavy ion synchrotrons (invited)

A status overview of the development of laser ion sources suited to heavy ion synchrotrons is presented. The results of experimental and theoretical studies, recently obtained at a number of laboratories, for laser-produced highly charged heavy ions are summarized for plasmas heated by long wavelength lasers. Design of a powerful repetition rate CO2 laser, target interaction chamber, and extraction system suited for reliable long term operation mode with real accelerators is discussed. Requirements for the final performance of the laser ion sources for ion beam injectors at the ITEP-Moscow and CERN accelerator facilities are given.

Laser ion source for heavy ion synchrotrons

A status overview of the development of laser ion sources suited to heavy ion synchrotrons is presented. The results of experimental and theoretical studies, recently obtained at a number of laboratories, for laser-produced highly charged heavy ions are summarized for plasmas heated by long wavelength lasers. Design of a powerful repetition rate CO2 laser, target interaction chamber, and extraction system suited for reliable long term operation mode with real accelerators is discussed. Requirements for the final performance of the laser ion sources for ion beam injectors at the ITEP-Moscow and CERN accelerator facilities are given.

Study of multicharged heavy ion generation from CO 2 laser-produced plasma

The results of lead ion generation with charge state from Pb 10+ to Pb 35+ from laser-heated plasma are presented. CO 2 lasers producing 10.6-μm wavelength radiation at power densities in the range 4.10 11 -6.10 14 W/cm 2 in TBKI and CERN were used. Results of detailed numerical simulations presented in the paper are in good agreement with the experimental data. Work done in collaboration with CERN, ITEP, and TBKI was aimed at the specification of requirements for a laser system that will be able to drive an ion source for the hadron collider (LHC) at CERN.

The generation of fast particles in plasmas created by laser pulses with different wavelengths

By means of spatially resolved high-resolution X-ray spectroscopy, we have investigated the generation of fast ions at various laser installations with different flux densities and laser wavelengths. It is demonstrated that the fast ion generation in laser-produced plasma can be achieved for a very low level of the averaged laser intensity on the target. The time-of-flight mass spectrometry ion diagnostics and X-ray spectrographs give very close results for the energy distribution of the thermal ion component. For higher energies, however, we found significant differences: the spatially resolved high-resolution spectrographs expose the presence of suprathermal ions, while the time-of-flight method does not. Suprathermal ion energies Eion plotted as a function of the qλ2 parameter show a large scatter far above the experimental errors. The cause of these large scatters is attributed to a strong nonuniformity of the laser intensity distribution in the focal spot. The analysis by means of hydrodynamics and spectral simulations show that the X-ray emission spectrum is a complex convolution from different parts of the plasma with strongly different electron density and temperature. It is shown that the highly resolved Li-like satellite spectrum near Heαcontains significant distortions even for very low hot electron fractions. Non-Maxwellian spectroscopy allows determination of both the hot electron fraction and the bulk electron temperature.

High-Power CO2 Laser System with Repetition Rate Operation for High Current Multicharged Heavy Ion Generations

Experimental and numerical calculation results devoted to development of an optical system for an ion source based on a repetition rate CO2 laser are described. The laser chain consists of a master oscillator, gas absorber cells, and a four-pass amplifier. The optical system provides smooth laser pulses with variable duration and high spatial quality that ensures efficiency for plasma heating and ion generation. The parameters of the plasma ion component measured in the CERN laboratory are applied for a lead target illumination.

The “Katran” CO2 Laser with High Specific Output Power and Stable Parameters

The design and parameters of the UV-preionized discharge module “Katran” are described. A particular feature of the scheme is a high-voltage pulse formation technique for sharp discharge current ignition to stabilize the self-sustained glow discharge. The free-running laser based on the discharge module allows one to obtain high specific laser power exceeding 145 MW/liter in the P(20) line for the 10-μm band for an active volume of 3 liters. Duration of the first spike of generation is 30 ns FWHM and energy content is about 65% of the total pulse energy. The high reliability and reproducibility of the modules operation for a wide range of parameters ensures laser suitability for different scientific and technical applications.

Study of angular dependences of ion component parameters in CO2-laser-produced plasma

CO 2 -laser-produced plasma ion component parameters were studied for aluminium and lead targets at laser intensity of P = 4 × 10 13 W cm -2 and pulse duration of τ = 15 ns experimentally and numerically. Angular dependences of ion number density for different charge states, average velocity and its spread were measured by time-of-flight method. Ion charge state distribution shows high-charge and low-charge state groups at normal expansion direction. Ions in these groups have different average expansion velocity and longitudinal velocity spread. Angular distribution of high-charge states is narrower than that of the low-charge stale ion group, maximum yield of low-charge states occur at some angle from normal. For Al target results show similar trends as for Pb target, hut simulations have indicated that the effect of laser ponderomotive force is more pronounced in this case.

Generation of intense beams of Pb+4 to Pb+10 ions in a laser ion source

Experiments have been carried out to optimize the yield of Pb+4 ions from the plasma produced by a 100 J CO2 laser. The laser power density on the target surface was varied between 1010 W/cm2 and 9×1010 W/cm2 by changing the focal spot size. Data on the production of Pb+4 to Pb+10 ions are presented for the 15 and 40 ns laser pulse durations. The 10 mA/80 μs pulses of Pb+4 ions (about 1012 ions per pulse) were directed into an extraction aperture of 3.4 cm in diameter for optimal irradiation conditions. This is comparable with the parameters of the MEVVA ion source. Laser ion sources can be especially attractive due to the absence of the “noise” problem, typical for the MEVVA ion source, and because of the possibility of generating higher charge states. The emittance of the lead ion beam extracted from the laser-produced plasma was measured by using a 5 J laser, which provided plasma parameters (the electron temperature, ion velocities, and the charge state distribution) close to those of the plasma gener...

Study of the ion composition of an expanding magnesium plasma produced by a CO2 laser

The evolution of the ion composition of a laser plasma during its expansion over a large distance is studied. The plasma is produced by a TIR CO2 laser with a pulse energy up to 100 J and duration of ∼20 ns. X-ray diagnostics with the use of a spectrograph and X-ray PIN diodes was applied to study the plasma near the target surface. At large distances from the target surface, time-of-flight neutral-particle diagnostics with the use of an electrostatic analyzer and ion collector was applied. Calculations performed with the GIDRA-1 code agree well with experimental data.

Temperature dynamics in a multicharge ion plasma generated by CO2 laser pulses

Time evolution of the X-ray spectrum of a lead ion plasma generated by CO2 laser pulses with an energy of 100 J and a duration of 15 ns was measured using an X-ray polychromator with six channels covering the quantum energy range from 180 to 1850 eV. The plasma temperature was determined by comparing the results of measurements with the calculated X-ray emission spectra. The electron temperature measured well agrees with the calculated data.