R. Ali

State-selective Charge Transfer Studies Relevant to Solar Wind-Comet Interactions

We report relative experimental and absolute theoretical n-state-selective, nondissociative, single-electron capture cross sections for a number of collision systems typical of the solar wind-comet interactions. The experimental measurements were carried out using the technique of cold-target recoil-ion momentum spectroscopy and involved the N7+ and O7+ projectile ions and, for the first time, the H2O, CO2, and CO molecular targets, as well as the He atomic target. The theoretical calculations were performed using the classical trajectory Monte Carlo (CTMC), the Landau-Zener (LZ), and the classical over-the-barrier (COB) models. The models, with CTMC favored, agree reasonably well with the measurements and can be used in the near term to aid in the modeling of cometary X-ray and EUV emission. The pathways through which multiple-electron capture processes contribute to the cometary X-ray and EUV emission are also discussed.

The KSU-CRYEBIS: A unique ion source for low-energy highly charged ions

The CRYogenic electron beam ion source at Kansas State University has been in operation since spring 1989. It produces up to Ar18+, Kr34+, and Xe44+ on a regular basis. Acceleration tubes and a beamline system were added during 1990. The ion source is mounted on a high voltage platform, which can be used to vary the ion energies between 2 and 200 kV per charge. The extraction‐, analyzing‐, and beamline systems were designed to accept a wide range of ion masses and charge states with the mass energy product (M⋅E/q2) stretching over four orders of magnitude. The system is used to study the low‐energy highly charged ions interacting with electrons, atoms, thin foils, and surfaces.

Multiparameter data acquisition system for spectroscopy

A powerful and versatile, simple to use multiparameter data acquisition system has been implemented for use in spectroscopy. In its standard configuration, the system can acquire signal from 16 time-to-digital converter channels, 16 analog-to-digital converter channels, and 12 scaler inputs. The system was put to use on the electron beam ion trap experiment to record the output from four position-sensitive proportional counters in two soft x-ray spectrometers together with the signal from an x-ray pulse height analyzer. Also recorded are the electron beam energy and the pulse height distribution of the proportional counters. All data are recorded as a function of time. Because the relevant parameters are recorded simultaneously, software gates instead of hardware gates are used to select the data of interest. This has led to a substantial cost saving over earlier data acquisition systems. Data are stored in binary or in ascii format for system-independent processing. The operation of the system is demonst...

CRITICAL TEST OF SIMULATIONS OF CHARGE-EXCHANGE-INDUCED X-RAY EMISSION IN THE SOLAR SYSTEM

Experimental and theoretical state-selective X-ray spectra resulting from single-electron capture in charge exchange (CX) collisions of Ne10+ with He, Ne, and Ar are presented for a collision velocity of 933 km s–1 (4.54 keV nucleon–1), comparable to the highest velocity components of the fast solar wind. The experimental spectra were obtained by detecting scattered projectiles, target recoil ions, and X-rays in coincidence; with simultaneous determination of the recoil ion momenta. Use and interpretation of these spectra are free from the complications of non-coincident total X-ray measurements that do not differentiate between the primary reaction channels. The spectra offer the opportunity to critically test the ability of CX theories to describe such interactions at the quantum orbital angular momentum level of the final projectile ion. To this end, new classical trajectory Monte Carlo calculations are compared here with the measurements. The current work demonstrates that modeling of cometary, heliospheric, planetary, and laboratory X-ray emission based on approximate state-selective CX models may result in erroneous conclusions and deductions of relevant parameters.

Charge Transfer Data Needs for Cometary X‐ray Emission Modeling

The emission of x‐rays has been observed from nearly twenty comets and evidence exists that it is the result of radiative decays from highly‐excited, highly‐charged solar wind ions following charge exchange with neutral species, mostly water, in the cometary atmosphere. We review the progress to date in constructing models of the x‐ray emission. However, the construction of accurate models is impeded by the near lack of reliable state‐selective charge exchange cross section data for the relevant neutral species (H2O, CO, CO2, etc.). The progress, and difficulties, of theoretical studies for the relevant collision processes is discussed with a particular focus on the breakdown of approximations made in the emission models.

State-selective single-electron capture in Ne4+-He collisions

Abstract A cold-target recoil-ion momentum spectroscopy technique (COLTRIMS), capable of measuring simultaneously the energy-gain and the scattering angle of the projectile products, has been used for the study of state-selective single-electron capture from He by 8 keV Ne4+ ions. The dominant reaction channel is due to single-electron capture into the 3s 4P state of the Ne3+ from the ground state incident Ne4+ ions. Also, there is clear evidence of capture into the 3s 2P state. State-selective differential cross-sections for capture into the 3s 4P and 2P states have also been measured and compared with the semi-classical multichannel Landau–Zener calculations.

Investigation of multi-electron processes in 60 keV O6++Ar collisions using a triple coincidence technique

Multiple electron capture processes in 60 keV O6++Ar collision system have been investigated by means of time-of-flight triple-coincidence measurements of Auger electrons, scattered projectile and target ions. This technique is particularly suited for the investigation of electron capture processes involving capture of three or more electrons. From the measured sub-partial Auger spectra, it can be seen that double electron capture dominantly populates the configurations (3,n) with n=3–5. Triple electron capture is found to dominantly populate the configurations (3,3,3) and (3,3,4), while quadruple electron capture populates the (3,3,3,3) configuration.

Production, operation and status of the KSU CRYEBIS facility

The KSU CRYEBIS is a CRY ogenic Electron Beam Ion Source located on a high voltage platform, dedicated to the exploration of the physics of the highly-charged, low-energy ions. This paper summarizes the research accomplished by our users over the last three years. It discusses the experiences encountered in the operation and production over the last three years. The major improvements accomplished over the last three years and the present capabilities are also described. The paper ends with a discussion of the user facility, the available techniques and equipment.

The VUV spectrum from fast heavy-ion induced excitation of

We have measured the spectrum of vacuum ultraviolet radiation (500 - 1700 A) arising from the impact of 625 MeV xenon ions with . The spectral features are due primarily to emission from neutral and ionized carbon atoms. These photons mask sensitivity to either the giant dipole resonance or to excited dimers. We compare with data obtained in collisions of xenon ions with methane and isobutane. Decay times of several of the lines were also measured. Some of the lines persist for times long compared to the lifetimes of the corresponding states in neutral and ionized carbon.

The interactions of high-energy, highly charged Xe ions with buckyballs

Ionization and fragmentation have been measured for C{sub 60} molecules bombarded by highly charged (up to 35+) xenon ions with energies ranging up to 625 MeV. The observed mass distribution of positively charged fragments is explained in terms of a theoretical model indicating that the total interaction cross section contains roughly equal contributions from (a) excitation of the giant plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule. Preliminary results of measurements on VUV photons emitted in these interactions are also presented.