D. Fry

Analog gain of microchannel plates for 1.5–154 keV/q Arq+(3⩽q⩽16)

The gain of microchannel plates operated with low bias voltages in the analog mode has been measured for Arq+ ions (3⩽q⩽16) with energies in the range from 1.5 to 154 keV/q. The results show that the gain, most likely due to the varying number of secondary electrons emitted upon impact of the detected ions, depends substantially on the charge as well as the energy of the ions. The measured gain is shown as a function of the charge state for five different ion energies per charge to assist in the interpretation of the results from the ion sources. The measured gain is also shown as a function of ion impact velocity for all measured charge states, which indicates a rather complex dependence on the ion impact velocity. The interpolated gain is also shown as a function of charge states for four different ion impact velocities. For the lowest ion impact velocity, the gain seems to increase linearly with the ions’s potential energy with the gain measured for Ar16+ being roughly twice as large as the gain measur...

Method of processing ion energy distributions using a Thomson parabola ion spectrograph with a microchannelplate image converter camera

A Thomson parabola ion spectrograph (TP) is a very useful tool for the investigation of pulsed laser ablation. Measurements performed with the TP give useful information about physical processes, ion species and their energy distributions, as well as charge states. For ions with the lower charge states, q<20, complete information about energy distributions of all ionization states of ions can be obtained from a single laser shot. For ions with higher ionization states, parabolas generated in the TP interfere and it is impossible to get energy distributions for all the ion species. In this situation, the registered ions are composed of a few groups with different charge states and different energies. The TP enables the charge states and energetic ranges of different ion groups to be estimated. This presentation describes a method of processing experimental results, obtained from a TP, using a microchannelplate (MCP) image converter. Ion energy distributions for C1+–C6+ and Ta1+–Ta12+ are shown, and the eff...

Developments on the KSU-CRYEBIS, a user facility for low energy, highly charged ions

The KSU-CRYEBIS, a CRYogenic electron beam ion source, supplies experiments with low-energy, highly charged ions of numerous species. The supplied charge states cover the range from 1+ to 52+, with typical beam currents of a nA for low charge states and a few pA for the highest charge states. The ion energies cover the range from 0.3 to 165 keV per charge. This is an unusually broad range of final ion energies and hence requires an unusual dynamic ion transport system. This paper presents advances made with respect to the CRYEBIS ion beam transport, diagnostics, and identification. In addition, an update on the developments of ion beams with very high duty cycles is given.

The effect of the first dynode’s geometry on the detection efficiency of a 119EM electron multiplier used as a highly charged ion detector

Abstract The ion counting as well as the current gain of an electron multiplier type 119EM with BeCu dynodes having a Venetian blind structure was measured in terms of the dependence on the position where ions impact the surface of the first dynode. The dependence of the 119EMs detection efficiency on the impact position exhibited large variations across the Venetian blind of the first dynode. The highest detection efficiency was localized at the first dynode’s surface near its output area into the second dynode region. The lowest one was measured at the input area of the first dynode region that is far from the second dynode. The measurements also show that the 119EM is not very reliable for ion counting. The analog particle gain derived from the mean current gain measured across a single slat increases with increasing charge state as well as with ion energy for Coq+(10⩽q⩽26) and Taq+(14⩽q⩽34) ions with kinetic energy per charge from 33 keV/q to 163 keV/q. The gains were derived from comparison with the Faraday cup measurements.

Secondary-electron yield from Au induced by highly charged Ta ions

Abstract The total electron yields, γ , for the emission of electrons induced by the impact of Ta q + (11⩽ q ⩽41) ions with kinetic energy per charge from 15 to 150 keV/q on clean polycrystalline Au are presented. The experimental data are analyzed with use of the relations γ(θ)=γ(0) cos −f θ and γ(θ)=γ above +γ below cos −1 θ . Fits of experimental data give a range of f from ∼0.6 to ∼0.17 and ratio γ above / γ below >1. The analysis also shows that the above-surface electron yield, γ above , strongly depends on the charge state ( γ above ≈ q ) and the below one, γ below , is proportional to the ion impact velocity ( γ below ≈ v ). The correction of cos −1 θ -dependence for fit improvement is discussed.

Electron yield per ion charge-state correction for an ion collector with unsuppressed secondary electron emission

The electron yield per ion charge-state γ/q was measured for emission of electrons from clean polycrystalline gold induced due to impact of Taq+ (11≤q≤41) ions with kinetic energy per chargeEi/q from 15 keV/q to 150 keV/q. The dependence of γ on angle of incidence was analyzed with use of relation γ(ϑ)=γ0 cos−fϑ. The fitting of experimental data gives a range of γ0/q from 1 to 1.75 for Ta13+ and from 1.5 to 1.73 for Ta39+. The dependence of γ0/q onq andEi is discussed with respect to measurement of ion currents emitted from laser-produced plasmas with an ion collector with unsuppressed secondary electron emission.

Calibration of the Galileo microchannel plates with the Xe2+–Xe13+ and C2+–C6+ ions in the energy range from 0.5 to 150 keV/q (abstract)

The procedure of calibration of the detector assembly consisting of the two Galileo microchannel plates (MCPs) operated in a chevron configuration is described. The current gains and the analog particle gains of MCPs for Xe ions with charge states from q=3+ to q=13+ and C ions, with charge states from q=1+ to q=6+ and ion impact energies to charge state ratios from 0.5 to 150 keV/q have been measured. These results were compared to the earlier results obtained of calibration of this detector assembly with Xe ions with the charge states from q=7+ to q=43+ and ion impact energies to charge state ratios from 2 to 154 keV/q. We have shown the areas of ion parameters in which the secondary ion-electron emission coefficient of the investigated MCPs was dominated by kinetic or potential emission.

Observation of different Ta and Pt ion groups produced by laser radiation with the intensities of I λ2∼1015 W cm−2 μm2

Ions produced in a process of interaction of the intense laser radiation of the iodine laser system PERUN (λ=1.315 μm, EL⩽50 J, τ∼350 ps, Iλ2∼1015 W cm−2 μm2) with the solid state tantalum and platinum targets have the ionization states from z=1 up to z∼50 and energies at least a few MeV. The Thomson parabola (TP) ion spectrograph with a registration system based on the micro channel plate (MCP) used in the experiment, gives a general view of ionization states and energies of all types of ions created in one laser shot. The data registered by the PC, gives on-line information on the obtained experimental results. As shown, the calibration measurements of MCPs, made with Ta ions (MCPs different from these used with the TP), analog particle gain of the MCPs rises with the increase in the ion charge states and energy. This attribute causes an increase in sensitivity of MCPs on the highly charged, high energy ions. The registered ions are composed of a few groups of ions with different charge states and diffe...

New improvements on the Kansas State University cryogenic electron beam ion source, a user facility for low energy, highly charged ions

The Kansas State University cryogenic electron beam ion source supplies low energy ion beams to users of the Department of Energy user facility for highly charged ions. The ions escape the source with an initial energy between 1.6 and 5 kV per charge and are analyzed in a 90° dipole magnet located on the high voltage platform. When leaving the platform the ions can be accelerated by up to 160 kV per charge or can be decelerated to about 20% of their initial energy, covering 2.5 orders of magnitude. We are in the process of adding another order of magnitude to the range of available ion energies as a newly installed lens allows for deceleration down to a very few percent of the initial energy. In addition we present the current microbunching and chopping system which has been substantially improved over the past 2 yr.