D.A. Knapp

The use of an electron beam ion trap in the study of highly charged ions

The Electron Beam Ion Trap (EBIT) is a relatively new tool for the study of highly charged ions. Its development has led to a variety of new experimental opportunities; measurements have been performed with EBITs using techniques impossible with conventional ion sources or storage rings. In this paper, I will highlight the various experimental techniques we have developed and the results we have obtained using the EBIT and higher-energy Super-EBIT built at the Lawrence Livermore National Laboratory.

A high-energy electron beam ion trap for production of high-charge high-Z ions

Abstract We have developed a new high-energy electron beam ion trap, the first laboratory source of low-energy, few-electron, high- Z ions. We describe the device and report measurements of its performance, including the electron beam diameter, current density and energy, and measurements of the ionization balance for several high- Z elements in the trap. This device opens up a wide range of possible experiments in atomic physics, plasma physics, and nuclear physics.

High‐resolution x‐ray spectrometer for an electron beam ion trap

A high‐throughput von Hamos‐type Bragg crystal spectrometer is described that is operated with the Livermore electron beam ion trap. The spectrometer is employed to measure high‐resolution x‐ray spectra from highly charged heliumlike and neonlike ions. Data from heliumlike Ti20+ and Fe24+ and from neonlike Au69+ are presented to demonstrate the utility of the new instrument.

Confinement in a cryogenic penning trap of highest charge state ions from EBIT

The retrapping of highly charged Xe44+ and Th68+,72+ ions extracted from an ‘‘electron‐beam ion trap’’ (EBIT) is demonstrated after injection of the ions into RETRAP, a cryogenic Penning trap (up to 6 T magnetic field) currently with an open cylinder design. Ion extraction in a short pulse (5–20 μs) from EBIT, essential for efficient retrapping, is employed. The ions are slowed down upon entering a deceleration tube mounted above the trap within the magnetic field. The potential is then rapidly (100 ns) decreased, enabling low‐energy ions to enter the trap. Capture efficiencies up to 25% are observed via detection of the delayed ion release pulse with a detector below the trap. Signal voltages induced in a tuned circuit due to single and multiple ions have been observed by tuning the ion resonant axial oscillation frequencies for different ions. Results from transporting and retrapping of the ions, as well as their detection, are described and the trapping efficiency is discussed. The motivation for these...

Evaporative cooling of highly charged ions in EBIT: An experimental realization

Both the total number and trapping lifetime of near‐neon‐like gold ions held in an electron beam ion trap have been greatly increased by a process of ‘evaporative cooling.’ A continuous flow of low‐charge‐state ions into the trap cools the high‐charge‐state ions in the trap. Preliminary experimental results using titanium ions as a coolant are presented.

Studies of the interaction of slow very highly charged ions with solid surfaces using the LLNL EBIT facility

A summary of the present status of the LLNL EBIT based research program on highly charged ion-solid surface interaction is presented. New results for coincidence measurements of K”-KP X-ray emission for Fe 26f incident on Al, using two Ge detectors are presented. It is shown that excellent resolution of the satellite and hypersatellite lines are achieved, in excess of what is possible with single Ge detector measurements. Recent results from ongoing investigations on electron emission, sputtered ion and energy loss phenomena are presented. Results from charge-state analysis of grazing incidence specular scattering of highly charged ions off atomically flat surfaces of gold, carbon and mica indicate that the incident ion essentially reaches ground state of its electronic distribution within the ion-surface interaction time of - 100 fs. Atomic force microscopy is used to investigate the formation of a new type of ion induced surface defect, peculiar to highly charged ion-surface interactions. A linear correlation, between the defect volume and the incident ion charge, supports a mechanism of defect formation due to potential energy induced electron emission and subsequent collective displacement due to local charge imbalance.

Studies of He‐like krypton for use in determining electron and ion temperatures in very‐high‐temperature plasmas

High‐resolution measurements of the He‐like Kr K‐shell radiation are presented showing the direct excitation lines as well as Li‐ and Be‐like dielectronic recombination lines appearing in the KLL resonance. The measurements were performed on the Electron Beam Ion Trap (EBIT) facility and motivated by the need for accurate atomic data of high‐Z He‐like K‐shell transitions for diagnostic applications in determining the central ion and electron temperature of very‐high‐temperature plasmas produced in next‐generation tokamaks, such as the International Thermonuclear Experimental Reactor (ITER).

The super electron beam ion trap

A 200-keV super electron beam ion trap is being used to study the few electron ions of heavy elements. This device can produce and trap any highly charged ion at rest in the laboratory, including bare U92+ ions. Measurements of the ground state binding energies of hydrogenlike and heliumlike ions, and the 2s-2p transition energies in lithiumlike through fluorinelike ions are being used to determine the QED energies in high-Z ions. The ionization cross sections for hydrogenlike and heliumlike high-Z ions are being directly measured for the first time. There are future opportunities for several new kinds of experiments.

EBIT: Electron beam ion trap

An electron Beam Ion Trap (EBIT) has been built as an instrument for in situ studies of atomic physics. Based on the EBIS concept, EBIT incorporates several novel features including ion cooling using light ions and plasma instability control using a short trap length. To understand the operation of EBIT, measurements have been made of the electron beam behavior. The radius of the beam is observed to follow Herrmann Theory during compression. The electron beam displays an energy dispersion that is larger than theory. However, this energy dispersion is only about 15% of the electron temperature in the trap due to the adiabatic compression of the beam.

Dielectronic recombination measurements of highly‐charged heliumlike and neonlike ions using an electron beam ion trap

The electron beam ion trap (EBIT) at LLNL is a unique device designed to measure the interactions of electrons with highly‐charged ions. We describe three methods used at EBIT to directly measure the dielectronic recombination (DR) process: (1) The intensity of the stabilizing X rays is measured as a function of electron beam energy; (2) The ions remaining in a particular ionization state are counted after the electron beam has been held at a fixed electron energy for a fixed time; and (3) High‐resolution spectroscopy is used to resolve individual DR satellite lines. In our discussions, we concentrate on the KLL resonances of the heliumlike target ions (V21+ to Ba54+), and the LMM resonances of the neonlike target ions (Xe44+ to Th80+).