Exciting Atomic Physics

This is a material edited from the presentation of the

Electron Beam Ion Trap at Lawrence Livermore National Laboratory

captured and edited for teaching purposes by

L. Kocbach

ORIGIN: http://www-phys.llnl.gov/N_Div/ebit.html
AUTHOR: David Knapp

EBIT - The Electron Beam Ion Trap

Project Leader: Dieter H. G. Schneider (schneider2@llnl.gov)

An Electron Beam Ion Trap (EBIT) is a device that produces, traps, and excites very highly charged ions. We have two EBITs at the Lawrence Livermore National Laboratory, called EBIT and Super-EBIT. With these devices, we have performed a wide range of physics experiments. The ions can either be observed in the trap itself or extracted from the trap for external experiments.

Experiments with highly charged ions are at the leading edge of physics research in several areas today. These ions are used to study relativity, quantum electrodynamics, plasma physics, and surface physics.

Recently, we produced bare uranium (U⁹²⁺) in the lab using Super-EBIT, the first time this feat has been accomplished without the use of high-energy particle accelerators.

What an EBIT is and how it works

Research Highlights:

Bare Uranium produced in Super-EBIT
Electron-Ion Interaction Research
X-Ray Spectroscopy
Ion-Surface Interaction Research
RETRAP -- A new trap for ions created in EBIT

Another EBIT has been built at NIST in Gaithersburg, MD.

What is an EBIT?

An Electron Beam Ion Trap, or EBIT, is a device that makes and traps very highly charged ions by means of a high current density electron beam. The EBIT was invented at the Lawrence Livermore National Laboratory by Mort Levine and Ross Marrs. Here is a nice artist's concept of the EBIT. It was an idea based upon the Electron Beam Ion Source (EBIS), a design for an ion source intended for use in atomic physics and as an injector into heavy-ion accelerators. In this country, EBISes have been built at Kansas State, Brookhaven National Laboratory, Cornell University, and (in collaboration with our group) at LBL.

The EBIT is the only ion source in the world that can create highly charged ions at rest. All other sources of highly charged ions involve accelerators that accelerate the ions to very high energies. EBIT, therefore, allows us to study an otherwise inaccessible domain in which the potential energy of an ion is comparable to its kinetic energy.

How an EBIT Works

An EBIT consists of a high-current-density electron beam (up to 5000 A/cm^2) passing through a series of three drift tubes. Ions are trapped radially by the space charge of the electron beam itself, and axially by voltages applied to the end drift tubes.

The electron beam is magnetically compressed by a high magnetic field from a pair of superconducting Helmholtz coils. The electron beam energy in the trap is determined by the voltage applied to the central drift tube.

As electrons collide with the ions in the beam, they strip off electrons until the energy required to remove the next electron is higher than the beam energy. Our original EBIT is capable of an electron beam energy of about 30 keV, enough to make neonlike uranium (U⁸²⁺, or a uranium atom with only 10 of the usual 92 electrons). We have built a high-energy EBIT, named Super-EBIT, with a floating electron gun, that can achieve an electron beam energy of 200 keV, enough to make bare uranium (U⁹²⁺, a uranium nucleus with no electrons around it).

To find out about experiments done with the EBITs, go back to the EBIT Introduction .

The original of this page was prepared by David Knapp
dk@llnl.gov

UCRL-MI-119598