Manufacturing Bits: April 24

Super electron guns; liquid cell TEMs; material partnerships.


Super electron guns
The Department of Energy’s SLAC National Accelerator Laboratory is developing a new type of electron gun based on superconducting technology.

The new superconducting electron gun recently produced its first beam of electrons, according to SLAC. The technology is being developed for future high-energy X-ray lasers and ultra-fast electron microscopes.

Electron guns are used to produce a beam of high-energy electrons. In operation, an electron gun knocks electrons out of atoms with a laser beam. Then, the electrons can be accelerated to nearly the speed of light in giant storage rings. Researchers use storage rings to conduct various experiments.

Traditional electron guns use cavities, which are made of copper. In contrast, SLAC’s new electron gun makes use of superconducting technology. The cavity is made of niobium. Superconductors are devices that have zero electrical resistance, making them attractive for a range of applications. But superconductors must be cooled down to temperatures at or near absolute zero on the Kelvin scale to work.

SLAC’s accelerator scientists are testing a superconducting electron gun (Dawn Harmer/SLAC National Accelerator Laboratory)

Originally, SLAC’s superconducting gun was built for a project at the University of Wisconsin. Then, two years ago, the electron gun was re-located to SLAC, where it is being used in the field of future electron sources.

Initially, SLAC installed the gun at its Next Linear Collider Test Accelerator (NLCTA). The NLCTA is a facility designed to study accelerator physics and other technologies. In the facility, a 60-150 MeV high-brightness electron beam linear accelerator supports a range of studies.

In the future, the new electron gun could be used for new X-ray lasers. These lasers take X-ray snapshots of atoms and molecules at work, revealing fundamental processes in materials.

SLAC is currently building a new X-ray laser, dubbed the LCLS-II. The laser will use the new electron gun.

Ultrafast electron diffraction and microscopy (UED/UEM) are other applications. Using X-ray techniques, UED/UEM “reveal motions of electrons and atomic nuclei within molecules that take place in less than a tenth of a trillionth of a second,” according to SLAC.

“Superconducting electron guns have the potential to outperform current guns,” said Theodore Vecchione, coordinator of the SLAC project. “For instance, while the electron gun that’s being installed as part of the future LCLS-II will generate electron pulses at an extremely high repetition rate, the superconducting gun should be able to produce similar pulses at four times higher beam energy. It should also be able to achieve twice the beam acceleration over a given distance, producing a tighter beam of electrons with extraordinary average brightness.”

SLAC accelerator physicist Renkai Li added: “In addition to advancing X-ray science, the superconducting technology could also turn into an electron source for the UED/UEM techniques we’re developing. It would further improve the quality of atomic-level images and movies we’re able to capture now.”

Liquid cell TEMs
Michigan Technological University and others have advanced a technology called liquid cell transmission electron microscopy (LC-TEM).

LC-TEM is a version of transmission electron microscopy (TEM). TEM is a destructive metrology technique, where a beam of electrons passes through a sample.

In LC-TEM, the instrument allows for the characterization of a sample in a hydrated state. The samples are liquid or are suspended in liquid. They must be sealed to ensure quality sampling. This technology has some challenges in terms of repeatability. This limits the fidelity and control of the samples.

Researchers from Michigan Technological University and others have advanced an LC-TEM. Researchers said they have created a tiny device “that allows more of the microscope’s electron beam to pass through liquid samples.” This expands the available imaging area. It enables a platform for investigating electron flux history on the sample.

“We have designed and fabricated new devices for holding liquid samples which give us more ‘window’ regions to collect images than were previously available,” said Trevor Moser, a researcher at the Pacific Northwest National Laboratory (PNNL). Moser is also a doctoral student at Michigan Tech.

“Using these multiple windows, we were able to study how the history of electron irradiation influences the nucleation and growth of silver nanoparticles, the growth properties of which are sensitive to the radicals that are generated with the beam. We also used them to study how these radicals impact bacterial cells and demonstrate the extreme sensitivity of these biological samples to the electron beam,” Moser said.

Material partnerships
The Department of Energy’s PNNL and the University of Washington recently formed the Northwest Institute for Materials Physics, Chemistry and Technology (NW IMPACT).

The joint research program will explore and develop materials for use in energy, telecommunications, medicine, information technology and other fields.

Some of the areas in which NW IMPACT will initially focus include: materials for energy conversion and storage; quantum materials; materials for water separation and utilization; and biomimetic materials.

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