World’s highest-voltage gun fires 70 billion electrons at record 80% light speed

Scientists at the US Department of Energy’s (DOE) Brookhaven National Laboratory have created and tested the highest-voltage polarized electron gun to date.

This technology is critical to building the first fully polarized Electron-Ion Collider (EIC).

In order to study the innermost components of visible matter, scientists are building the state-of-the-art nuclear physics facility known as the EIC at Brookhaven in collaboration with the DOE’s Thomas Jefferson National Accelerator Facility (Jefferson Lab).

According to the team, the facility will accelerate and collide polarized electrons with polarized protons and ions, or atoms stripped of their electrons.

“This gun not only exceeds the EIC requirements, but we also get world-leading results,” said Erdong Wang, a physicist at Brookhaven and the chief architect and implementor of the device, in a statement.

Polarized beam innovation

The direct-current, laser-driven polarized electron gun at the Electron-Ion Collider (EIC) serves as a starting point for one of the collider’s particle streams. It launches electrons at 80 percent of the speed of light in just two inches, and its key function is delivering beams with aligned particle spins.

This means the acceleration speed of 500 million miles per hour in just “two ten-billionths of a second.”

Scientists want to map the internal structure of the proton and learn more about how proton spin develops from quarks and gluons by colliding polarized electrons with polarized protons. The polarization is essential for researching proton spin, an enigmatic aspect of matter.

A group led by Wang created a special gallium arsenide photocathode, designed in conjunction with Old Dominion University and Jefferson Lab, to satisfy the demands of the EIC.

This structure produces highly polarized beams because of its reflecting coatings and layers. Quark-gluon interactions are studied further by applying a high voltage between the photocathode and anode, which drives low-energy electrons into the collider.

High electron acceleration

The scientists use a laser to free electrons from the photocathode, tuning its wavelength to optimize electron polarization and efficiency.

Quick laser pulses produce brief electron bunches, with roughly 70 billion electrons in each, that are perfect for acceleration. The group can swiftly reverse the spin direction of the released electrons by polarizing the laser differently, which enables comparison during collisions.

The apparatus’s enclosure in an extremely high vacuum safeguards the photocathode. According to a statement , the group created a unique high-voltage connector that was installed inside the gun, eliminating the necessity for insulating gases like sulfur hexafluoride, a strong greenhouse gas.

This creative design keeps the system cool by preventing voltage leakage through the use of a cone-shaped connector filled with dielectric fluid. To further ensure safety, a semiconductor coating on the cable drains potentially hazardous charges. This configuration lowers safety concerns and improves the system’s environmental friendliness because it produces no greenhouse gases.

The Brookhaven team dealt with issues such as hydrogen gas leaking into the vacuum from stainless steel, which might cause interference with the electron beams. To avoid this, they gently used crushed corn cobs to polish the stainless-steel sections to a mirror finish after baking them at 1,650°F to remove trapped gases.

After assembling the gun and removing surface contaminants through another bake, the gun was tested. It reached 350 kilovolts in 23 hours and operated maintenance-free for six months, producing high-quality electrons for the EIC.

The team is now developing higher-voltage guns and next-stage acceleration components.

The details of the team’s research were published in the journal Applied Physics Letters .