Amazing stuff!
"... The machine is known as the Electron-Ion Collider (EIC) and it is being developed by scientists at the US Department of Energy's Brookhaven National Laboratory. The goal of the machine is to be able to accelerate electrons in one stream and collide them with atoms that have been stripped of their own electrons traveling in another stream in the opposite direction. This will all take place in a circular collider measuring 2.4 miles in circumference. ...
Accelerating the electrons is just one of the tasks assigned to the gun. The other is to be able to create tightly packed groups of the particles and control their spin as well. To accomplish this, the researchers created a photocathode – the component that creates photoelectric electrons – out of thin nanosheets of gallium arsenide crystals. By striking this cathode with a laser, the team was able to release electrons and control whether they spun in a forward or backward direction. ..."
"Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have designed and tested the world’s highest voltage polarized electron gun, a key piece of technology needed for building the world’s first fully polarized Electron-Ion Collider (EIC). The EIC ... will accelerate and collide polarized electrons with polarized protons and ions — atoms stripped of their electrons — so scientists can investigate the innermost building blocks of visible matter. ..."
From the abstract:
"The polarized electron source is a critical component in accelerator facilities such as the electron–ion collider, which requires a polarized electron gun with higher voltage and higher bunch charge than existing sources. One challenge we faced was the surface charge limit of the distributed Bragg reflector GaAs/GaAsP superlattice (DBR-SL-GaAs) photocathode. We suppressed this effect by optimizing the surface doping and heat cleaning procedures. We achieved up to 11.6 nC bunch charge of polarized electron beam. In this report, we discuss the performance of tests of a DBR-SL-GaAs photocathode in the high voltage direct current gun. Possible reasons for the observed peak quantum efficiency wavelength shift are analyzed, and we addressed it by using a wavelength tunable laser. In addition, the impact of the DBR layer and laser on the lifetime is investigated in this paper. The optimal DBR-SL-GaAs operating zone has been proposed, which gave us a long lifetime and high polarization at 30 μA operation. The success of this polarized gun will be key to the future of the nuclear sciences."
High-Voltage Gun Accelerates Electrons from Zero to 80 … Percent the Speed of Light (original news release) "Scientists and engineers develop world's highest-voltage, highest-intensity polarized photocathode electron gun, a crucial component for the future Electron-Ion Collider"
High-intensity polarized electron gun featuring distributed Bragg reflector GaAs photocathode (no public access)
EIC [electron–ion collider] schematic: This graphic shows the location of the photocathode electron gun (Electron Source) that will produce the electron beam that enters the electron accelerator and storage rings for collisions with protons or ions traveling in the opposite direction.
The photoelectric effect: Incident light (wavy line) with sufficient energy can knock electrons (violet spheres) free from a photoelectric material. For the EIC electron gun, the light will come from a laser and the photocathode will be a thin layered wafer of gallium arsenide with a periodic structure that ensures electrons are emitted with their spins aligned.
Polarized electron gun: The cone-shaped high-voltage (HV) feedthrough connector delivers current to gun. When laser photons strike the gallium-arsenide (GaAs) photocathode, emitted electrons flow from cathode to anode and out of the gun as a highly polarized electron beam (e-beam).
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