Plasma lenses, with their extra-large focusing strength, may be a natural complement to high-gradient, plasma-based accelerators. Beam focusing by plasmas has been demonstrated both for electrons and positrons but has not yet achieved the tight beam sizes required for collider applications. Studies of plasma lenses at FACET will explore several potential means to improve performance through tests of lens formation and characteristics.
By tweaking the properties of the electron beam, the plasma, and the environment they sit in—effectively a plasma lens—scientist hope to discover the ultimate limit for how tightly a beam can be focused by a plasma and use that knowledge to design the best possible accelerator.
The combination of a well-characterized high-energy, high-density electron beam, a plasma source, specialized instrumentation, and techniques developed for the plasma acceleration research are critical components to any plasma lens program and make FACET a natural facility for conducting this research.
Dielectric Wakefield Acceleration
Future accelerators with ultra-high fields will not be based on conventional metallic resonant cavities, because the power necessary to drive such structures becomes excessive. This forces consideration of devices that operate at higher frequencies, such as terahertz linear accelerator structures.
In a dielectric wakefield accelerator, electromagnetic power is radiated by an ultra-short, intense "driving" electron bunch propagating in a hollow dielectric fiber. This power is then used to accelerate another "witness" bunch just as in the case of the plasma wakefield accelerator.
Sufficient available power for high acceleration gradients depends on having high peak currents, a small inner radius of the hollow dielectric fiber, and, therefore, a drive beam with high-charge, short duration and a very small profile to propagate through the fiber. The required beam can be provided only by FACET, making it a one-of-a-kind facility for exploring dielectric wakefield acceleration.