— Project will enable staging of multiple plasma accelerator modules, key step towards a new generation of compact high energy particle accelerators
A second beamline of the BELLA Petawatt laser is being constructed as a DOE Accelerator Improvement Project via the Office of High Energy Physics. The second beamline will enable experiments combining two laser driven plasma accelerator stages at multi-GeV scale, as well as experiments on high brightness beam injection and controllable structures for precision beams. In May, a major subsystem, the beam compressor, was successfully installed.
Plasma based accelerators achieve accelerating gradients (the amount of energy added to the beam per unit of distance) thousands of times higher than conventional accelerators. The BELLA Center recently set a record of 8 GeV energy gain in just 20 centimeters, an energy that would require hundreds of meters in a conventional accelerator. GeV energies enable a range of photon source applications, including mono-energetic photon sources for security and medicine, as well as compact free-electron lasers.
Realizing the potential of plasma accelerators to extend the energy frontier of high energy physics, enabling future discoveries in fundamental physics, requires collision of beams at energies of the TeV scale, a hundred times current records. Achieving these energies with efficiency, and with the beam charge that is suitable for a collider, will require combining many stages in sequence, each adding a few to 10 GeV of energy to the beam. Previous experiments showed that this is possible at lower energies.
The new second beamline will allow combination of stages at multi-GeV energies, a key step in the roadmap for plasma accelerator based future colliders. The project will split the output of the BELLA Petawatt laser, allowing the driving of two stages. Each stage will be driven by an independent laser pulse to allow control and to prototype the structure of a future collider which would use one laser per stage to distribute power requirements. Each arm must have a separate pulse compressor, the optical system that creates the short duration pulse required to drive the plasma accelerator from the longer pulse that is amplified in the laser.
Besides staging, providing two independent laser pulses additionally enables other critical experiments that will advance the development of plasma accelerators. A second laser pulse can be used to inject a high quality particle bunch into the accelerator, or to form specially tailored plasmas that could improve the acceleration process for electrons. It could also be used to create and accelerate positrons. Each of these is required for plasma accelerators to reach the performance needed for collider and other applications.
In May, the second beamline compressor was successfully installed by vendor Thales. This builds on months of ATAP and Engineering effort preparing and installing the vacuum chamber and supporting systems. This compressor is the largest subsystem in the project. Inside the large vacuum chamber are very specialized optics that compress the incoming, relatively long laser pulse to ultrashort durations (tens of femtoseconds), which then enables experiments at very high peak laser power (up to 1 PW). Compressor installation is a major project milestone that required coordinated work between the ATAP Division and Engineering Division teams and external vendor personnel. Members of the ATAP Operations Team, EHS Division, Human Resources Shared Services, the International Researchers and Scholars team (IRSO), Security and Emergency Services, and Facilities collaborated with the BELLA Center team to enable work by external personnel. The installation was successfully completed. Installation of the laser beamlines that will deliver the pulses from the laser to the compressor and then to the target area is now in progress.
The second stream of laser pulses that the project will provide will support future experiments ranging from staging of multiple modules, to creation of ultra-bright beams, to positron acceleration and stage efficiency, that will advance the critical aspects of plasma-based accelerators for future particle colliders and related applications.