Plasma Acceleration: Intro to Laser Plasma Accelerators

Particle acceleration is one of the most important scientific instruments of the modern world. Without it, we wouldn’t understand nuclear physics, astrophysics, or even fundamental physics (to this degree). Moreover, the technology has a vast application in medical science and industry.

The biggest problem with particle acceleration is that you can only achieve it in massive particle accelerators like at SLAC, CERN, Fermilab, KEK, or DESY. In other words, the process is incredibly expensive and limited to just a few facilities worldwide.

This is why plasma acceleration may be seen as such a great alternative. By interacting with plasma, high-powered lasers can accelerate charged particles. This would achieve a similar effect much more cost-effectively.

This doesn’t just mean saving money. It also means creating more simultaneous instances of particle acceleration, which could lead to scientific discoveries so far undreamed.

For those interested in learning more, here’s how the laser-plasma accelerator may change the world as we know it.

What are the types of accelerators?

To understand this subject better, we should briefly address the types of conventional particle accelerators currently in use. There are several types that you might have encountered in your research:

• Linear accelerators: As their name suggests, linear accelerators accelerate particles in a straight line. These are most commonly used for industrial or medical radiation purposes. In this process, radiofrequency cavities accelerate particles, which generates electromagnetic fields.
• Cyclotrons: This accelerator combines electric and magnetic fields to make particles spiral outward in a circular path. The acceleration happens because they gain energy with each revolution. This type of accelerator is most commonly used in the medical field (isotopes for imaging and cancer treatment).
• Storage rings: This accelerator bends the particle trajectory through the combination of magnets. This method stores and circulates high-energy particles, and its most common application is in physical experiments.
• Synchrotrons: Similar to cyclotrons in nature, Synchrotrons can accelerate particles to much higher energies than its counterpart. Most commonly, they’re used for intense X-ray radiation.

Even though lasers may be an improvement over many of these existing technologies, these accelerators are already well-established and in decades-long use.

What is plasma acceleration?

Plasma is the fourth fundamental state of matter (aside from solid, liquid, and gas), an ionized gas consisting of charged particles (ions and electrons). Since plasma is electrically conductive, high in energy, and highly responsive to fields (both electric and magnetic), it can create an electric field that accelerates charged particles in response to the electric field in an ultra-intense laser pulse" or "its interaction with the electric field in an ultra-intense laser pulse can create an electric field that accelerates charged particles.

Specifically, the laser pulse exerts its force on the plasma electrons, which expels electrons in a specific region, creating an electron-density depression or bubble. Inside this bubble, there are only ions, so it has a net positive charge. At the back of the bubble, there is an electron wall, which has a net negative charge. The combination of these creates a strong electric field that travels at the speed of light in the plasma, accelerating any electrons trapped in that field to relativist speeds".

Generally speaking, there are two major types of plasma acceleration:

• PBA: Plasma-based acceleration in which the laser pulse directly drives plasma waves.
• LWFA: Laser Wakefield Acceleration, where the electrons need to be trapped in the electric field created in the plasma (like we’ve already described). The biggest limit to the maximum achievable repetition rate is the recovery time of a plasma Wakefield accelerator.

While all of this sounds pretty great, the system is still new and crude, which is why there are many improvements to be made before the end.

What are particle accelerators used for?

To understand the importance of this development, it’s important that you understand what particle accelerators were used for in the past. The applications are numerous:

• When we say that our understanding of fundamental physical principles has deepened significantly since we started dabbling in particle acceleration is by no means an exaggeration. Understanding basic particles like leptons and quarks would be near-impossible without particle acceleration. Phenomena like Higgs boson and dark matter have brought us closer to understanding the early universe, its origin, and the fundamental structure of matter. Generally speaking, laser science research is proving to be a far greater breakthrough than anyone expected.
• In manufacturing and industrial development, particle acceleration (and, by extension, plasma particle accelerator) may help us understand how different materials act in extreme environments. Not to mention that irradiation and ion implantation are incredibly important in material modification and enrichment processes.
• Particle therapy and proton therapy may be the answer we’re looking for in our struggle against cancer. By precisely targeting tumors, we can eliminate them with minimal damage to the healthy surrounding tissues. This could minimize (or eliminate) the side effects of some highly-aggressive treatments.
• Finally, the laser accelerator may help us understand our own planet a lot better. Since we can develop a better analysis of the composition of materials, we can make much more accurate estimates in archeology and geochemistry. This way, our understanding of planetary formation and evolution  will become far more dependable.

With the introduction of plasma acceleration, the availability of this scientific method will grow exponentially.

Reasons why plasma acceleration is the future

First of all, plasma laser accelerators are incredibly compact in their design. They’re made to be smaller, more pragmatic, with higher acceleration gradients in shorter distances. Beyond doubt, this will make them more accessible in various industries.

Beam quality is also marking a huge improvement over the last several years. The energy spread is drastically reduced, and the stability has been greatly improved.

Electron acceleration is not the only field that’s marking growth. Namely, laser-driven ion acceleration is also getting more attention than ever before. This could introduce the field of nuclear physics into a new millennium faster than anyone expected.

Finally, integration with other acceleration techniques is more feasible than ever before. This means that instead of being its staple (or only component), they can be coupled with  conventional acceleration methods to form hybrid accelerators Already groups in the the U.S. and Europe are working on hybrid designs.

Wrap up

Most importantly, this field is rapidly evolving, and with increased results, there’s bound to be an increased interest in the field. Increased interest inevitably leads to greater talent attention and investments, which will exponentially grow the development of this field in the future. In other words, improving particle acceleration with the help of high-powered lasers is highly anticipated. We just need to wait and see when and how it will reach its full swing.

Join us at LaserNetUS to enhance your knowledge of laser plasma accelerators.