For the first time, scientists have obtained images of a rare plasma instability, capturing high-energy electron beams forming into spaghetti-like filaments.
This breakthrough was achieved by researchers at the Imperial College London. They provided crucial insights into a phenomenon that impacts plasma-based particle accelerators and fusion energy research. The researchers utilized a high-intensity infrared laser to generate and then image a “Weibel-like current” instability.
Plasma is a super-hot mixture of charged particles. It can experience instabilities when particle flow varies. This causes some particles to clump together into thin filaments. These filaments generate magnetic fields that further destabilize the plasma. This process can disrupt important applications like triggering fusion.
Dr. Nicholas Dover is a research fellow at Imperial College London and the John Adams Institute for Accelerator Science. He said, “The reason we are particularly interested in instabilities is because they tend to mess up the applications, like injecting energy into plasma to trigger fusion. Normally, we want to avoid instabilities, but to do that we need to understand them in the first place.”
The experiment involved firing a high-intensity laser into a stationary plasma, creating a high-energy electron beam. Instead of passing smoothly, the beam disrupted the plasma, triggering fluctuations that caused electrons to clump into thin filaments. This process further destabilized the plasma in a “snowball effect” of magnetic field generation.
Scientists have long inferred this instability, however, directly observing it has been a serious challenge. This study marks the first successful capture of images of this phenomenon in a laboratory.
The research team is a collaboration between Imperial College London’s John Adams Institute for Accelerator Science, Stony Brook University, and Brookhaven National Laboratory. Their study utilized two synchronized lasers.
The two lasers consisted of a unique high-intensity, long-wave infrared laser at Brookhaven’s Accelerator Test Facility and a shorter wavelength optical probe laser.
The infrared laser created the electron beam, and the optical laser captured images of the instability. The long-wave infrared laser allowed researchers to control energy deposition in the plasma. This enabled observation with the visible laser probe. This accomplishment is typically difficult with standard lasers due to plasma density.
The plasma in this research was generated using gas targets, allowing precise tuning of plasma density. Adjusting the density allowed researchers to study how filament size changed, resulting in unprecedented close-up images of the instability. Dr. Dover added, “We were really amazed by how good the photographs were because with optical lasers, it’s really hard to take nice photographs of the plasma.”
Brookhaven’s Accelerator Test Facility intends to upgrade the optical laser to enable clearer, more precise images in shorter time intervals. This change will allow real-time observation of laser-plasma interactions.
Professor Zulfikar Najmudin is the Deputy Director of the John Adams Institute. He emphasizes the potential of this research, noting that achieving ten million electron volt energy levels in such a small gas target is virtually unheard of in other interactions.
The findings of this research can have a major impact on ongoing fusion research. Plasma stability is one of the most critical requirements for sustaining nuclear fusion reactions and generating power.
The current fusion world record is for twenty-two-minute plasma stability. It was recently set by France at the Tungsten (chemical symbol “W”) Environment in Steady-state Tokamak (WEST) reactor. Now, scientists across the world are trying to increase the duration of plasma stability to develop nuclear fusion for commercial use.
