Hot Plasma and Fast Ions: High-Performance Laser PHELIX Celebrates Ten-Year Anniversary
As of this month, the high-performance laser PHELIX at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt will have been in operation for ten years. At PHELIX, scientists from around the world have the unique opportunity to conduct experiments that combine laser beams and ion beams produced in the existing accelerator facility. This makes it possible to study extreme states of matter, such as those that occur in stars or inside large planets.
PHELIX (Petawatt High-Energy Laser for Ion Experiments) is one of the most powerful lasers in the world. It can deliver laser pulses with energies of up to 1,000 joules and laser pulses with a power of up to half a petawatt. The output power is quintillion times (billions of billion times) greater than that of a laser pointer or a laser in a CD player.
PHELIX is so large that it takes up an entire building the size of a two-story house with a clean-room atmosphere inside. The laser beam, which has a diameter of 30 cm, is guided to the site of the experiment using special mirrors and focused on a point. A laser pulse can be generated only about every 90 minutes.
Since it was first started up in the year 2008, PHELIX has completed a total of 115 operational periods or “beam times.” Over 100 experiments were successfully performed during these periods, resulting in more than 70 scientific publications. For years, there has been great demand among the research community for beam time at PHELIX. The amount of beam time requested regularly exceeds what can be offered. For this reason, there is an established selection procedure to allow research groups to carry out their experiments at PHELIX. Following the calls to submit proposals for experiments, these proposals are examined by an international committee, and experiments are then selected based on scientific relevance and feasibility.
“At PHELIX, in combination with the GSI accelerator facility scientists can conduct experiments that aren’t possible anywhere else in the world,” says Dr. Vincent Bagnoud, head of the “Plasma Physics/PHELIX” research department at GSI. “The objective is to study matter when it exists in the form of what is called plasma. In this state, the electron shell of atoms is completely or partially separated from the atomic nuclei. This is only possible under extreme conditions and above all at high temperatures of the sort found in stars or inside large planets such as Jupiter.” Plasma is one of the four states of matter — the other, more familiar states being solid, liquid and gaseous. In our everyday lives, we encounter less energetic types of plasma, such as a candle flame or a bolt of lightning during a thunderstorm.
In their experiments, the researchers expose samples of matter to radiation. These samples can be heated up with the laser beam to such a degree that a plasma forms. Just fractions of a second later, they can be bombarded with ions. An analysis of the resulting reactions makes it possible to study the properties of the plasma.
The possibility of using the laser beam to accelerate ions and then transfer them to stationary conventional accelerator structures is also being studied. This combined use of the laser and ion accelerator is unique and enables the generation of very brief ion pulses with high particle counts.
Further improvements are contemplated for the future, especially for use at the FAIR accelerator facility: In the long term, researchers are aiming to use ion acceleration with the laser to achieve different sorts of ions, higher energies and greater intensities. An increase in the pulse repetition rate of the laser is also planned.