Supercomputers Fire Lasers to Shoot Gamma Ray Beam

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"To do that, we needed to be able to use many, many processors simultaneously in order to evolve the system in a meaningful length of time to observe what we're trying to find. That was one of the major challenges," Stark said.

"That's why we turned to TACC. We started out by using Lonestar 4. And now we've started working with Stampede more. We're using both 2D and 3D simulations. We're using thousands of processors simultaneously for all these simulations and running them for the better part of a day. We're talking about tens of thousands, up to 60,000 processor hours for one simulation, just to get all the data out. So, we realistically needed to use the facilities here at TACC in order to achieve what we're looking for," Stark said.

What's more, as the particles move through their plasma, they generate the gamma ray photon particles. "The number of particles increases dramatically during the simulations," Arefiev said. "The memory requirements are also very stringent. Stampede, with the extra memory resources was very helpful." And then once you are done with the simulation, you have a lot of data. Even for just a 2-D output, one snapshot can be hundreds of megabytes. That can be tens of gigabytes for a 3D output. And then you have tens and tens of those files."

Hundreds of thousands of computing hours on Stampede and Lonestar were needed not only for the computation but also for the visualization and post-processing of the laser experiment data, said Arefiev.

"The supercomputer can run for a day, but then to post-process the data and to assemble it to determine which electron emitted what photon, that was pretty demanding too. And after that, the visualization takes a lot of time. This would not have been possible without the resources that TACC provided to us," Arefiev said.

"One of the big assets of having Stampede at TACC available for our research is, of course, you can do a lot of productive runs," Toncian said. "You can do parameter variations that you wouldn't have been able to do in the past."

One of the further possibilities opened up by advanced computing in this laser research is the creation of antimatter -- the mirror nemesis of the ordinary matter that makes our existence. When matter and antimatter meet, they annihilate and create gamma rays. Arefiev's team want to reverse the process.

"Potentially," said Arefiev, "you could have a gamma ray collider, which seemed not even feasible until recently, in a laboratory on Earth, to collide two beams of light and actually produce matter. Not just a couple of particles, but a lot of them." Plentiful antimatter creation has eluded even the world's biggest science labs like CERN. It would cost over one million billion dollars to make one gram of antimatter, according to Symmetry magazine.

"There would be a substantial amount of matter in the vacuum created out of light," Arefiev continued. "This can potentially allow people to study some of the processes that are underpinning a lot of phenomena in the universe, in the laboratory."

"Scientists are generally very, very curious," Toncian said. "Their curiosity drives them. In Europe, there is a laser consortium sponsored by the European Union to build a huge laser facility. This huge laser facility would be at least 10 times bigger than what we have here in Texas at UT Austin, in terms of the Texas Petawatt Laser. These are 10 petawatt lasers. They have a huge and broad scientific case in order to be able to finance a lot of these envisioned studies."

Toncian said that what they're doing in Texas with their laser could pave the way for bigger science with the proposed EU laser. "I think the most important outcome of our study is that we can now actually fast track a lot of the science that was planned to be done basically just with this future 10 petawatt laser," said Toncian.

But Texas scientists aren't just going to wait around. Real tests based on the simulations will be performed in 2016 with the Texas Petawatt Laser led by Professors Manuel Hegelich and Todd Ditmire from the Center for High Energy Density Science at UT Austin. "So very soon (at the time of interview), an experiment will probe for the first time the intensity regime we just predicted up to now, theoretically," Arefiev explained. "It's going to be a very interesting time for us to see if these effects will really be seen and measured."

Arevfiev joked that he didn't want to become a victim of his own success. "I told the guys to let me know when they do their runs. The gamma rays are so intense and so energetic that they don't even need to remove the aluminum flanges to detect them. So I would like to stay at home when they do the experiment, just in case everything works," Arefiev said.

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