NIF&PS Scholar Shows Spark for Laser Experiments

In his spare time, Florida A&M student Jerry Clark figured out how to fix his school’s spheromak fusion reactor, which went unused because one of the diodes would fail during experiments.

After reading the specs and a paper on the device’s design, he concluded there wasn’t enough downward compression on the diodes.

"So, I designed new plates to hold the diodes to compress them more," he said. "That allowed it to fire without blowing up the diodes."

His initiative demonstrated the kind of adaptability that helped lead the 27-year-old Clark to LLNL as a NIF & Photon Science Summer Scholar.

"Experimentalists have to be good in terms of text books, but also have to have an ability to make things work, and he has that extra spark," said NIF Physicist Ronnie Shepherd, Clark’s Lab mentor.

"One of the things that I look for in training students is how well they work in the laboratory, how quickly they adapt to problems, which are always happening in experiments, how quickly you can adjust and recover," Shepherd said. "And he does a very good job of that."

Clark arrived in May and is on an extended stay at the Lab to work on collaborations between NIF and two fusion research projects from outside universities.

One is a followup to Colorado State University experiments, led by Professor Jorge Rocca, using ultra-fast laser pulses to directly heat targets that are arrays of deuterated polyethylene nanowire. Clark is designing experiments that will measure the time-dependent temperature and density of those targets. He’ll likely travel to that school in October.

Radiative Collapse

He’s also working with researchers at Cornell College who are studying the physics of the radiative collapse of plasma being squeezed by a magnetic field. Clark will be using a lab-modified x-ray streak camera (Shepherd calls it "the world’s fastest" of its kind) to measure rising temperatures and densities that should provide signatures of the radiative collapse. He’ll probably head to Cornell in December or January.

Both topics were new to Clark, who pointed to a drawer in his desk to explain how he got up to speed.

"The whole bottom drawer is filled with books on high energy density physics and spectroscopy," he said.

As a youngster growing up in Miami, Clark wanted to work for an outfit with major facilities in another part of Florida—NASA. That made his LLNL tasks this year particularly compelling because "those things are important when you deal with stars and stellar interiors. The luminosity of the star is determined by the opacity of the materials in the star. And the radiation transfer is related to the cooling of the star."

He had always liked chemistry and math, which in a roundabout way led him to physics. "When I went to college, chemistry majors had to take a lot of biology and I wasn’t interested in that at all," he said. "So, I took physics. That’s like math and chemistry without the biology. I enjoyed it, so I stuck with it."

He’s been a research assistant at Florida A&M’s Center for Plasma Science and Technology (CePaST), where he worked on the school’s Spheromak Fusion Reactor. He also has operated a compact neutral particle analyzer at the University of Wisconsin as part of a collaboration with Florida A&M.

In 2014, Clark was an LLNL summer intern in computational chemistry and materials science. After he told Shepherd and inertial confinement fusion physicist Bruce Remington how he revitalized the Florida A&M spheromak, they encouraged him to return to the Lab.

Shepherd said Clark could potentially work on his PhD thesis while at the Lab. That would be fine with Clark, who is excited about his upcoming physics experiments.

"If you have a question you want to answer, a good starting place is always physics," he said.