## Posts Tagged ‘accelerator technology’

### Superconducting test accelerator achieves first electron beam

Monday, March 30th, 2015

Last week the first SRF cavities of Fermilab’s superconducting test accelerator propelled their first electrons. Photo: Reidar Hahn

The newest particle accelerators and those of the future will be built with superconducting radio-frequency (SRF) cavities, and institutions around the world are working hard to develop this technology. Fermilab’s advanced superconducting test accelerator was built to take advantage of SRF technology accelerator research and development.

On Friday, after more than seven years of planning and building by scientists and engineers, the accelerator has delivered its first beam.

The Fermilab superconducting test accelerator is a linear accelerator (linac) with three main components: a photoinjector that includes an RF gun coupled to an ultraviolet-laser system, several cryomodules and a beamline. Electron bunches are produced when an ultraviolet pulse generated by the laser hits a cathode located on the back plate of the gun. Acceleration continues through two SRF cavities inside the cryomodules. After exiting the cryomodules, the bunches travel down a beamline, where researchers can assess them.

Each meter-long cavity consists of nine cells made from high-purity niobium. In order to become superconductive, the cavities sit in a vessel filled with superfluid liquid helium at temperatures close to absolute zero.

As RF power pulses through these cavities, it creates an oscillating electric field that runs through the cells. If the charged particles meet the oscillating waves at the right phase, they are pushed forward and propelled down the accelerator.

The major advantage of using superconductors is that the lack of electrical resistance allows virtually all the energy passing through to be used for accelerating particle beams, ultimately creating more efficient accelerators.

The superconducting test accelerator team celebrates first beam in the operations center at NML. Vladimir Shiltsev, left, is pointing to an image of the beam. Photo: Pavel Juarez, AD

“It’s more bang for the buck,” said Elvin Harms, one of the leaders of the commissioning effort.

The superconducting test accelerator’s photoinjector gun first produced electrons in June 2013. In the current run, electrons are being shot through one single-cavity cryomodule, with a second, upgraded model to be installed in the next few months. Future plans call for accelerating the electron beam through an eight-cavity cryomodule, CM2, which was the first to reach the specifications of the proposed International Linear Collider (ILC).

Fermilab is one of the few facilities that provides space for advanced accelerator research and development. These experiments will help set the stage for future superconducting accelerators such as SLAC’s Linac Coherent Light Source II, of which Fermilab is one of several partner laboratories.

“The linac is similar to other accelerators that exist, but the ability to use this type of setup to carry out accelerator science experiments and train students is unique,” said Philippe Piot, a physicist at Fermilab and professor at Northern Illinois University leading one of the first experiments at the test accelerator. A Fermilab team has designed and is beginning to construct the Integrable Optics Test Accelerator ring, a storage ring that will be attached to the superconducting test accelerator in the years to come.

“This cements the fact that Fermilab has been building up the infrastructure for mastering SRF technology,” Harms said. “This is the crown jewel of that: saying that we can build the components, put them together, and now we can accelerate a beam.”

Diana Kwon

### Fermilab contributes to SLAC LCLS-II with cutting-edge technology and expertise

Wednesday, February 11th, 2015

Fermilab is developing superconducting accelerating cavities similar to this one for SLAC’s Linac Coherent Light Source II. Photo: Reidar Hahn

Now one year into its five-year construction plan, the Linac Coherent Light Source II, an electron accelerator project at SLAC, will produce a high-power free-electron laser for cutting-edge scientific explorations ranging from refined observations of molecules and cellular interactions to innovative materials engineering. Cornell University as well as Argonne National Laboratory, Lawrence Berkeley National Laboratory, Fermilab and Thomas Jefferson National Accelerator Facility are partners in the SLAC-directed project.

“We at the laboratories are all developing close ties,” said Richard Stanek, Fermilab LCLS-II team leader. “The DOE science lab complex will be stronger for this collaboration.”

In 2015, Fermilab will intensify its LCLS-II contribution in the overlapping areas of superconducting radio-frequency (SRF) accelerator technology and cryogenics, critical components that distinguish LCLS-II from SLAC’s current LCLS facility, whose laser production has enabled noted scientific investigations in cancer treatment and other important areas.

SLAC physicist Marc Ross, LCLS-II cryogenics systems manager, said LCLS cannot keep up with scientists’ requests for use. The existing LCLS facility and LCLS-II combined will offer researchers laser X-rays with a wide range of properties.

“This new approach will transform the repetition rate of LCLS — from 120 pulses per second to up to 1 million per second,” Ross said. “This will allow a completely new class of experiments and, eventually, a much larger number of experimental stations operated in parallel.”

Fermilab Technical Division physicists Hasan Padamsee, division head, and Anna Grassellino and their team are working on SRF technology for LCLS-II, in particular on implementing Fermilab’s two recent findings to reduce the needed cryogenic power. In one innovation, known as nitrogen doping, Grassellino found that infusing a small amount of nitrogen gas when preparing the superconducting cavities — the structures through which beam is accelerated — reduces two main causes of the usually expected resistance to radio-frequency currents.

“It is exciting to see our discovery becoming an enabling technology for LCLS-II,” Grassellino said.

Grassellino’s high-Q team has also found that the cavities’ cooling dynamics significantly helps expel magnetic flux, another major source of cavity power dissipation. The Fermilab high-Q team, together with Cornell University and Jefferson Lab, are currently working on calibrating the cooling thermogradient for LCLS-II.

Stanek said Fermilab is advancing its SRF work with its LCLS-II participation.

“I see this project taking us from an R&D phase of SRF technology, which is where we have been the past six to eight years, and moving our expertise into production,” Stanek said. “This is a big step forward.”

Fermilab and Jefferson Lab are working closely together on the cooling systems that enable the cavities’ superconductivity. Fermilab scientist Camille Ginsburg leads LCLS-II cryomodule production at Fermilab, and Fermilab engineer Arkadiy Klebaner manages the LCLS-II cryomodules distribution system.

“To build a high-energy beam using SRF technology, LCLS-II needed expertise in cryogenics,” Klebaner said. “So Jefferson Lab and Fermilab, who both have special expertise in this, were ready to help out.”

A cryogenic plant generating the refrigeration, a cryogenic distribution system for transporting the refrigeration into cryomodules and the cryomodules themselves make up the LCLS-II cryogenics. Jefferson Lab will provide the cryogenic plant, and Fermilab is in charge of developing the cryogenic distribution system. Jefferson Lab and Fermilab are jointly developing LCLS-II’s 35 cryomodules, each one about 10 meters long.

Fermilab’s contribution draws on the Tevatron’s cryogenics and on SRF research begun for the proposed International Linear Collider. The lab’s LCLS-II experience will also help with developing its planned PIP-II accelerator.

“So when we build the next accelerator for Fermilab, PIP-II, then we will have already gotten a lap around the production race course,” Padamsee said.

All labs have something special to contribute to LCLS-II, Ross said.

“The Fermilab team have figured out a way to make this kind of accelerator much better operating in the cold temperature that superconducting technology requires,” Ross said. “It is worthy of special recognition.”

Rich Blaustein

### New technique for generating RF power may dramatically cut linac costs

Monday, November 3rd, 2014

A team from the Accelerator Division has successfully powered this small SRF cavity with a magnetron. Now they aim to power a large, application-specific model. Photo: Brian Chase, Fermilab

If you own a magnetron, you probably use it to cook frozen burritos. The device powers microwave ovens by converting electricity into electromagnetic radiation. But Fermilab engineers believe they’ve found an even better use. They’ve developed a new technique to use a magnetron to power a superconducting radio-frequency (SRF) cavity, potentially saving hundreds of millions of dollars in the construction and operating costs of future linear accelerators.

The technique is far from market-ready, but recent tests with Accelerator Division RF Department-developed components at the Fermilab AZero test facility have proven that the idea works. Team leaders Brian Chase and Ralph Pasquinelli have, with Fermilab’s Office of Partnerships and Technology Transfer, applied for a patent and are looking for industrial partners to help scale up the process.

Both high-energy physics and industrial applications could benefit from the development of a high-power, magnetron-based RF station. The SRF cavity power source is a major cost of accelerators, but thanks to a long manufacturing history, accelerator-scale magnetrons could be mass-produced at a fraction of the cost of klystrons and other technologies typically used to generate and control radio waves in accelerators.

“Instead of paying $10 to$15 per watt of continuous-wave RF power, we believe that we can deliver that for about \$3 per watt,” Pasquinelli said.

That adds up quickly for modern projects like Fermilab’s Proton Improvement Plan II, with more than 100 cavities, or the proposed International Linear Collider, which will call for about 15,000 cavities requiring more than 3 billion watts of pulsed RF power. The magnetron design is also far more efficient than klystrons, further driving down long-term costs.

The magnetron project members are, from left: Brian Chase, Ed Cullerton, Ralph Pasquinelli and Philip Varghese. Photo: Elvin Harms, Fermilab

But the straightforward idea wasn’t without obstacles.

“For an accelerator, you need very precise control of the amplitude and the phase of the signal,” Chase said. That’s on the order of 0.01 percent accuracy. Magnetrons don’t normally allow this kind of control.

One solution, Chase realized, is to apply a well-known mathematical expression known as a Bessel function, developed in the 19th century for astronomical calculations. Chase repurposed the function for the magnetron’s phase modulation scheme, which allowed for a high degree of control over the signal’s amplitude. Similar possible solutions to the amplitude problem use two magnetrons, but doubling most of the hardware would mean negating potential savings.

“Our technique uses one magnetron, and we use this modulation scheme, which has been known for almost a hundred years. It’s just never been put together,” Pasquinelli said. “And we came in thinking, ‘Why didn’t anyone else think of that?'”

Chase and Pasquinelli are now working with Bob Kephart, director of the Illinois Accelerator Research Center, to find an industry partner to help them develop their idea. Inexpensive, controlled RF power is already needed in certain medical equipment, and according to Kephart, driving down the costs will allow new applications to surface, such as using accelerators to clean up flue gas or sterilizing municipal waste.

“The reason I’m not retired is that I want to build this prototype,” Pasquinelli said. “It’s a solution to a real-world problem, and it will be a lot of fun to build the first one.”

Troy Rummler