In Case You Missed It, February 2019

Expanding access to key capabilities
“High-intensity and ultrafast lasers have come to be essential tools in many of the sciences, and in engineering applications as well,” said James Symons, Berkeley Lab’s associate laboratory director for its Physical Sciences Area.

Such lasers have a broad range of uses in basic research, manufacturing, and medicine. For example, they can be used to recreate some of the most extreme conditions in the universe, such as those found in supernova explosions and near black holes. They can generate high-energy particles for high-energy physics research (being explored at the BELLA Center) or intense X-ray pulses to probe matter as it evolves on ultrafast timescales. Laser-based systems can also cut materials precisely, generate intense neutron bursts to evaluate aging aircraft components, and potentially deliver tightly focused radiation therapy to tumors, among other uses.

The petawatt-class lasers of the LaserNetUS partners generate light with at least 1 million billion watts of power. A petawatt is nearly 100 times the output of all the world’s power plants, and yet these lasers achieve this threshold in the briefest of bursts. Using a technology called “chirped pulse amplification,” which was pioneered by two of the winners of this year’s Nobel Prize in physics, these lasers fire off bursts of light shorter than a tenth of a trillionth of a second.

Maintaining U.S. leadership in a fast-moving global endeavor
The U.S. was the dominant innovator and user of high-intensity laser technology in the 1990s, but now Europe and Asia have taken the lead, according to a recent report from the National Academies of Sciences, Engineering, and Medicine titled “Opportunities in Intense Ultrafast Lasers: Reaching for the Brightest Light.” Currently, 80 to 90 percent of the world’s high-intensity ultrafast laser systems are overseas, and all of the highest-power research lasers that are currently in construction or have already been built are also overseas. The report’s authors recommended establishing a national network of laser facilities to emulate successful efforts in Europe.

LaserNetUS is holding a nationwide call for proposals that will allow any researcher in the U.S. to request time on one of the high-intensity lasers at the LaserNetUS host institutions.. The proposals, due March 18, will be peer reviewed by an independent proposal review panel. This call will allow any researcher in the U.S. to apply for time on one of the high intensity lasers at the LaserNetUS host institutions. The initial “Run 1” experiments are expected to take place in the second half of calendar 2019.

Their Nobel-winning research brought “chirped pulse amplification,” a method of generating high-intensity, ultra-short pulses, to lasers. In a mere three pages, their 1985 paper “Compression of Amplified Chirped Optical Pulses” (Optics Communications 56, 3 (1 December 1985), pp. 219-221) sparked a revolution. The concept was implemented widely and almost immediately, ending a decade-long plateau in laser performance.

Today, CPA and follow-on developments are used near-universally at the peak-power frontier of very large research lasers, and also to increase the peak power of relatively small lasers for a wide variety of industrial and medical applications as well as research. (To take just one of many examples, some of you may be reading this with vision corrected by LASIK surgery, a technology made feasible for widespread use by CPA.)

We were immensely gratified to see laser-plasma acceleration, and specifically the multi-GeV electron beams obtained at the BELLA facility, mentioned as one of the examples of the benefits of CPA in the Nobel committee’s scientific background document. The BELLA Petawatt system is a 1 Hz repetition rate Ti:sapphire laser based on the CPA technique pioneered by Strickland and Mourou. In addition to the discussion, the Nobel backgrounder used a conceptual diagram of the LPA principle from the 2010 White Paper of the ICFA/ICUIL Joint Task Force on High Power Laser Technology for Accelerators —a figure that had originally appeared in an article by Wim Leemans and Eric Esarey in the March 2009 issue of Physics Today.

The white paper was produced by a joint task force, chaired by then-ATAP Division Director Wim Leemans, of the International Committee on Future Accelerators and International Committee on Ultra-high Intensity Lasers, and was based on a workshop series held first at GSI and then here at LBNL. The notional BELLA follow-on, which we call k-BELLA for its kilohertz repetition rate / kilowatt average power performance class, is an example of such a next-generation laser.

CPA is also one of the techniques used in an exciting collaborative project being conducted through our Berkeley Accelerator Controls and Instrumentation (BACI) Center: development of a laser system that uses “coherent combining” to achieve both high peak power and high average power from arrays of fiber-optic lasers.

The scientific stature and the widespread, ongoing societal impact of the research by Drs. Mourou and Strickland, as well as their co-laureate Dr. Arthur Ashkin, are formidable. (Ashkin is a pioneer of laser trapping and the inventor of “optical tweezers” that use lasers to grasp tiny physical particles such as bacteria or viruses. His work had already figured into the 1997 Nobel Prize in Physics for our former Lab director and Secretary of Energy Steven Chu, who had worked with Ashkin at Bell Labs.) Their achievements have given us both game-changing tools and inspiration. This is a time for all of us to be proud of the important role we play as research pioneers and the resulting benefit to humankind.

In “Lasers for Plasma Accelerators” (pp. 13-15), Almantas Galvanauskas of the University of Michigan, then-ATAP Division and BELLA Center Director Wim Leemans, and Jay Dawson of Lawrence Livermore National Laboratory summarize the challenges and opportunities for building ultrafast lasers with both high average and high peak power, as needed by future generations of laser-plasma accelerators.

“Modeling Future Accelerators on the Eve of Exascale Computing” (pp. 16-17), by Jean-Luc Vay, head of ATAP’s Accelerator Modeling Program, describes the prospects for powerful, high-fidelity tools for the design, optimization, and perhaps even predictive control of particle accelerators. A rendering from a plasma accelerator simulation, using the Berkeley Lab Accelerator Simulation Toolkit code WARP3D, was chosen as the cover illustration for the report.

In “The U.S. Magnet Development Program” (pp. 24-27), Soren Prestemon, Director of the USMDP (and ATAP’s Deputy Division Director for Technology), together with Fermilab’s Gueorgui Velev, the USMDP Deputy Director, survey the goals and progress of this Berkeley Lab-based, multi-institutional effort to develop transformational magnet technologies for high-energy physics.

The issue was edited by Alysson Gold and Nihan Sipahi, Early Career Members-at-Large of the APS-DPB Executive Committee.

These are just a few of the 15 articles about exciting technical topics in our field. Click here for the Newsletter.

Synchrotron light facilities—electron storage rings that produce intense, laserlike x-ray beams—have become vital infrastructure for a broad range of sciences. As the science and technology of these rings has progressed, accelerator researchers are finding ways to build rings that approach the “diffraction limit,” with an electron beam so orderly that, for a given photon wavelength, both its emittance and that of the photon beam produced from it are almost zero.

DLSRs have become a hot topic in the synchrotron-radiation community; some 150 registered participants came from 25 labs around the world to discuss progress toward achieving truly diffraction-limited x-rays from high-brightness storage ring sources. The workshop emphasized both technical challenges and new research opportunities, and focused on the design, construction, commissioning, and operation of accelerator, beamline, and experimental systems that will be required.

The ultra-low electron beam emittance that will be available at these new and upgraded facilities will enable dramatic improvements in many areas of x-ray science, especially for experiments that directly require transversely coherent x-ray wavefronts. Worldwide, ten upgrades of existing machines and ten more new facilities are in some phase of study, R&D, or construction.

Berkeley Lab is on the front lines of this revolution. ALS-U, now in a design phase, exemplifies this push toward the fundamental, theoretical limits of what can be done. It will transform the ALS, which was among the bellwethers of the third generation of synchrotron light sources, into a fourth-generation source, ready for another 20 years of providing the beams needed for cutting-edge research.

		Scenes from the future of synchrotron light: At left, with Halloween close at hand, Elke Arenholz, deputy for operations at the ALS, worked a seasonal theme into the summary talk on Experimental Systems. Upper right: Chair Andreas Streun (Swiss Light Source, left) and speaker Riccardo Bartolini (Diamond Light Source, right) fielded a question. Lower right: At the poster session Christoph Quitmann (MAX IV, left) and Will Waldron (LBNL, right) discussed fast kickers, one of the technical challenges for ALS-U.

The workshop presented an opportunity to showcase efforts underway for ALS-U. Dave Robin gave an overview of the ALS-U Project in the Monday plenary session, while several speakers from the ALS and ATAP Divisions covered various aspects of ALS-U in their breakout presentations. They included Stefano De Santis of ATAP’s Berkeley Accelerator Controls and Instrumentation program (BACI), who presented an overview of fast kicker requirements for DLSRs and described progress made on fast stripline kicker development for injection in ALS-U.

This was just part of a diverse program. It had been seeded with topic suggestions from an international scientific program committee, which elicited many interesting contributions. The workshop presentations were well attended and prompted lively follow-up discussion during breakouts. Additional discussion sessions built into the schedule allowed for an exchange of thoughts on progress thus far as well as remaining challenges and possible solutions.

Much positive feedback was received for the workshop, which benefited greatly from solid support by Berkeley Lab’s Yeen Mankin, Jason Templer, Candy Lao, and Michele Pixa.

After a well-attended close-out came the announcement that the next DLSR Workshop would be held in the summer of 2020 in Lund, Sweden. It will be hosted by MAX IV, the first source to come online using the multibend achromat (MBA) lattice—the arrangement of magnets generally chosen for the fourth-generation rings being studied or planned, including ALS-U.