Berkeley Lab

ATAP News, April 2016

LCLS-II Sees CD-2 and -3
Major Milestones for APEX, LCLS-II Injector Source
Berkeley Lab Magnet Help is Key to LHC Upgrade
Workshops Forge Plasma Accelerator Futures

Outreach Events Coming Up — Volunteers Wanted
Communication Channel for Parking and Vehicle Access
ATAP Safety Day Was a Sweeping Success

SXRdetail_100x94y Fernando-Sannibale-APEX-LBNL-100x98y CERN_LARP_easteregg_.100x99y
twoworkshops_100x100y DTSW_100x101y TothRileySafetyDay_100x100y

Director’s Corner

Leemans_Wim_Headshot_2014_150_captioned One of the flagship facilities in the Office of Science portfolio, SLAC’s Linac Coherent Light Source-II, has received approval as a construction project. This issue features LBNL’s prominent roles, including FEL undulator design and the injector source. Another project with a major milestone is US-LARP, aimed at a luminosity upgrade of CERN’s LHC and prominently featuring advanced magnets developed in part by our Berkeley Center for Magnet Technology. A pair of workshops look toward the future of plasma-based colliders and their applications, and we also look toward future generations of scientists and engineers with outreach events. Read on to learn more!


Numerous LBNL contributions will be part of multi-institutional project to build soft-x-ray free-electron laser

LCLS-II, a major upgrade to the Linac Coherent Light Source at SLAC National Accelerator Laboratory, is now a formally approved construction project. After extensive reviews, the Department of Energy made Critical Decisions 2 and 3 in March. LCLS-II is being built at SLAC by a collaboration that also includes LBNL, Argonne National Laboratory, Fermilab, Jefferson Lab, and Cornell University. Critical contributions from ATAP and elsewhere in LBNL include the injector source (see next story), soft x-ray undulator, horizontal-gap vertically polarized undulator, and low-level RF control systems.

“We couldn’t do this without our collaborators. To bring all the components together and succeed, we need the expertise of all partners, their key infrastructure and the commitment of their best people.”
— LCLS-II project team head John Galayda, SLAC


Undulators, or permanent-magnet arrays that make an electron go in a rapidly wiggling rather than straight path, and thus make it give off electromagnetic radiation, are at the heart of a free-electron laser like LCLS-II. They are an area of special expertise in ATAP and LBNL’s Engineering Division.

The LBNL-designed SXR (soft X-ray) undulator prototype HXU-32 has demonstrated performance exceeding the stringent LCLS-II requirements. With this work concluded, HXU-32 has been delivered to SLAC for long-term testing. A pre-production unit is now being fabricated at industrial vendors, and will be delivered to LBNL for magnetic measurements and tuning this spring. Production contracts for 21 undulators, plus 2 spares, can be awarded now that CD-2 and -3 approval has been granted. Assembly of these devices will be split between industry and LBNL to maximize schedule flexibility.

Design of the production HGVPU (horizontal gap vertically polarized undulator) is progressing well, and a preliminary design review was held March 21. March also saw a handoff meeting among LBNL, ANL, and SLAC to transition between prototype work at ANL and production here at LBNL.

LCLS-II SXR line Left: Soft-X-ray line will include 21 horizontally polarizing undulators like these; two spares will also be produced. Right: HGVPUs will go into the hard-X-ray line; the undulator was developed for production and optimized magnetic performance by LBNL, based on a concept initiated and prototyped at Argonne. The hard-X-ray line will have 32 segments like the ones shown here. Click pictures for larger versions. LCLS-III_HXR_layout_1000x407y

Low-Level RF Controls Pass Preliminary Design Review

The electromagnetic field in the superconducting cavities of the LCLS-II linac is extremely sensitive to external stimulation, and exquisite control of both RF input and mechanical tuning of each cavity is required to maintain beam parameters and allow stable FEL operation. LBNL has responsibility for technical aspects and performance of the LCLS-II low-level RF (LLRF) controls systems. ATAP and Engineering Division staff work in a collaborative team with Jefferson lab, Fermilab, and SLAC staff in designing these systems to control the cavity field. The LLRF system successfully passed preliminary design review in March, and now the team will focus on prototype development and tests scheduled for this summer on the first LCLS-II cryomodules.

To Learn More…

Berkeley Lab Working on Key Components for LCLS-II X-ray Lasers,” by Glenn Roberts of LBNL Public Affairs, gives an overview of ATAP and Engineering efforts toward the LCLS-II FEL undulators and electron injector source.

Major Upgrade will Boost Power of World’s Brightest X-Ray Laser,” a SLAC news release, on the occasion of CD-2 and -3 approval, that gives an overview of what LCLS-II is and how scientists will use it.


Researchers preparing for reliability demonstration after successful reviews

The Injector Source for LCLS-II will be based on the Advanced Photoelectron Project (APEX), an R&D project at LBNL. After meeting major milestones in a performance review conducted last month by an outside panel of experts, Berkeley Lab scientists are working on a final demonstration of APEX. This electron-beam system will serve as a prototype for the injector system of LCLS-II.

The Beam Dynamics Acceptance Review focused on the capabilities of the VHF-Gun, the injection source of novel design at the heart of APEX. It which produces intense, rapid-fire electron pulses that must meet many demanding parameters — notably, stringent requirements on beam emittance and energy spread in order for LCLS-II to successfully lase. These parameters were achieved in a few months of APEX experimental operations once the hardware had been commissioned.

The committee reviewed experimental results and modeling simulations and concluded that the LCLS-II beam quality requirements with a charge of 20 picocoulombs had been demonstrated. Additionally VHF-gun design enhancements that were born in experience with the APEX gun met with approval, and a final design review for the gun and the cathode load-lock systems had a very favorable outcome.

Fernando Sannibale, a senior scientist at Berkeley Lab who oversaw the development of APEX and is also working on the fabrication of the LCLS-II electron gun, says that the the positive review was important because “it formally acknowledges the capacity of the VHF-Gun of delivering the beam performance required to operate at the challenging regime imposed by X-ray FELs such as the LCLS-II.” Sannibale adds, “The achievement is remarkable not only because of the quality of the beam produced during the tests, but also considering that it was obtained in only about two months.”

Berkeley Lab’s Advanced Photoinjector Experiment - APEX at the Advanced Light Source (ALS). LCLS-II performance requirements as demonstrated at APEX

Charge ≥ 20 pC
Energy ≥ 10 MeV
95% transverse rms
normalized slice emittance*
≤ 0.25 m
High-order residual
rms energy spread**
≤ 15 keV

* Removing space charge limitations of experimental technique
** Whole beam rms energy spread after removing linear and quadratic correlations

Following the installation of prototype 90° elbow coaxial RF power components (the result of one of the earlier lessons-learned), reliability of the gun under continuous (CW) operation will be assessed in APEX operations from April onward. Proposals for additional measurements for the benefit of LCLS-II, notably beam emittance and energy spread at higher bunch charge, are being developed.

With the successful completion of these reviews, the team is prepared to begin production now that LCLS-II has CD-2 and -3 approval in hand. The actual LCLS-II electron gun system, to be built at Berkeley Lab, will incorporate much of the prototype’s design.

The LCLS-II Injector Source is a key item in the quality of the electron beam and thence the performance of the entire facility. These results indicate that the technical risk of LCLS-II injector source performance is mitigated, a major achievement for the team and reassurance for the project.



The Berkeley Center for Magnet Technology (BCMT), along with colleagues at Fermilab and Brookhaven National Laboratory as well as CERN, is in the midst of a successful series of tests of a fundamentally new and far more powerful focusing quadrupole that will be key to the upcoming luminosity upgrade of CERN’s Large Hadron Collider. Both this advanced technology and the multi-lab and international collaboration model will doubtless be among many BCMT and ATAP contributions to Hilumi-LHC and whatever is beyond it in circular colliders for high-energy physics.

History and Context

Major accelerators tend to be repeatedly upgraded over the years, maximizing the scientific return on the investment. Before the LHC was even completed in its present version (famed as the discovery site of the Higgs boson), scientists and engineers were planning upgrades. LBNL has had a primary role since the inception of the four-laboratory US Large Hadron Collider Accelerator Research Program (US-LARP) collaboration that helps design and build components for these upgrades.

The latest effort is aimed at an order-of-magnitude increase in beam luminosity. This translates into a similar increase in the rate of particle collisions and thus the detail with which LHC users can explore the Standard Model of Particles and Interactions and search for new physics within the LHC’s energy reach. Hilumi-LHC made its official transition at CERN from an R&D program to a construction project last year, and US-LARP is under review for Critical Decision Zero (statement of mission need), a key go-ahead as a Department of Energy project.

An important ingredient in that tenfold luminosity increase is a set of new, unprecedentedly powerful focusing quadrupoles that will be installed just upstream of the interaction points for final focus of the beams just before collision. These quadrupoles will double the luminosity all by themselves, a major contribution to the factor-of-10 overall luminosity upgrade.


The quadrupole upon arrival at Fermilab for testing, which at this writing in its second round. Photo courtesy G. Ambrosio (Fermilab) and P. Ferracin and E. Todesco (CERN).

“We’re dealing with a new technology that can achieve far beyond what was possible when the LHC was first constructed,” says Giorgio Apollinari, Fermilab scientist and Director of US LARP, in a recent article in the Fermilab/SLAC magazine Symmetry. “This new magnet technology will make the HL-LHC project possible and empower physicists to think about future applications of this technology in the field of accelerators.”

This will represent the first major use of the high-field niobium-tin (Nb3Sn, pronounced “niobium-three-tin”) superconductor in an operating accelerator. The version of the LHC presently operating, like other major colliders, uses the older niobium-titanium (NbTi) superconductor. The technology developed by LARP over the last decade will allow these magnets to achieve higher fields in significantly larger apertures, and will provide greater temperature margin, compared to the present interaction-region quadrupoles.

The new conductor called for innovative magnet designs. NbTi cable is ductile, but Nb3Sn is embrittled by the heat treatment that is needed to render it superconducting. It has to be wound into finished coils before the heat treatment, requiring an entirely new approach to constructing the magnet.

“Niobium-three tin is much more complicated to work with than niobium titanium,” Peter Wanderer, head of the Superconducting Magnet Division at Brookhaven National Lab, told Symmetry. “It doesn’t become a superconductor until it is baked at 650 degrees Celsius. This heat-treatment changes the material’s atomic structure and it becomes almost as brittle as ceramic.”

LBNL played vital early leadership roles in the development of Nb3Sn magnet technology, making it seem reasonable that this challenging new material could be the stuff of practical accelerator magnets. It took scientists and engineers here, along with other LARP collaborators, 10 years to devise and perfect the process to wind, form, bake and stabilize these coils.

Success with a New Model Magnet — And Model for Co-Operation


Cutaway of a magnet of this type shows coils and the thick aluminum shell, which must not only withstand the “hoop stress” of the magnetic field but also prevent the conductors from moving even a tiny amount. A sophisticated mechanical design prestresses the coils to thousands of pounds per square inch during assembly. Photo by Reidar Hahn, Fermilab.

For these quadrupoles, BCMT, a joint venture of ATAP and the Engineering Division, has primarily been involved in cabling (weaving cables out of the strands of multifilamentary superconducting wire), structural design and analysis, and assembly of the final magnet prior to testing at Fermilab. Brookhaven and Fermilab are both going to wind, react, and pot the coils, and Brookhaven will also perform testing.

The magnet being tested, designated MQXFS1, is a so-called “model” quadrupole because it is at scale (1.5 rather than 4 m) in length, but it is full scale — in fact, of the final design — in all other aspects. (This use of magnets that are scaled down in length but otherwise full-sized is an established time and money saver. Most of the challenges occur at or near the ends or are brought about by an increase in the bore diameter.)

Achieving such success with the very first prototype required not only use of a novel superconductor and a magnet design that could take advantage of it, but also the right scheme for international cooperation and management. “US LARP is a unique collaboration where expertise in all areas of the magnet technology is shared among the participating laboratories, resulting in a very tightly interwoven team,” says Soren Prestemon of LBNL’s Berkeley Center for Magnet Technology.

The interwoven team approach has been extended to include the CERN HiLumi magnet team in the design, fabrication, and test of this first prototype, Prestemon explains, adding that “it bodes well for the future HiLumi project,” as both the US and CERN will be contributing magnets for the LHC luminosity upgrade. “Building this magnet prototype was truly an international effort,” adds Lucio Rossi, the head of the HiLumi project at CERN. “Half the magnetic coils inside the prototype will be produced at CERN, and half at laboratories in the United States.”

The result is shaping up as both a technology knowledge base and a collaboration model that will serve well not only HiLumi-LHC, but also circular colliders of even higher energy. Though many years in the future, such colliders are already the subject of lively discussion in the high-energy physics community, which even as it makes use of the present state of the art,has always focused on what can be achieved next.

To Learn More…

Physicists Build Ultra-Powerful Accelerator Magnet,” Symmetry Magazine, April 7.
HiLumi-LHC Project Transitions from Design Study to Machine Construction Phase,” ATAP News, November 2015.
High Luminosity LHC Project website.
US LHC Accelerator Research Program website.


Mapping the way from here through k-BELLA to colliders… and ions too
ATAP’s Berkeley Lab Laser Accelerator (
BELLA) Center is one of the leaders among laboratories worldwide investigating plasma-based accelerators, a relatively young technology that holds the promise of far more compact and cost-effective particle acceleration. A pair of workshops hosted by ATAP in January, with results that are feeding into higher-level strategic-planning processes in the plasma-based-accelerator and laser-technology communities, will have implications for the next moves of BELLA and the future of accelerators. Future articles will cover these exciting topics in greater depth.

Plasma-Based Accelerator Concepts for Colliders

The Plasma-Based Accelerator Concepts for Colliders Workshop was intended to “identify the key physics and technology R&D needed to realize a plasma-based collider, and to formulate a nationally and internationally coordinated roadmap for carrying out this research over the next two decades.”

Part of a process flowing from the Particle Physics Prioritization Panel (“P5”) Report, and into a subsequent panel that assessed DOE’s accelerator R&D portfolio, it is part of a larger effort to develop R&D roadmaps, with milestones and down-selection criteria, for advanced accelerator technologies, ultimately leading to a multi-TeV electron-positron collider.

This long-term (midcentury) goal is an international one, and so are the accelerator concepts and technology development efforts that could help achieve it. The 55 participants represented 21 universities, laboratories, agencies, and foundations in six countries.

Plasma-Based Accelerator Concepts for Colliders participants. Click for large version.

Three days of intensely interactive discussions covered both of the major approaches to plasma-based accelerators — laser-beam-driven approaches such as the one we are pushing forward at BELLA, and particle-beam-driven approaches — as well as the needed advancements in laser technology that will provide the requisite power and repetition rate. The event was organized by Wim Leemans, Eric Esarey, and Carl Schroeder of BELLA Center, with support from LBNL.

The result was input for a roadmap to a collider, which is now being incorporated at higher levels as part of a strategy for advanced accelerator development. Both the ultimate goal of a high-energy-physics collider and various spinoff applications along the way are included. Examples include extreme-ultraviolet free-electron lasers for ultrafast science, as well as a Thomson-scattering gamma ray source for nuclear security; and of course the laser technology advancements could be tremendously important to many fields.

We plan that one of the steps along the way in the next few years will be a joule-class laser system with a kilohertz repetition rate, which we are calling “k-BELLA,” for laser plasma accelerator R&D.

Workshop on High Energy Density Physics with BELLA-i
Besides electrons, the present and future BELLA lasers and laser-plasma acceleration concepts also offer the prospect of compact, efficient acceleration of ions. The repetition rate, spot size, and intensity of BELLA lasers could open new doors for discovery science related to plasma physics, high-energy-density physics, and nuclear physics, with spinoff prospects including cancer treatment and nuclear security.

Attendees from five national laboratories, 11 universities, three private-sector companies in the US, and 13 international universities and institutions representing 8 countries discussed this unique opportunity for discovery science as well as applications. The workshop was organized by Thomas Schenkel and Qing Ji of the Fusion Science & Ion Beam Technology Program, and Sven Steinke and Wim Leemans of BELLA Center, with support from LBNL. The development prospects are foreseen as three phases that extend from present BELLA capabilities to a new user facility.
Workshop on High Energy Density Physics with BELLA-i participants. Click for large version.


The Labwide Daughters and Sons to Work Day will be held Thursday, April 21. In a future issue we’ll look at ATAP contributions to Nuclear Science Day for Scouts (Saturday, April 23) and the Oakland Unified School District’s “Dinner with a Scientist” series, where researchers reach out to the district’s top science teachers and their prize students over dinner at the Oakland Zoo.

Daughters and Sons to Work Day, Thursday, April 21

DTSW_75x84y This Labwide event allows Lab employees to bring their children (or grandchildren) to work with them. The kids tour LBNL facilities and experience hands-on science experiments. ATAP’s outreach and diversity coordinator Ina Reichel will teach three liquid nitrogen workshops (as she does every year) with the help of volunteers.

If the kids and volunteers look as though they’re having lots of educational fun, please consider being a part of this event next year by signing your kids up or volunteering. contact Ina directly. To volunteer in some other role, please contact Joe Crippen in the Workforce Development & Education Office.

You don’t need to be a scientist or engineer to help. Behind our scientific discoveries are thousands of people in dozens of trades and professions — come share what you find rewarding about what you do and where you do it. After all, the 2050 Nobel Prize in Physics is going to go to somebody; what if she’s a ten-year-old you inspired?

One Kind of Space That Unfortunately Isn’t Expanding — Parking Space

ParkingFlux_77x88y As announced intramurally in February, Lab management has formed a Vehicle Access and Alternative Transportation Advisory Group (VAATAG) to help tackle the upcoming parking shortage. ATAP’s Stefano de Santis is part of the advisory group.

The group is tasked not only with providing immediate feedback on proposed access policies before they are implemented, but also with the proactive function of presenting suggestions to the LBNL Director and Chief Operating Officer.

In the brief time that VAATAG has been meeting, they came to the realization that, while the Lab has accurate counts of parking spaces available and of permits issued, information about utilization of those spaces — how many and when — was not as complete. Therefore, since mid-March the vehicles entering the lab have been counted.

Wait… “Upcoming Parking Shortage?”
Initial data suggests that the first round of parking spaces reduction (~ 250 spaces) coming in July, due to construction work in the former Bevatron site, will not have an impact as dramatic as previously believed. People should still be able to find parking, although their search could take a little longer and end farther away from their offices.

To mitigate the shortage and try to avoid an access fee — especially when parking spaces will become even less abundant in the longer term — a revision of the current preferential parking policy (i.e., the Blue Triangle permits) is being studied. Their number would be increased from the current ~10% of total spaces level, and access to them reassessed. These new preferential spaces would also be more evenly distributed throughout the Lab.

One possibility is that displaying two or more general permits on the dashboard would allow use of a preferred space, thus incentivizing carpooling, which is an effective and relatively painless way to reduce parking demand and traffic.

Let Your Voice Be Heard
A new commuter survey is in the final stages of preparation, and you should receive it shortly. More than ever your response is important, since amongst other things the data will be used in determining if an access fee has to be implemented.

You can read more about the advisory group activities, including meeting minutes, and submit your feedback at

Continued contact between VAATAG members and other employees is particularly important so that input from the panel is more representative of the entire workforce.

As a VAATAG member, Stefano desires to keep ATAP staff informed of any proposed policy changes (in addition to direct communication from the Laboratory Directorate) and to obtain our feedback. If you have ideas or concerns regarding parking and commuting, please feel welcome to contact him directly.


ATAP Safety Day makes a clean sweep

On March 23, ATAP held its annual Safety Day, emphasizing de-cluttering and organization this time. The day began with a kickoff meeting, followed by a morning of all-hands cleanup. Shelf after shelf of old reports and magazines and catalogues became multiple wheelie-bins of recyclable paper. Earthquake-refuge space appeared under desks as people concluded that they never were going to use that Windows 98 computer. Metal-recycling bins became heavy with scraps and leftovers, and disused equipment was dispatched to the excess-property center.

In the afternoon came QUEST evaluations of the results by 15 Quality Assurance, Environment, and Safety Teams, followed by management walkthroughs. More than 100 suggestions that required more time and planning, special skills, or expenditure were documented by the QUEST teams for follow-up.

For an investment of less than 0.5% of the work year, the payoff was impressive in terms of immediate safety benefits alone, as well as the improved efficiency of a tidy workspace. The Labwide Cleanup website has pictures from this and similar events in other divisions, along with other resources for conducting cleanups.