“We feel that Accelerator Technology and Applied Physics better reflects the broadening contributions of accelerators and related technologies to today’s science and technology challenges,” said Leemans. “The new name also recognizes the origins and core mission of the Division.”
Incoherent Pulse Combining Could Open Doors for LPAs
A new study by Carlo Benedetti et al., published in May as the cover story of the journal Physics of Plasmas, shows that one can significantly relax those requirements, making combining laser pulses much more attractive than previously thought. The authors used analytical calculations and a fully self-consistent particle-in-cell (PIC) simulations to study the wake-field generated by a variety of laser pulses. They looked at three different ways of incoherently combining the laser pulses and compared the results to laser pulses combined in a coherent manner.
Those incoherent methods are effective because the generation of the wakefield is not sensitive to the small-scale fluctuations that characterize the energy density of incoherently combined pulses.
As future applications of LPAs will require higher repetition rates, further studying various methods of incoherently combining laser pulses could lead to further optimization of this technique.
To Learn More: C. Benedetti, C.B. Schroeder, E. Esarey, and W.P. Leemans, “Plasma wakefields driven by an incoherent combination of laser pulses: A path towards high-average power laser-plasma accelerators,” Physics of Plasmas 21 (27 May 2014) 056706. The work is summarized and interpreted in this news release by American Institute of Physics staff and this story by LBNL Public Affairs.
Winding the Way to Better Superconducting Magnets
ATAP’s Superconducting Magnet Group is working to develop a high-field magnet system based on the canted-cosine-theta (CCT) concept. The CCT design is based on multiple superimposed layers of windings, each layer composed of a structural tube supporting a tilted solenoidal winding scheme that produces both a dipole and solenoidal field component. Consecutive layers are configured so as to cancel the solenoidal field components but add the dipole components. In each layer, the magnet windings are supported in a continuous groove machined into a mandrel.
Above, left: This computer-aided-design image shows the major parts of a CCT dipole, including two superimposed coils with opposite skew. CCT, a 1969 concept by Meyer and Flasck at Michigan, has received renewed interest as a way to achieve a pure cosine-theta field of high quality, along with intrinsic stress management, when using brittle high-field superconductors to make accelerator magnets. Above, right: Two computer-aided-design views of a Canted Cosine Theta dipole show how the windings are arranged and how ribs separate turns of conductor, substantially reducing and controlling stress on the conductor, with the goal of minimizing the need to “train” the magnet and thus the risk of quenches.
The CCT concept has been developed to address three critical issues with very-high-field accelerator magnets. First, by integrating the structure and coil windings, the magnetic forces can be transmitted directly, and locally, to the support structure. Calculations indicate that by using this approach fields beyond the 16-T record dipole field (set by LBNL’s HD1 magnet) can be produced — in fact, stress may no longer be a design limitation at any field strength.
Second, the field produced by each layer is intrinsically very close to a pure dipole field (i.e., it has very little harmonic content). Additional layers will not change the shape of the magnetic field, just its strength. Therefore the combined field of many layers should be of very high quality, simplifying the design and fabrication process.
Third, the layered approach provides a natural assembly process; manufacturing is anticipated to be less complex than for other superconducting dipole magnet configurations.
A plan is in place to build sequential layers and perform multiple tests, culminating in an 18-T system in about three years. Phase One will consist of several layers (added two layers at a time) of Nb3Sn coils. It will start with two layers, reaching 10 T, and then we will add six additional layers two at a time. At the end of Phase One the magnet is expected to reach 16 T.
In Phase Two a high-temperature-superconductor insert will add to the field; the goal is to achieve 18 T. The HTS insert will first be tested on its own before being assembled into the magnet. A first prototype of the HTS insert has already been designed and partially fabricated.
Simulations have been done to calculate expected field quality, loads and mechanical stresses for the various stages of the project. The current focus is on developing fabrication processes and simple and cost-effective tooling concepts — including reaction and vacuum impregnation tooling — to allow rapid fabrication and testing of the magnet layers.
A Critical Decision In Favor of LCLS-II
Many of the grand scientific challenges of the 21st century involve understanding and controlling matter and the flow of energy at the finest and therefore most fundamental relevant values of time (attoseconds), space (nanometers), and energy (milli-electron-volts). A prominent tool for addressing these questions is a source of coherent beams of x-rays made up of ultrafast pulses at a high repetition rate and with unprecedented average brightness. We in ATAP, together with colleagues in the Engineering Division, have been working for some years to define a next-generation light source that can meet these national needs.
Currently we are collaborating with SLAC National Accelerator Laboratory, Fermilab, Jefferson Laboratory, and Cornell in the LCLS-II project based at SLAC.LCLS-II is a free electron laser (FEL) facility based on a high-repetition-rate electron gun and a superconducting linear accelerator feeding multiple FELs. The collaborators will have to meet state-of-the-art challenges in accelerator physics and technology from end to end.
The LCLS-II project achieved Department of Energy Critical Decision One (CD-1, approval of alternative selection and cost range) in August of 2014, after receiving a CD-0 decision (statement of mission need) in 2013. The collaboration is currently preparing for a CD-2/3 review (approval of performance baseline and of start of construction) in early 2015, in pursuit of a schedule that will provide first light to experiments in 2019.LBNL has crucial responsibilities in the LCLS-II project, including two major deliverables: the injector source and the two FEL undulator arrays, one each for hard and soft X rays. The LCLS-II injector is based on APEX, the Advanced Photo-Injector Experiment, in which we are developing the extraordinarily demanding electron gun that will be needed by next-generation light sources.
The LBNL-designed LCLS-II injector source, based on the APEX R&D project. Major items shown are (from left) cathode vacuum load-lock apparatus, VHF gun cavity, focusing solenoids, buncher cavity, and diagnostics. APEX, located in the Beam Test Facility of LBNL’s Advanced Light Source, is now in the second of three major phases.
FEL Undulators for LCLS-II
Undulator design and engineering is a core strength shared by ATAP and Engineering. ATAP is also contributing to the project through accelerator physics and technology studies in beam dynamics, low-level-RF and accelerator controls, and cryogenics systems.
Shown at left is a prototype LCLS-II undulator installed in the magnetic measurement facility at LBNL. The main features are magnetic modules and a strongback structure to position the magnetic modules — and move them upon command — with micron accuracy in the face of tens of thousands of kg of magnetic repulsion. Each LCLS-II undulator array will consist of several individual sections like this one. Undulators are precision series of powerful magnets, alternating in polarity along the beam path, that make the electron beam move up and down with a period of a few to several centimeters. This causes the beam to emit intense, highly directional photon beams with coherence properties that can be amplified by an FEL resonator. The gap between the two rows of magnets (shown here at several cm) is adjustable, allowing the photon wavelength to be tuned without changing the electron beam parameters. State-of-the-art undulators have always been among the defining characteristics of LBNL’s Advanced Light Source; undulator design and engineering has remained a core strength of LBNL Engineering, going hand in hand with FEL physics design in ATAP.
To Learn More:
Visit our Special Projects Section page.
NDCX-II Reaches Energy Goal of 1.2 MeV
Understanding “warm dense matter” is important in many areas of astrophysics (for example, the study of planetary cores) and it also provides foundational data to the quest for inertial fusion energy. This state of matter cannot be directly accessed in the natural world, so laboratory plasmas (such as those which can be created by accelerators) are important tools for measuring its charcteristics.
NDCX-II — our Neutralized Drift Compression Experiment — was funded by the DOE Office of Fusion Energy Science for the implementation of an ion beam pulse capability that will reliably heat samples to a temperature of 10,000 degrees, or 1 electron-volt. When reached, this will enable first-in-class precision studies of warm dense matter.
The NDCX-II team , led by Will Waldron and Peter Seidl, recently achieved a major step towards a WDM facility by accelerating pulses of potassium ions to an energy of 1.2 MeV, meeting that design goal on time and within the budget. The next step, now beginning, will compress the intense ion beam pulses to 1 ns and focus them onto 1 mm spots. At that point, the beams from this unique accelerator will uniformly heat metal target foils to about 10,000 degrees, making this elusive state of matter available for studies by a community of users.
The unique capabilities with short, tunable pulses also enable new classes of experiments on defect dynamics and materials processing relevant to both magnetic and inertial fusion energy.
To Learn More
For more information, please contact the Program Head of the Fusion Science and Ion Beam Technology program in ATAP, Thomas Schenkel, T_Schenkel@lbl.gov.
Above left: Photo of NDCX-II, an induction linac for intense, pulsed ion beams in building 58. Above right: Time trace from a pulse of potassium ions accelerated to 1.2 MeV with a series of Blumlein high voltage generators.
4th Annual Diversity Festival October 30
Berkeley Lab will be hosting its 4th Annual Diversity Cultural Festival on Thursday, October 30th from 11:30 a.m. to 1:30 p.m. at the Cafeteria patio. This year’s theme will be “Weaving the Fabric of Diversity,” a whirlwind tour around the world celebrating our community’s diversity, with representations of Lab employees’ cultures and backgrounds.
Berkeley Lab performers include: American jazz singer Amy Ukena, Hula dancer Adel Serafino, Ukulele Club, Dance Club, and the Karaoke Idols. UC Berkeley performers include: Lebanese and Egyptian Belly Dancer Christine Garibian; Naya at Berkeley Indian Classical Dancers; and the West Coast Rock Band.
Booths will include representation from: the African American Quilt Guild, Bay View Cafe, Diversity & Inclusion Council, Filipino-American Club, Lambda Alliance (LGBTQ club), Museum of African American Technology, UC Berkeley Recreational Sports & Martial Arts, and the Women Scientists and Engineers Council.
Sponsored by Berkeley Lab’s Diversity & Inclusion Council, the Diversity & Inclusion Speakers and Social Activities Subcommittee, and the Physical Biosciences Division.
Berkeley Lab is a global community. There are cultural riches waiting to be discovered and explored, and much to be celebrated!
Safety: The Bottom Line
LBNL has developed a new work planning and control system to describe work, identify hazards, identify controls appropriate to those hazards, and authorize workers. This new approach defines and analyzes work at the activity level rather than the worker level, and it takes a more integrated and efficient approach to work planning and control (WPC). LBNL has created a centralized database (dubbed Activity Manager) to authorize the diverse range of work activities that take place at the Lab.
Activity Manager will replace the Job Hazards Analysis (JHA) and Activity Hazards Documents (AHDs) for implementing Integrated Safety Management at the Lab. Our Division has developed a plan to transition all JHAs and AHDs to Activity Manager by the end of April. As with the JHA, everyone will need to be involved in the WPC process, especially people designated as Project Leads and/or Activity Leads. Pat Thomas will coordinate and Program Heads will oversee the transition of ATAP activities to Activity Manager.
So far, ATAP Activity Leads have initiated about 16 Activities. Congratulations to Carl Schroeder for completing ATAP’s first fully approved Activity, for BELLA Center Office Environments!
Please stay tuned for information about training and your role in this process. For additional information and an overview video, visit the at LBNL Work Planning and Control site.
Almost all electrical shocks, as well as “near-hit” incidents such as cutting live wires or leaving an electrical panel open, are preventable. Developing these six habits will help prevent shock hazards:
- If you are not a Qualified Electrical Worker, do not perform electrical work.
- If equipment appears to be unsafe or you are not sure whether it is safe, don’t use it. Report unsafe equipment to your supervisor.
- Plan your work. Identify the hazards and ensure the controls are in place.
- Take care of each other. Help your co-workers identify and correct unsafe behavior or conditions.
- For Qualified Electrical Workers, practice Lockout/Tagout and Test Before Touch.
- For Qualified Electrical Workers, determine approach boundaries and control access to the area to prevent exposure of other people to electrical hazards.
To Learn More: An LBNL Electrical Safety website is in development. Meanwhile, you can learn about Labwide electrical-safety policies here. If in doubt about the risks of the work you have in mind and whether a Qualified Electrical Worker must perform it, consult your division’s safety coordinator: in ATAP, that is Patricia Thomas, Building 71, Room 251B, extension 6098.
“Openness, Feedback, and Perseverance”: Fostering a Culture of Safety
The Laboratory’s Safety Culture website provides resources for people who wish to build safety into everything they do from the very beginning. The site now has a feature article describing how ATAP takes this approach.
Further News of ATAP Division
BELLA wins Secretary of Energy Achievement Award
The project team that built and commissioned BELLA has been commended by Energy Secretary Ernest Moniz for “outstanding ingenuity and exceptional project performance” resulting in a facility that is now “operating at unprecedented performance levels and enabling breakthrough advances”.
3D map of the longitudinal wakefield generated by the incoherent combination of 208 low-energy laser beamlets.
BELLA Center study points to easing of laser-pulse quality requirements for pulse combining in LPAs
One attractive approach to producing powerful laser pulses, as required in laser-plasma accelerators, involves combining many lower-powered pulses. Theory-guided modeling at the BELLA Center suggests that when the destination is the plasma of an LPA, the similarity of these pulses does not need to be as rigorous as previously thought—welcome news for the cost and complexity of LPA systems.
Their work is the cover story in the May 2014 issue of the refereed journal Physics of Plasmas, and is summarized and interpreted in this news release by American Institute of Physics staff and this story by LBNL Public Affairs.
Daniele Filippetto Named To DOE Early Career Program
Staff scientist Daniele Filippetto of ATAP’s Center for Beam Physics is one of four Berkeley Lab winners and 35 winners in all of DOE’s Early Career Award for 2014. The award is designed to bolster the nation’s scientific workforce by providing support to exceptional researchers during the crucial early stage of their careers. Here Daniele is shown working on APEX, the Advanced Photoinjector Experiment. APEX is part of a key contribution to next-generation x-ray sources based on free-electron lasers, such as LCLS-II.
Remembering Andy Sessler, 1928-2014
Center for Beam Physics accelerator physicist and LBNL Director-Emeritus Andrew Sessler passed away April 17, 2014. Even at age 85 and suffering a long illness, Sessler remained an active scientist who never stopped thinking about where the Laboratory might go and how to get there. He had very recently received the Enrico Fermi Award from President Obama.
His long and distinguished career was remembered in the San Jose Mercury-News and LBNL’s News Center, and an appreciation by retired AFRD Director and now US Particle Accelerator School Director Bill Barletta appears in the May 2014 AFRD Newsletter.
The BELLA laser bay at a late stage of construction, “front end” in foreground.
BELLA Laser achieves world record power at one pulse per second
July 20, 2012—On this night the BELLA laser system delivered a petawatt of power in a pulse just 40 femtoseconds long at a pulse rate of one hertz—one pulse every second. A petawatt is 1015 watts, a quadrillion watts, and a femtosecond is 10-15 second, a quadrillionth of a second. No other laser system has achieved this peak power at this rapid pulse rate. For further information, see the LBNL press release and this Scientific American news item.