“Can Do” on Canted Cosine-Theta Dipoles

In the excitement following the LHC’s discovery of the Higgs boson, several groups worldwide continued with renewed enthusiasm in their efforts to define a future circular collider, beyond even an upgraded LHC in its energy and thus its physics reach. Whatever the details of the next collider (and at this early point, there are many possibilities), it will almost certainly need superconducting magnets with a substantially higher field than anything in operational use today — and the magnets will have to deliver unfussy reliability and be cheaper as well.

Anticipating these requirements, ATAP’s Superconducting Magnet Program (SMP) is developing a high-field dipole based on a hitherto little-used design concept that turns out to be well adapted to future magnets: the Canted Cosine-Theta (CCT) winding geometry. We are nearing completion of a 2-layer, ~5 tesla niobium-titanium CCT as the first step in a campaign whose goal is a 16-T unit made with niobium-tin superconductor.

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The canted cosine theta (CCT) concept holds the promise of magnets that are both better and easier to make, especially when using the brittle superconductor needed to achieve the high fields of future colliders. An important aspect of the quality improvement comes from intrinsic stress management, which should reduce the “training” process by which a magnet approaches its maximum field through a series of quenches (losses of superconductivity) as the conductor beds in.

Although a 5-T NbTi dipole might seem unremarkable in these times, building a magnet with this ductile material is helping us develop tooling and procedures that give good results with the CCT geometry. Then we will test it (our test facility, equipped with a new power supply, is ready for operation).

What we learn will guide the next steps of our technology campaign. Following the test of the NbTi CCT, we will immediately start fabrication of an identical model using brittle Nb3Sn, resulting in a magnet that will approach 10 T in the bore. The culmination of the campaign will be an 8-layer 16-T dipole that can accommodate a high-temperature-superconductor (HTS) insert for an ultimate push toward 20 T.

Achieving this goal in a practical, cost-effective way will be an ambitious undertaking. In order to approach this goal our program will focus on the following Grand Challenges of our field:

  • Achieve a field of 16 T in a bore diameter of at least 50 mm.
    • Focus on simple, manufacturable designs.
  • Understand training of Nb3Sn magnets — the process by which they reach their full performance only after a succession of quenches, or losses of superconductivity — and develop ways to reduce or eliminate it.
  • Produce an HTS (Bi-2212/YBCO) insert with a self-field > 5 T and measure the field quality.
  • Reduce cost and improve performance of Nb3Sn.
    • Collaborate on increasing the current density by 30% using scalable sub-element structures.
    • Aim for a cost per kg similar to that of NbTi.
  • HTS development
    • Utilize Bi-2212 and YBCO in accelerator magnet configurations as technology drivers.
    • Contribute to development of higher performance and lower cost HTS conductors.

This will help lay the foundations for the future of collider-based high-energy physics. A recently released Particle Physics Project Prioritization Panel (P5) report recommends a very-high-energy proton-proton collider as “the most powerful future tool for direct discovery of new particles and interactions under any scenario of physics results that can be acquired in the P5 time window.” It goes on to state, “The U.S. is the world leader in R&D on high-field superconducting magnet technology, which will be a critical enabling technology for such a collider.”

SMP plays a major role in U.S. magnet development by pushing the limits of high field using innovative concepts, seeking opportunities for high-risk but high-potential-payoff R&D. The program has held a series of world records for field strength in an accelerator-style dipole, most recently 16.1 T.

This brings us to the Canted Cosine-Theta geometry. Originally defined by Meyers and Flasck at the University of Michigan in the early years of the Tevatron, it uses tilted solenoid windings to reduces stress on the conductor and make the winding process simpler. This intrinsic stress management is especially attractive when using brittle superconductors such as Nb3Sn to make the high-field accelerator magnets that will be needed in the future (the 8.4-T dipoles of the LHC represents an approximate limit of what can be done with ductile materials such as NbTi).

The canted cosine theta (CCT) concept holds the promise of magnets that are both better and easier to make, especially when using the brittle superconductor needed to achieve the high fields of future colliders. An important aspect of the quality improvement comes from intrinsic stress management, which should reduce the “training” process by which a magnet approaches its maximum field through a series of quenches (losses of superconductivity) as the conductor beds in.

Our CCT R&D campaign has the goal of magnets that are easier and more economical to manufacture, and which will deliver the field quality and reliability that are both needed by an operational collider — while operating routinely at what is now the record field for a handbuilt experimental magnet. Along the way we will define an envelope of parameters, and develop tools and procedures, that can be used to design magnets for a large variety of applications. It is an ambitious goal, to be sure, but our philosophy is that tackling the most difficult problems is the way to learn the most.

To Learn More…

National Security on the Move with High Energy Physics

After an article by Theresa Duque in Today at Berkeley Lab, April 21, 2015

Cameron Geddes at BELLA
Scientists are developing a portable technology that will safely and quickly detect nuclear material hidden within large objects such as shipping cargo containers or sealed waste drums. The researchers, led by Berkeley Lab scientists, have been awarded over $10 million from the Department of Energy’s National Nuclear Security Administration (NNSA) Defense Nuclear Nonproliferation R&D Office to combine the capabilities of conventional building-size research instruments with the transportable size of a truck for security applications on the go.

A Big Future for Small Accelerators

The core of the detection system is a next-generation source of high-energy photons, often referred to as X-rays or gamma rays. The technology will combine the capabilities of conventional building-size research instruments, such as Duke University’s High Intensity Gamma-Ray Source (HIGS), which precisely control the energy (or color) of the photons generated to improve sensitivity, with the compact size needed for use in most national security applications. The problem with current techniques, such as those used by HIGS, is that there are only a few ways to produce megaelectron-volt (MeV) photons — high-energy photons at energies a million times higher than visible light — within a narrow spread or range of energy, and those usually require an electron accelerator the size of a large building.

The compact photon source, which is being developed by Berkeley Lab, Lawrence Livermore National Laboratory, and Idaho National Laboratory, is tunable, allowing users to produce MeV photons within very specific narrow ranges of energy, an improvement that will allow the fabrication of highly sensitive yet safe detection instruments to reach where ordinary passive handheld sensors cannot, and to identify nuclear material such as uranium-235 hidden behind thick shielding. “The ability to choose the photon energy is what would allow increased sensitivity and safety. Only the photons that produce the best signal and least noise would be delivered,” explains project lead Cameron Geddes, a staff scientist at the Berkeley Lab Laser Accelerator (BELLA) Center.

The key to making the new compact photon source tunable within a narrow energy spread lies in colliding the high-quality electron beams obtained by the BELLA Center with a separately controlled “scattering laser.” The collision with the fast-moving electron beam up-shifts the energy of photons from the second laser, producing high-energy photons, all with the same energy within a range of around 10%.

To make a tunable photon source that is also compact, Geddes and his team will use one of BELLA’s laser plasma accelerators (LPAs) instead of a conventional accelerator to produce a high-intensity electron beam. By operating in a plasma, or ionized gas, LPAs can accelerate electrons 10,000 times “harder” or faster than a conventional accelerator. “That means we can achieve the energy that would take tens of meters in a conventional accelerator within a centimeter using our LPA technology,” Geddes says.

To make a source that can be truly portable, the team has recently demonstrated that a second compact LPA can be used to bring the energy of accelerated electrons back down. Decelerating the electron energy through another LPA could significantly reduce if not eliminate the expense, square footage, and weight required for safety shielding. Controlling the collision between the laser and electrons will similarly help reduce the size of the lasers required. This photon source will be the first to combine deceleration and an independent scattering laser in a compact design.

In addition to bringing the precision of current large-facility photon sources to small laboratories and eventually into the field, the project will lay the groundwork for a very bright laser-driven photon source within an even narrower energy range. To meet the needs for national security applications, the future system will fire pulses of photons thousands of times per second, delivering up to trillions of photons per second. Such accelerators are being developed by the DOE’s Office of Science, Office of High Energy Physics (HEP), for future particle colliders, and this photon source is a near-term application that exemplifies HEP’s stewardship of accelerators dedicated to the broad needs of discovery science and society.

“We are very excited about this project,” says Wim Leemans, Director of the Accelerator Technology and Applied Physics Division and the BELLA Center. “It has the potential to be the first major application of laser plasma accelerator technology that has been supported for many years by the Office of High Energy Physics at DOE.”

The technology’s better signal and less harmful radiation dose could also benefit other fields that currently use X-ray machines — from lower-dose, higher-precision computed tomography (CT) scans in medicine, to detecting mechanical or structural weaknesses in an engine or airplane wing before it fails, or locating hidden explosives.

To Learn More:

  • Visit the BELLA website.
  • Read Geddes et al., “Compact quasi-monoenergetic photon sources from laser-plasma accelerators for nuclear detection and characterization,” Nuclear Instruments and Methods in Physical Research B 350 (31 January 2015), pp. 116-121, available at doi:10.1016/j.nimb.2015.01.013 or on our website.

BELLA Simulation Team Receives NERSC HPC Award

For the second consecutive year, ATAP modeling work has been honored with a NERSC High Performance Computing Achievement Award. The NERSC HPC Achievement awards are given by the Department of Energy’s LBNL-hosted National Energy Research Scientific Computing Center.

Animation of a simulation of BELLA laser plasma interaction Computer simulation of the plasma wakefield as it evolves over the length of the 9 cm long channel in BELLA. For more details on the simulation aspects, see this news release from NERSC.

The open-category award for High Impact Scientific Achievement went to the Berkeley Lab Laser Accelerator (BELLA) Center for its use of NERSC supercomputers for the modeling of laser plasma accelerators, and in particular for the importance of modeling in the successful acceleration of electrons to 4.25 GeV in only 9 cm.

Extensive simulations using INF&RNO, a code developed under Benedetti’s leadership for modeling laser-plasma interactions, showed that the experiment and causes of fluctuations in beam energy and charge are well understood. These fully self-consistent, multi-dimensional particle-in-cell (PIC) simulations ran on the Cray XC30 supercomputer “Edison” at NERSC. They were of fundamental importance in modeling the propagation of a high-intensity laser in the plasma, characterizing the nonlinear wakefield excitation, and studying the details of particle self-trapping. The results were important in planning the experiment and also in helping us understand the results.

Winners of 2015 NERSC HPC Award standing on stairway ATAP physicist and simulation-code developer Carlo Benedetti (center) accepts a NERSC HPC Achievement Award on behalf of the BELLA Center team. Other winners included Taylor Barnes of Caltech (bottom) and Ken Chen, UC-Santa Cruz (top), as well as LBNL’s Craig Tull, SPOT Suite project (not pictured). The award ceremony took place February 24, 2015 at LBNL as part of the annual NERSC User Group meeting.

To Learn More:

LCLS-II Does Well in DOE CD-3b, Cost Reviews

The LCLS-II Project reached a pair of major milestones recently: both a Critical Decision-3b review (one in a series of peer reviews of the technical, cost, schedule, and management aspects of a construction project by the DOE Office of Science’s Office of Project Assessment) and an independent cost review by the Office of Acquisition and Project Management. At both these reviews, ATAP and Engineering Division staff, as key contributors to the SLAC National Accelerator Laboratory-based LCLS-II project, were involved in planning and making presentations and in discussions with reviewers.

ATAP physics modeling received praise from the CD-3b review’s accelerator physics subcommittee. This critical work aided in understanding the sources and effects of the microbunching instability that can deteriorates FEL performance, and in design of systems to mitigate these effects. The high-resolution multiphysics code IMPACT, developed within ATAP, has been an essential design tool in this work.

Progress in the Advanced Photoinjector Experiment (APEX) was recognized by the injector and linac subcommittee, which encouraged timely completion of the experimental characterization of beams. APEX is an R&D project, led by ATAP staff, that will serve as the basis for the LCLS-II injector source. APEX plans to complete its demonstration of the beam quality required by LCLS-II by the end of fiscal year 2015.

LBNL-designed undulators are scheduled for final design review at the end of calendar year 2015, following final tests this summer and fall of a prototype magnet system and a pre-production full undulator unit. The undulators subcommittee gave full credit to the team, based in the Engineering division, for being ready to support DOE project critical decisions in the planned timeframe.

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Above, left: ATAP’s Daniele Filippetto works on the Advanced Photoinjector Experiment (APEX). The VHF gun of APEX, based on a new concept developed at LBNL, became the baseline for the injector source of LCLS-II. As one of its major contributions to that facility, LBNL is responsible for the design, construction and commissioning of the LCLS-II injector source.

Above, right: A prototype LCLS-II undulator installed in the magnetic measurement facility at LBNL. The design of the challenging FEL undulator is another major LBNL role in LCLS-II, and is one of the LBNL strengths that will be brought together in the Berkeley Center for Magnet Technology (see the first article on this page).

Safety: Always the Bottom Line

ISMCircleOfSafety_350x350y The 2015 ATAP Integrated Safety Management (ISM) Plan is now available online, the result of its first revision cycle since the creation of ATAP.

The ISM Plan is the master document that guides our division’s environment, safety, and health policies and practices.

All employees are encouraged to read it, keeping in mind that depending on their role and the nature and area of their work, more than one section may be applicable. Highlights include the phase-in of the Laboratory’s new Work Planning and Control system, which replaces the old system of Job Hazard Assessments and Activity Hazard Documents.

We revised the rest of the ATAP EH&S website at the same time, and invite you to settle into a good comfortable ergonomic position at the computer, have a look around, and let us know how it could better serve your needs.