An incubator for concepts and technologies with wide-ranging benefits that serve LBNL, DOE, and beyond
As particle accelerators grow ever more powerful, and the needs of their scientific users become more subtle and precise, their instrumentation and control systems must become ever more sophisticated. Instrumentation is the “eyes and ears” of the control system that uses this input to manipulate the particle beam; controls and instrumentation thus naturally go together and are often referred to as AC&I. ATAP’s new BACI Program serves as a central resource for expertise in these areas throughout the accelerator community.
Focus on areas that combine expertise and need
BACI’s areas of focus were selected because they are built upon existing LBNL expertise — world-leading in many cases — and stand to be of widespread benefit.
|
Advanced RF Design and Engineering • CW normal-conducting cavities and RF structures • RF measurement and characterization • Beam impedance modeling and measurement |
Ultrahigh-Precision Controls and Laser Innovation • RF controls • Femtosecond synchronization • Controls for complex systems |
High-Dynamic-Range Beam Instrumentation • Beam orbit feedback systems • Halo measurement and control |
Ultrafast High-Resolution Electron Diffraction |
Advanced RF Design and Engineering
Radiofrequency (RF) design for accelerating, manipulating, and controlling beams is a longtime area of strength for BACI that integrates accelerator physics and engineering. Over the past three decades we have developed a number of demanding ion-accelerator “front ends,” including units for the Spallation Neutron Source and a recent radiofrequency-quadrupole linac for Fermilab’s PIP-II project.
 Click for larger version |
A selection of RF structures built at Berkeley Lab over the past two decades illustrates capabilities in advanced RF for both electron and proton accelerators. Clockwise from upper left: A schematic of the APEX photocathode RF gun, which was selected as the LCLS-II injector; the PEP-II B-Factory main higher-order-mode-damped RF cavities; the Muon Ionization and Cooling Experiment (MICE) cavity with beryllium window; the Spallation Neutron Source (SNS) RFQ; the Relativistic Heavy Ion Collider (RHIC) Schottky cavity pickups; and the Advanced Light Source (ALS) harmonic cavity. |
Studying and mitigating the deleterious effects of beam impedance — interaction of the fields of an intense beam with the vacuum chamber and accelerator components — is another of our longtime strengths.
In recent years Berkeley Lab has developed a unique capability in developing normal-conducting structures for continuous (CW) acceleration, hitherto the province of more-expensive superconducting cavities. Berkeley Lab has also become a leader in the design of broadband RF structures such as kickers for fast beam manipulation (key to upcoming projects such as ALS-U, the Advanced Light Source Upgrade), as well as in ultrafast sources of high-quality electron beams, vital to LCLS-II and already providing a spinoff application in the form of the HiRES tool for ultrafast electron diffraction.
Ultrahigh-Precision Controls and Laser Innovation
The stability of accelerators is in large part determined by the stability of the electromagnetic fields that accelerate and guide the beam. Berkeley Lab has become a center of excellence in low-level RF controls; building upon success with RF controls on behalf of the Spallation Neutron Source linac at Oak Ridge and then the FERMI@Elettra free-electron laser, we are now leading a multilab effort on this aspect of the LCLS-II project and looking forward to contributing to PIP-II, with its superconducting linac.
Another challenge is the synchronization of accelerators with lasers, which are used in many applications throughout modern accelerator complexes. We have applied our RF control approach to stabilizing mode-locked laser oscillators, a critical technique for a wide variety of accelerator applications, such as photocathode RF guns, laser-based beam diagnostics, and staged laser-plasma acceleration.
An area of special expertise is high-precision fiber-optic distributed timing and synchronization systems that can operate across wide areas. Though the idea had been invented elsewhere, LBNL brought unique innovations and a high degree of development to this system. Its femtoseconds-across-kilometers capability has proved especially useful to LCLS and now LCLS-II.
A spinoff of our expertise is being explored: the use of field-programmable gate arrays to read the outputs of microwave-sensed outputs in quantum computing.
APEX, the Advanced Photo-injector Experiment, has not only yielded the injector design baseline for LCLS-II, but is also supporting a user-science instrument: HiRES, the High Repetition-rate Electron Scattering apparatus for ultrafast electron diffraction. This is expected to provide another way to address one of the grand challenges in the understanding of materials: following the dynamics of atoms and molecules. Shown here is DOE Early Career Award recipient Daniele Filippetto, leader of the HiRES experiment.
To learn more about HiRES and ultrafast electron diffraction, see “Seeing Atoms and Molecules in Action with an Electron ‘Eye’,” an April 2015 feature by Glenn Roberts of LBNL Public Affairs, or “APEX-Enabled Scattering Experiment Expected to Become New Research Tool for Materials Science” in the February 2016 edition of the ATAP Newsletter.
Laser Design and Control
Besides the numerous uses of lasers throughout accelerators, the future is likely to include new paradigms (such as the one being explored by ATAP’s BELLA Center) in which lasers actually power accelerators, setting up the potential gradient that accelerates the beams. These accelerators hold great promise for being much more compact and perhaps ultimately relevant to high-energy-physics colliders. Moving this type of accelerator forward requires great improvement in high-average-power, high-repetition-rate, ultrafast lasers.
BACI and collaborators, including the University of Michigan (where a key coherent beam-combining technique was invented) and Lawrence Livermore National Laboratory, are working on a highly promising set of approaches to these problems by combining pulses and combining the output of many fiber apertures. We intend to integrate this with the temporal combination scheme described above, together with other methods of amplifying ultrashort pulses, to produce useful high-power systems. The DOE Office of Science Accelerator Stewardship Program provides support for this effort.
 |
Block diagram of laser architecture shows the interrelationships of the concepts we are working to combine in order to achieve stepping-stone and, ultimately, HEP LPA driver levels of performance. (Click for larger version.) |
High-Dynamic-Range Beam Instrumentation
Instrumentation serves as the “eyes and ears” of all accelerators and covers a wide variety of technologies, techniques and required resolution and bandwidth. Facilities and laboratories have generally developed custom solutions to their specific instrumentation needs. However, there are several commonalities among facilities that would share benefit from R&D, including real-time beam orbit control and the measurement and control of beam loss.
At Berkeley Lab we have developed world-leading expertise in beam orbit measurement and feedback control in storage rings, particularly low-emittance electron rings, that enables transverse stability of the beam at the level of microns over time periods of days. Two important steps are needed to reach this level of performance: high-fidelity measurement of the beam position using RF beam signals, and a real-time feedback network to distribute the information and apply corrections at a rate of tens of kHz. We operate this system on the Advanced Light Source and maintain an instrumentation laboratory for development and testing of hardware improvements.
High-power proton and ion accelerators of the future — not only the LHC and its coming upgrades, but also neutrino sources, spallation neutron sources, and accelerator-driven waste transmutation systems — will have to pay more attention than ever to “halo” and other losses of their multi-megawatt beams. One particular focus of Berkeley Lab work will be a new ring paradigm, the “integrable nonlinear focusing lattice,” that offers the promise of beam current and intensity substantially beyond what is possible with traditional ring layouts and their highly linear focusing elements. Berkeley Lab’s contributions include particle detector instrumentation, with several groups already performing relevant R&D.
Steps Forward
BACI is off to a running start with existing efforts that include laser pulse combining, AC&I for ALS-U, LLRF and timing distribution for LCLS-II, as well as spinoff applications in quantum-computing readouts and a nascent user facility for ultrafast electron diffraction. Challenging future prospects include the PIP-II project at Fermilab, an electron-ion collider, and a next generation of our own Advanced Photoelectron Experiment. We look forward to serving the needs of the accelerators of tomorrow.
