ADVANCED LIGHT SOURCE STRATEGIC PLAN
January 2008
With the approaching full realization of former Director Chemla’s original strategic plan, the Advanced Light Source (ALS) stands at a pivotal point in its history. The emphasis of the new strategic plan outlined below is to keep the ALS at the cutting edge for the next 2–3 decades by the honing of our existing stock and by the creation of sharper tools that exploit the very significant advances in accelerator and insertion-device technology that have occurred since the ALS began operation. The plan dovetails neatly with the scientific priorities of the DOE Office of Basic Energy Sciences. It is also responsive to the needs of our users, not only in the provision of scientific tools, but also in the provision of a safe and supportive research environment.
Table of Contents |
Strategic Plan Background |
Elements of the Strategic Plan |
1. Strategic Plan Background
The core capabilities of the ALS include:
- Angle-resolved photoemission spectroscopy (ARPES) for understanding complex materials, including magnetic and correlated electron systems, with meV resolution.
- Magnetic systems measurement capabilities, including magnetic circular dichroism, at fields up to several Tesla under static and dynamic conditions.
- Elastic/inelastic soft x-ray scattering for the study of strongly correlated electron systems.
- Scanning transmission x-ray microscopy (STXM), as well as full-field imaging microscopy, extending from the water window up to a few keV, providing spectromicroscopy capabilities across all relevant absorption edges with resolution to the optics limit of 15–25 nm.
- Lensless imaging with resolution beyond what is possible using zone-plate optics.
- Ultrafast x-ray scattering for the study of atomic, chemical, and material dynamics, utilizing absorption and diffraction, throughout the soft and hard x-ray spectrum.
- State-of-the-art photoemission electron microscopy (PEEM) with spatial resolution extending to the nanometer level.
- Ambient-pressure photoemission for the study of real-world reactive systems.
- Macromolecular and protein crystallography facilities that are world class, and competitive in productivity and throughput, most utilizing superbend technologies.
- Microdiffraction studies with spatial resolution down to the submicron level.
- Small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) for the study of soft materials.
- Additional capabilities include gas-phase chemical dynamics, AMO, environmental, EUV lithography, high-pressure, infrared, x-ray microprobe, and optics calibration.
With these capabilities, we address many fundamental questions, broadly including:
- Where are the electrons and how can we manipulate them?
- Where are the atoms and how can we control them?
- Where are the spins and how can we direct them?
A major focus throughout our strategic planning process has been on the qualitatively new science that will be enabled by the upgrading of various aspects of the facility. The challenging areas that will be addressed at the ALS include:
- Size-dependent and dimensional-confinement phenomena at the nanoscale.
- Correlation and complexity in physical, biological, and environmental systems.
- Temporal evolution, assembly, dynamics, and ultrafast phenomena.
These areas dovetail with the recent BESAC Report, “Directing Matter and Energy: Five Challenges for Science and the Imagination,” in which the following broad challenge areas were identified:
- How do we control material processes at the level of electrons?
- How do we design and perfect atom- and energy-efficient synthesis of revolutionary forms of matter with tailored properties?
- How do the remarkable properties of matter emerge from complex correlations of the atomic or electronic constituents and how can we control these properties?
- How can we master energy and information on the nanoscale to create new technologies with capabilities rivaling those of living systems?
- How do we characterize and control matter away—especially very far away—from equilibrium?
2. Elements of the Strategic Plan
The ALS Strategic Plan has been developed to keep our facility at the cutting edge for at least the next two decades. At the same time, it is important to recognize that we have filled the available space around the storage ring, and our challenge now is to renew our capabilities. Accordingly, our strategic plan focuses on an orderly renewal and upgrade of the ALS, at modest cost. It comprises three major components:
(1) Upgrade of the storage ring
- Top-off: $5M (funded)
- Klystron Upgrade: $3M (funded)
- Control System Upgrade: $5M
- Higher Brightness Upgrade $4M
(2) Replacement of older insertion devices (costs included in sector upgrades below).
(3) Addition of new application-specific beamlines
- Sector 7.0: $16M
- Sector 8.0: $13M
- Sector 10.0: $11M
- Sector 2.0: $10M
- Sector 6.0: $1M (second insertion device)
- Optics Development and Upgrades: $3M/year
- Metrology Program: $2M/year
- Detector Development Program: $2M/year
Accelerator Upgrades
Top-Off Operation. Our highest priority for upgrade of the accelerator is to complete top-off operation of the storage ring. The plan is to inject current (top-off) every 30 seconds and maintain an average beam current of 500 mA. We expect to benefit from a 100% increase in time-averaged current and flux, much-improved beam stability, and a four-fold decrease in the beam vertical emittance that provides an increase in vertical brightness. In addition, we plan to operate with small-gap in-vacuum undulators, further enhancing the brightness, especially in the important energy range above 500 eV. In addition to upgrading the booster energy from 1.5 GeV to 1.9 GeV, a milestone we reached late last year, top-off requires significant changes to the radiation-protection system and a variety of other hardware and control improvements. Top-off operation will be introduced by Fall 2008.
Klystron Upgrade. The klystron used to power the RF system is 15 years old, has operated longer than any other tube in its family, and is obsolete. Because specific or compatible replacement tubes are no longer manufactured, a failure could result in an extended downtime for the ALS. The U.S. Department of Energy (DOE) responded in a very timely fashion by providing initial funds last summer to fast track an upgrade to our rf system. The plan is to replace the klystron with an inductive output tube (IOT) system in an FY09 annual shutdown, with additional upgrades to follow in the next years. Should there be a catastrophic failure of the current system before then, the ALS has plans to move rapidly with replacement klystron technology (in-house and potential loans) followed by implementation of a new system in a shorter time frame.
Control-System Upgrade.The ALS control system, designed more than 20 years ago, is woefully out of date, and a potential source of a major failure. The initial design goals of the planed upgrade include a network of distributed controllers that are not dependent on a specific operating system or hardware interface, with a generic software interface allowing everyone from operators to accelerator physicists to create control applications. The existing cable plant limits us to the present control-room location, so we will build a “new” control room in parallel with the current operation, then switch over. Finally, the challenge of porting control software cannot be overstated: 20 years of software development on one “platform” will have to be moved to another.
High-Brightness Upgrade.To keep the ALS at the forefront of synchrotron radiation sources, we have identified a low-cost, low-risk way to significantly improve the horizontal brightness and flux density, which will benefit many experiments at the ALS, particularly microscopes and protein crystallography. The horizontal brightness is inversely proportional to the horizontal emittance, presently 6.3 nm×rad at the ALS. Simulations have shown that, with the addition in the ALS of two sextupole magnet families, the horizontal emittance can be reduced by a factor of 2.5. This lattice would increase the brightness by a factor of three in the center-bend-magnet beamlines and up to a factor of two in the insertion-device straights. The sextupoles provide flexibility for other potentially interesting operational modes—short-pulse low alpha and coherent terahertz. This upgrade involves replacing the 48 straight-section correctors with combined function magnets with sextupole components. The upgrade can be done in stages and would not require a long shutdown.
Bringing New Beamlines into Full Operation
Among six beamlines in the commissioning or advanced construction stage, three are based on undulator sources, two are based on regular bend magnets, and one on a superbend. Bringing these into full user operation in a timely manner has the highest beamline priority.
PEEM-3 (Beamline 11.0.1). The photoemission electron microscope PEEM-3 is the next step in the development of advanced imaging capabilities at the ALS. Installed at an undulator beamline designed specifically as a source for aberration-corrected photoemission microscopy, PEEM-3 has recently come into operation, with its last component, the aberration-correcting electron mirror, currently being designed at the ALS. The mirror is planned to improve the spatial resolution from the current 30 nm to a few nanometers and increase transmission by more than an order of magnitude. The system is primarily used for studying magnetic and polymer nanostructures.
Ultrafast X-Ray Facility (Beamlines 6.0.1 and 6.0.2).For this undulator beamline, designed to increase the flux of femtosecond x rays at the ALS a thousand-fold over an existing bend-magnet beamline, we have one insertion device feeding two monochromators, one for the soft x-ray region and one for the hard x-ray region. The intent has been to install a second insertion device (an EPU) to service the soft x-ray monochromator and a program on ultrafast magnetism. . Many of the ultrashort pulse x-ray techniques to be developed on these beamlines will find direct applications in the experimental program at the new Linac Coherent Light Source (LCLS) under construction at SLAC but, in addition, will provide unique capabilities in spectroscopy that will not be available at free-electron laser (FEL) sources.
MERLIN (Beamline 4.0.3). Low-energy excitations are crucial to understanding the behavior of strongly correlated systems. MERLIN is an undulator beamline with full polarization control from a quasiperiodic EPU in the VUV energy range below 150 eV. It is designed to provide ultrahigh energy resolution for angle-resolved photoemission and inelastic x-ray scattering. It is expected to start user operation in late 2008.
Soft X-Ray Microscope XM-2 (Beamline 2.1.2). A bend-magnet beamline has been constructed as a “National Center for X-Ray Tomography” for high-resolution soft x-ray microscopy and tomography of biological cells. It is funded jointly by the National Institutes of Health (NIH) and DOE’s Office of Biological and Environmental Research (DOE/BER).
Microdiffraction (Beamline 12.3.2). The x-ray microdiffraction program was developed on Beamline 7.3.3. In this technique white x-rays are focused to a sub-micron spot; phase, grain orientation, stress, defect density, and other parameters are derived from Laue diffraction patterns; and 2D maps are built up by sample scanning. Unlike conventional x-ray diffraction, x-ray microdiffraction gives structural information on the microscopic spatial scale of grains. The highly successful 7.3.3 program recently was moved to superbend Beamline 12.3.2. The availability of higher-energy x-rays gives access to hugely improved strain resolution and the possibility of 3D information.
SAXS/WAXS (Beamline 7.3.3). Small-angle x-ray scattering (SAXS) combined with wide-angle x-ray scattering (WAXS) is a powerful tool to study the structure of matter on length scales from the atomic to the micron lengths. The technique is universally applied to follow the organization of complex systems, so is tightly linked to the program of the Molecular Foundry (LBNL’s Nanoscale Science Research Center). In addition, SAXS has become a powerful tool in structural biology, where it is used primarily to look at the morphology of large assemblies of proteins, in situations where crystallization is impractical, and to study the assembly process itself. The new Beamline 7.3.3 SAXS-WAXS facility makes use of an existing beamline that was freed up when the microdiffraction program moved to a superbend beamline, as well as detectors from the ALS structural biology program.
New Beamline Initiatives
Top-off operation will make possible the replacement of our 12-year-old, 5-m-long undulators with pairs of chicaned 2-m-long modern insertion devices with superior performance, feeding a new generation of beamlines to address the outstanding problems of the coming decades. In rough order of priority, these include:
Coherent Scattering and Diffraction Microscopy, COSMIC (Sector 7.0). As our highest priority among new initiatives, we propose to establish in half of Sector 7.0 a beamline to provide coherent light in the 0.5–3 keV range with full polarization control. One branch of this beamline will serve the soft x-ray coherent scattering community, where much of the interest is in magnetic phenomena. This approach is designed to study time correlation as well as magnetic-field and temperature-dependent correlation and hysteresis phenomena. The other branch will be devoted to diffraction microscopy. This new form of lensless imaging is designed to provide 3D structures to 10-nm resolution for frozen hydrated biological specimens and even higher resolution where radiation damage is not a limitation. This will be a major new venture in the use of soft x rays as a nanoscale probe. We emphasize that the novel, ground-breaking performance of this proposed beamline is coherence-based and is considerably enhanced by the top-off and brightness upgrades of the accelerator.
Microscopy and Electronic Structure Observatory, MAESTRO (Sector 7.0.) ARPES at the ALS and elsewhere has emerged as a leading technique for understanding the electronic structure of high-temperature superconductors and other complex oxides. Small probe sizes enable the isolation of more homogeneous, perfect materials than can be achieved by interrogating the entire sample. Smaller probe size translates to better science. In some other cases (as with transuranics), larger specimens would pose unacceptable hazards. Work done by the LBNL Center for X-Ray Optics (CXRO) at the ALS has led to the development of truly remarkable optics. In collaboration with CXRO, we propose to use zone-plate optics to create a 50-nm probe for a nanoARPES facility in the other half of Sector 7.0. This will be a unique capability for the study of surfaces and structures that cannot be prepared in larger formats and for nanostructures created in the Molecular Foundry. NanoARPES will specialize in valence photoemission spectroscopy in the energy range of 20–600eV.
Enhanced VUV Spectroscopy (Sector 10.0). We need to keep some of the flagship beamlines, which have been operating for a decade in an ever-more oversubscribed mode, at the cutting edge. The highest priority in this area is to chicane the Sector 10.0 straight section and give each branch—the condensed-matter-physics photoemission branch (HERS) and the atomic/molecular physics branch—a separate EPU of its own for full polarization control and simultaneous operation. Each of the new, separate beamlines will be application specific, optimized for the scientific program of the two user communities, without the need for the compromises in current use.
Soft X-ray Scattering in Partnership with the Molecular Foundry (Sector 8.0). What are the rules that govern self-organization—at length scales that range from the atomic scale of correlation of electrons in solids to the micron-size scale of ordering in many forms of soft matter? The new materials studied apply to many national missions, including energy. A new undulator beamline will be constructed for time-resolved soft x-ray scattering to follow, in real-time and with elemental and chemical discrimination, the synthesis and self-assembly of novel nanostructures. This capability will facilitate the development of joint programs with the Molecular Foundry. We envision the establishment of two chicaned undulators in Sector 8.0, one to feed the soft x-ray scattering program outlined here, the other to enhance the very productive energy-resolved fluorescence spectroscopy program already in place.
Q-Resolved Inelastic Scattering Beamline, QERLIN (Sector 2.0). While the MERLIN beamline is designed for the ultimate energy resolution in the energy range below 150 eV, there is a great need to extend the capability for ultrahigh-resolution inelastic x-ray scattering (IXS) investigations to energies up to 2 keV, so as to be able to access the most important dipole transitions for complex materials, i.e., the 1s–2p of carbon and oxygen, the 2p–3d of the transition metals, and the 3d–4f of the rare earths. In doing so, one also can naturally access a q-vector range out to the Brillouin zone boundary. The elemental, spin, and orbital sensitivity of resonant soft x-ray scattering offers a unique combination of capabilities that will lead to many high-impact experiments. We plan to build on the experience at MERLIN in designing this new facility, which should fit into Sector 2.0 with a modest rearrangement of accelerator components. The incorporation of very high-resolution photoemission in the range up to 2 keV would be considered.
Infrared Beamline Development (Beamline 5.4). The ALS is at the forefront of environmental and biological science uses of synchrotron infrared (IR) spectromicroscopy and the development of coherent synchrotron radiation as a powerful broadband terahertz (THz) source. A new beamline (Beamline 5.4) will have a novel light-extraction port located just outside the bend-magnet source, which allows a greater collection angle and therefore improved performance for the IR and exploitation of high-power coherent synchrotron radiation pulses available from both femto-sliced bunches and from a new picosecond bunch mode of operations made possible by the improved lattice discussed earlier. In the longer term, we are examining the scientific drivers and possibility of funding an IR ring, Coherent InfraRed CEnter (CIRCE).
Supporting Technical Capabilities
Currently there are 35 beamlines that operate simultaneously at the ALS, including eight beamlines dedicated to macromolecular crystallography. These form the core resource for the increasing scientific impact and productivity of the facility. While some of the older beamlines will be retired as new, more powerful beamlines come on line, the rest need to be maintained or further improved to reach the state-of-the-art level. This is a highly cost-effective way to keep the facility at the cutting edge. Additionally, it has been widely recognized that one of the most effective ways to increase the productivity of existing and planned high-brightness sources is to develop and utilize new detector technology.
Optics Development and Upgrades. World-leading performance depends on state-of-the-art optical components. Development of zone-plate focusing devices needed by our x-ray microscopies requires advanced lithography support, provided by our collaboration with the Center for X-Ray Optics at LBNL. In addition, CXRO also has pursued the development of improved efficiency gratings. Most beamlines use mirrors and gratings. Deterioration of mirror optics due to thermal and ion-induced roughening as well as shape changes due to thermal stress will become more severe as we go into top-off operation. We therefore need to replace many of the beamline optical components around the ring in an orderly fashion based on accumulated experience and on vigorous R&D efforts into improved mechanical support, thermal stress alleviation, and figure accuracy.
Metrology Program. To retain the high brightness of the source, beamline optical surfaces have to be manufactured to extremely high tolerances for the angular deviation from the perfect surface (~100 nanoradians) and for height deviations typically of nanometer precision. Continual investments are necessary to upgrade our optics and metrology program to be commensurate with the increased brightness of the ALS and the increased demands of the experiments. In particular, we need to make a transition to measurements at short wavelength using x-rays, to make substantial investments in manufacturing R&D with a vendor outside of normal beamline projects, and to investigate the latest advances in manufacturing. Finally, there are still opportunities for fundamental advances in soft x-ray optics, such as the use of very high-order multilayer blazed gratings, based on anisotropic etched silicon substrates, which have the potential to revolutionize ultrahigh-resolution soft x-ray spectroscopy.
Detector-Development Program. Available detectors are not well matched to the capabilities of the ALS and other high-brightness synchrotron radiation sources. There is need for a broad-based program to benefit the community to create high-rate, and for the ALS, high-sensitivity imaging detectors. In addition, high-speed streak cameras are needed to fully utilize the femtosecond sources coming online. An effort is now underway to leverage LBNL’s demonstrated expertise in semiconductor detectors for nuclear and high-energy physics, the unique resources of LBNL’s Microsystems Lab, and the largest integrated circuit design group in the Office of Science to address the needs for speed and sensitivity at the ALS. We intend to target both the basic R&D needed to develop new, high-performance x-ray detectors, as well as apply our skills to deliver state-of-the-art imaging systems. At a base program level to support development and deployment of new detectors, a minimum of 3 FTEs and associated hardware costs are needed.
Next Generation Light Source
In order to meet the increasing needs of existing as well as potential new ALS users for higher coherent flux, higher flux with increased time resolution, and higher flux with increased spectral resolution, LBNL and other facilities have held a series of major workshops. These workshops have laid out the scientific need for the increased capabilities that appear to be consistent with the output of a new high-repetition-rate, soft x-ray, seeded, free-electron laser (FEL). The next generation light source (NGLS) would be expected to have the capabilities requested by users in order to undertake the Grand Challenge science outlined in the BESAC report “Directing Matter and Energy.” Proposed NGLS parameters include:
- High repetition rate (up to 1 MHz)
- High coherent power (up to several watts)
- Full longitudinal and transverse coherence
- Spectral resolution to the millielectron-volt range
- Spectral coverage from soft x-ray to a few keV
- Temporal and spatial synchronization with a variety of other beams (IR–visible)
In order to address the needs of the light source community, we formed a multidivisional institute at LBNL called the Advanced Photon Science Initiative (APSI). Its work involves coordination across the scientific divisions at LBNL (ALS, MSD, and CSD) as well as the engineering and acceleration divisions (ENG and AFRD). We have submitted a proposal to BES for initial R&D towards the NGLS, called the Advanced Photo-Injector Experiment (APEX), which will include development of new photocathode sources, superconducting accelerator technology, rapid electron-beam switching, optical laser seeding, electron-beam manipulation, and other technologies. Because it involves extensive use of the capabilities at LBNL but also utilizes our colleagues at other DOE laboratories, with initial support from LBNL LDRD, we have begun to consider how to launch such a coordinated program.