Focus Research Areas
Fundamental Accelerator Physics: Theory
Accelerator physics research is normally associated with specific accelerator projects. As a scientific discipline, however, it is useful to study fundamental accelerator phenomena decoupled, as much as possible, from specific project aspects. Pursuit of fundamental accelerator physics in this sense has contributed significantly to the advance of the accelerator physics knowledgebase during the last several decades, clarifying the limitations and suggesting ways to overcome those limitations. Such basic research tends to be discouraged in a project-driven environment. For sustained and significant progress in accelerator science, however, fundamental research should be encouraged, and a proper balance between project-oriented and fundamental research should be maintained.
Opportunities at Argonne
Partly due to the fact that the accelerator research at Argonne in the past has been carried out by small independent groups scattered over different divisions, research in fundamental accelerator physics has not been strongly encouraged at Argonne. The situation is improving with the coordination of accelerator research—the enhanced productivity will allow room for basic research in accelerator physics. The topics of fundamental accelerator research pursued and coordinated by the AAI include Hamiltonian mechanics, phase-space manipulation, EM-mediated collective instabilities, and quantum effects in free-electron lasers. However, Argonne productivity in fundamental accelerator research needs to be further strengthened by the addition of new staff and students.
- High-Brightness Electron Gun and Related Techniques
- Large-Scale Accelerator Modeling
The study and design of higher-performance accelerators require correspondingly higher-performance computational power due to the needs for higher-precision calculations and the higher complexity of the accelerator systems. Expertise in efficient, large-scale accelerator modeling is one of the critical requirements in research for study and design of future high-performance accelerators.
Opportunities at Argonne
Argonne has the opportunity to significantly impact the progress of large-scale accelerator modeling by taking advantage of the computing resources at Argonne’s Mathematics & Computer Science (MCS) division, one of the nation’s emminant power house in advanced computing. One of the principal codes used at the APS is elegant, a flexible optimization and simulation code that has been applied to design of linacs, storage rings, and transport lines around the world. The Physics division at ANL has developed the beam dynamics code TRACK over the last few years as a starting point for an end-to-end simulation tool that will address design of advanced hadron accelerators such RIA. An effort to make these codes much more efficient and versatile by parallelization began last year as a collaboration between the Accelerator and Petascale-Computing initiatives. There are also excellent opportunities to greatly enhancing the power of accelerator modeling by incorporating more advanced computing techniques such as the Spectral Element Method. With the enhanced visibility of Argonne’s accelerator modeling capabilities, we are aiming to participate in the second phase of the SciDAC program, the major funding source for large-scale scientific computing in the U.S.
- International Linear Collider
If the world community approves construction of the International Linear Collider, it will be the largest accelerator project to date. In the U.S., and possibly the world, the most probable site of the ILC is Fermilab. The project requires extensive R&D in many areas of accelerator physics and technology. Argonne should work towards securing a fare share of that funding, positioning ourselves to be one of the leading partner laboratories, and assisting Fermilab in its bid to host the project.
Opportunities at Argonne
ILC research is an excellent opportunity for Argonne to strengthen its accelerator expertise and leadership. Argonne can contribute significantly to the R&D of the ILC in several areas based on existing expertise in the APS, the AWA, and ATLAS/RIA groups: Damping ring Beam dynamics, diagnostic, alignment, gamma ray undulator; Positron source beam dynamics with the modeling expertise by the AWA group; Surface processing of SCRF cavities (more on this in section 4.5). Since its inception in 2002, CARA has supported ILC-related research topics with a view to becoming a partner if the ILC becomes a funded project. CARA also played a role in the 2005 ITRP selection of superconducting rf (SCRF) technology for the ILC over warm copper cavities, and it participated in discussions at Snowmass 2005 and other meetings regarding the formation of the ILC Global Design Effort (GDE). In FY2006 Argonne received a small amount of GDE-recommended DOE support for ILC-related activities. We expect this support to increase significantly in FY2007.
- Exotic Beams and High-Power Hadron Linacs
There are at least two possible accelerator projects that could have construction initiated in the next five years. One of these is an advanced exotic beam facility based on a high-power superconducting heavy ion linac, and the other is a proton driver linac for a high-intensity neutrino source. The concept of an advanced exotic beam facility evolved from the Rare Isotope Accelerator (RIA) concept. The OMB and the DOE Office of Science are encouraging the development of concepts for a facility that would cost ~$600M rather than the ~$1.1B dollar estimated for the full RIA concept. They are tentatively planning for the Project Engineering and Design part of the construction to begin in 2011. This means that site selection and a CDR must be completed before that, beginning some time in 2008. The priority given to this project is based on several studies, carried out in the U.S. and around the world, emphasizing the opportunities for discoveries in nuclear science that are enabled by such facilities.
Opportunities at Argonne
The team that developed the concepts that became the underpinnings of the original RIA proposal is now at Argonne, ready to develop the modified proposal for an advanced exotic beam facility as currently envisioned by the DOE. There are several aspects to be developed for the modified design such that the full 400-kW beam power proposed for RIA would still be provided by the half-scale facility. The initiative is also broadened to include basic R&D that is potentially useful in the advancement of exotic beam capabilities worldwide. These efforts are being addressed via an “exotic beam” subinitiative of the Broadly Baed Accelerator R&D Strategic Initiatve. An overview of the exotic beam subinitiative is presented in an appendix to this report.
- Surface Processing of SCRF Structures
The development of superconducting RF structures during the last two decades, for both the velocity-of-light structures for electron accelerators as well as the low-velocity structures for hadron accelerators, provided a convincing case for the use of SCRF technology in the next-generation accelerators that will require high accelerating gradients and/or high average power. Nearly all major accelerators in the future will employ SCRF cavities: the ILC, fourth-generation x-ray facilities (either x-ray lasers or energy recovery linacs), and advanced exotic beam facilities. A critical element for high-performance SCRF cavities is the processing of the niobium surfaces by a combination of chemical processing and electropolishing (EP). The current design of the proposed ILC linac with CM energy of 500 GeV requires about 17,000 Tesla-type 9-cell SCRF cavities. To limit the length of the accelerator and the power consumption, the accelerating gradient and the quality factor (Q0) are specified at 35 MV/m and 1010, respectively. Cavities with the specified performance have been produced by electropolishing (EP), which is currently the baseline approach for ILC cavity production. However, the performance of each individual cavity is sensitive to the details of the EP parameters. It is critically important to find the optimal EP parameters that can reliably produce the specified ILC performance.
Opportunities at Argonne
The pioneering development of low-velocity SCRF structures for acceleration of heavy ions by the ATLAS group in the ANL Physics division during the 1970s led to the world’s first superconducting linac for hadrons. This group has continued to evolve and is currently a leader in the development of surface processing for high-performance SCRF cavities. A new processing facility, called the Joint Argonne-Fermilab Superconducting Cavity Surface Processing Facility (AFSCSPF), located at Argonne, was constructed as an Argonne-Fermilab joint project beginning in 2002 (before the SCRF-based ILC project was formulated). The original intent of the facility was for processing of low-velocity structures for Argonne and buffered chemical processing of the velocity of the light structures for Fermilab. With this upgrade of Argonne’s cavity processing capability, an opportunity has been created for Argonne to contribute to the development of high-gradient SC cavities for ILC by electropolishing 9-cell elliptical cavities. Argonne’s effort will be a very significant contribution towards demonstrating the U.S.’s capability to build, process, and operate state-of-the-art 9-cell elliptical cavities for the ILC.
The technology for high performance velocity of light structures will be important also for other possible future accelerator projects at Argonne, such as developing continuous wave (CW) deflecting cavities for x-ray pulse compression at the APS, or a future light source that makes use of x-ray free-electron lasers.
- Laser-Driven Advanced Acceleration Techniques
It is generally thought that high-energy accelerators beyond the TeV scale will need to be based on accelerating structures drastically different from metallic structures employed in current accelerators. Laser wakefield accelerators have been pursued for some time with the hope of producing extremely high-gradient, GeV/cm rather than 20-50 MeV/m in the current state-of-the-art machines. Although the high gradient capability has been experimentally confirmed, the basic problems with the laser wakefield accelerators have been that beams are produced with large phase-space spread and jitter. However, significant advances have been made recently that allow better control of beam quality and jitter by operating in the highly nonlinear “bubble regime.” Beams of up to 1-GeV energy, a few percent energy spread, a few mm-mrad emittance, and up to 100-kA current have been reported by several groups around the world. It is therefore possible that the laser wakefield technique could have practical impact within a few years.
Opportunities at Argonne
The first proof-of-principle demonstration of particle acceleration in plasma was performed by the AWA group at Argonne. Recently, the advanced accelerator research at AWA has been focused on dielectric-based schemes. There is an excellent opportunity for AWA group members to widen their expertise and contribute to the development of laser wakefield accelerators by collaborating with scientists at the Chemistry (CHM) and Accelerator Systems (ASD) divisions. The laser scientists at CHM have recently constructed the Terawatt Ultrafast High Field Facility (TUHFF), which is capable of delivering peak powers in excess of 20 Terawatts (0.6 J in 30 fs). The TUHFF system has successfully generated multi-MeV electron beams through the laser wakefield accelerator. We are embarking on a new project that uses the TUHFF laser to drive the wakefield in the bubble regime. The Argonne Accelerator Institute will allow us to take advantage of the many resources available at Argonne to make this project a success. These include expertise in laser and optics, accelerator physics, and free-electron laser physics, and equipment such as undulators, and x-ray and beam diagnostics. In addition, last year a plasma computation LDRD was established to support the laser plasma experiment. The success of this project will be greatly enhanced through a close collaborative effort between CHM, HEP, and ASD.
- Other Accelerator Research Activities at Argonne
This section summarizes accelerator research topics that are currently supported mainly by programmatic funding. However, most these topics are closely connected to the AAI activities.
Beam physics topics associated with high-brightness storage rings, such as lattice optimization, dynamic aperture study, collective phenomena, and injection schemes are all closely connected to topics in the ILC damping ring study. Novel techniques to improve the performance of the APS, such as x-ray pulse compression by means of RF deflection cavities, are of interest as fundamental accelerator physics. The APS accelerator physicists are currently working on a proposal for APS2 to modify the ring lattice and employ novel new insertion devices.
The APS Magnetic Devices group has expertise in constructing state-of-the-art undulators that produce high brightness x-rays for third-generation synchrotron radiation facilities (e.g., the APS) as well as for more challenging long devices for free-electron lasers such as LEUTL, the pioneering high-gain FEL in the VUV radiation at the APS and the Linac Coherent Light Source (LCLS), the first x-ray free-electron laser under construction at SLAC. Recently, the group embarked on a program to develop superconducting undulators for higher-energy photons. The technology is directly relevant to the helical undulator required for the polarized positron source of the ILC.
- Time-resolved imaging from visible to x-rays
- Utilize a variety of the sources; undulator radiation, optical diffraction radiation, and optical transition radiation (OTR)
- OTR for hadron beams in the Tevatron accelerator chain
- The Advanced Accelerator Group at the High Energy Physics (HEP) Division
The Advanced Accelerator Group (AAG) in Argonne’s High Energy Physics division has been involved with the development of several new concepts and experimental techniques that can directly enhance the U.S. collaboration on high gradient studies. The group has been operating the Argonne Wakefield Accelerator (AWA) for pioneering experiments on wakefield acceleration in plasma as well as in dielectric structures. Currently, the major research topics of the group are on two different, but intimately related, areas: electron-beam-driven wakefield acceleration and novel RF-driven dielectric and metallic accelerating structures. The research topics are:
- Dielectric structure based on a two-beam acceleration scheme that uses a train of low-energy, high-current electron bunches (the drive) to accelerate a second electron bunch (the witness) to higher energy
- High-power tests of external RF powered dielectric-based, X-band structures in collaboration with NRL and SLAC.
- Schottky-enabled photoelectron production and its application to RF breakdown study
- Theory and simulation study of high-brightness electron guns and experiments in collaboration with other institutions
- Chemistry (CHM) Division
- Radiolysis study at the TUHFF
- Thermal positron source development using a high peak current15-MeV linac
- Physics (PHY) Division
- ATLAS Facility
- Spoke cavity development
- Heavy ion beam dynamics
- Joint Argonne-Fermilab SCRF Surface Processing Laboratory
- Intense Pulsed Neutron Source (IPNS)
- Operation of a high-intensity rapid-cycling proton synchrotron for neutron production
- Concept development of a Very Cold Neutron Source (VCNS) proposed to replace the IPNS
- The ONR Project Office
It is the intent of the Office of Naval Research (ONR) to support the construction of a kW-class free-electron laser at Los Alamos National Laboratory, as part of an overall development program towards higher output powers. The development of the FEL will exclude high risk technology not required for the FEL, namely there will be no research aimed at breakthrough improvements in FEL technology. There is a strong interest of the part of ONR for development of new technologies in areas relevant to beam physics and applications. This includes novel electron beam sources; beam halo detection and control; advanced energy-recovery linac lattice design; single-bunch and bunch-train non-intercepting diagnostics development; and improved merge/extraction optics. These topics overlap with the topics discussed in section 4.2 and may be pursued at Argonne.
High-brightness electron beam generation based on a laser-driven photocathode gun (either DC or RF) is an essential element of linac-based future light sources, whether they are energy recovery linac (ERL) sources or high-gain x-ray free-electron lasers (FELs). The gun specifications for these applications are at a level believed to be achievable but not yet convincingly demonstrated. Thus advances in the photocathode gun are of basic importance, requiring fundamental theoretical insights, detailed simulations, and rigorous experimentation. There is also a proposal to combine the high-brightness gun with a novel emittance manipulation technique to produce electron beams suitable for the electron arm of the ILC, thus obviating the electron (but not the positron) damping ring.
Opportunities at Argonne
The APS Accelerator Physics Group has extensive experience operating RF photocathode guns during the pioneering high-gain FEL experiment at UV wavelengths in 2000. Since then, research to explore novel gun configurations has been pursued in the Injector Test Stand (ITS). The Advanced Accelerator Group (AAG) in the High Energy Physics (HEP) division also has extensive experience in RF photocathode gun operation and design, having constructed a very high-charge (100 nC) gun for producing the drive beams for the Argonne Wakefield Accelerator (AWA). Plans are underway to perform a demonstration experiment of the emittance manipulation technique in collaboration with the Beam Physics and Astrophysics Group at NIU and the Fermilab A0 Group.
There is an opportunity to install a superconducting linac at Argonne, capable of producing up to 50-MeV electron beams, by inheriting a Tesla-type superconducting accelerating structure from Stanford University due to the termination/decommissioning of the Stanford Free Electron Laser Laboratory in the Hansen Physics Laboratory (HEPL). Although the transfer is estimated to require substantial funding, it may be feasible by establishing a multi-institutional consortium including Argonne, ONR, NIU, and possibly Fermilab.