In pursuit of Jefferson Lab's basic nuclear physics mission, a number of core technologies have been and continue to be developed with the potential for industrial development. These include:
- superconducting accelerating cavities
- accelerator-related technologies
- accelerator-driven light sources
- real-time control system software
- cryogenic systems
- magnet technology
- radio frequency power systems
- accelerator diagnostics
- particle detectors and data acquisition systems
- advanced accelerator research and development
Superconducting Accelerating Cavities
Cavities being produced for Jefferson Lab by industry are the first with features that make them practical for large-scale application. Developed at Cornell University, the technology was transferred to industry first by a Cornell-Jefferson Lab team, then later by the superconducting radio frequency (SRF) technology group at Jefferson Lab.
The Jefferson Lab accelerator requires 338 superconducting radio frequency cavities, operating at a frequency of 1,497 MHz to produce an electric field that accelerates a continuous, virtually speed-of-light charged particle beam. The cavities are made of the metallic element niobium, which is a superconductor when cooled to very low temperatures. Jefferson Lab's cavities operate near absolute zero at two degrees Kelvin.
Performance of the accelerating structures is measured against two main criteria: accelerating gradient and quality factor (Q). Gradient is defined as the energy gain per unit length of accelerating structure. Quality factor, which describes the cavity's ability to store energy in the form of an oscillating electromagnetic field, is an inverse measure of radio frequency power losses. In tests, the industrially produced cavities that Jefferson Lab is currently installing in the accelerator have an average gradient above 9.9 MV per meter and above 5 x 109 for Q. For continuous wave operation - a key requirement for many applications - the older accelerating technology utilizing room-temperature copper cavities can only be expected to achieve gradients about 2 MV per meter and a Q around 104. However, Jefferson Lab cavities have continued to increase in performance to the point where many of the cavities now perform at twice the design specifications. The efficiency of radio frequency power transferred to the beam, using Jefferson Lab as an example, is 99.8 percent for superconducting cavities, as compared to 0.3 percent for a copper cavity under similar beam loading conditions.
Advances made by the Jefferson Lab team in the design of higher-order mode couplers have given the cavities much higher current-carrying capacity. In addition, field degrading difficulties that previously restricted gradient have been largely overcome by a number of improvements such as the development of high-thermal conductivity niobium, fabrication and surface treatment processes that keep the interior surface of the cavity clean and defect-free, as well as design features that minimize multipacting and the growth of disruptive resonant modes.
Accelerator-related technology development and transfer opportunities exist for the use of Jefferson Lab cavities in both basic and applied research. The cavities can be used in high-energy electron/positron storage rings, low-current pion accelerators, and microtrons. Variants with improved gradient and quality factor performance could be used in a linear collider on an energy scale far surpassing those that are presently feasible.
Accelerator-Driven Light Sources
Jefferson Lab's superconducting cavities have capabilities that make them ideal for use in high-power, free-electron lasers (FEL) to provide tunable, monochromatic laser light for industrial research and development, and for scientific applications.
Jefferson Lab's Industrial Advisory Board has recommended that Jefferson Lab build an infrared and ultraviolet FEL utilizing Jefferson Lab superconducting radio frequency (SRF) accelerator technology. Light from these FELs could be used in basic physics, chemistry, biology, medicine, and surface and materials science. Industrial applications include photochemical processing of materials, micromachining, and improvement of metals.
Real-Time Control System Software
Operating the Jefferson Lab accelerator requires real-time management of roughly 100,000 input/output points using a distributed computer-based control system. This control system must provide supervisory I/O, local feedback control, analysis capability, and operator interfaces for numerous accelerator subsystems, including:
- The superconducting injector, which is the region of the accelerator that originates and initially accelerates the beam.
- The radio frequency (RF) system that establishes and controls the accelerating fields inside the cavities.
- The 2,000 magnets that guide and focus the beam in up to five orbits around the machine.
- The monitoring devices that track the beam's status and behavior.
- The refrigerator and supply system for the liquid helium that enables the cavities to operate superconductively.
- The vacuum system that maintains appropriate conditions inside the accelerator.
- The interlocks and other devices that ensure safety for both personnel and the machine itself.
These requirements are met by a system developed at Jefferson Lab and in collaboration with other research laboratories using industry standards and off-the-shelf hardware whenever possible.
The extensible system has a computer hierarchy of two levels, supervisory and local, and can be configured to support a large number of supervisory consoles (Unix based) each directly communicating with the local computers (40 for Jefferson Lab) via a local area network. The local computers run a commercial real-time operating system for optimal performance.
Hardware is interfaced to the system using a wide variety of industry standard systems including VME, GPIB, RS-232, and CAMAC (among others). In some cases embedded processors are used for time critical applications.
The software technology employed is state-of-the-art, utilizing modern control theory techniques, C and C++ coding, and object oriented databases.
Other Technology Transfer
Besides the primary opportunities listed above, additional potential for technology development and transfer exists in a number of other areas.
Complex Cryogenic Systems
Jefferson Lab operates the world's largest refrigerator for liquefying helium for use at two degrees Kelvin. Utilizing some two kilometers of transfer lines, the plant is the fifth largest of all such facilities world wide.
Large superconducting magnets are the basis for the spectrometers and detectors in each hall. It takes over 2,000 conventional magnets, powered by an elaborate direct-current (dc) power system to guide and focus the beam through its orbits of the accelerator and into the experimental halls, the implementation of which required substantial Jefferson Lab staff expertise in the design and computer modeling of magnet systems.
Radio Frequency Power System
The accelerating fields that are so efficiently sustained and exploited in the superconducting cavities are established by a complex radio frequency power and control system.
The challenge of the real-time system that controls the beam is met by the collection of extensive and accurate data. Gathering this data is accomplished through a network of devices designed to measure various beam properties.
Particle Detectors and Data Acquisition Systems
Jefferson Lab's nuclear physics research program requires development of a wide array of detectors for the photons, electrons, and other collisions between electrons in the beam and the nuclei in a given experimental target. For the subsequent analysis of the thousands to millions of such interactions in a given experiment, extremely sophisticated data acquisition systems are being developed.
Advanced Accelerator Research and Development (AARD)
To remain on the cutting edge of technology in our core competencies, Jefferson Lab is planning an advanced accelerator research and development (AARD) program that will build on staff experience and capitalize on existing infrastructure to advance technology for the next generation of high-brightness, moderate-to-high-energy electron beams. The AARD effort will develop technical improvements of superconducting RF accelerating cavities and the cryomodules in which the cavities operate, focusing first on cavity fabrication and processing, and later on critical ancillary technologies such as couplers, peripherals, and cryogenics.
The program will define fundamental technology limitations and determine ways of increasing cost-effectiveness and system reliability. Existing technology will be developed systematically to increase both gradient and quality factor and to decrease the spread presently observed in cavity performance. Supporting this technology development, AARD accelerator physics modeling experiments will be carried out to increase the understanding of superconducting RF beam dynamics. Because of its potential for industrial spin-offs, the AARD program will be conducted in collaboration with industrial partners to the greatest possible extent.