Accelerator physics plays a major role in modern physics and technology applications. Many experiments in nuclear and particle physics test the fundamental laws of physics by colliding a high-energy beam of particles, such as electrons or protons from an accelerator, with a fixed target or with another beam of particles. Modern light sources, which are capable of producing high-energy photons such as X-rays, operate by "bending" the path of electrons in an accelerator with dipole magnets and wiggler magnets to generate radiation. State-of-the-art cancer treatment facilities, such as the Midwest Proton Radiotherapy Institute located at the Indiana University Cyclotron Facility, utilize high-energy proton and heavier ion beams to treat inoperable tumors.
The goals of the Indiana University accelerator physics group are to design novel accelerators for applications at the IUCF and abroad, to develop new theoretical and advanced computational methods for aiding in the design and study of accelerators, to design new accelerator components for existing accelerators, and to develop new methods for studying data at existing accelerator facilities.
Advanced Electron-Photon Facility (ALPHA)
Professors S. Y. Lee and Paul Sokol are currently leading the design effort of a multipurpose electron accelerator which will be operated under a joint collaboration between Crane Naval Surface Warfare Center and the IUCF. This accelerator will serve the Department of Defense's requirements for testing radiation effects, as well as IU's interest in a compact high-brightness x-ray source. ALPHA will be composed of two parts: 1) an injector which is an existing Crane linear accelerator that is capable of producing electron energies of up to 60 MeV and 2) a 20 m electron storage ring. The dipole magnets that will be used in the storage ring were previously used in the Cooler Injector Synchrotron (CIS) at the IUCF.
One of the primary requirements for Crane's radiation effects testing program is the uniformity of the electron radiation dose. It is necessary that the electron beam bunch does not have a frequency dependence in the (1-10 GHz) range since this would interfere with existing Crane diagnostics. In order to overcome this difficulty, the storage ring has been designed to produce a highly uniform electron pulse with a pulse length of up to 50 ns.
When operating as an X-ray source, the storage ring will form electron bunches approximately 10 ps in length that will collide with a laser pulse with approximately ~ 1 micron wavelength (near infrared-visible range). The collision between the electron beam and the laser beam will produce photons through the Inverse Compton Scattering process, with energies far greater than the laser beam. For a 50 MeV beam, it is possible to produce photon wavelengths ~ 0.03 nm (hard X-ray).
ALPHA will serve as a user facility for the IU community in a variety of scientific research areas. X-ray and VUV sources are of great importance to the scientific community for probing the structure and properties of biological and condensed matter systems. Small labs that conduct research in these areas typically utilize a rotating anode, which is a compact X-ray source. One of the drawbacks of the rotating anode is that it has a relatively low X-ray flux, which ultimately limits the quality of experiments that can be conducted. One of the great advantages of ALPHA is that it is possible to produce X-ray fluxes which are a factor of 10,000 times greater than the rotating anode.
The ALPHA accelerator will be an exciting new component to the IUCF which will jointly serve the needs of the Navy and the IU community.
Electron Source Modeling
Prof. Mark Hess is currently leading an intensive effort to develop novel computational methods and to understand the limitations of existing methods for modeling state-of-the-art electron sources. A typical example of an electron source which is used at high-energy particle accelerators to produce high-quality beams is a photocathode source. In a photocathode source the electron beam is generated through a photoemission process from a laser beam which is focused onto a metal surface. The photocathode source then accelerates the electrons to a few MeV using radio-frequency electric fields which are pumped externally into the source's metallic cavity structure, and focuses the beam using one or multiple solenoidal magnetic fields. The following figure shows a diagram of a photocathode source accelerating a bunch of electrons (red).
Since the beam is at relatively low energy at the source, the effects of beam generated electromagnetic fields, aka space-charge fields, are highly important and need to be included when modeling the source. The problem is further complicated by the fact the metallic cavity walls give rise to image charge and current effects.
The research efforts at Indiana University in regards to the study of electron beams have been focused on two areas: 1) understanding the limits of existing electron source codes which usually compute the space-charge fields electrostatically, using a Poisson solver, or electromagnetically on a grid, using a Yee-type algorithm and 2) develop novel computational methods which can circumvent the limitations of the existing codes. An example of a limitation on a grid based algorithm is the presence of an
USPAS - Particle Accelerator School
The US Particle Accelerator School together with the Indiana University Department of Physics offers an opportunity to earn a Master of Science Degree in Beam Physics and Technology. Students earn credit toward the Indiana University diploma at USPAS/university-sponsored courses by selecting their USPAS course for Indiana University credit. Award of a Master of Science Degree requires 30 hours of credit with a grade point average of B or above; a maximum of 8 credit hours may be transferred into the program; some credits earned at previous USPAS courses also may be eligible for transfer. There is a strict five year limit to obtain the Master of Science degree.
Interested students may go to the IU Physics Department and click on "apply now" under the graduate program to apply to the IU/USPAS Master's Degree program electronically. Applicants must send a copy of their undergraduate transcript(s) and provide three letters of recommendation. Students are also encouraged to supply a copy of their Graduate Record Exam (GRE) score. For more information, visit the USPAS site.
