| |
|
Spring 2004 |
Summer & Fall 2004 |
In the spring of 2004 (as part of Phys 4052W - Methods of Experimental Physics II) we attempted to generate a small quantity of microwave Cerenkov radiation by passing a narrow, low-energy (3KeV) electron beam in close proximity over the surface of a high dielectric material (titanium dioxide ceramic). Such radiation is characterized by its angular distribution, wavelength dependence on distance between the beam and the dielectric, and by its threshold dependence on the energy of the beam. If the electrons are not of a high enough energy (velocity), then no radiation should be detected. At the end of the spring term, what data had been collected was inconclusive at best. In the summer of 2004 (as part of Phys 4501 - Experimental Project), and continuing into the fall (under Phys 4950H - Senior Thesis), the experiment was continued and refined. Increases in resolution and sampling rate made it more likely that the weak Cerenkov radiation signal could be detected. Trials were also performed to see whether or not the microwave diode used to detect the radiation was indeed operational in a vacuum. The new data shows a clear correlation between the diode's signal fluctuations and the modulations in electron beam energy. This is indicative of Cerenkov radiation being the reason for the diode's fluctuations. A system to show the dependence of the radiation on the proximity of the beam to the dielectric was designed and installed.
For an overview of the progress of this project up until the end of the summer term, see the Senior Honors Seminar Presentation. This presentation was prepared as part of the Junior/Senior Honors Seminar course and was intended to be a brief, non-technical summary of the work done so far.
Introduction
Cerenkov radiation, known primarily as the source of the bluish-white light emanating from nuclear reactors, is generated by one of the most interesting phenomena in nature. When light (photons) enters a substance, they slow down. Consequently, other particles, such as electrons, can move through the substance at a speed greater than the speed of light in that substance. When this condition is met, the “super-luminous” particle emits energy as Cerenkov radiation [1]. The wavelength of this radiation is merely a function of the speed of the particle and the new speed of light. If, however, one moves the beam out of the substance, and instead passes it over the surface, the distance between the beam and the surface also becomes a factor. This project aims to generate microwave Cerenkov radiation by these means, and to characterize two of these criteria of generation for the radiation, namely the speed of the electrons and the distance between the dielectric and the beam.
Based on the low-energy (3 KeV) electron beam used to generate the radiation, and on the width of the beam, one is limited in the frequency domains that can be easily worked in. Although Cerenkov radiation can be emitted in an incredibly wide array of bands (from x-ray to radio, and beyond [1]), by comparing power estimates, my ability to position the beam, and my ability to measure the radiation once it is generated, I chose to generate radiation in the X-band (3.75-2.4 cm or 8-12 GHz).
Next Page
