Session chairperson and summary author: Gregory Nusinovich
Among five papers scheduled for this Session, there were 2 papers submitted by Russian and 1 by Ukranian scientists who were unable to attend the Conference. This fact by itself indicates that in the future the Conference organizers should pay more attention to the ability of scientists from Eastern Europe to attend conferences.
Two papers, which were presented at the Session, were quite impressive. The first one presented by Yuval Carmel from the University of Maryland describes the progress in studies of plasma-assisted slow-wave oscillators (PASOTRONs). These plasma-filled high-power microwave sources were initially developed at Hughes Research Laboratories (Malibu, CA). Later, starting from the late 1990ís, AFOSR started to support the investigation of various physical processes in these tubes at the University of Maryland. Recall that in these devices an electron beam is focused by plasma ions (Bennett pinch) instead of the guiding magnetic field used in other microwave tubes. A thorough analysis showed that in the absence of guiding magnetic field the beam electrons may experience under the action of the axial and radial components of the wave electric field a two-dimensional motion. The radial motion can be very beneficial for those electrons, which are injected near the waveguide axis, because it moves the electrons from the region of a weak slow-wave field towards the slow-wave structure surface where the field is strong. This not only increases the beam coupling to the wave, but also can greatly enhance the efficiency. In accordance with this concept developed in previous theoretical studies, an experimental configuration of the pasotron was modified. This resulted in the efficiency increase from about 20% to more than 50%.
The second paper was presented by Lawrence Ives from Calabazas Creek Research (CCR), Inc. As follows from the list of authors given in the advance program, this work was done in collaboration with the Russian company "Istok", which is known as a manufacturer of submillimeter-wave backward-wave oscillators (BWOs) for spectroscopy studies. Authors reported very impressive results of the development of Terahertz Backward-Wave Oscillators (THz BWOs). This work is sponsored by NASA because there is a strong interest in the development of frequency-tunable, light-weight local oscillators for heterodyne receivers in a THz frequency range. Such devices are needed for numerous radioastronomy observations, which include the spectroscopy of Earth and other planetary atmospheres and investigations of the interstellar medium. The authors decided to use an advanced manufacturing technology (LIGA instead of the EDM) for fabricating the tiny microwave circuits at frequencies up to 1.5 THz. To develop such a process, CCR collaborates with Sandia National Laboratory. Presently, the circuits, which were manufactured already, operate at frequencies in the range from 600 GHz to 700 GHz. The authors proposed an interesting method of scraping an initially generated sheet electron beam into five parallel beamlets, each of which propagates between two parallel rows of pintles forming a slow-wave structure. Since the interaction efficiency should be less than 5%, they also plan to use a single-stage depressed collector. Simulations indicate that by using this technique more than 80% of the energy in a spent beam can be recovered. This would greatly reduce the power consumption from 270 W to less than 80 W and eliminate the water cooling. This CCR initiative seems to be extremely promising for numerous applications of tunable sources in the THz spectroscopy.