waves and beams

Research in the Waves & Beams Division is divided into four major areas:

High Power Microwave Sources

In recent research, we have completed two major advances in creating high quality output beams from gyrotrons. In a 1 MW, 110 GHz gyrotron we have succeeded in creating an output beam, which is nearly a perfect Gaussian beam the gyrotron efficiency is increased and the design of auxiliary transmission line components is greatly simplified. That work was carried out in collaboration with Communication and Power Industries of Palo Alto, CA and General Atomics of San Diego, CA. In a second application, the same techniques have been applied to the design of phase correcting mirrors for use on the LHD stellarator experiment in Japan as part of an international collaboration program. To extend this research to higher power levels needed in future ERH experiments, we have initiated a study for a 1.5 MW, 110 GHz gyrotron. A prototype gyrotron has been built and is being tested at MIT to be followed by a CW gyrotron that will be built by industry.

A new idea for a gyrotron microwave window, a dome shaped window capable of handling megawatt level CW power has been demonstrated. This research is primarily sponsored by MIT Lincoln Lab through their Advanced Concepts Committee (ACC) internal funding program. In research on a 250 GHz gyrotron oscillator for use in sensitivity-enhanced nuclear magnetic resonance through dynamic nuclear polarization, successful operation was achieved at CW power levels of up to 25 W. This research, funded by the NIH in collaboration with Prof. Robert G. Griffin, Director of the Francis Bitter Magnet Laboratory, is a pioneering effort in high field dynamic nuclear polarization studies. Recently, a 460 GHz CW second harmonic gyrotron oscillator developed for DNP studies has generated a record CW power level of over 8 W.

We have completed a research program on Innovative Vacuum Electronics, which was sponsored as an MURI consortium. We have successfully demonstrated the operation of a novel 140 GHz gyrotron oscillator with a highly overmoded interaction structure. A second harmonic gyrotron oscillator experiment is currently in progress to demonstrate the effectiveness of quasi-optical open resonators for mode selective operation in gyrotron. We are also exploring alternative ideas for interaction structures for high frequency (100-1000 GHz) microwave tubes. We have demonstrated a new idea for building high frequency microwave tubes with overmoded interaction structures made of photonic band gap (PBG) structures. A proof-of-principle experiment æ a novel gyrotron with a PBG resonator was successfully operated in a very high order mode without mode competition over a wide frequency bandwidth. We have begun research on a gyrotron amplifier at 95 GHz. Initial experiments for the amplifier are planned at 140 GHz and the device is being readied for testing.

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High Gradient Accelerators

We are involved in normal conducting accelerator research at high frequency, namely 17.14 GHz. With an available 25 MW of RF power we can run independant experiments, such as RF guns, as well as experiments with beams on our 25 MeV electron linac line.

We have demonstrated over 350 MV/m in an RF gun. We have demonstrated the first accelerator structure with a Photonic Band Gap structure. We have demonstrated bunch length measurements from Smith Purcell radiation observations. And we have developed an electric field integral equation code in support of Smith Purcell Radiation experiments, which has been verified through both Smith Purcell and Coherent Transition radiation experiments.

Novel Electromagnetic Structures

The division is also involved in the development of novel electromagnetic structures for use in microwave vacuum electronics such as photonic band gap (PBG) structures and novel cathodes. We have experimentally demonstrated the benefits of using PBG structures in high gradient accelerators and high frequency microwave sources.

Intense Beam Theoretical Research

Our research encompasses a broad range of topics related to high-intensity charged particle beams. One area of research that we are currently investigating is that of periodically focused intense charged-particle beams, which is useful in the study of high-power microwave sources. We are also researching topics in chaos and coherent structures in beams, and in particular, we are analyzing the nonlinear dynamics of heavy ion beams for use in fusion technology. Our group is currently working closely with the Waves & Beams experimental group and with a number of other universities in a MURI (Multidisciplinary University Research Initiative) program to study the physics of vacuum electronics. We have also extended our vacuum electronics research to include an STTR on the investigation of crossed-field devices, e.g. the magnetron. Finally, our group has been theoretically studying the physics of small plasma toroids through a separate STTR program

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