TECHNOLOGY AREAS: Ground/Sea Vehicles, Electronics, Weapons

OBJECTIVE: The objective of this proposal is to develop a high-power 95 GHz millimeter wave RF vacuum source employing permanent or conventional solenoid magnets. The goal is to reduce weight and cost, improve reliability and, most importantly, eliminate the cool-down time of the current Active Denial System without imposing or increasing additional constraints (e.g. prime power) on the system. A source with output power exceeding 30 kW average (100 kW goal) utilizing permanent magnets is desired. The development of such a source would be a major step forward for the deployment of this technology and the resultant capabilities. Furthermore, this technology would have other significant military (e.g. mm-wave radar) as well as scientific and commercial (e.g. sources for materials processing, plasma heating and diagnostics, etc.) application.

DESCRIPTION: The frequency band near 95 GHz is of interest for a number of applications, one of which is Active Denial [1]. This is due to a natural atmospheric transmission window at this band [2]. Another major military application at this frequency is mm-wave radar for detection of small, elusive targets and remote sensing such as cloud mapping [3-5]. In addition, the gyrotron presently used in the Active Denial System is fundamentally similar to other gyrotrons (at various mm-wave frequencies), almost all of which are used in scientific (e.g. plasma heating, confinement and diagnostics) and industrial (e.g. materials processing) applications [6,7]. Applications in these fields would also benefit, as the technology should readily scale to other frequencies.

Presently, high-power gyro-sources above 30 GHz almost exclusively employ superconducting magnets [8]. This is fundamental as the frequency of operation is directly determined by the magnetic field [6, pp. 8-11]. Superconducting magnets are expensive and difficult to transport, operate and maintain in the field. In scientific and industrial applications they account for significant expense as cryogenic magnets are typically used, requiring considerable amounts of liquid Helium. The elimination of the superconducting magnet would be a major advancement in the development of systems designed to exploit the 94-96 GHz frequency band in particular and the upper mm-wave band in general.

Harmonic operation, the technique to eliminate the superconducting magnet in gyro-devices, is (theoretically) well known [9-11]. That is, the frequency of operation, f, is directly proportional to the magnetic field, B. However, the frequency of operation can be generated as a harmonic, n, of the fundamental frequency, fo, of the device (that is, f=nfo is proportional to B). Therefore, the magnetic field can be reduced by the harmonic number (i.e. f

B/n). Although the physics are relatively straight forward, the technological developments required for viable harmonic operation are challenging. Since the vast majority of gyrotrons produced to date have been for the scientific and industrial communities (which have the benefits of controlled environment and schedule), the impetus for research and development in this area has not been seen as outweighing the technical risks. This is not so for military applications.

Presently, efficient generation of 94-96 GHz mm-wave power requires a magnetic field of approximately 38-40 kG. The best published result for permanent magnets (in a gyro-device) is around 10 kG [12]. Therefore, operation at a harmonic of n=4 or more is anticipated. However, present gyro-device technology exhibits a prohibitive decline in efficiency above the n=2 harmonic (see [13] for the present state-of-the-art of gyro-devices operating in both fundamental and harmonic modes). Techniques for efficient, high-harmonic operation have been proposed [9-11], including operation in slotted cavities and/or with axis-encircling electron beams (and typically with depressed collectors), but not yet effectively realized. It is this challenge (realization of efficient, high-power, high-harmonic operation) that represents a major advancement of the art. To that end, demonstration of an efficient (>35%), high power (>30 kW) 95 GHz source with permanent magnets presents an opportunity for innovative research.

PHASE I: The Phase I technical objective is to design an experimental vacuum device operating at (approximately) 95 GHz, utilizing permanent or conventional solenoid magnets and capable of producing 30 kW at 35% efficiency. The design need not be intended to produce 30 kW average power (it may be a device with 30 kW or more peak power operated at a lower duty cycle. However, this is only intended to mitigate the Phase I cost (and risk) and the technology may not have a fundamental physical limitation which would prohibit its application to the 30 kW average power goal.

PHASE II: The Phase II technical objective is to (1) build a prototype device designed in Phase I, (2) demonstrate the performance of the device, and (3) modify the design to achieve the goal of 30 KW average power output, prepare and provide the design for Phase III implementation.

PHASE III: Build and evaluate an Engineering Development Model (EDM) 30+ kW device for system application.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Success of this project would allow development of a family of high power, compact, mobile, mm-wave sources since the technology should translate easily to other frequencies. Furthermore, harmonic generation applies to amplifiers as well as oscillators. Therefore, another immediate Phase III application would be high-resolution mm-wave radar for detection of, for example, space debris, small fast moving targets, and targets hidden in clutter. Furthermore, the advantages of such a radar for remote sensing (e.g. storm cloud mapping) have been demonstrated [14]. Mobile, high data rate (high bandwidth), communication systems would be another probable application.

Successful demonstration of this device will lead to wide interest in commercialization of the technology. Spin-offs would include cheaper sources for advanced materials processing (e.g. mm-wave sintering of ceramics and metals), plasma heating and spectroscopy.

REFERENCES:
1. Active Denial Web site � http://www.de.afrl.af.mil/fact sheets/Active denial.html
2. E. S. Rosenblum, "Atmospheric absorption of 10-400 KMCPS radiation, summary and bibliography to 1961," Microwave Journal, vol. 4, pp. 91-96, March 1961.
3. V. L. Granatstein and A. V. Gaponov-Grekhov, "High-power microwave electronics: a survey of achievements and opportunities," in Applications of High Power Microwaves, A. V. Gaponov-Grekhov and V. L. Granatstein, Ed. Norwood MA: Artech House, 1994, pp. 18-19.
4. A. W. Fliflet, et. al., "Cloud imaging using the NRL WARLOC radar," Conference Record of the RF 2003 Workshop, pp329-338, 2003.
5. J. B. Mead, et. al., "Millimeter-wave radars for remotely sensing clouds and precipitation," Proc. IEEE, vol. 82, pp. 1891-1906, Dec. 1994.
6. M. V. Kartikeyan, E. Borie, and M. K. A. Thumm, Gyrotrons, High Power Microwave and Millimeter Wave Technology. Berlin: Springer-Verlag, 2004, pp. 185-192.
7. Communication and Power Industries, "Products: Gyrotron", Online: http://www.cpii.com/mpp/products/gyrotron.shtml.
8. K. L. Felch, B. G. Danly, H. R. Jory, K. E. Kreischer, W. Lawson, B. Levush, and R. J. Temkin, "Characteristics and applications of fast-wave gyrodevices," Proc. IEEE, vol. 87, pp. 752-781, May 1999.
9. K. R. Chu, "The electron cyclotron maser," Rev. Modern Physics, vol. 76, pp. 489-540, April 2004.
10. R. C. Stutzman, D. B. McDermott, Y. Hirata, D.A. Gallagher, T.A. Spencer and N. C. Luhmann, Jr., "94 GHz sixth-harmonic slotted gyrotron," in IEEE Conf. Record - Abstracts, The 27th IEEE Int. Conf. on Plasma Sci., 2000, p171.
11. D. B. McDermott, A. J. Balckum, and N. C. Luhmann, Jr., "35-GHz 25-kW CW low-voltage third-harmonic gyrotron," IEEE Trans. Plasma Sci., vol. 24, pp. 613-619, June 1996.
12. T. Idehara, et. al., "A high harmonic gyrotron with an axis-encircling electron beam and a permanent magnet," IEEE Trans Plasma Sci., vol. 32, pp. 903-909, June 2004.
13. M. K. Thumm, "State-of-the-art of high power gyro-devices and free electron masers, update 2004," Forschungszentrum Karlsruhe, Karlsruhe, Germany, Tech. Rep. FZKA 7097, February, 2005.
14. W. M. Manheimer, et. al., "Initial cloud images with the NRL high power 94 GHz WARLOC radar," Fourth IEEE Int. Vacuum Electronics Conf. (IVEC 2003) - Conf. Record, p. 378, May 28-30, 2003.

KEYWORDS: Gyrotron; Gyro-device; Millimeter-wave; Harmonic; Oscillator; Super conducting

TPOC: Lawrence Dressman
Phone: (812)854-4804
Fax: (812)854-3676
Email: [email protected]
2nd TPOC: Thomas Ball
Phone: (812)854-5220
Fax: (812)854-3676
Email: [email protected]

** TOPIC AUTHOR (TPOC) **

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