Electric lamp and discharge devices: systems – Cathode ray tube circuits – Combined cathode ray tube and circuit element structure
Reexamination Certificate
2001-11-21
2003-10-14
Lee, Benny T. (Department: 2817)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Combined cathode ray tube and circuit element structure
C315S005330, C315S005140, C315S005350, C315S005370, C315S005120, C313S1030CM, C313S104000
Reexamination Certificate
active
06633129
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to electron guns for producing bunched electrons and subsequently using those electron bunches to generate rf energy. More specifically, the present invention is related to an electron gun that uses an rf cavity subjected to a rotating and oscillating electric field at a given frequency for the production of bunched electrons and uses an output cavity for the production of a higher frequency and higher power oscillating electric field than that power and frequency in the input cavity.
BACKGROUND OF THE INVENTION
The development of high-current, short-duration pulses of electrons has been a challenging problem for many years. High-current pulses are widely used in injector systems for electron accelerators, both for industrial linear accelerators (linacs) as well as high-energy accelerators for linear colliders. Short-duration pulses are also used for microwave generation, in klystrons and related devices, for research on advanced methods of particle acceleration, and for injectors used for free-electron laser (FEL) drivers. During the last few years, considerable effort has been applied to the development of high power linac injectors [J. L. Adamski et al., IEEE Trans. Nucl. Sci. NS-32, 3397 (1985); T. F. Godlove and P. Sprangle, Part. Accel. 34, 169 (1990).] and particularly to laser-initiated photocathode injectors [J. S. Fraser and R. L. Sheffield, IEEE J. Quantum Elec. QE-23, 1489 (1987); R. L. Sheffield, E. R. Gray and J. S. Fraser, Proc. 9th Int'l FEL Conf., North Holland Publishing Amsterdam, p. 222, 1988; P. J. Tallerico, J. P. Coulon, LA-11189-MS (1988); M. E. Jones and W. Peter, IEEE Trans. Nucl. Sci. 32 (5), 1794 (1985); and P. Schoessow, E. Chojnacki, W. Gai, C. Ho, R. Konecny, S. Mtingwa, J. Norem, M. Rosing, and J. Simpson, Proc. of the 2nd Euro. Part. Accel. Conf (1990), p. 606.]. The best laser injectors have somewhat higher quality beams than more conventional injectors such as in reference [J. L. Adamski et al., IEEE Trans. Nucl. Sci. NS-32, 3397 (1985)], but the reliability depends on the choice of photocathode material, with the more reliable materials requiring intense laser illumination.
The methods used to date are rather complex, cumbersome, expensive, and have very definite limits on performance.
The next generation of TeV linear colliders for high energy physics will require rf sources capable of 500 MW/m of rf power with a typical pulse length of 50 ns. This requires a 50 MW source with a corresponding pulse width of 1 &mgr;s at a frequency between 10 and 20 GHz before pulse compression [R. Ruth, ed., Report of the Linear Collider Working Group, Proceedings of the 1990 Summer Study on High Energy Physics, Snowmass, Colo., Jun. 25-Jul. 13, 1990]. Because the cost of the rf sources will be a large fraction of the operating cost of the accelerator, there is a need for high-power microwave sources capable of multi-megawatt performance at high efficiency. To ensure that modulator costs do not become excessive, the potential driver should also be able to satisfy the above requirements working at a voltage of about 600 kV.
Considerable effort has gone into extending the frequency and power capabilities of “conventional” klystrons [T. G. Lee, G. T. Konrad, Y. Okazaki, Masuru Watanabe, and A. Yozenawa, IEEE Trans. Plasma Sci., PS-13, No. 6,545 (1985); M. A. Allen et al, LINAC Proc. 508 (1989) CEBAF Report No. 89-001; M. A. Allen et al, Phys. Rev. Lett. 63, 2472 (1989)] to cope with the requirements of future linear colliders. At this frequency range, klystrons tend to become small and rf breakdown in the cavities and gaps becomes very difficult to avoid. The output power of the device is then constrained by the maximum electric field that the gap can sustain. As the frequency is increased the gap is reduced and so is the output power. In recent X-band klystron experiments at SLAC designed to produce 100 MW output power at 11.4 GHz, 52 MW was obtained with 1 &mgr;s pulses at an efficiency of 30%. Output power was limited by breakdown in the output structures [G. Caryotakis, SLAC-PUB-6361 September 1993 (A)] and problems such as beam interception in the beam tunnels were also encountered.
Interest has increased in recent years in pursuing other methods of microwave generation oriented towards coping with the requirements of future TeV linear colliders. A group at the University of Maryland is pursuing an X-band gyroklystron amplifier [V. L. Granatstein et al “High-power Microwave Sources for Advanced Accelerators”, Am. Inst. of Phys. Conf. Proc. 253 (1991); W. Lawson, J. P. Calame, B. Hogan, P. E. Latham, M. E. Read, V. L. Granatstein, M. Reiser and C. D. Striffler, Phys. Rev. Lett. 67, 520 (1991); W. Lawson, J. P. Calame, B. Hogan, M. Skopec, C. D. Striffler, V. L. Granatstein, and W. Main, IEEE Trans. Plasma Sci. 1992; and S. Tantawi, W. Main, P. E. Latham, G. Nusinovich, B. Hogan, H. Matthews, M. Rimlinger, W. Lawson, C. D. Striffler, and V. L. Granatstein, IEEE Trans. Plasma Sci. (1992)]. At Novosibirsk, in the former Soviet Union, a significant advance has been made with the invention of the magnicon [Karlimer, et al, Nucl. Inst. and Meth A269 (1988), pp 459-473] which has produced 2.6 MW at 0.915 GHz with an impressive conversion efficiency of 76%. In the magnicon the proper adjustment of a focusing static magnetic field allows the electrons in the beam to maintain temporal phase coherence with the rotating modes contained in suitable microwave resonators. This results in long and efficient interactions i.e., longer cavities, which is an advantage over klystron and gyro-klystron cavities. In the United States, a harmonic experiment is currently being conducted at the Naval Research Laboratory (NRL). The input scanner resonator is driven at 5.7 GHz and power is extracted from a gyroresonant harmonic interaction (TM
210
rotating mode) at 11.4 GHz [W. M. Manheimer, IEEE Trans. Plasma Sci. 18, 632 (1990); and B. Hafizi, Y. Seo, S. H. Gold, W. M. Manheimer and P. Sprangle, IEEE Trans. Plasma Sci. 20, 232, (1992)].
SUMMARY OF THE INVENTION
The described invention is a high power frequency multiplying device that utilizes a “Gatling” Micro-Pulse Gun (GMPG). The GMPG produces a number of electron bunches per rf period using a natural bunching process that results from resonant amplification of a current of secondary electrons in an rf input cavity. This natural bunching provides high-current densities (0.005-10 kA/cm
2
) in short-pulse (1-100 ps) beams, which when combined with a rotating mode, can produce many bunches per rf period and therefore can be used for frequency multiplication in an output cavity. The GMPG is an outgrowth of a simpler device, the Micro-Pulse Gun (MPG) [Patent Pending], that operates on the same fundamental principle but with only one bunch per rf period. Unlike thermionic or field emission devices which have a relatively short lifetime, the GMPG secondary emission process does not cause erosion or evaporation and therefore will have a longer lifetime. Furthermore, the natural bunch formation is a resonant process which is not prone to phase instability.
A system is described for producing a high-power high frequency microwave generator using a Gatling Micro-Pulse Gun. The system consists of five distinct components: (1) the GMPG which includes an output grid; (2) a post-acceleration section; (3) a radial magnetic compression section; (4) an output cavity; and (5) a beam collector. The system has been characterized in detail for: the transverse normalized emittance [“The Physics of Charged-Particle Beams”, I. D. Lawson, Clarendon Press, Oxford, (1977), p. 181], energy spread, and bunch expansion throughout the entire system. This is important for determining the output power and system efficiency.
The basis of the concept is a novel device to generate multiple, high-current density, micro-pulse electron bunches. The device is named the Gatling Micro-pulse Gun (GMPG).
Lee Benny T.
Mako Frederick M.
Schwartz Ansel M.
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