Experimental Observation of Cyclotron Superradiance under Group Synchronism Conditions

Zotova, I. V.; Sergeev, A. S.; Konoplev, I. V.; Phelps, A. D. R.; Cross, Adrian W.; Cooke, S.J.; Shpak, V. G.; Yalandin, M. I.; Shunaĭlov, S. A.; Ul’maskulov, M. R.

doi:10.1103/physrevlett.78.2365

Cited by 98 publications

(19 citation statements)

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“…The pulses must be shorter than the relaxation time, typically requiring subnanosecond (or picosecond) pulse lengths [8]. Picosecond microwave pulses have been demonstrated in a vacuum electron device by superradiance [9], but such pulses cannot be used for spectroscopy. Subnanosecond pulses must contain a spectral bandwidth exceeding the transform limit, that is, exceeding 1 GHz.…”

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confidence: 99%

Amplification of Picosecond Pulses in a 140-GHz Gyrotron-Traveling Wave Tube

et al. 2010

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An experimental study of picosecond pulse amplification in a gyrotron-traveling wave tube (gyro-TWT) has been carried out. The gyro-TWT operates with 30 dB of small signal gain near 140 GHz in the HE 06 mode of a confocal waveguide. Picosecond pulses show broadening and transit time delay due to two distinct effects: the frequency dependence of the group velocity near cutoff and gain narrowing by the finite gain bandwidth of 1.2 GHz. Experimental results taken over a wide range of parameters show good agreement with a theoretical model in the small signal gain regime. These results show that in order to limit the pulse broadening effect in gyrotron amplifiers, it is crucial to both choose an operating frequency at least several percent above the cutoff of the waveguide circuit and operate at the center of the gain spectrum with sufficient gain bandwidth.Gyrotrons are a form of electron cyclotron maser capable of producing kilowatts to megawatts of output power in the microwave, millimeter wave, and terahertz bands [1][2][3][4]. In recent years gyrotron amplifiers have demonstrated high output power levels with significant gain bandwidths [5][6][7]. One important application of millimeter waves is in spectroscopy, where coherent pulses on a subnanosecond or picosecond time scale are needed for optical pumping of molecular states. The pulses must be shorter than the relaxation time, typically requiring subnanosecond (or picosecond) pulse lengths [8].Picosecond microwave pulses have been demonstrated in a vacuum electron device by superradiance [9], but such pulses cannot be used for spectroscopy. Subnanosecond pulses must contain a spectral bandwidth exceeding the transform limit, that is, exceeding 1 GHz. In the conventional microwave bands, at frequencies of one to several GHz, the required gain bandwidth to amplify such picosecond pulses is generally not available, since the GHz bandwidth is a large fraction of the carrier frequency. In recent years, high power, wideband amplifiers in the millimeter wave band have been developed that are suitable for amplifying picosecond pulses. For example, a form of klystron called an extended interaction klystron has been developed at 95 GHz with a gain bandwidth of about 1 GHz. This amplifier has been used to successfully amplify 1 kW output pulses as short as 800 picoseconds [10]. A gyrotron-traveling wave tube (gyro-TWT) at 95 GHz has been demonstrated with a gain bandwidth of 6.5 GHz at an output power level of 2 kW [7]. This gyro-TWT could, in principle, be used to amplify a 150 ps pulse. To our knowledge, amplification of picosecond pulses has not been tested with these or other powerful wideband gyro-amplifiers. Because of the possibility of distortion in amplification of picosecond pulses, detailed studies are needed of the amplification process in such devices. In this paper, we report a detailed study of amplification of pulses as short as 400 ps in a 1 kW, 140 GHz gyro-TWT with a gain bandwidth exceeding 1 GHz. To our knowledge, this is the first report o...

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confidence: 99%

Amplification of Picosecond Pulses in a 140-GHz Gyrotron-Traveling Wave Tube

et al. 2010

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“…In the experiment on observation of cyclotron SR [22], a high-current subnanosecond RADAN-303 accelerator [11] generating subnanosecond (250-500 ps) electron bunches with a current of 200 A and a particle energy of 250 keV was used. The transverse velocity (the pitch factor of order unity) was imparted to electrons during their transit through the region of a strongly nonuniform magnetic field (kicker).…”

Section: Cyclotron Superradiance In the Regime Of Group Synchronismmentioning

confidence: 99%

“…In this respect, in Sec. 2 we present a brief theoretical analysis of SR effects based on various mechanisms of stimulated radiation, as well as results of the first experimental observations of these effects [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. In those experiments, SR pulses with maximum peak power and uniquely short duration (less than 300 ps) were obtained during theČerenkov interaction of a rectilinearly moving electron bunch with a slow spatial harmonic of the counterpropagating electromagnetic wave in a periodic slow-wave system.…”

Section: Introductionmentioning

confidence: 99%

Generation of high-power ultrashort electromagnetic pulses on the basis of effects of superradiance of electron bunches

Zotova

Pegel

Rostov

et al. 2007

Radiophys Quantum El

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One of the promising methods for generation of ultrashort electromagnetic pulses (with duration of about ten periods of high-frequency oscillations) is radiation from spatially localized electron ensembles (bunches), which can be considered a classical analog of Dicke superradiance known in quantum electronics. In classical electronics, superradiance can be related to various mechanisms of stimulated radiation. Until now, cyclotron, undulator, andČerenkov (in the case of interaction with both copropagating and counterpropagating waves) superradiance of electron bunches as well as superradiance during stimulated scattering of a pump wave have been studied theoretically and experimentally. As a result of these studies based on high-current RADAN and SINUS accelerators and their modifications, a new class of oscillators producing pulsed electromagnetic radiation has been created. They have such unique characteristics as pulses of high peak power (up to 1 GW and 3 GW in the millimeter-and centimeter-wave ranges, respectively) and ultrashort duration (from 300 ps to 1 ns, respectively). In this case, regimes with a peak radiation power exceeding the electron-beam power are experimentally realized. Regimes with high (kilohertz) pulse repetition rate and high average power (up to 2.5 kW) are obtained.

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“…The SR of classical electrons can be associated with different mechanisms of stimulated emission, such as cyclotron, Cherenkov, and bremsstrahlung. All the above types of SR are observed experimentally at millimeter and centimeter wavelength bands [13]- [25]. Currently, the SR pulses with the highest peak power are obtained for the Cherenkov mechanism of SR when the electrons interact with synchronous harmonics of the backward wave propagating in slow wave structures (SWSs) [17]- [25].…”

mentioning

confidence: 99%

Generation, Amplification, and Nonlinear Self-Compression of Powerful Superradiance Pulses

Zotova

Cross

Phelps

et al. 2013

IEEE Trans. Plasma Sci.

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The Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. Abstract-Superradiance (SR) of electron bunches can be considered an effective method of production of ultrashort electromagnetic pulses. Different types of SR associated with different mechanisms (cyclotron, Cherenkov, and bremsstrahlung) of stimulated emission are observed experimentally in the millimeter and centimeter wavelength bands. Progress in this research has enabled a new type of generator to be created capable of generating unique short (under 200-300 ps) electromagnetic pulses at super high peak powers exceeding 1 GW in the millimeter and 3 GW in the centimeter waveband. Some new methods for further increasing of the SR pulse peak power along with the promotion of such sources to higher frequency bands are discussed. These new methods include phase synchronization of several SR pulse generators, the amplification of an SR pulse during its propagation along a quasi-stationary electron beam and nonlinear compression in the process of induced selftransparency.

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Experimental Observation of Cyclotron Superradiance under Group Synchronism Conditions

Cited by 98 publications

References 5 publications

Amplification of Picosecond Pulses in a 140-GHz Gyrotron-Traveling Wave Tube

Amplification of Picosecond Pulses in a 140-GHz Gyrotron-Traveling Wave Tube

Generation of high-power ultrashort electromagnetic pulses on the basis of effects of superradiance of electron bunches

Generation, Amplification, and Nonlinear Self-Compression of Powerful Superradiance Pulses

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