High Harmonic Operation Research Articles

Robust Parity-Time-Symmetric WPT System With Reduced Switching-Frequency and Improved Step-Down Conversion Ratio

In this paper, combining the phase synchronization method (PSM) and high harmonic operation (HHO), a novel parity-time(PT)-symmetric wireless power transfer (WPT) system with reduced switching frequency and improved step-down conversion ratio is proposed, where the power transferred to receiver side is carried by the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> th harmonic. We demonstrate that constant current (CC) and constant voltage (CV) independent of coupling coefficient and load resistance can also be obtained without wireless communication and additional dc-dc converters. Here, a new implementation of a negative resistor based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> th harmonic operation is proposed, which is a necessary condition of a PT-based system. In contrast to the standard PT-based system with the same resonant frequency, the switching frequency is reduced to 1/n due to the use of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> th harmonic, thereby realizing low switching losses and high system efficiency. Besides, an inherently improved step-down conversion ratio can be obtained. A prototype with a 6 A charging current and a 36 V charging voltage is built to verify the feasibility of the proposed method.

Oxygen vacancy engineering of MOF-derived ZnO/Co3O4 nanocomposites for high harmonic mode-locking operation

In this contribution, MOF-derived ZnO/Co3O4 composites were fabricated and applied to realize harmonic mode-locking operation in an Er-doped fiber laser, producing the highest repetition rate of 1.46 GHz and a pulse duration of ∼1.5 ps.

Harmonic terahertz gyrotron with a double confocal quasi-optical cavity

To reduce mode competition in a high-harmonic terahertz gyrotron, the gyrotron with a quasi-optical confocal cavity is proposed. Theoretical and experimental investigations demonstrate that the confocal cavity has good-mode selection and is suitable for high-harmonic operation. However, due to the transverse nonuniformity of the radio frequency field, the beam–wave interaction efficiency is low in the confocal cavity. To mitigate this drawback, the double confocal cavity is investigated in this study. Through three-dimensional particle-in-cell simulation on a designed 330-GHz gyrotron with a double confocal cavity, the physical mechanism of beam–wave interactions in a double confocal cavity is analyzed and presented.

Method of Providing the High Cyclotron Harmonic Operation Selectivity in a Gyrotron With a Spatially Developed Operating Mode

An electrodynamic method for suppressing low-frequency oscillations at the fundamental cyclotron resonance in a gyrotron at a high cyclotron harmonic is proposed and theoretically investigated. According to simulations, the use of this method in the terahertz gyrotron at the second cyclotron harmonic operating at the spatially developed mode TE63,15 can provide a multiple excess of the starting currents of the parasitic modes over the starting current of the desired oscillations.

Improvement of Stability of High Cyclotron Harmonic Operation in the Double-Beam THz Gyrotrons

A double-beam scheme of a short-wavelength gyrotron operating at the second cyclotron harmonic is studied both within the framework of the averaged self-consistent approach and using 3-D particle in cell simulations. The analysis shows that the introduction of an additional generating electron beam allows drastically increasing the operating current of a second-harmonic gyrotron with the simultaneous suppression of self-excitation of spurious modes at the fundamental harmonic. As a result, the radiated power of a double-beam gyrotron exceeds the power of a single-beam gyrotron by a factor of four. The developed concept makes it possible to realize high-power (several hundred watts) single-mode gyrotrons in the 0.7–1.0-THz frequency range.

Multi-mode high harmonic operation in a terahertz gyrotron

In order to develop compact,reliable and high power terahertz radiation sources,multi-mode second-harmonic operation in a terahertz gyrotron was investigated theoretically and experimentally.The theoretical calculation results show that there are five second-harmonic modes which operate at single-mode oscillation state in the gyrotron by adjusting the design parameters.Experimental results demonstrated that there are four second-harmonic modes(TE16,TE64,TE46 and TE26) in the gyrotron operating with a 1.5A/41kV electron beam.Output powers of 1.5,2.1,3.0 and 1.4 kW can be generated at the corresponding frequencies of 0.391,0.404,0.416 and 0.423 THz,respectively.

Enhanced Stability of Second- and Fourth-Harmonic Gyrotrons Driven by a Frequency-Doubled Prebunched Beam

There is currently considerable interest in operating gyrotrons at the second and higher cyclotron harmonics in order to access the near-terahertz regime while reducing magnetic field requirements. High-frequency gyrotrons have successfully operated at the second harmonic. However, competition from the fundamental harmonic increasingly limits operation in the higher order modes needed for the near-terahertz regime. Savilov recently proposed a scheme for frequency-doubled phase bunching of gyrating electron beams in a waveguide resonator formed from Bragg reflectors and with the drive frequency equal to the cyclotron frequency. The advantages of phase prebunching at twice the cyclotron frequency include suppression of the fundamental harmonic, enhanced second-harmonic operation, and increased likelihood of fourth-harmonic operation. We have investigated the use of this phase bunching technique to enhance higher harmonic operation in gyrotron oscillators with annular beams. We compute the frequency-doubled bunching produced by a Bragg-type prebunching cavity and use a large-signal, multimode, and multiharmonic gyrotron oscillator code to simulate the effect of this bunching on a highly overmoded output cavity. Regimes of stable operation are predicted for the second- and fourth-harmonic point designs.

Design Study of a Compact Cyclotron for Accelerator Mass Spectrometry

An accelerator mass spectrometer (AMS) utilizing a small cyclotron has been designed. The system has a mass resolving power of over 4000, which is su cient to analyze a few AMS radioisotopes, including 14C, for tracing or chronometric dating. The cyclotron can provide a high resolving power with a large number of turns and a high harmonic operation of the rf system and has the advantage of using both negative and positive ions in the analysis. A high transmission e ciency is, in fact, a major goal in the design to compete with a Tandem AMS. A compact magnet with high stability, a sawtooth harmonic buncher and at-topping rf system are the components adopted to achieve the goal. Also, large turn separations at injection and extraction are required, which can be done with adequate uses of the rst harmonic component of the main magnetic eld. The design of the cyclotron and injection beam line for the AMS has been studied.

Design of Cavities for a Short Pulse Powerful Large Orbit Gyrotron

Designs of cavities for fundamental and high harmonic operation in Large Orbit Gyrotron (LOG) are discussed. The fundamental operation allows one to use beam currents in the range from 200 A to 300 A achieve output power of the order of 9–10 MW at frequency 143.6 GHz. Mode competition calculations show that stable oscillations in the TE1,4 mode using high beam currents are possible even with the pitch factor 1.3 which is significantly lower than the design value 1.55. For the second harmonic operation, the maximum current used for excitation of the TE2,4 mode is 60 A and the optimum magnetic field is 7.6 T. A cavity design for fourth harmonic operation using the TE4,4 mode is also presented.

Gyro peniotron forward wave oscillators

The pulse spreading of the forward propagating absolute instability in gyro-peniotron interaction can be utilized to provide the feedback mechanism for establishing forward wave oscillators. By properly choosing the interaction length and beam current, high efficiency stable output at high harmonic operation can be attained. This is demonstrated by performing computer simulations which also reveal that the peniotron interaction is able to suppress the gyrotron interaction and reaches the maximum efficiency despite the influence of the gyrotron mode.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Angular spectrum property of spontaneous emission in a two-dimensional undulator free-electron laser

The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that thes-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for whichl=s, so the harmonic number can be selected by selectingl. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively.

High brightness electron beam sources for FEL applications

Abstract A new generation of field emitter array (FEA) cathode materials is under development at SAIC, in collaboration with NRL and GTE Laboratories. The emitter structures under consideration consist of large area ( ∼ 1 cm 2 ) arrays of large numbers ( ∼ 10 6 ) of microscopic field emitting tips. The structures can be fabricated so as to choose an emitter tip microstructure that is a solid cone, a hollow cylinder, or a variety of other shapes. These microstructures evidence very high local field enhancement factors, controllable from a factor of ∼ 200 to > 2000 . This large local field enhancement allows quantum field emission of significant current from the large area array while the applied macroscopic electric field is still quite low ( ∼ 20 kV/cm ). Single-tip, noninteracting particle, multigrid simulations indicate that the beam brightnesses B n = I/π 2 ϵ n 2 >10 10 A/cm 2 rad 2 may be possible. Beams with such high brightness allow for a greatly expanded field of FEL applications, including high gain and harmonic operation in the FIR wavelength regime. Experiments have so far demonstrated DC average current densities > 1 A/cm 2 , uniform emission, and improved characteristics when run for long periods of time ( > 100 h, DC ). Our present efforts are concentrated on optimizing the available cathode current density, measuring the actual beam brightness, and including self-field and 3-D effects in the numerical simulations.

Single-mode operation of a submillimeter wave gyrotron at the third-harmonic resonance

If gyrotrons are to attain higher frequencies, high harmonic operation is necessary. In this Letter, the single-mode operation of a submillimeter wave gyrotron at the third harmonic of the electron cyclotron frequency is reported.

Design requirements and calculated performance of an XUV FEL oscillator operating on a higher harmonic

We study, using numerical simulation methods, the design requirements for the electron beam, wiggler, and optical resonator of an extreme-ultraviolet (XUV, 100 ≥ λ ≥ 10 nm) free electron laser oscillator operating on a higher harmonic. Our previous theoretical studies of an XUV FEL oscillator have assumed operation at the fundamental wavelength. Higher-harmonic operation is attractive because the energy of the electrons can be reduced, thus reducing the cost of the linac. A further reduction in beam energy is possible with the use of short-period wigglers: in the present work, we use the expected properties of pulsed-wire wigglers. Operation of a FEL oscillator on the third harmonic has been experimentally demonstrated at Stanford University and Los Alamos, and this mode of operation may also be both possible and desirable for an XUV device.

Determination of the shape of the dee electrodes in the SINR minicyclotron used as AMS for 14C dating

The exact shapes of the “sandwich” dee electrodes in the Shanghai Institute of Nuclear Research (SINR) minicyclotron used as accelerator mass spectrometer (AMS) are determined based upon their effects on both the energy gain and the phase shift of the particles in acceleration mode, in order to meet the demands of both injecting, accelerating and extracting radioactive particles and discriminating background particles. Besides, two additional effects induced by the asymmetry of the electric force at two sides of a dee gap under the high-harmonic operation will be described.

Enhancement of high-harmonic gyrotron gain by a dielectric rod

A dielectric rod is shown to reduce the energy requirements of the electron beam for high-harmonic gyrotron operation. A large interaction filling factor can occur for moderate-energy electrons (∼80 keV) spiralling around the rod within the evanescent region of a dielectric waveguide mode. Since the magnetic field strength is reduced by an order of magnitude in an interaction at the tenth harmonic of the cyclotron frequency, a submillimeter-wave gyrotron is now truly feasible because the acceleration voltages can be conveniently produced by DC power supplies.