Cyclotron Resonance Maser Research Articles

Analysis of undulator and gyro-synchrotron radiation for application at tera-hertz

We analyze the undulator and gyro-synchrotron radiation of the devices by equating the number of periods of the helical trajectory of the gyrating motion to the number of undulator periods. The gyro radiation is characterized by cyclotron resonance maser interaction exhibits superior line width quality but higher sensitive to beam energy spread when operated at tera-hertz due to finite larmor radius effects.

Cyclotron Resonance Maser With Zigzag Quasi-Optical Transmission Line: Concept and Modeling

A microwave system in the form of a quasi-optical (QO) transmission line is proposed as an interaction circuit of an amplifier or an oscillator based on the cyclotron resonance maser (CRM) instability. The circuit consists of periodically spaced along the horizontal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -axis focusing mirrors, which transport the Gaussian wave beam along a zigzag path with vertical and inclined segments. A beam of electrons having sufficiently high perpendicular velocities is guided by a static B-field along the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -axis so that the e-beam periodically crosses the wave beam. The CRM instability occurs in regions where an electromagnetic wave having a Bz-component, as in a gyrotron, propagates strictly across the e-beam resulting in the interaction with minimal sensitivity to particle velocity spread. Three-dimensional Particle-In-Cell (3-D PIC) simulations demonstrate the attractiveness of this “zigzag” CRM for the implementation of relatively broadband amplifiers or oscillators with unique (more than an octave bandwidth) frequency tunability at wavelengths of 1–2 mm.

Frequency Tuning in Short-Wave Gyrotrons with Irregular Cavities

We study the process of frequency tuning of a cyclotron resonance maser with a quasiregular sectioned cavity, which is based on gyrotron excitation of a higher longitudinal mode. It is shown that a regime can be achieved, in which the generation frequency varies fast (during one pulse) with no variation in the power of the output radiation.

Synchrotron radiation loss of a laser accelerator based on an inverse electron cyclotron resonance maser.

A laser accelerator based on an electron cyclotron resonance maser is described. Important losses that give rise to saturation length and saturation power are included in the analysis. The results are compared with results from an inverse free-electron laser accelerator.

Electron Cyclotron Resonance Gain in the Presence of Collisions

A cyclotron resonance maser source using low-effective-mass conduction electrons in graphene, if successful, would allow for generation of far infrared (FIR) and terahertz (THz) radiation without requiring magnetic fields running into the tens of tesla. In order to investigate this possibility, we consider a situation in which electrons are effectively injected via pumping from the valence band to the conduction band using an IR laser source, subsequently gyrate in a magnetic field applied perpendicular to the plane of the graphene, and give rise to gain for an FIR/THz wave crossing the plane of the graphene. The treatment is classical, and includes on equal footing the electron interaction with the radiation field and the decay in electron energy due to collisional processes. Gain is found even though there is no inversion of the energy distribution function. Gain can occur for electron damping times as short as hundreds of femtoseconds.

Development of simulation tools for numerical investigation and computer-aided design (CAD) of gyrotrons

As the most powerful CW sources of coherent radiation in the sub-terahertz to terahertz frequency range the gyrotrons have demonstrated a remarkable potential for numerous novel and prospective applications in the fundamental physical research and the technologies. Among them are powerful gyrotrons for electron cyclotron resonance heating (ECRH) and current drive (ECCD) of magnetically confined plasma in various reactors for controlled thermonuclear fusion (e.g., tokamaks and most notably ITER), high-frequency gyrotrons for sub-terahertz spectroscopy (for example NMR-DNP, XDMR, study of the hyperfine structure of positronium, etc.), gyrotrons for thermal processing and so on. Modelling and simulation are indispensable tools for numerical studies, computer-aided design (CAD) and optimization of such sophisticated vacuum tubes (fast-wave devices) operating on a physical principle known as electron cyclotron resonance maser (ECRM) instability. During the recent years, our research team has been involved in the development of physical models and problem-oriented software packages for numerical analysis and CAD of different gyrotrons in the framework of a broad international collaboration. In this paper we present the current status of our simulation tools (GYROSIM and GYREOSS packages) and illustrate their functionality by results of numerical experiments carried out recently. Finally, we provide an outlook on the envisaged further development of the computer codes and the computational modules belonging to these packages and specialized to different subsystems of the gyrotrons.

Statistical properties of cooperative emission of an ensemble of nonisochronous electrons–oscillators

Shot noise, intrinsic to the ensemble of nonisochronous electrons-oscillators, is the cause of statistical fluctuations in cooperative radiation generated by single-pass cyclotron-resonance masers (CRMs). Autophasing time --- the time required for the cooperative radiation power to peak --- is the critical parameter characterizing the dynamics of electrons-oscillators interacting via the radiation field. Shot-noise related fluctuations of the autophasing time imposes appreciable limitations on the possibility of coherent summation of electromagnetic oscillations from several single-pass CRMs. Premodulation of charged particles leads to a considerable narrowing of the autophasing time distribution function. When the number of particles $N_e$ exceeds a certain value that depends on the degree to which the particles have been premodulated, the relative root-mean-square deviation (RMSD) of the autophasing time $\delta_T$ changes from a logarithmic dependence on $N_e$ ($\delta_T\sim1/\ln N_e$) to square-root ($\delta_T\sim1/\sqrt{N_e}$). As a result, there is an increased probability of coherent summation of electromagnetic oscillations from several single-pass generators. A slight energy spread ~($\sim$4\%) results in a twofold drop of the maximum attainable power of cooperative radiation.

Analysis and Design of the Resonator in a 110 GHz Gyrotron Oscillator

Gyrotron oscillators are powerful millimeter, sub-millimeter and even potential THz wave sources, capable of reaching megawatt power levels. They are widely studied today to use for electron cyclotron resonance heating, current drive, stability control and active diagnostics of magnetically confined fusion plasmas. To suppress the parasitic modes and improve the efficiency of the over-mode resonator is a important object for the design of high power gyrotrons. On the basis of electron cyclotron resonance maser theory and generalized transmission line theory, we compiled programs to analyze the resonant cavity in a 110 GHz gyrotron. The results shows that the coupling coefficient to parasitic modes of gradually tapered cavity is obviously less than line-joint cavity. By calculating and studying different gradual-varying and line-joint resonant cavities, we designed a gradually tapered resonator for a 110 GHz gyrotron, which is good at suppressing the parasitic modes, improving the purity of the operating mode and the efficiency of the beam–wave interaction.

Progress towards numerical and experimental simulations of fusion relevant beam instabilities

In certain plasmas, non-thermal electron distributions can produce instabilities. These instabilities may be useful or potentially disruptive. Therefore the study of these instabilities is of importance in a variety of fields including fusion science and astrophysics. Following on from previous work conducted at the University of Strathclyde on the cyclotron resonance maser instability that was relevant to astrophysical radiowave generation, further instabilities are being investigated. Particular instabilities of interest are the anomalous Doppler instability which can occur in magnetic confinement fusion plasmas and the two-stream instability that is of importance in fast-ignition inertial confinement fusion. To this end, computational simulations have been undertaken to investigate the behaviour of both the anomalous Doppler and two-stream instabilities with the goal of designing an experiment to observe these behaviours in a laboratory.

The Gyrotron at 50: Historical Overview

Gyrotrons form a specific group of devices in the class of fast-wave vacuum electronic sources of coherent electromagnetic wave radiation known as electron cyclotron masers (ECMs) or cyclotron resonance masers (CRMs). The operation of CRMs is based on the cyclotron maser instability which originates from the relativistic dependence of the electron cyclotron frequency on the electron energy. This relativistic effect can be pronounced even at low voltages when the electron kinetic energy is small in comparison with the rest energy. The free energy for generation of electromagnetic (EM) waves is the energy of electron gyration in an external magnetic field. As in any fast-wave device, the EM field in a gyrotron interaction space is not localized near a circuit wall (like in slow-wave devices), but can occupy large volumes. Due to possibilities of using various methods of mode selection (electrodynamical and electronic ones), gyrotrons can operate in very high order modes. Since the use of large, oversized cavities and waveguides reduces the role of ohmic wall losses and breakdown limitations, gyrotrons are capable of producing very high power radiation at millimeter and submillimeter wavelengths. The present review is restricted primarily by the description of the development and the present state-of-the-art of gyrotrons for controlled thermonuclear fusion plasma applications. The first gyrotron was invented, designed and tested in Gorky, USSR (now Nizhny Novgorod, Russia), in 1964.

Low-Voltage Cyclotron Resonance Maser

The gyrotron, which is the most powerful cyclotron resonance maser (CRM), is an extremely effective device to generate high-power microwave radiation. It is used in microwave heating of thermonuclear plasma, radar, and other industrial applications. However, the gyrotron has one basic problem. It requires relativistic (very high energy) electrons. These require very high voltages to produce, and, in turn, relativistic electrons produce intense and dangerous X-rays in the collector region. In this paper, we discuss an alternate method of operation that does not require high voltages. We have also constructed a low-voltage CRM that operates at 2.2 kV and produces 8 GHz at a magnetic field of 0.3 T. In principle, the device should operate at even lower voltages.

An exact linear dispersion relation for CRM instability

An exact self-consistent linear dispersion relation of a large orbit electron beam including two principles of cyclotron emission with oscillation frequencies above and below the relativistic electron frequency is derived and analyzed numerically for the first time in the literature. The two principles are cyclotron resonance maser (CRM) instability and Cherenkov instability in the azimuthal direction. Self-consistency in the formulation and inclusion of proper boundary conditions have removed the unphysical instability existing for infinitely large kz observed in conventional dispersion relations of CRM instability.

Functional and shunt states of bacteriorhodopsin resolved by 250 GHz dynamic nuclear polarization–enhanced solid-state NMR

Observation and structural studies of reaction intermediates of proteins are challenging because of the mixtures of states usually present at low concentrations. Here, we use a 250 GHz gyrotron (cyclotron resonance maser) and cryogenic temperatures to perform high-frequency dynamic nuclear polarization (DNP) NMR experiments that enhance sensitivity in magic-angle spinning NMR spectra of cryo-trapped photocycle intermediates of bacteriorhodopsin (bR) by a factor of approximately 90. Multidimensional spectroscopy of U-(13)C,(15)N-labeled samples resolved coexisting states and allowed chemical shift assignments in the retinylidene chromophore for several intermediates not observed previously. The correlation spectra reveal unexpected heterogeneity in dark-adapted bR, distortion in the K state, and, most importantly, 4 discrete L substates. Thermal relaxation of the mixture of L's showed that 3 of these substates revert to bR(568) and that only the 1 substate with both the strongest counterion and a fully relaxed 13-cis bond is functional. These definitive observations of functional and shunt states in the bR photocycle provide a preview of the mechanistic insights that will be accessible in membrane proteins via sensitivity-enhanced DNP NMR. These observations would have not been possible absent the signal enhancement available from DNP.

Cyclotron-resonance maser with adiabatic magnetic pumping in a low-density plasma

The conditions under which the magnetic adiabatic compression of a plasma in a direct magnetic trap is accompanied by the accumulation of high energy in the hot anisotropic electron component are found. The basic instabilities resulting in the emission of the accumulated energy in the form of a pulse of stimulated electromagnetic radiation are analyzed. The possibility of creating terahertz radiation sources with the use of the magnetic compression of the plasma is discussed.

Development of material processing system by using a 300 GHz CW gyrotron

High power THz-frequency material processing has great potential for the applications. The gyrotron is a microwave tube capable of delivering very high microwave power in the pulse and CW operation at the THz frequencies. The frequency of gyrotron is proportional to the intensity of magnetic field, because the operation results from the mechanism of "cyclotron resonance maser". Therefore, in order to achieve high frequency operation, we need a high magnetic field which superconducting magnets or pulsed-magnets produce. We developed the material heating system by using a 300 GHz gyrotron. This system consists of a 300 GHz, 3.5 kW, CW gyrotron (Gyrotron FU CW I) with a cryogen-free 12 T superconducting magnet, a corrugated circular waveguide and an applicator.

Cyclotron resonance maser operating in a nonresonant electron bunching regime

A new scheme of the cyclotron resonance maser (CRM) based on the phenomenon of electron bunching in a nonresonant wave field is proposed. In this scheme, the electron-wave interaction space is divided into two regions due to magnetic field profiling. In the first (input) region, the magnetic field is such that the working traveling wave is relatively far from the resonance with electrons. It is established that, under certain conditions, the motion of electrons in a nonresonant wave field is accompanied by their effective bunching without significant changes in the energy. In the second (output) region, the magnetic field is close to the resonance and the bunched electron beam effectively radiates at the working wave frequency. Thus, the regular electrodynamic system features an electron-wave interaction of the klystron type with spatially separated processes of the electron bunching and wave emission. The proposed scheme can be used for increasing the efficiency of CRMs with various configurations. It is especially advantageous in CRMs with frequency multiplication, where the electron bunching in a low-frequency nonresonant wave field is accompanied by wave emission at a multiple frequency.

A laboratory experiment to investigate auroral kilometric radiation emission mechanisms

If an initially mainly rectilinear electron beam is subject to significant magnetic compression, the conservation of the magnetic moment results in the ultimate formation of a horseshoe distribution in phase space. A similar situation occurs where particles are accelerated into the auroral region of the Earth's magnetic dipole. Such a distribution has been shown to be unstable to a cyclotron resonance maser type of instability and it has been postulated that this may be the mechanism required to explain the production in these regions of auroral kilometric radiation (AKR) and also possibly radiation from other astrophysical objects such as stars with a suitable magnetic field configuration. In this paper we describe a laboratory experiment to investigate the evolution of an electron beam subject to a magnetic compression of up to a factor of 30.

Electron Bunching at the Doubled Frequency of the Input Wave and the Use of This Effect in Klystron-Type Frequency Multiplicators

A method of organizing electron-wave interaction at the doubled frequency of the signal wave is proposed. This type of electron-wave interaction provides doubled-frequency electron bunching, which means better bunching at the even harmonics of the input-signal frequency and, simultaneously, the absence of bunching at the odd harmonics. This effect is attractive for the use in the bunching sections of klystron-type cyclotron resonance masers with frequency multiplication as a way to increase the output frequency and to improve selectivity.

Efficiency Enhancement of Coaxial-Cavity Electron Cyclotron Resonance Maser by Tapering Guide Magnetic Field

A coaxial-cavity cyclotron resonance maser (CRM) oscillator with tapered guide magnetic field is proposed. It is shown that the transmission quality can be improved by tapering the guide magnetic field. Simulation indicates that the efficiency of a millimeter-wave gyrotron oscillator may be reached up to 38.7% by optimizing the tapered magnetic field.

Synchronized autooscillations in a distributed system of the “helical electron beam-opposite electromagnetic wave” type

The phenomenon of synchronization of self-oscillations is studied for the first time in an active distributed system of a helical electron beam interacting with an opposite wave in a waveguide (representing a cyclotron-resonance opposed-wave maser). The parameters of oscillations in the distributed self-oscillatory system are considered in the regime of synchronized self-oscillations and upon escape from this regime.