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A scalable microplasma reactor designed specifically for the dissociation of CO2 and other feedstock gases has been demonstrated. An array of linear microchannels, having a width and depth of ∼100 µm, and ∼200 µm, respectively, were fabricated in a 400 µm thick glass substrate by a combination of chemical and micropowder ablation techniques. Electrodes were deposited on both sides of the substrates...
The mode analysis in a klystron-like relativistic backward wave oscillator (RBWO) with a transverse dimension to free-space wavelength about four is presented. The particle in cell simulations with a 2.5-D full electromagnetic code reveal that microwaves with power of 1.75 GW, frequency of 13.7 GHz are generated with efficiency of 42% when diode voltage is 380 kV, beam current 11 kA, and magnetic...
The development of periodic structures for use as oscillators and amplifiers in the millimetre and sub-millimetre region has been an important topic in science in recent years [1–4]. The 2D periodic structure used in this instance to form the interaction region has a potential for application in sources of high power microwave and THz radiation [5]. Such a structure can be observed using a hollow,...
The axis of symmetry of the magnetic field is not always ideally aligned to the mechanical axis of the gyrotron, mainly for two reasons: (i) misalignment of the coils in the magnet and (ii) mechanical inaccuracies on the gun and cavity position. In this work, the effects of the magnetic field misalignment are numerically studied for the coaxial cavity EU gyrotron1 for ITER. First, the degradation...
This presentation describes a study on gas evolution of plasma expansion in a reflex-triode virtual cathode oscillator (vircator) at ultra-high vacuum (UHV). Research has shown that explosive electron emission (EEE) processes at the cathode and ion / electron bombardment at the anode cause material erosion that produces regions of localized plasma. This plasma expansion has shown to lower gap impedance,...
Use of low-loss magnetic materials in high-power microwave devices can improve significantly their performance. We have demonstrated1 that the electromagnetic losses in the composite structure can be reduced by up to two orders of magnitude, compared to those of the uniform magnetic sample made of the same lossy magnetic material. Importantly, the dramatic absorption reduction is not a resonance effect...
In a companion abstract we presented recent improvements in the start-up and efficiency of the A6 magnetron with radial extraction and axial extraction (MDO) [1]. Here we describe recent advances in mode switching and mode control.
At present, gyrotron oscillators, as sources of high power millimeter waves, play a central role in fusion energy research. Recently, spurious oscillations in high power gyrotrons gained attention as an influencing factor on the overall efficiency: in the up-taper/launcher section, a region exists where the decreasing magnetic field is alleged to excite spurious oscillations1. Numerical investigations...
The start-oscillation-current of a gyro-TWT determines the stable operating current level of the device. The amplifier is susceptible for oscillations when the operating current level is higher than the start-oscillation current. There are several ways of calculating the start-oscillation current, including using the linear theory of a gyro-TWT. In this paper, we present a simple way of determining...
Coaxial gyrotrons offer the potential to generate microwave power in the multi-megawatt levels at frequencies well above 100 GHz1, since very high-order volume modes can be used. The presence of the coaxial insert reduces the voltage depression and eliminates the restrictions of mode selectivity, making it possible to maintain the cavity ohmic losses at a reasonable low level (<2kW/cm2) allowing...
In high-power gyrotrons sweeping systems are used in order to distribute the energy of the spent beam in a larger area of the collector1. Currently, there are two common types of sweeping systems, the axial and transversal sweeping system2. In the first case, the sweeping coils surround the collector creating a harmonically varying magnetic field that is coaxial to the externally applied one. In the...
Dynamic Nuclear Polarization (DNP) is a technique used to increase sensitivity of nuclear magnetic resonance (NMR) by transferring the higher polarization of unpaired electron spins to nuclear spins. The polarization transfer is driven by high frequency millimeter-wave radiation. CPI has developed continuous wave (cw) gyrotrons at 263 GHz, 395 GHz, and 527 GHz for Bruker Biospin's DNP spectrometers...
As is known, the operating magnetic fields in gyrotrons can be significantly decreased by using high-cyclotron-harmonic radiation of an axis-encircling electron beam. This configuration of so-called Large Orbit Gyrotron (LOG) improves both the electron-wave coupling and mode selectivity. Recently, a unique third-harmonic 1 THz/80 kV LOG has been realized at the IAP [1]. It should be noticed that because...
Gyrotrons find use in several diverse fields, ranging from plasma heating and plasma diagnostic to spectroscopy and materials processing. However, with demand for high power coherent radiation at THz frequencies, the confining magnetic fields required for gyrotrons operating at the fundamental harmonic become increasingly restrictive. However, considerable promise lies with the concept of the gyro-multiplier...
In GYRO-TWT, the RF wave propagates in the smooth wall cylindrical waveguide structure with a speed greater than the speed of a light. Such type of interactions structure used in gyro-TWTs are not capable of providing fairly wide device bandwidth due to rapid change in group velocity with frequency, at or near the cut off frequency of waveguide, which causes a narrow band coalescence between beam...
Cyclotron masers1 are fast wave devices which typically operate in the centimetre to submillimetre region of the electromagnetic spectrum. They find application in numerous fields such as radar, plasma science and materials processing. Two amplifer devices have been studied to establish their potential for efficiency enhancement. By tapering either the magnetic field or the physical dimensions of...
Linear and nonlinear behaviors of gyrotron backward wave oscillators (gyro-BWO) were investigated by both analytical theories and direct numerical calculations. Employing two-scale-length expansion, an analytical linear dispersion relation corresponding to absolute instabilities in a finite-length system has been derived. Detuning from the beam-wave resonance condition due to the finite amplitude...
Low frequency oscillations (LFOs) have been obtained in a 3D time domain simulation for the first time. From our preliminary simulation studies, it is found that not only magnetic compression profile but initial velocity or velocity ratio play an important role in the operation of a MIG electron gun. In addition, the secondary emission effects on the LFOs are also studied. The frequency of LFOs has...
In this work, a self-consistent general thermal field (GTF) emission model is formulated and the space charge effect on the original GTF equation developed by Jensen at NRL is studied analytically. We have also implemented the GTF algorithm in VORPAL, a conformal finite-difference timedomain (CFDTD) particle-in-cell (PIC) code. This analytic model could serve as a benchmark standard for the GTF CFDTD...
Reported on is the progress of the counter streaming, fully self-consistent model development in the MICHELLE Ebeam [1,2,3] code. This GPU-based software module performs high accuracy simulations of electron and ion beams including the effects of stochastic space charge.
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