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Gyro-devices are fast wave devices based on the principles of the electron cyclotron maser1,2. Gyro-oscillators have been successfully developed in the form of gyrotrons3,4. Gyro-amplifiers have been studied for approximately as long as gyro-oscillators but in the early years the amplifiers exhibited stability issues. Gyro-amplifiers include broadband gyro-TWTs and the narrower band gyro-klystrons...
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...
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...
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...
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...
Microwave pulse compression has applications in radar technology and plasma diagnostics. The pulse compressor requires a dispersion curve with a monotonic group velocity and low losses in a reasonable wide frequency band. It can be achieved by the helically corrugated waveguide (HCW) [1–3] with both axial and azimuthal periodicity that couples modes in the circular waveguide to generate new operating...
A key design process in the construction of a waveguide component is the cold-test stage, involving measuring the response of the component to radiation, propagating with a specific electromagnetic mode and a certain frequency, or range of frequencies. However, for components that require high order modes, such as resonant cavities used in high-power1, or high-harmonic gyrotrons, it can be challenging...
A quasi-optical corrugated horn has been constructed for a W band gyro-TWA1,2 based on a cusp electron beam source3–5 with a helically corrugated interaction region6–8. The design is intended to provide an effective method to decouple the radiation and the beam so that a depressed collector energy recovery system may be used9–11. The horn converts a cylindrical TE11 mode into a free-space TEM00 mode...
The European Gyrotron Consortium (EGYC) is responsible for developing one set of 170 GHz mm-wave sources, in support of Europe's contribution to ITER1. The original plan of targeting a 2 MW coaxial gyrotron is currently under discussion, in view of essential delays and damages. This paper reports on the latest results and plans with regard to the 2 MW gyrotron prototypes.
In ITER it is foreseen to control different types of MHD instabilities by means of modulated Electron Cyclotron Current Drive (ECCD) with modulation frequencies up to 5 kHz. This has direct consequences for the EC system of ITER, since both the gyrotons and power supplies have to be capable of modulated operation. Since the electron gun of the 2 MW EU gyrotron is a diode type gun and the gyrotron...
Megawatt gyrotrons have a variety of applications including electron cyclotron heating (ECH) of plasmas in fusion devices. High efficiency operation is necessary to minimize the prime power required and to ensure good reliability of the device over its lifetime. To achieve high power and efficiency at the required frequencies, the gyrotrons must utilize large, overmoded cavities that face severe mode...
At KIT, high power gyrotrons of conventional (1 MW CW at 140 GHz for the stellarator Wendelstein 7-X) and coaxial type (2 MW short-pulse at 170 GHz for ITER) for fusion applications are developed and verified experimentally.
The attractiveness of operation at cyclotron harmonics was well understood from the first steps of development of cyclotron resonance masers and gyrotrons. Magnetic fields required to fulfill the cyclotron resonance condition are inversely proportional to the harmonic number. Therefore, by operating at cyclotron harmonics one may significantly reduce the size and cost of superconducting magnets. For...
The gyrotron is the most wide-spread variety of electron cyclotron masers based on excitation of a near-cutoff mode of an open microwave cavity. Along with advantages (good selectivity, weak sensitivity to the velocity spread), the use of near-cutoff wave results in several disadvantages (significant Ohmic losses, difficulty to provide frequency tuning). In this work, a new regime of the cyclotron...
Electron Cyclotron Resonance (ECR) ion sources produce high charge state, intense heavy-ion beams for many high energy and nuclear physics accelerators. Several third generation sources utilizing superconducting magnet structures and gyrotrons operating at frequencies greater than 20 GHz are now in operation. Recent results from the LBNL 28 GHz ECR ion source VENUS include 3000 eµA of O6+ and more...
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