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The development of a 2 MW, 170 GHz short-pulse coaxial-cavity gyrotron pre-prototype for electron cyclotron heating and current drive (ECRH&CD) of magnetically confined plasmas in upcoming fusion devices is in progress at Karlsruhe Institute of Technology (KIT). Significant design modifications have been done recently. First experimental tests of a modified setup show two important unwanted effects...
A Broadband frequency tunable gyrotron operating at fundamental resonance for 600 MHz DNP-NMR has been developed. A cavity resonator and a magnetron injection gun are newly designed. In the preliminary experiments, the continuously frequency tuning bandwidth was 1.3 GHz and the output power was increased up to 100 W.
We investigate, by numerical simulations, the effects of a misaligned (i.e. shifted with respect to the resonator axis) electron beam on the beam-wave interaction in a 170 GHz, 2 MW coaxial gyrotron. The correlation of the simulations results with the experimental findings, which motivated the present study, is discussed.
The results of simulation of both electron-optical system and the cavity of the low-voltage planar cyclotron resonance maser (CRM) have been presented. The electron-optical system (EOS), which forms a sheet helical electron beam (HEB) with the value of the pitch factor ≥ 1 was obtained. Electron beam energy characteristics were obtained as the result of trajectory analysis for EOS. Also the CRM cavity...
A self-consistent code is introduced to develop a continuous frequency tunable gyro-BWO. A cavity is designed with TE8,5 mode for 400 GHz band second harmonic oscillation. The experimental verification has been carried out and 2 GHz tunability is observed with output powers of higher than 40 W.
A method is described to form a laminar electron beam for a high power gyrotron. An optimum potential profile is investigated to adjust each electron trajectory in between cathode and 1st anode. A high quality laminar beam is realized with a wide operation window.
We have build THz multilayer mirrors based on fabricated z-cut quartz wafers of 25 mm diameter. Using THz time-domain spectroscopy initial measurements show that the mirror reflectivity can be tuned at least up to 98.6%. We also observed cavity modes in a THz cavity made from such mirrors.
We present an analysis of the linear behavior of the gyrotron interaction in both the forward-wave regime with positive parallel wavevector, k∥ and the backward-wave regime with k∥ < 0. The considered electromagnetic (EM) structures are longitudinally non-homogeneous and the electron beam properties have, in general, also a longitudinal dependence. The set of time-dependent linearized self-consistent...
Introducing antireflection slits at the boundaries of a finite-size coupled terahertz cavity in a metal air-gap waveguide can minimize reflections at the boundaries. The optimal design parameters for the minimal reflection were obtained using the one-dimensional antireflection coating theory and finite-difference time-domain simulations. We experimentally demonstrated that the optimized antireflection...
The effect of the tilt of the electron beam axis on the gyrotron operation is investigated. It is commonly accepted that the tilt deteriorates the efficiency of cylindrical cavity gyrotrons. Our study showed that this deterioration can be mitigated by a proper displacement of the electron beam axis at the entrance. Also, in some cases, when the aftercavity interaction lowers the gyrotron efficiency,...
Europe is making a significant joint effort to develop high power microwave sources (gyrotrons) for nuclear fusion applications. KIT is taking a large part in this. It is involved into the developments for W7-X and ITER, and it is starting research for gyrotrons which, in future, shall operate at multi-megawatt levels at above 200 GHz and shall allow step-frequency tunability. To enable this, KIT...
The possibilities to obtain efficient operation of sub-THz gyrotrons at cyclotron harmonics are analyzed and the evolution of gyrotron optimal parameters is presented. 3D PIC simulations of THz band gyrotrons have been performed. The reasonable agreement with experimental results is demonstrated, that allows one to analyze some effects resulting from ellipticity of cavities, non-uniform emission and...
Development of two 460 GHz second harmonic gyrotrons for 700 MHz DNP-NMR spectroscopy is presented. One gyrotron is frequency-fixed and the other is frequency tunable in the bandwidth of 1.5 GHz. In addition, the former has a function of frequency modulation.
During last year several new steps in gyrotrons development have been done at IAP/GYCOM. The main ITER requirements to a gyrotron have been demonstrated: 170 GHz frequency, 1MW power, 1000 seconds pulse duration, 53% efficiency. The operation regime of 1.2 MW was found for 100 second pulses. For a multi-frequency gyrotron a novel scheme for a tuneable window was developed. Additionally some other...
Long pulse operation of a dual frequency gyrotron for JT-60SA, which can oscillate both 110 GHz and 138 GHz waves, was started. Oscillations at ∼ 0.4 MW for 2 s (both frequencies) and 0.7 MW for 1 s (110 GHz) were obtained, so far. Temperature increase in the cavity, the output window and some components, which absorb stray radiation in the gyrotron, were measured and cavity loss power and the dielectric...
A high-energy, low threshold THz-wave output has been experimentally demonstrated with intracavity terahertz-wave parametric oscillator based on surface-emitted configuration. The maximum THz-wave output energy of 283nJ/pulse was obtained at 1.54THz under the pump threshold of 12.9mJ/pulse in the cavity. The continuously tunable range from 0.75 to 2.75 THz was realized.
A new model of vacuum tube amplifier, designed to produce over 10 Watts at 263 GHz is in development at CPI Canada. This device uses CPI's Extended Interaction Klystron technology, which has previously demonstrated good results from 17 to 220 GHz. With recent completion of a 264 GHz CW tunable oscillator, the amplifier development will extend the demonstrated envelope for EIKs to a frequency and power...
The possibility of parasitic gyrotron interaction in a realistic stacked beam-tunnel geometry is proposed and investigated. The simulation methodology presented here involves the combination of a cold electromagnetic code with a fixed-field interaction code. The presented scheme can simulate the beam-wave interaction and calculate starting currents for this type of parasitic interaction in gyrotron...
Numerical 3D PIC code simulations show that Slow-Wave-Structures SWSs demonstrate excellent potential as a virtual dielectric in a Cherenkov based Backward Wave Oscillator (BWO). CST Microwave Studio confirms internal mode coupling between a volume TM0,6 and surface HE20,1 modes resulting in the creation of a high-Q cavity, necessary for the Cherenkov mechanism to be exploited. MAGIC 3D demonstrates...
The Spatial Harmonics Method (SHM) has been employed to study TE modes in a coaxial cavity with corrugations both on the inner and the outer wall. Such cavities seem to have the potential for superior mode-selectivity and could be employed for the development of multi-MW gyrotrons above 200 GHz.
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