A5083040403- Gyrotron and Vacuum Electronics Research
- Particle accelerators and beam dynamics
- Microwave Engineering and Waveguides
- Magnetic confinement fusion research
- Particle Accelerators and Free-Electron Lasers
- Pulsed Power Technology Applications
- Quantum Chromodynamics and Particle Interactions
- Particle physics theoretical and experimental studies
- Nuclear physics research studies
- Ionosphere and magnetosphere dynamics
- Acoustic Wave Resonator Technologies
- Quantum, superfluid, helium dynamics
- Superconducting Materials and Applications
- High-Energy Particle Collisions Research
- Atomic and Subatomic Physics Research
- Plasma Diagnostics and Applications
- Atomic and Molecular Physics
- Solar and Space Plasma Dynamics
- Nuclear Physics and Applications
- Superconducting and THz Device Technology
- Quantum chaos and dynamical systems
- Muon and positron interactions and applications
- Terahertz technology and applications
- Advanced NMR Techniques and Applications
- Complex Systems and Time Series Analysis
University of Latvia
2013-2022
University of Fukui
2006-2019
Institut für Technische und Angewandte Physik (Germany)
2017
University of Craiova
2011-2013
Chinese Academy of Sciences
2011
Helsinki Institute of Physics
2000-2009
Budapest University of Technology and Economics
2009
Tekes
2001-2008
University of Helsinki
1977-2008
Research Council of Finland
2008
The feasibility of manufacturing a 2-MW CW coaxial cavity gyrotron at 170 GHz has been demonstrated and data required for fabrication an industrial tube have obtained. An engineering design prototype started recently with the goal to provide gyrotrons microwave output power International Thermonuclear Experimental Reactor (ITER). critical components as electron gun, RF system will be verified under realistic conditions short pulses using experimental Forschungszentrum Karlsruhe.
Most of the present-day millimeter-wave gyrotrons developed for plasma experiments in controlled fusion reactors utilize cylindrical cavities operating high-order modes. The choice modes should obey certain restrictions dictated by achievable mode selection and maximum admissible level density microwave ohmic losses cavity walls. Even with these restrictions, developers have successfully manufactured quasi-continuous-wave short millimeter wavelength bands that are capable delivering power on...
The European Union is working toward providing 2-MW, coaxial-cavity, continuous-wave (cw) 170-GHz gyrotrons for ITER. Their design based on results from an experimental preprototype tube having a pulse length of several milliseconds, in operation at Forschungszentrum Karlsruhe (FZK) years now. first industrial prototype was designed cw but, phase, aimed 1 s the Gyrotron Test Facility Lausanne, Switzerland, as part phased testing/development program (1 s, 60 cw). this gyrotron are reported...
In the development of powerful gyrotrons capable long-pulse or continuous wave operation cardinal problem is to provide stable, single-mode highly efficient at desired mode with an acceptable level ohmic losses in resonator walls. present paper selective properties various coaxial resonators as well microwave power outer and inner conductors are considered. The start-up scenario discussed. results numerical simulations a 1 MW, 280-GHz gyrotron presented which demonstrate that successive...
The paper shows the calculation of resonant frequency, Q-value and field profiles eigenmodes tapered gyrotron resonators, taking into account coupling modes induced by taper. mode is negligible for taper angles only a few degrees, but must be taken if angle exceeds about 10°.
The feasibility of fabrication coaxial cavity gyrotrons with an output power up to 2 MW, continuous wave (CW) has been demonstrated and information necessary for a technical design obtained. Experiments gyrotron equipped newly designed components-electron gun, cavity, RF system-have performed. In short pulses, maximum radio frequency (RF) 2.2 MW reached in stable operation. At the nominal 1.5 efficiency 30% achieved. This enhanced 48% operation single-stage depressed collector. stability...
A theory is developed which describes gyro-backward wave oscillators (gyro-BWO's) with arbitrarily relativistic electron beams and tapered external magnetic field waveguide wall radius. For the case of linear tapering optimal parameters are found that correspond to highly efficient operation. The frequency tunability as function voltage deviations has been analyzed. It shown how use results given in terms normalized for designing concrete gyro-BWO's. one design effect velocity spread on...
The basic investigations on a coaxial cavity gyrotron operating at 165 GHz have been accomplished and the feasibility of manufacturing 2-MW continuous-wave 170 has demonstrated. In last measurements, data required for fabrication an industrial tube completed. influence misalignment insert operation investigated. limitation high-voltage performance electron gun due to buildup Penning discharge suppressed leakage current measured as function retarding collector voltage.
In this paper we investigate non-complete sawtooth reconnection in the ASDEX Upgrade tokamak. Such phenomena are associated with internal m/n = 1/1 kink mode which does not vanish after crash phase (as would be case for complete reconnection). It is shown that cannot fully described by pure and higher harmonics play an important role during phase. We employ Hamiltonian formalism reconstructed perturbations to model incomplete reconnection. demonstrated stochastization appears due excitation...
The theory of multicavity gyrodevices has been developed for the case when two prebunching cavities may operate at different harmonics cyclotron frequency. It is shown that first cavity operates fundamental and second harmonic, harmonic content in an electron beam current efficiency operation third, output are higher than these fundamental. four was studied with account velocity spread both, single- two-harmonic cases. results obtained permit one to estimate its sensitivity spread.
The authors present the mathematical analysis for calculation of dispersion relation, field distributions, and ohmic losses TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,p</sub> modes in an infinite coaxial waveguide with a longitudinally corrugated insert. method employed is based on appropriate eigenfunction expansion, its main advantage very fast convergence few spatial harmonics. properly extended to include tapered cavities varying,...
In the first part of this paper, status 140-GHz continuously operated gyrotrons with an output power 1 MW for stellarator Wendelstein 7-X will be described. With series tube, 1000 kW has been achieved in short pulse operation (milliseconds) electron beam current 40 A, and 1150 at 50 A. a length 3 min limited by available high-voltage (HV) supply, 920 about A efficiency 45% mode purity 97.5% obtained. At reduced 29 570 was measured 1893 s without significant increase tube pressure. The energy...
The crash phase of the sawteeth in ASDEX Upgrade tokamak [Herrmann et al., Fusion Sci. Technol. 44(3), 569 (2003)] is investigated detail this paper by means soft x-ray (SXR) and electron cyclotron emission (ECE) diagnostics. Analysis precursor postcursor (1,1) modes shows that does not affect position resonant surface q=1. Our experimental results suggest sawtooth models should contain two ingredients to be consistent with observations: (1) mode structure survive (2) flux changes small...
The theory describing the operation of gyrotrons with tilted and shifted electron beams has been developed. Effects tilt shift are studied for a 1 MW, 170 GHz gyrotron, which is presently under development in Europe cyclotron resonance plasma heating current drive International Thermonuclear Experimental Reactor. It shown that one should expect significant deterioration gyrotron such when angle exceeds 0.4°–0.5° parallel beam axis respect to microwave circuit larger than 0.4–0.5 mm. At same...
The onset of stochastic oscillations in gyrotrons is studied by means the self-consistent theory describing nonstationary processes. Complicated alternating sequences regions stationary, automodulation, and chaotic are found plane generalized gyrotron variables: cyclotron resonance mismatch dimensionless current. results investigations important connection with attempts to increase output power raising
Ohmic losses in coaxial gyrotron cavities with corrugated insert are calculated on the basis of two theories-the surface impedance model (SIM) and singular integral equation (SIE). It is found that SIE predicts significantly lower losses.
A theory is presented which describes the dependence of multimode operation a gyrotron on modulation and beam voltages. Nonlinear nonstationary processes are considered. An approximate start-up scenario determined makes it possible to achieve single-mode excitation high-efficiency in desired mode, as well switch tube similar other modes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Abstract Two approaches to the study of a complex cavity with mode conversion are developed. In first method system coupled second order differential equations, which takes into account non-principal modes, is solved. This applicable cavities gradual transition. The based on use field-matching technique and abrupt Numerical results presented for TE02/TE06 in cold fixed field approximation
Larger scale plasma instabilities not leading to an immediate termination of a discharge often result in periodic nonlinear perturbations the plasma. A minimal possible model is formulated for description system with drive and relaxation processes which have different time scales. The based on two equations: first being responsible dynamics second drive. can be generalized describe pellet injection.