Prototype Gyrotron Research Articles

Trajectory analysis in a collector with multistage energy recovery for a DEMO prototype gyrotron. Part III. Influence of the spent electron beam parameters

The influence of the spent electron beam parameters on the possibilities of multistage energy recovery in the prototype gyrotron developed for the DEMO project is determined. The characteristics of electrodes and magnetic coils in a collector with four-stage recovery were optimized considering the distributions of electrons' coordinates and velocities obtained as a result of calculating the electron-wave interaction in the cavity. In the trajectory analysis in the collector, a sectioned electron beam was used to suppress the negative influence of the bundles of a toroidal solenoid used to create an azimuthal magnetic field. The possibility of achieving the total efficiency of the gyrotron of approximately 78% was shown, which is close to the maximum total efficiency with ideal separation of electron fractions with different energies, with the current of electrons reflected from the collector not exceeding 1% of the total current of the electron beam. Keywords: Microwave electronics, gyrotron, electron beam, energy recovery.

Траекторный анализ в коллекторе с многоступенчатой рекуперацией энергии для прототипа гиротрона DEMO. Ч. III. Влияние параметров отработанного электронного потока

The influence of the spent electron beam parameters on the possibilities of multistage energy recovery in the prototype gyrotron developed for the DEMO project is determined. The characteristics of electrodes and magnetic coils in a collector with four-stage recovery were optimized considering the distributions of electrons' coordinates and velocities obtained as a result of calculating the electron-wave interaction in the cavity. In the trajectory analysis in the collector, a sectioned electron beam was used to suppress the negative influence of the bundles of a toroidal solenoid used to create an azimuthal magnetic field. The possibility of achieving the total efficiency of the gyrotron of approximately 78% was shown, which is close to the maximum total efficiency with ideal separation of electron fractions with different energies, with the current of electrons reflected from the collector not exceeding 1% of the total current of the electron beam.

Development and Initial Experimental Results of a Terahertz Pulsed Field Gyrotron in the WHMFC

We report the design and initial experimental results of an 800-GHz second harmonic gyrotron prototype, in which a 15-T pulsed magnet is applied. This gyrotron prototype is developed at the Wuhan National High Magnetic Field Center (WHMFC). An in-house software for analyzing and designing terahertz gyrotrons and an experimental research platform are developed. In addition, alignment adjustments, eddy current effects, and radiation tests are discussed. The initial experimental results show that the prototype gyrotron can irradiate ~40 W at fundamental harmonic 383.7-GHz (TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,4</sub> ) waves at 14.14 T and a few milliwatts at second harmonic 0.8-THz (TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8,5</sub> ) waves at 14.86 T.

The Development of 170 GHz, 1 MW Gyrotron for Fusion Application

This paper presents the overall conceptual design of a 170 GHz, 1 MW gyrotron for plasma heating applications in thermonuclear fusion reactors. The operating mode is carefully selected with consideration of mode competition. The TE25,10 mode is determined as the operating mode in the present study. A weakly tapered conventional resonator is used for the study of the RF behavior, and multimode calculations are carried out for power and efficiencies. The optimized structure of the beam tunnel can further attenuate low-frequency oscillation. The design studies of a triode-type magnetic injection gun, quasi-optical mode converter, and single-disc sapphire window are also described. In addition, novel cold test methods which can effectively validate assembles are designed. In 2021, a prototype gyrotron was fabricated to validate the electronic–optic system and RF system. The current results obtained support an output power of 210 kW and efficiency of 15.9% through an initial low-power experiment. On the basis of the optimized design, an industrial prototype gyrotron is under fabrication as the heating source for the thermonuclear experimental reactor.

Experimental Testing of the European TH1509U 170-GHz 1-MW CW Industrial Gyrotron—Long Pulse Operation

The upgraded European 1-MW, 170-GHz continuous wave (CW) industrial prototype gyrotron (TH1509U) for electron cyclotron resonance heating and current drive in ITER was tested at the Karlsruhe Institute of Technology (KIT). In this work, we report on the major achievements during the experimental campaigns that took place intermittently between October 2020 and July 2021. The upgraded gyrotron clearly surpassed the performance of the previous TH1509 tube. In particular, TH1509U delivered (i) 0.9 MW in 180 s pulses (maximum possible pulse length with the KIT test stand) and (ii) more than 1 MW at a pulse length limited to 40 s, due to an unforeseen problem with the test stand cooling circuit at that time. In addition, it was possible to also demonstrate gyrotron operation at (iii) 0.5 MW in 1600 s pulses. The experiments will be continued at the FALCON test stand at the École Polytechnique Fédérale de Lausanne (EPFL).

A New Lumped Approach for the Simulation of the Magnetron Injection Gun for MegaWatt-Class EU Gyrotrons

In the framework of the ITER (International Thermonuclear Experimental Reactor) project, one of the key components of the reactor is the ECRH (Electron Cyclotron Resonance Heating). This system has the duty to heat the plasma inside the tokamak, using high frequency and power radio waves, produced by sets of 1MW gyrotrons. One of the main issues related to the gyrotron operation is the output power drop that happens right after the beginning of a pulse. In this work, we study the underlying phenomena that cause the power drop, focusing on the gyrotron’s MIG (Magnetron Injection Gun) of the 1MW, 170 GHz European Gyrotron prototype for ITER. It is shown how the current emission and the temperature of the emitter are tightly bound, and how their interaction causes the power drop, observed experimentally. Furthermore, a simple yet effective lumped-parameter model to describe the MIG’s cathode thermal dynamics is developed, which is able to predict the power output of the gyrotron by simulating the propagation of the heat inside this component. The model is validated against test results, showing a good capability to reproduce the measured behavior of the system, while still being open to further improvements.

Towards a 1.5 MW, 140 GHz gyrotron for the upgraded ECRH system at W7-X

• 1.5 MW gyrotron development for the ECRH system upgrade at the stellarator W7-X. • Numerically verified complete design of the 1.5 MW 140 GHz CW gyrotron. • Low-power tests of the gyrotron quasi-optical output coupler for theTE 28,10 mode. For the required upgrades of the Electron Cyclotron Resonance Heating system at the stellarator Wendelstein 7-X, the development of a 1.5 MW 140 GHz Continuous Wave (CW) prototype gyrotron has started. KIT has been responsible to deliver the scientific design of the tube (i.e. the electron optics design and the RF design), with contributions from NKUA and IPP. The prototype gyrotron has been ordered at the industrial partner, Thales, France, and is expected to be delivered in 2021. In parallel, a short-pulse pre-prototype gyrotron has been developed at KIT, to provide the means for a first experimental validation of the scientific design in ms pulses, prior to the construction of the CW prototype. This paper reports on the status of the 1.5 MW CW gyrotron development, focusing on the scientific design and its numerical and experimental validation.

Trajectory Analysis in a Collector with Multistage Energy Recovery for a DEMO Prototype Gyrotron. Part I. Idealized Magnetic Field Distribution

This paper presents the results of simulation of the collector of a prototype gyrotron designed for the DEMO project. Trajectory analysis in a collector with four-stage recovery of the residual beam energy based on the method of spatial separation of electrons in crossed azimuthal magnetic and axial electric fields was carried out. In this part of the research, the azimuthal magnetic field was formed using a conductor located on the axis of the device. The study was carried out for a spent electron beam with a particle velocity and coordinate distribution close to those obtained in experiments with high-power gyrotrons. As a result of optimizing the geometry and potentials of the collector sections, an overall efficiency of the gyrotron higher than 80% was achieved, which is close to the maximum efficiency with ideal separation of electron beam fractions with different energies. The data obtained will be used to design a toroidal solenoid for creating an azimuthal magnetic field.

Траекторный анализ в коллекторе с многоступенчатой рекуперацией энергии для прототипа гиротрона DEMO. Часть II. Тороидальное магнитное поле

The results of modeling of a collector with four-stage recovery of the residual beam energy for the prototype gyrotron designed for the DEMO project are presented. For spatial separation of electrons with different energies, the azimuthal magnetic formed by a toroidal solenoid is used. An increase of the recovery efficiency and a decrease of the flow of electrons reflected from the collector are achieved by reducing the spread of radial position of the leading centers of electron trajectories at the optimal parameters of the toroidal solenoid, as well as by using a sectioned electron beam. Trajectory analysis of the spent beam with electron velocity and coordinate distributions close to those obtained in experiments with high-power gyrotrons showed the possibility of achieving an overall efficiency of the gyrotron higher than 80 %, which is close to the maximum efficiency at ideal separation of electron beam fractions with different energies.

Траекторный анализ в коллекторе с многоступенчатой рекуперацией энергии для прототипа гиротрона DEMO. Часть I. Идеализированное распределение магнитного поля

The results of modeling of collector for the gyrotron prototype being developed for the DEMO project are presented. A trajectory analysis in a collector with a 4-stage recovery of the residual beam energy based on the method of spatial separation of electrons in crossed azimuthal magnetic and axial electric fields was performed. In this part of the study, the formation of the azimuthal magnetic field was carried out using a conductor located on the axis of the device. The study was performed for a spent electron beam with a velocity and coordinate distribution of particles close to those obtained in experiments with powerful gyrotrons. Due to a thorough choice of the geometry of the collector sections, a total gyrotron efficiency of more than 80% was achieved, which is close to maximum efficiency with perfect separation of fractions of an electron beam with different energies. The data obtained will be used for development of a toroidal solenoid designed to create an azimuthal magnetic field.

Development and Experimental Verification of an XY-Table for the Optimization of the Alignment of High-Power Gyrotrons

The proper alignment of the electron beam with the interaction cavity is essential in order to achieve efficient operation of modern high-power, high-frequency gyrotrons. However, tolerances, manufacturing, and magnetic field alignment errors may lead to the less optimal positioning of the electron beam in the gyrotron cavity. In this paper, we describe in detail the in-house design and development of a simple and low-cost prototype gyrotron-alignment XY-table, which can be used for the optimization of the alignment of the electron beam with the cavity axis. The efficient operation of the device is verified experimentally by operating the European ITER 170-GHz, 1-MW short-pulse prototype gyrotron in the Oxford Instruments superconducting magnet that is available at the Karlsruhe Institute of Technology gyrotron test-stand and is equipped with a set of dipole coils.

Recent experiments with the European 1MW, 170GHz industrial CW and short-pulse gyrotrons for ITER

The European Gyrotron Consortium (EGYC) is developing the European 1 MW, 170 GHz Continuous Wave (CW) industrial prototype gyrotron for ITER in cooperation with Thales Electron Devices (TED) and Fusion for Energy (F4E). This conventional, hollow-cavity gyrotron, is based on the 1 MW, 170 GHz Short-Pulse (SP) modular gyrotron that has been designed and manufactured by the Karlsruhe Institute of Technology (KIT) in collaboration with TED. Both gyrotrons have been tested successfully in multiple experiments. In this work we briefly report on the results with the CW gyrotron at KIT and we focus at the experiments at the Swiss Plasma Center (SPC). In addition, we present preliminary results from various upgrades of the SP tube that are currently tested at KIT.

Metrology techniques for the verification of the alignment of the EU gyrotron prototype for ITER

The EU gyrotron for the ITER Electron Cyclotron (EC) heating system has been developed in coordinated efforts of the EGYC Consortium, Thales ED (TED) and Fusion for Energy (F4E) and under the supervision of ITER Organization Central Team. After the successful verification of the design of the 1MW, 170 GHz hollow cylindrical cavity gyrotron operating at the nominal TE32,9 mode with a short pulse gyrotron prototype at KIT, an industrial CW gyrotron prototype was manufactured by TED and tested at ~0.8 MW output power and 180 s pulse duration, which is the limit of the HV power supply currently available at KIT. The experiments are being continued at SPC in 2018 to extend further the pulse duration, taking advantage of the existing CW full-power capabilities of the gyrotron test facility recently upgraded for the FALCON project. The gyrotron cavity interaction is very sensitive to the alignment of the internal mechanical parts of the gyrotron tube with the magnetic field generated by the superconducting magnet within a typical range of 0.2 – 0.5 mm. The control of the tolerances and deformations becomes therefore critical to achieving the target performances. With the EU gyrotron prototype it was possible to adjust the alignment of the gyrotron tube with respect to the magnetic field axis during the installation and commissioning phase. The actual shift and tilt movements were verified using advanced metrology methods such as photogrammetry. In this paper, the alignment control techniques and procedures will be discussed also in view of enhancing the reproducibility of gyrotron performance during series production.

Report of recent experiments with the European 1 MW, 170 GHz CW and SP prototype gyrotrons for ITER

The European 1 MW, 170 GHz industrial CW prototype gyrotron has been designed within EGYC (European GYrotron Consortium) in collaboration with the industrial partner Thales Electron Devices (TED) and under the coordination of Fusion for Energy (F4E). This is a conventional (hollow) cavity gyrotron that is based on the 1 MW, 170 GHz short-pulse (SP) modular gyrotron, which has been designed and manufactured by KIT in collaboration with TED. The SP prototype has been tested in multiple experimental campaigns since 2015 and the nominal cavity mode TE32,9is exited at 170.1 GHz, producing RF power above 1 MW with 35 % interaction efficiency. The first phase of the experiments with the CW industrial gyrotron was successfully completed at KIT in 2016, verifying most of the ITER specifications. Short pulses (&lt;10ms) deliver RF power higher than 0.9 MW with a total efficiency of 26 % (in non-depressed collector operation). The Gaussian mode content of the RF beam is 97 %. Pulses with duration of 180 s (limited by the high-voltage power supply at KIT) produce power more than 0.8 MW with maximum efficiency 38 % (in depressed collector operation). In this work the achievements with the SP and the CW prototype gyrotrons are summarized.

Tests and developments of a long-pulse high-power 170 GHz absorbing matched load

The future EC systems will consist of several gyrotron sources providing MW-level millimeter wave power at a frequency around or above 170 GHz. The development of matched loads is necessary to test the new sources, the components for the transmission lines and the launchers, and must ensure high qualification for compatibility with the nuclear environment. The development at IFP-CNR and LTC of several compact high-power prototypes during the last decade led to a refinement of the overall design, resulting in the present low-reflectivity vacuum-compatible loads. The activity on loads is supported by F4E in view of the development of the EU gyrotron for ITER and required high-power tests at QST (Naka, Japan). Qualification is now supported by new tests at SPC (Lausanne, Switzerland) using the FALCON test-bed designed to test components and the EU gyrotron prototype for the EC system of ITER. These high-power tests, performed on the first CW prototype load (provided with 16 + 16 cooling channels in parallel) and shown in this paper, highlighted the need to improve the mechanical, vacuum and hydraulic design to reach the final goal of 1000s at ∼1 MW.

Numerical Studies on the Influence of Cavity Thermal Expansion on the Performance of a High-Power Gyrotron

An iterative procedure is described, which models the influence of the thermal expansion of the gyrotron cavity on the expected gyrotron performance. It is a multiphysics simulation method, which involves electrodynamic, thermal-hydraulic, and thermo-mechanical simulations. The method is applied to the first European 170-GHz, 1-MW continuous wave prototype gyrotron for the ITER. According to the simulations, a performance reduction of ~15% is expected at nominal operating parameters, because of the thermal expansion of the cavity. Alternative operating points to mitigate this effect are proposed and numerically validated. The numerical results are discussed in light of experimental findings.

A portable control and data acquisition solution using EPICS, MARTe and MDSplus

A modern Control and Data Acquisition System (CODAS) must provide an integrated management of supervision, data acquisition and real-time control and a data centric view of the system combining raw, elaborated and configuration data. These requirements have been addressed by the CODAS system of the SPIDER experiment in the ITER Neutral Beam Test Facility. The solution adopted in SPIDER CODAS integrates, by means of few interface components, three frameworks used in nuclear fusion and accelerator communities. A further refinement has recently started, aiming at providing a solution that is complete and generic, and, as such, easily portable to new applications, ranging from small systems to future fusion experiments. The refined system described in the paper will be deployed in the ECT-FALCON Test Facility, used to test the ITER EC launcher components and the European Gyrotron prototype. Its implementation in other test facilities is foreseen, in order to provide a fast track to the development of complete and integrated control and data acquisition.

A 0.4-THz Second Harmonic Gyrotron with Quasi-Optical Confocal Cavity

Mode density is very relevant for harmonic gyrotron cavity. Theoretical investigations suggest that quasi-optical confocal waveguide performs low mode density and good mode-selective character. By selecting the appropriate mode and optimizing the cavity parameters, the quasi-optical confocal cavity is suitable for high-harmonic terahertz gyrotron without mode competition. In order to verify the theoretical analysis, a 0.4-THz second harmonic gyrotron has been designed and experimented. Driven by a 40-kV, 4.75-A electron beam and 7.51-T magnetic field, the gyrotron prototype could generate 6.44 kW of output power at 395.35 GHz, which corresponds to an electron efficiency of 3.4%. There is no mode competition between the second harmonic and fundamental observed in the experiments.

CW Experiments With the EU 1-MW, 170-GHz Industrial Prototype Gyrotron for ITER at KIT

The European 1-MW, 170-GHz continuous wave industrial prototype gyrotron for electron cyclotron resonance heating and current drive on international thermonuclear experimental reactor was during 2016 under test at the Karlsruhe Institute of Technology (KIT) test facility. In order to optimize the gyrotron operation, the tube was at first thoroughly tested in the short-pulse regime, with pulses that did not exceed 10 ms, for a wide range of operational parameters. Then, and after proper conditioning of the tube, the operation was extended to longer pulses with duration up to 180 s, which is the maximum pulselength possible at the KIT test facility. In this paper, we present in detail the achievements of the long-pulse experimental campaign.

Experimental verification of the European 1 MW, 170 GHz industrial CW prototype gyrotron for ITER

The EU 1MW, 170GHz gyrotron with hollow cylindrical cavity have been designed within the European GYrotron Consortium (EGYC) in collaboration with the industrial partner Thales Electron Devices (TED) and under the coordination of Fusion for Energy (F4E). In the frame of the EU program, the short-pulse (SP) version of this tube was designed and manufactured by KIT in collaboration with TED. The experimental verification of the SP gyrotron prototype was successfully completed in 2015. The achieved experimental results show a very stable gyrotron operation with RF output power above 1MW at good cavity interaction efficiency around 35%. The gyrotron was operated up to 10ms pulse length; the nominal cavity mode TE32,9 has been excited at the frequency 170.1GHz in agreement with the corresponding ITER specification. The Gaussian mode content of the output RF beam was about 98% and the total level of internal stray radiation was in the range of 2–3%. The manufacturing of the first industrial continuous-wave (CW) prototype gyrotron, based on the SP gyrotron design, was completed in November 2015 at TED. The tube was delivered to KIT and the experimental verification started in February 2016. Operation of the gyrotron with ms pulse duration resulted in stable excitation of the nominal mode at 170.22GHz for a wide range of operating parameters and with a level of stray radiation comparable with the SP version. The maximum RF power achieved up to now in short-pulse operation at a level of 1MW. The measured Gaussian mode content of the RF beam is 97%. Currently, further preparation for the CW operation of the gyrotron is in progress.