J.-P. Hogge

EU megawatt-class 140 GHZ CW gyrotron

The first series tube of the gyrotrons for the 10-MW electron cyclotron resonance heating system of the stellarator W7-X was tested at Forschungszentrum Karlsruhe (FZK) and yielded a total output power of 0.98 MW, with an efficiency of 31% (without a single-stage depressed collector) in short-pulse operation and of 0.92 MW in pulses of 180 s (efficiency of almost 45% at a depression voltage of 29 kV). The Gaussian mode output power was 0.91 MW. The pulselength at full power (1 MW) is limited at FZK by the available power supply. At a reduced electron beam current, it is possible to operate at longer pulselengths. At an output power of 0.57 MW (electron beam current of 29 A), the pulselength was increased to 1893 s. There was no physical reason for a limitation of this pulse: The pressure increase during the pulse was less than a factor of two and ended up at a very low value in the 10-9 mbar range. The tube was delivered to Max-Planck-Institut fuumlr Plasmaphysik Greifswald for tests at full power and up to 30-min pulselength. The Gaussian mode RF output power, measured in a calorimetric load after a 25-m-long quasi-optical transmission line (seven mirrors), was 0.87 MW at a total output power of 0.92 MW in 30-min pulses. Again, no indications for a limitation in pulselength were found. The second series tube was tested in short-pulse operation and showed a strange behavior concerning a mode hopping which has not yet been understood. The third series gyrotron delivers up to now 0.65 MW at a pulse duration of 180 s. Preliminary operation of the prototype tube as a two-frequency gyrotron delivered 0.41 MW in 10-s pulses at 103.8 GHz (TE21,6 mode)

Note: stacked rings for terahertz wave-guiding.

We demonstrate the construction of corrugated waveguides using stacked rings to propagate terahertz frequencies. The waveguide allows propagation of the same fundamental mode as an optical-fiber, namely, the HE(11) mode. This simple concept opens the way for corrugated wave-guides up to several terahertz, maintaining beam characteristics as for terahertz applications.

Design of a frequency-tunable gyrotron for DNP-enhanced NMR spectroscopy

We report on the design of a modular low-power (10–50W) high-frequency gyrotron (265–530GHz) for DNP enhanced Solid-State NMR spectroscopy. With the view of covering a wide range of frequencies, a 9.7T helium-free superconducting magnet (SCM) is planned for the gyrotron operation on either the fundamental or second harmonic of the electron cyclotron frequency. The gyrotron design is based on a triode electron gun (Vk=15kV, Ib=100mA, Va= 6–8kV) which is very flexible for adapting the electron beam properties to a wide variety of cavities operating at the fundamental or at the second harmonic. The gyrotron is designed for a lateral output with an internal Vlasov-type converter. The reference parameters for application of DNP-enhanced NMR spectroscopy on a 400MHz (1H) spectrometer are optimized with a RF frequency tunability corresponding to twice the proton NMR frequency. The modularity of the construction of the gyrotron allows for the possibility of changing only some elements like the cavity-uptaper system in order to adapt to the wide range of NMR spectrometers existing at EPFL.

Design study of a test stand for ITER gyrotron

Abstract In the frame of development of the ITER electron cyclotron wave (ECW) system, a two MW CW coaxial cavity gyrotron will be developed during the Sixth Framework Program (2003–2006). Such development relies on the availability of a test stand capable of providing the electrical energy and cooling capacity. This test stand will possibly be used, in a later stage, for the component test of the ITER ECW system. This paper will first present the main parameters of this new coaxial gyrotron. Then we describe the test stand itself, including the general requirements for testing and evaluating the behaviour of the RF source and then a description of the electrical system design. Compared to the ITER reference design, the test stand emphasises the requirement of flexibility, which is necessary during the development of the gyrotron. The additional electrical equipment is included in the overview of the electrical system. The cooling system will be an important part of the design study. Indeed, the design efficiency of such a depressed collector gyrotron is ≈50%, implying >4 MW of continuous heat dissipation and evacuation by the cooling equipment. The specifications of the cooling system must also comply with ITER reference design values.

Parameterization technique for the preliminary gun design of the EU 170GHz 1MW conventional cavity gyrotron for ITER

A preliminary gun design for the EU 170 GHz, 1 MW conventional cavity gyrotron, for the TE32,09 mode [1], will be presented. The ASG magnet of the EU 170 GHz, 2 MW coaxial cavity gyrotron for ITER is used for the required magnetic field. A parameterization of the diode gun has been defined. Using the Ariadne++ code [2] the geometry has been optimized with respect to several criteria, such as the small velocity spreads, the acceptable width of the beam radius at the cavity, etc. The neutralization effect has been taken into account using a simple model.

Design of Electron Cyclotron Heating and Current Drive System of ITER

Since the end of EDA, the design of the Electron Cyclotron Heating and Current Drive (ECH&CD) system has been modified to respond to progress in physics understanding and change of interface conditions. Nominal RF power of 20 MW is shared by four upper launchers or one equatorial launcher RF beams are steered by front steering mirrors providing wide sweeping angle for the RF beam. DC high voltage power supply may be composed of IGBT pulse step modulators because of high frequency modulation and design flexibility to three different types of 170 GHz gyrotrons provided by three parties. The RF power from the 170 GHz gyrotron is transmitted to the launcher by 63.5 mmφ corrugated waveguide line and remotely switched by a waveguide switch between the upper launcher and the equatorial launcher. The ECH&CD system has also a start‐up sub‐system for assist of initial discharge composed of three 127.5 GHz gyrotrons and a dedicated DC high voltage power supply. Three of transmission lines are shared between 170 GHz ...

Design of a low-power high-frequency gyrotron for DNP-enhanced NMR spectroscopy

Summary form only given as follows. We report on a design of a modular low-power (10-50 W) high-frequency gyrotron (200-530 GHz) for DNP-enhanced NMR spectroscopy. For covering this wide range of frequencies a 9.5 T helium-free superconducting magnet (SCM) with a warm bore diameter of 75 mm is foreseen. Considering the wide frequency range, the SCM field level is compatible with an operation of the gyrotron at both the fundamental or second harmonic of the electron cyclotron frequency. The gyrotron design is based on a triode electron gun (Vk=15 kV, Ib=100 mA, Va= plusmn5 kV) which is very flexible for adapting the electron beam properties to a wide variety of cavities operating at the fundamental or at the second harmonic. The gyrotron is designed for an axial output and a quasi-optical mode-converter to a Gaussian mode will be placed after the gyrotron window. The reference parameters for the first application of DNP-enhanced NMR spectroscopy on a 400 MHz (1H) spectrometer are: frequency = 263.5 GHz, frequency tunability = 0.12%, RF-power = 10-50 W. The modularity of the gyrotron refers to the possibility to change only some elements like the cavity-uptaper system to be adapted to the wide range of NMR spectrometers existing at EPFL.

Development of new generation software tools for simulation of electron beam formation in novel high power gyrotrons

Computer aided design (CAD) based on numerical experiments performed by using adequate physical models and efficient simulation codes is an indispensable tool for development, investigation, and optimization of gyrotrons used as radiation sources for electron cyclotron resonance heating (ECRH) of fusion plasmas. In this paper, we review briefly the state-of-the-art in the field of modelling and simulation of intense, relativistic, helical electron beams formed in the electron-optical systems (EOS) of powerful gyrotrons. We discuss both the limitations of the known computer codes and the requirements for increasing their capabilities for solution of various design problems that are being envisaged in the development of the next generation gyrotrons for ECRH. Moreover, we present the concept followed by us in an attempt to unite the advantages of the modern programming techniques with self-consistent, first-principles 3D physical models in the creation of a new highly efficient and versatile software package for simulation of powerful gyrotrons.

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.

Development of High Power Gyrotrons for Fusion Applications at FZK Karlsruhe

Summary form only given. 140 GHz gyrotrons with a hollow waveguide cavity at 1 MW, CW output power have been developed at FZK Karlsruhe in cooperation with European institutions tor use at the stellarator W7-X at IPP Greifswald, Germany. TE28.8 is the operating mode. The utilized advanced quasi-optical (qo) mode converter has an excellent performance with respect to low amount of stray radiation (< 3%) and high Gaussian content (> 97%) of the RF output beam. Two prototype tubes have been built and tested successfully. With a first series tube, out of seven, the required specifications have been fully demonstrated. At a pulse length of 30 mm a power of 920 kW has been measured in the Gaussian mode. The corresponding overall RF output efficiency was nearly 45%. The fabrication of the series gyrotrons is in progress. Results and problems with tubes number 2, 3 and 4 are reported and discussed. Based on results obtained on an experimental coaxial cavity gyrotron at 165 GHz at FZK, the development of a 2 MW, CW, 170 GHz coaxial cavity gyrotron for ITER is in progress in a European cooperation. In the meantime a first industrial prototype of the 170 GHz coaxial gyrotron has been fabricated and is ready for operation, which is expected to start in April 2007. In tests with an experimental pre-prototype tube, operated at short (les 5ms) pulses, the design of the main gyrotron components has been confirmed, in general. The mechanism of parasitic low frequencv (LF) oscillations has been identified and the intensity of the LF oscillations has been reduced significantly by performing some minor geometrical modifications on the coaxial insert. The performance of the q.o. RF output svstem is not satisfying mainly with respect to the Gaussian content of the RF output beam. An improved design is in progress. Results are reported and discussed. In addition, work on a high power, multi-frequency gyrotron is going on. A SC magnet which will allow a fast (~sec) variation of the magnetic field has been specified and ordered. The optimization of the q.o. RF output system for a number of different modes is in progress. Results are reported.