Pushing the KIT 2 MW Coaxial-Cavity Short-Pulse Gyrotron Towards a DEMO Relevant Design

Magnetic fusion is one approach to generate thermonuclear fusion power in an environmental friendly way. The Electron Cyclotron Resonance Heating is considered as the major concept for startup, heating and control of the fusion plasma. Megawatt-class gyrotrons generate the required microwave power. This work focuses on advanced key components and technologies for a DEMO relevant 2 MW gyrotron. One major focus is on the development of advanced Magnetron Injection Guns. Another focus is on the red

Status and First Operation of Gyrotron Teststand FULGOR at KIT

FULGOR, the new KIT gyrotron teststand for megawatt-class gyrotrons, will be presented. Results of initial experiments using a 1.5 MW 140 GHz short pulse pre-prototype gyrotron will be discussed

170/204 GHz Dual-Frequency Mode Generator for Verification of the Quasi-Optical Output Coupler of a 2 MW Coaxial-Cavity Gyrotron

The 2 MW 170 GHz single-frequency coaxial-cavity short-pulse pre-prototype is upgraded to operate also at 204 GHz. Therefore, the quasi-optical output coupler, which is a gyrotron key component, has been modified. Before the newly manufactured quasi-optical output coupler is installed into the gyrotron, a low-power cold measurement for the verification is performed. Therefore, a mode generator is designed and adjusted to excite the relevant operating gyrotron modes, namely the TE 34,19 mode at 170 GHz and TE 40,23 mode at 204 GHz, with excellent purity and a low counter-rotating amount of < 0.5 % for both modes. The TE 40,23 mode is the mode with the highest eigenvalue ever excited in cold tests. After the successful mode excitation, first the fabricated launcher and then the entire quasi-optical output coupler are verified, showing excellent agreement with the simulation

Theoretical Study on the Operation of the EU/KIT TE34,19-Mode Coaxial-Cavity Gyrotron at 170/204/238 GHz

The 170 GHz 2 MW TE34,19-mode coaxial-cavity modular short-pulse pre-prototype gyrotron at KIT was recently modified in order to verify the multi-megawatt coaxial-cavity technology at longer pulses. In parallel, theoretical investigations on a possibility to operate the 170 GHz TE34,19-mode coaxial-cavity prototype at multiple frequencies up to 238 GHz have been started, with a goal to find a configuration at which the tube could operate in the KIT FULGOR gyrotron test facility using the new 10.5 T SC magnet. This paper indicates which adjustments have to be made and show the feasibility of the multi-frequency operation. Small modifications at the gyrotron cavity will support an RF output power of more than 2 MW at 170/204 GHz. Furthermore, a new gyrotron launcher has been designed capable of producing a Gaussian microwave beam with a Gaussian mode content of more than 96% at these frequencies

Computer-Controlled Test System for the Excitation of Very High-Order Modes in Highly Oversized Waveguides

The generation of a specific high-order mode with excellent mode purity in a highly oversized cylindrical waveguide is mandatorily required for the verification of high-power components at sub-THz frequencies. An example is the verification of quasi-optical mode conversion and output systems for fusion gyrotrons. A rotating high-order mode can be excited by taking a low-power RF source (e.g. RF network analyser) and by injecting the RF power via a horn antenna into a specific adjustable quasi-optical setup, the so-called mode generator. The manual adjustment of the mode generator is typically very time-consuming. An automatized adjustment using intelligent algorithms can solve this problem. In the present work, the intelligent algorithms consist of five different mode evaluation techniques to determine the azimuthal and radial mode indices, the quality factor, the scalar mode content and the amount of the counter-rotating mode. Here, the implemented algorithms, the design of the computer-controlled mechanical adjustment and test results are presented. The new system is benchmarked using an existing TE28,8 mode cavity operating at 140 GHz. In addition, the repeatability of the algorithms has been proven by measuring a newly designed TE28,10 mode generator cavity. Using the described advanced mode generator system, the quality of the excited modes has been significantly improved and the time for the proper adjustment has been reduced by at least a factor of 10

Triode magnetron injection gun for the KIT 2 MW 170 GHz coaxial cavity gyrotron

Considering the recent understanding of the physics of electron trapping mechanisms taking place in the magnetron injection gun (MIG) region of gyrotrons and the sensitivity of the emitter ring manufacturing tolerances on the electron beam quality, a MIG has been designed and manufactured for the 2 MW, 170 GHz coaxial cavity gyrotron developed at Karlsruhe Institute of Technology. The new MIG has the following novelties: (i) the design satisfies the criteria for the suppression of the electron trapping mechanisms, (ii) a new type of emitter ring is used for the suppression of the influence of the manufacturing tolerances and misalignments on the quality of the generated electron beam, and (iii) the design was optimized to generate a good beam quality in a wide variety of magnetic field profiles to increase the flexibility. An additional important feature of the new triode MIG design is the possibility to operate with only two power supplies by using a special start-up scenario. The first experimental results of the coaxial cavity gyrotron with the new MIG are presented

Overview of KIT activities on high power, high frequency gyrotron development and the role of the new FULGOR teststand at KIT

For a future DEMOnstration fusion power plant two challenging trends with respect to gyrotron features are recognized: (a) the operating frequency will be above 200 GHz and (b) the requested total efficiency of the gyrotron should be as high as possible. ECRH systems for future plants (DEMO) or Fusion Power Plants (FPP) will most probably require multi-megawatt and continuous wave gyrotrons which are able to oscillate at a frequency significantly above 200 GHz. The coaxial cavity technology which is under investigation and development at KIT since several years, seems to have the optimum properties to fulfill the requirements towards sub-THz operation in the MW output power regime. To benefit from these advantages and to profit from the existing experience on this technology the modular 2 MW 170 GHz gyrotron has been taken as a starting point for a 170/204/238 GHz multi-frequency gyrotron design study. Recent activities for improvement of the performance of this gyrotron and preparations for long pulse operation will be shown. In a first step we aim at ~ 100 ms operation, in a second step, with the tube being equipped with an improved cooling system, 1 s operation is envisaged. KIT is currently constructing a new gyrotron teststand, FULGOR, having specific features, such as: 10 MW electrical input power in CW, magnetic field up to 10.5 T with 261 mm warm bore hole of the SCM and several voltage taps from the high-voltage DC power supply. The CW HV Power supply (120 kV, 130 A) has already been delivered and accepted, a dry superconducting magnet will be delivered in 2019. For the first time it will be possible with FULGOR to test Multistage Depressed Collector (MDC) gyrotrons which are supposed to increase the overall efficiency from 50 % (state of the art) to 60 % or even higher. There are two concepts for gyrotron MDC: a axisymmetric concept, which relies on the demagnetization combined with non-adiabatic magnetic transitions and a concept based on E×B drifts to sort electrons. First considerations of a proof-of-principle design for the ExB drift concept will be shown