Accurate gyrotron magnetic axis determination

A way to determine the magnetic axis of gyrotron cryomagnets, and more generally magnets composed of coils wound around a single mandrel is presented. The method is based on measurements of the longitudinal component of the magnetic field performed at suitable locations with a high accuracy (100 ppm) Hall probe [1]. The tilt and the shift of the magnetic axis with respect to the mechanical axis can be determined with a typical accuracy of 0.01deg and 0.1 mm respectively

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 H E11 mode. This simple concept opens the way for corrugated wave-guides up to several terahertz, maintaining beam characteristics as for terahertz applications

Experimental study from linear to chaotic regimes on a terahertz-frequency gyrotron oscillator

Basic wave-particle interaction dynamics from linear to chaotic regimes is experimentally studied on a frequency tunable gyrotron generating THz radiation in continuous mode (200W) at 263GHz which will be used for dynamic nuclear polarization nuclear magnetic resonance spectroscopy applications. In the studied system, the nonlinear dynamics associated to the waveparticle interaction is dominated by longitudinal mode competition of a given transverse TEm;p cavity-mode. This study covers a wide range of control parameter from gyro-traveling wave tube (gyro-TWT) to gyro-backward wave oscillator (gyro-BWO) like interactions for which extensive theoretical studies have been performed in the past on a simplified system. Besides the common route to chaos characterized by period doubling, other routes have been identified among which some are characterized by line-width frequency-broadening on the side-bands. The complex nonlinear dynamics is in good agreement with the theory and the experimental results are discussed on the basis of the prediction obtained with the nonlinear time-dependent selfconsistent codes TWANG and EURIDICE both based on a slow-time scale formulation of the self-consistent equations governing the wave-particle dynamics. V

Status of the EU 170 GHz/2 MW/CW Coaxial Cavity Gyrotron for ITER: The Dummy Gun Experiment

A mock-up gun has been manufactured as exact replica of the refurbishment first prototype EU 170 GHz/2MW/CW coaxial cavity gyrotron, but without emitter ring in order to validate the voltage standoff stability. The experimental results of the mock-up gun tests are presented

European 1 MW, 170 GHz CW Gyrotron Prototype for ITER - long-pulse operation at KIT -

The upgraded EU 1 MW, 170 GHz continuous wave (CW) industrial prototype gyrotron (TH1509U) for Electron Cyclotron Resonance Heating and Current Drive (ECRH&CD) in ITER was tested at the Karlsruhe Institute of Technology (KIT). The gyrotron surpassed the performance of the previous TH1509 tube. In particular, TH1509U delivered (i) 0.9 MW in 180 s pulses (max. pulse length of the KIT test stand) and (ii) more than 1 MW at a pulse length limited to 40 s, due to a problem with the test stand cooling circuit at that time. In addition, it was possible to demonstrate gyrotron operation at (iii) 0.5 MW in 1600 s pulses

A new 3MW ECRH system at 105 GHz for WEST

The aim of the WEST experiments is to master long plasma pulses (1000s) and expose ITER-like tungsten wall to deposited heat fluxes up to 10 MW/m$^2$. To increase the margin to reach the H-Mode and to control W-impurities in the plasma, the installation of an upgraded ECRH heating system, with a gyrotron performance of 1MW/1000s per unit, is planned in 2023. With the modifications of Tore Supra to WEST, simulations at a magnetic field B$_0$∼3.7T and a central density n$_{e0}$∼6 × 10$^{19}$ m$^{−3}$ show that the optimal frequency for central absorption is 105 GHz. For this purpose, a 105 GHz/1MW gyrotron (TH1511) has been designed at KIT in 2021, based on the technological design of the 140 GHz/1.5 MW (TH1507U) gyrotron for W7-X. Currently, three units are under fabrication at THALES. In the first phase of the project, some of the previous Tore Supra Electron Cyclotron (EC) system components will be re-installed and re-used whenever possible. This paper describes the studies performed to adapt the new ECRH system to 105 GHz and the status of the modifications necessary to re-start the system with a challenging schedule

Energy Confinement in Shaped TCV Plasmas with Electron Cyclotron Heating

The effects of plasma shape on confinement and sawtooth stability are studied for positive and negative discharge triangularity and for different elongations with 1.5 MW centrally deposited ECH powe

Preliminary Confinement Studies during ECRH in TCV

Within the range of plasma shapes and plasma currents investigated, the electron confinement time, Tau_E increases with density, elongation and negative triangularity (-0.4<delta<+0.4), similar to Ohmic heating (in these low density discharges). In addition, TauEe increases with q_a up to q_a~5 after which it decreases. There is little dependence of TauEe on the heating location provided it is inside the q= I surface. As the heating location is moved outside the q=l surface, TauEe decreases. This may be the explanation of the observed decrease in TauEe at high q_a. The power-induced degradation exponent found is generally as expected: alpaha_P = -0.5

EFFECT OF LOCALISED ELECTRON CYCLOTRON HEATING ON ENERGY CONFINEMENT AND MHD IN TCV

Within the range of plasma shapes and plasma currents investigated, the electron confinement time, tau_Ee, increases with safety factor, density and negative triangularity similar to the Ohmic heating case. There is little dependence of tau_Ee on the heating location provided power deposition occurs inside the q=1 surface; as power deposition moves out of the inversion surface, tau_Ee decreases. The power-induced energy confinement degradation exponent (tau_Ee~PaP) is as usual: alpha_P ~-0.5. As a general trend, central relaxations decrease in amplitude with increasing qa, P_EC, or negative delta, in a situation where the confinement time increases

Recent progress in the upgrade of the TCV EC-system with two 1MW/2s dual-frequency (84/126GHz) gyrotrons

The upgrade of the EC-system of the TCV tokamak has entered in its realization phase and is part of a broader upgrade of TCV. The MW-class dual-frequency gyrotrons (84 or 126GHz/2s/1MW) are presently being manufactured by Thales Electron Devices with the first gyrotron foreseen to be delivered at SPC by the end of 2017. In parallel to the gyrotron development, for extending the level of operational flexibility of the TCV EC-system the integration of the dual-frequency gyrotrons adds a significant complexity in the evacuated 63.5mm-diameter HE11 transmission line system connected to the various TCV low-field side and top launchers. As discussed in [1], an important part of the present TCV-upgrade consists in inserting a modular closed divertor chamber. This will have an impact on the X3 top-launcher which will have to be reduced in size. For using the new compact launcher we are considering employing a Fast Directional Switch (FADIS), combining the two 1MW/126GHz/2s rf-beams into a single 2MW rf-beam