Electron Cyclotron Launcher Research Articles

Electromagnetic analysis on conceptual design of the EU DEMO EC equatorial laucher

The EU DEMO Tokamak is foreseen to be equipped with Electron Cyclotron (EC) launching systems for plasma heating, MHD control and thermal instability suppression. Up to six launchers will be installed into equatorial ports with the aim to inject a maximum of 130 MW millimeter wave power at dedicated positions into the plasma. The integrated design of the EC launcher is made of two equatorial port plug modules mounted into the equatorial port extensions of the vacuum vessel that mainly serve as housing for the eight optical system´s mirrors.To guarantee reliable operation of the launcher, in the latest year, a structural system has been designed which provides secure fastening and alignment of the optical components, sufficient heat dissipation and protection of sensitive areas against nuclear loads from neutrons by adequate shielding capability.To prove the fastening concept of the port plug modules and mirrors, a set of mechanical loads acting on these components is essential. EM loads caused by plasma instabilities are major contributions of mechanical load set for components close to the plasma.The present paper describes the EM analysis carried out to support the assessment of the pre-conceptual design solution. A dedicated Finite Element (FE) model was developed using ANSYS® solid236 element type (edge-based formation). Transient electromagnetic analysis was performed under centered plasma disruption event. Total force and moment due to Lorentz and ferromagnetic loads on the EC launcher port plugs and mirrors were computed. The resulting EM loads can be used for the preliminary design assessment.

Main Nuclear Responses of the DEMO Tokamak with Different In-Vessel Component Configurations

Research and development of the DEMOnstration power plant (DEMO) breeder blanket (BB) has been performed in recent years based on a predefined DEMO tritium breeding ratio (TBR) requirement, which determines a loss of wall surface due to non-breeding in-vessel components (IVCs) which consume plasma-facing wall surface and do not contribute to the breeding of tritium. The integration of different IVCs, such as plasma limiters, neutral beam injectors, electron cyclotron launchers and diagnostic systems, requires cut-outs in the BB, resulting in a loss of the breeder blanket volume, TBR and power generation, respectively. The neutronic analyses presented here have the goal of providing an assessment of the TBR losses associated with each IVC. Previously performed studies on this topic were carried out with simplified, homogenized BB geometry models. To address the effect of the detailed heterogeneous structure of the BBs on the TBR losses due to the inclusion of the IVCs in the tokamak, a series of blanket geometry models were developed for integration in the latest DEMO base model. The assessment was performed for both types of BBs currently developed within the EUROfusion project, the helium-cooled pebble bed (HCPB) and water-cooled lead–lithium (WCLL) concepts, and for the water-cooled lead and ceramic breeder (WLCB) hybrid BB concept. The neutronic simulations were performed using the MCNP6.2 Monte Carlo code with the Joint Evaluated Fission and Fusion File (JEFF) 3.3 data library. For each BB concept, a 22.5° toroidal sector of the DEMO tokamak was developed to assess the TBR and nuclear power generation in the breeder blankets. For the geometry models with the breeder blanket space filled only with blankets without considering IVCs, the results of the TBR calculations were 1.173, 1.150 and 1.140 for the HCPB, WCLL and WLCB BB concepts, respectively. The TBR impact of all IVCs and the losses of the power generation were estimated as a superposition of the individual effects.

Shutdown dose rates in-cryostat outside the EU-DEMO vacuum vessel

Future fusion reactors using deuterium–tritium fuel will exhibit high fluences of high-energy neutrons inside and around the reactor vacuum vessel (VV). As well as causing material damage, fusion neutrons will activate materials, the decay of which leads to radiation fields in and around the reactor after shutdown. Gamma-ray emission from activated materials is a particular radiological hazard during periods of reactor shutdown. This must be accounted for in the design of the reactor shielding to ensure that risks are reduced as low as reasonably achievable.Recent neutronics work has evaluated the shutdown dose rates (SDDRs) in the EU DEMOnstration power plant (DEMO) around the ports and throughout the cryostat, incorporating prospective shielding improvements to the VV and ports. Prior to the proposed shielding design improvements, calculations for the model including the helium-cooled pebble bed (HCPB) blanket showed that radiation leakage through the blanket and VV leads to biological-equivalent SDDRs (following 12 days’ decay) above 103μSv/h throughout the cryostat, ignoring additional contribution from radiation streaming through the port openings. Inclusion of the proposed VV changes reduces this dose rate to below 100 μSv/h. The work finds an approximate order-of-magnitude reduction in SDDR throughout the cryostat when all proposed shielding improvements are applied, leading to dose rates in the cryostat in the range of hundreds to thousands of μSv/h for the full model. The work shows that to further reduce dose rates inside the cryostat, improving the shielding performance of the ports is required, with particular emphasis on the lower port and the equatorial electron–cyclotron launcher which currently dominate the dose rates.

High power mm-wave loss measurements of ITER ex-vessel waveguide components at the FALCON test facility at the Swiss Plasma Center

Many future fusion devices will rely heavily, if not solely, on electron cyclotron (EC) heating subsystems to provide bulk heating, instability control (neoclassical tearing mode (NTM) stabilization), and thermal instability control. Efficient use of the installed heating power (gyrotrons) requires low-loss transmission of the power over 100s of meters since the mm-wave sources need to be installed where the stray magnetic field has a small amplitude. Transmission lines are used to propagate the mm-wave power over this long distance. Quasi-optical techniques (mirrors) are used at W7X and are planned for DTT, for example. Guided components are installed at DIII-D, TCV and elsewhere and are planned at JT60SA and ITER. High power test facilities exist to evaluate the power transmission of assemblies of guided components (transmission lines). The European test facility FALCON was setup by Switzerland and Fusion for Energy (F4E) in Lausanne Switzerland at the Swiss Plasma Center (SPC) in the Ecole Polytechnique Fédérale de Lausanne (EPFL). Operations are funded through a framework contract with F4E. SPC operates the facility. Two ITER-class 170GHz gyrotrons are housed within the facility and used to evaluate the thermal behaviour of components provided by various ITER partners. Loss measurements are presented for miter bends and waveguides of several materials at two different diameters. The results are used to model the expected losses in the ITER ex-vessel waveguides (EW) of all five EC launchers.

Preconceptual Design of the Port Cell Section for the EU DEMO Equatorial EC System

The EU demonstration power plant (DEMO) Tokamak will be equipped with an electron cyclotron (EC) system for plasma heating and magnetohydrodynamic (MHD) control. Up to six launchers will be installed into equatorial ports with the aim to inject maximum 130-MW millimeter-wave (mm-wave) power at dedicated positions into the plasma. The mm-waves will be generated in gyrotrons placed in a distinct building at distant location. From this gyrotron hall, a combined transmission line (TL) system of quasi-optical multibeam mirrors and individual waveguides (WGs) will propagate the mm-waves into the tokamak building. That followed, an optical system, composed of miter bends, diamond windows, valves, and microwave bellows, connects the TL through the gallery and the port cell with the EC launchers. This article presents the preconceptual computer-aided design (CAD) of this latter section of the EC system. Based on its general scheme and the given WG trajectories, the model takes into account the available space in the port cell with respect to required clearance for supply systems, assembly, and maintenance. At the preconceptual state, the design includes CAD models of all relevant mm-wave components in realistic dimensions at a level of details, appropriate to demonstrate the feasibility of the concept.

Conceptual design studies of the Electron Cyclotron launcher for DEMO reactor

A demonstration fusion power plant (DEMO) producing electricity for the grid at the level of a few hundred megawatts is included in the European Roadmap [1]. The engineering design and R&D for the electron cyclotron (EC), ion cyclotron and neutral beam systems for the DEMO reactor is being performed by Work Package Heating and Current Drive (WPHCD) in the framework of EUROfusion Consortium activities. The EC target power to the plasma is about 50 MW, in which the required power for NTM control and burn control is included. EC launcher conceptual design studies are here presented, showing how the main design drivers of the system have been taken into account (physics requirements, reactor relevant operations, issues related to its integration as in-vessel components). Different options for the antenna are studied in a parameters space including a selection of frequencies, injection angles and launch points to get the best performances for the antenna configuration, using beam tracing calculations to evaluate plasma accessibility and deposited power. This conceptual design studies comes up with the identification of possible limits, constraints and critical issues, essential in the selection process of launcher setup solution.

Overview of the FTU results

Since the 2012 IAEA-FEC Conference, FTU operations have been largely devoted to runaway electrons generation and control, to the exploitation of the 140 GHz electron cyclotron (EC) system and to liquid metal limiter elements. Experiments on runaway electrons have shown that the measured threshold electric field for their generation is larger than predicted by collisional theory and can be justified considering synchrotron radiation losses. A new runaway electrons control algorithm was developed and tested in presence of a runaway current plateau, allowing to minimize the interactions with plasma facing components and safely shut down the discharges. The experimental sessions with 140 GHz EC system have been mainly devoted to experiments on real-time control of magnetohydrodynamic (MHD) instabilities using the new EC launcher with fast steering capability. Experiments with central EC injection have shown the onset of 3/2 and 2/1 tearing modes, while EC assisted breakdown experiments have been focused on ITER start-up issues, exploring the polarization conversion at reflection from inner wall and the capability to assure plasma start-up even in presence of a large stray magnetic field. A new actively cooled lithium limiter has been installed and tested. The lithium limiter was inserted in the scrape-off layer, without any damage to the limiter surface. First elongated FTU plasmas with EC additional heating were obtained with the new cooled limiter. Density peaking and controlled MHD activity driven by neon injection were investigated at different plasma parameters. A full real-time algorithm for disruption prediction, based on MHD activity signals from Mirnov coils, was developed exploiting a large database of disruptions. Reciprocating Langmuir probes were used to measure the heat flux e-folding length in the scrape-off layer, with the plasma kept to lay on thea internal limiter to resemble the ITER start-up phase. New diagnostics were successfully installed and tested, as a diamond probe to detect Cherenkov radiation produced by fast electrons and a gamma camera for runaway electrons studies. Laser induced breakdown spectroscopy measurements were performed under vacuum and with toroidal magnetic field, so demonstrating their capability to provide useful information on the surface elemental composition and fuel retention in present and future tokamaks, such as ITER.

On the criteria guiding the design of the upper electron-cyclotron launcher for ITER

Electron cyclotron waves injected from an antenna located in the upper part of the vessel will be employed in ITER to control MHD instabilities, particularly neoclassical tearingmodes (NTMs). The derivation of the NTM stabilization criteria used up to now to guide the optimization of the launcher is reviewed in this paper and their range of validity elucidated. Possible effects leading to a deterioration of the predicted performance through a broadening of the EC deposition profile are discussed. The most detrimental effect will likely be the scattering of the EC beams from density fluctuations, resulting in a beam broadening in the 100% range. The combined impact of these effects with that of beam misalignment (with respect to the targeted surface) is discussed for a time slice of the standard Q = 10 H-mode scenario.

On recent results in the modelling of neoclassical-tearing-mode stabilization via electron cyclotron current drive and their impact on the design of the upper EC launcher for ITER

Electron cyclotron wave beams injected from a launcher placed in the upper part of the vessel will be used in ITER to control MHD instabilities, in particular neoclassical tearing modes (NTMs). Simplified NTM stabilization criteria have been used in the past to guide the optimization of the launcher. Their derivation is reviewed in this paper and their range of applicability clarified. Moreover, possible effects leading to a deterioration of the predicted performance are discussed. Particularly critical in this context is the broadening of the electron-cyclotron (EC) deposition profiles. It is argued that the most detrimental effect for ITER is likely to be the scattering of the EC beams from density fluctuations due to plasma turbulence, resulting in a beam broadening by about a factor of two. The combined impact of these effects with that of beam misalignment (with respect to the targeted surface) is investigated by solving the Rutherford equation in a form that retains the most relevant terms. The perspectives for NTM stabilization in the Q = 10 ITER scenario are discussed.

Preliminary design of the ITER ECH Upper Launcher

The design of the ITER electron cyclotron launchers recently reached the preliminary design level - the last major milestone before design finalization. The ITER ECH system contains 24 installed gyrotrons providing a maximum ECH injected power of 20MW through transmission lines towards the tokamak. There are two EC launcher types both using a front steering mirror; one equatorial launcher (EL) for plasma heating and four upper launchers (UL) for plasma mode stabilization (neoclassical tearing modes and the sawtooth instability). A wide steering angle range of the ULs allows focusing of the beam on magnetic islands which are expected on the rational magnetic flux surfaces q=1 (sawtooth instability), q=3/2 and q=2 (NTMs).In this paper the preliminary design of the ITER ECH UL is presented, including the optical system and the structural components. Highlights of the design include the torus CVD-diamond windows, the frictionless, front steering mechanism and the plasma facing blanket shield module (BSM). Numerical simulations as well as prototype tests are used to verify the design

Hardware and software architecture for the integration of the new EC waves launcher in FTU control system

The role of high power electron cyclotron (EC) waves in controlling magnetohydrodynamic (MHD) instabilities in tokamaks has been assessed in several experiments, exploiting the physical effects induced by resonant heating and current drive. Recently a new EC launcher, whose main goal is controlling tearing modes and possibly preventing their onset, is being implemented on FTU. So far most of the components of the launcher control strategy have been realized and successfully tested on plasma experiments. Nevertheless the operations of the new launcher must be completely integrated into the existing one, and to FTU control system. This work deals with this final step, proposing a hardware and software architecture implementing up to date technologies, to achieve a modular and effective control strategy well integrated into a legacy system.The slow control system of the new EC launcher is based on a Siemens S7 Programmable Logic Controller (PLC), integrated into FTU control system supervisor through an EPICS11EPICS – Experimental Physics and Industrial Control System [1]. input output controller (IOC) and an in-house developed Channel Access client application creating an abstraction layer that decouples the IOC and the PLC from the FTU Supervisor software. This architecture could enable a smooth migration to an EPICS-only supervisory control system.The real time component of the control system is based on the open source MARTe22MARTe – Multi-Threaded Application Real-Time Executor [2]. framework relying on a Linux real time cluster, devoted to the detection of MHD instabilities and the calculation of the injection angles and the time reference for the radiofrequency power enable commands for the EC launcher.

Manufacturing studies of double wall components for the ITER EC H&CD upper launcher

To counteract plasma instabilities, Electron Cyclotron Launchers will be installed in four of the ITER Upper Ports. The structural system of an EC Upper Launcher accommodates the MM-wave-components and has to meet strong demands on alignment, removal of nuclear heat loads, mechanical strength and nuclear shielding. The EC Upper Launcher has successfully undergone the Preliminary Design Review in 2009 and is now in the final design phase. Nuclear heat loads from 0.1W/cm3 up to 0.8W/cm3 will affect the front area of the launcher main frame. To guarantee save and homogenous removal of those heat loads, the front part of the launcher main frame is designed as a double wall steel-casing with cooling channels inside the shell structure. To finalize the design of this double wall component, the main emphasis is now to define the cooling channels geometry and to identify the optimum manufacturing route to assure adequate flow of coolant and sufficient mechanical strength in compliance with required dimension tolerances and quality of the welds. Several manufacturing options have been investigated and were evaluated by computational analysis and fabrication of pre-prototypes. To come to a final design, the most promising route will be chosen to manufacture a full-size mock-up of the double wall main frame. It will be tested at the KIT Launcher Handling Test facility to check the compliance with the design goals related to geometrical accuracy and thermo-hydraulic characteristics. This paper describes the design and the manufacturing routes of the prototypic double wall main frame.

In vessel characterization and first power tests on plasma of the Real-Time controllable EC launcher on FTU Tokamak

The Electron Cyclotron (EC) fast launcher for real time control experiments has been installed on FTU and characterized to be fully integrated in a real-time MHD control module under development. The launcher scheme is based on a two module sys- tem, symmetric with respect to the equatorial plane of FTU, with a front steering concept and the launched beams are real-time controllable both in poloidal and toroidal directions. Specific design parameters, defined by the FTU MHD dynamics (typically island size and q profile changes), are the beam dimensions with zooming capabilities, the steering range and mirror speed with the most demanding requirement on poloidal speed of the Steering Mirror (SM) = 1 in 10 ms. A set of tests has been done to verify the system perfor- mance. High power tests of the launcher have been done on a 500 kA, 0.5 10 20 m -3 and 5.3 T plasma with 2 300 kW of EC power delivered to the plasma. The steering mechanism was tested under the automatic control system and showed a dynamic response in line with the requirements. Results of these tests will be presented in the paper.

Low power tests on the new front steering EC launcher for FTU

Abstract A new electron cyclotron (EC) antenna for real time control experiments on FTU tokamak has been tested at IFP-CNR laboratory. mm-Wave characterization was performed at the operating frequency of 140 GHz with low power measurements, primarily to test the internal optics of the launcher in terms of focusing properties and beam directivity. The antenna is devoted to the injection of high power EC waves in different working configurations using a front steering setup. The beam direction is controlled with a fast mirror (steerable both toroidally and poloidally) and the available launching angles have been determined to fix the steering mirror working space. Beam dimension can also be controlled, using a sliding structure in the plug-in system, equipped with a focusing mirror that provides zooming capabilities. This paper contains results of low power tests performed on the antenna in order to characterize the launcher in its quasi-optical design. Beams are found to be slightly astigmatic (maximum ratio w y / w x = 1.1 ) and with an expected beam radius in the plasma ranging from 18.6 to 26.0 mm due to cited zooming effects. Additional beam patterns and linear scans of the launched mm-wave power for different injection angles have been measured, in some cases in realistic conditions (using a mock-up of the FTU port provided with metallic side-walls) to evaluate diffraction and beam truncation effects.

Progress of ITER equatorial electron cyclotron launcher design for physics optimization and toward final design

The design of the equatorial electron cyclotron (EC) launcher has advanced toward a more reliable and manufacturable final design. The modification to quasi-optical layout of the millimeter wave transmission line leads to the launcher design being reliable and more realistic toward the final design and the cost reduction. It is proposed that one of three beam rows of the launcher is flipped so that the EC power enables to contribute the counter-EC current drive based on the ITER physics requirement. In addition, a poloidal beam tilt angle of 5° has been introduced in the top and bottom beam row so that all beams can access from on axis to near mid-radius. These design modifications render the EC system more flexible to adapt the needs of advanced ITER physics experiments. It is preliminarily estimated that the nuclear shielding capability of the present modified design satisfies the neutron flux criterion, but the shut down dose rate of γ-ray is slightly higher than the criterion.

Manufacturing studies of structural components for the ITER EC upper launcher

To counteract plasma instabilities, electron cyclotron launchers will be installed in four of the ITER upper ports. An EC launcher consists of a structural system which accommodates the MM-wave-components and has to meet demands on precise alignment, sufficient removal of nuclear heat loads, mechanical strength and proper nuclear shielding. The structural system consists of the Blanket Shield Module (BSM) and the Mainframe. Depending on the expected heat loads, the launcher components are designed as double-wall or single-wall elements, connected by massive flanges. Double-wall segments feature narrow cooling gaps with stiffening ribs between stainless steel shells. Single-wall segments consist of welded stainless steel plates with substantial material thickness. To investigate industrial manufacturing routes, characteristic sections of the BSM and the Mainframe were addressed in detail. To identify the optimum manufacturing strategy for double-wall components, three different concepts, namely HIP (Hot Isostatic Pressing), brazing and machining were studied and a total of four mock-ups of double-wall components were produced. Also for single-wall components appropriate manufacturing routes were investigated, optimum production parameters were determined and typical segments were manufactured. These prototypes are under study at the FZK Launcher Handling Test facility (LHT) where various ITER operating conditions can be simulated. Analyses and test series related to feasibility, prevention of residual stresses, contour accuracy, thermo-hydraulic behavior and also economical aspects were performed.

Real time control of plasmas and ECRH systems on TCV

Developments in the real time control hardware on Tokamak à Configuration Variable (TCV) coupled with the flexibility of plasma shaping and electron cyclotron (EC) heating and current drive actuators are opening many opportunities to perform real time experiments and develop algorithms and methods for fusion applications. The ability to control magnetohydrodynamic instabilities is particularly important for achieving high performance fusion plasmas and EC is envisaged as a key actuator in maintaining high performance. We have successfully demonstrated control of the sawtooth instability using the EC launcher injection angle to modify the current profile around the q =1 surface. This paper presents an overview of recent real time control experiments on TCV, developments in the hardware and algorithms together with plans for the future.

Electron Cyclotron Heating for W7-X: Physics and Technology

The Wendelstein 7X (W7-X) stellarator (R = 5.5 m, a = 0.55 m, B < 3.0 T), which at present is being built at Max-Planck-Institut für Plasmaphysik, Greifswald, aims at demonstrating the inherent steady-state capability of stellarators at reactor-relevant plasma parameters. A 10-MW electron cyclotron resonance heating (ECRH) plant with continuous-wave (cw) capability is under construction to meet the scientific objectives. The physics background of the different heating and current drive scenarios is presented. The expected plasma parameters are calculated for different transport assumptions. A newly developed ray-tracing code is used to calculate selected reference scenarios and optimize the electron cyclotron launcher and in-vessel structure. Examples are discussed, and the technological solutions for optimum wave coupling are presented. The ECRH plant consists of ten radio-frequency (rf) modules with 1 MW of power each at 140 GHz. The rf beams are transmitted to the W7-X torus (typically 60 m) via two open multibeam mirror lines with a power-handling capability, which would already satisfy the ITER requirements (24 MW). Integrated full-power, cw tests of two rf modules (gyrotrons and the related transmission line sections) are reported, and the key features of the gyrotron and transmission line technology are presented. As the physics and technology of ECRH for both W7-X and ITER have many similarities, test results from the W7-X ECRH may provide valuable input for the ITER-ECRH plant.

Progress on Design and Development of ITER Equatorial Launcher: Analytical Investigation and R&D of the Launcher Components for the Design Improvement

Progress on design of an International Thermonuclear Experimental Reactor (ITER) equatorial electron cyclotron launcher with analytical and research and development studies of the components is described. The modified design of the front shield module is proposed with electromagnetic and structure analysis. The analytical investigation of the modified steering mirror design shows that maximum temperature and stress intensity are 289°C and 336 MPa on the mirror surface (copper alloy) and the inner surface of the cooling tube (Type 316 stainless steel) in the mirror, respectively. Maximum stress intensity of the spiral tube to feed cooling water to the steering mirror is calculated to be 139 MPa. These values are less than the allowable level. High heat flux irradiation experiments of the mirror mock-up and fatigue tests of the spiral tube were carried out, and their results proved that the concept of the steering mirror structure was feasible. The results on neutron irradiation tests of the composing materials for an ultrasonic motor and the alternatives such as polyimide and liquid crystal polymer indicate that the motor with those materials is available for the ITER launcher. The remote maintenance scheme of the launcher, which corresponded one-to-one with the fabrication scenario, was also introduced. A “front-access scheme” and a “rear-access scheme” are considered, and their feasibilities are discussed.

Design Performance of Front Steering-Type Electron Cyclotron Launcher for ITER

The performance of a front steering (FS)-type electron cyclotron launcher designed for the International Thermonuclear Experimental Reactor (ITER) is evaluated with a thermal, electromagnetic, and nuclear analysis of the components; a mechanical test of a spiral tube for the steering mirror; and a rotational test of bearings. The launcher consists of a front shield and a launcher plug where three movable optic mirrors to steer incident multimegawatt radio-frequency beam power, waveguide components, nuclear shields, and vacuum windows are installed. The windows are located behind a closure plate to isolate the transmission lines from the radioactivated circumstance (vacuum vessel). The waveguide lines of the launcher are doglegged to reduce the direct neutron streaming toward the vacuum windows and other components. The maximum stresses on the critical components such as the steering mirror, its cooling tube, and the front shield are less than their allowable stresses. It was also identified that the stress on the launcher, which yielded from electromagnetic force caused by plasma disruption, was a little larger than the criteria, and a modification of the launcher plug structure was necessary. The nuclear analysis result shows that the neutron shield capability of the launcher satisfies the shield criteria of the ITER. It concludes that the design of the FS launcher is generally suitable for application to the ITER.