Search

The plasma diagnostic and control (D&C) system for a future tokamak demonstration fusion reactor (DEMO) will have to provide reliable operation near technical and physics limits, while its front-end components will be subject to strong adverse effects within the nuclear and high temperature plasma environment. The ongoing developments for the ITER D&C system represent an important starting point for progressing towards DEMO. Requirements for detailed exploration of physics are however pushing the ITER diagnostic design towards using sophisticated methods and aiming for large spatial coverage and high signal intensities, so that many front-end components have to be mounted in forward positions. In many cases this results in a rapid aging of diagnostic components, so that additional measures like protection shutters, plasma based mirror cleaning or modular approaches for frequent maintenance and exchange are being developed. Under the even stronger fluences of plasma particles, neutron/gamma and radiation loads on DEMO, durable and reliable signals for plasma control can only be obtained by selecting diagnostic methods with regard to their robustness, and retracting vulnerable front-end components into protected locations. Based on this approach, an initial DEMO D&C concept is presented, which covers all major control issues by signals to be derived from at least two different diagnostic methods (risk mitigation). [ABSTRACT FROM AUTHOR]

Optical lifetime of the first mirror is a critical issue for the ITER upper-port-plug core-charge-exchange-spectroscopy diagnostic. A fast shutter is engaged to protect the mirror from depositions between measurements. The prototype shutter will be examined in a test vacuum vessel that is now under development in Forschungszentrum Jülich, Germany. Being located near the plasma, the shutter operates under severe thermal and electromagnetic (EM) loads. The multifield analyses conducted for the shutter are presented in this paper. Since the fast shutter can operate within 0.7 s, its static structural analysis should be accompanied by dynamic studies. This paper gives details about the numerical strategy used for a multifield ANSYS modeling of a complex structure. The shutter structural performance under the service, thermal, and EM loadings is in line with the requirements. A solution for a problem of high local thermostresses revealed by the analysis is proposed. Problems connected with other possible port-plug–shutter layouts are discussed. [ABSTRACT FROM PUBLISHER]

Abstract: The ITER core charge exchange recombination spectroscopy (core CXRS) diagnostic system is designed to provide experimental access to various measurement quantities in the ITER core plasma such as ion densities, temperatures and velocities. The implementation of the approved CXRS diagnostic principle on ITER faces significant challenges: First, a comparatively low CXRS signal intensity is expected, together with a high noise level due to bremsstrahlung, while the requested measurement accuracy and stability for the core CXRS system go far beyond the level commonly achieved in present-day fusion experiments. Second, the lifetime of the first mirror surface is limited due to either erosion by fast particle bombardment or deposition of impurities. Finally, the hostile technical environment on ITER imposes challenging boundary conditions for the diagnostic integration and operation, including high neutron loads, electro-magnetic loads, seismic events and a limited access for maintenance. A brief overview on the R&D and design activities for the core CXRS system is presented here, while the details are described in parallel papers. [Copyright &y& Elsevier]

• EU-DEMO relies on the same plasma scenario as ITER, since this minimizes the risks in the extrapolation. • However, there are some ITER solutions which are not applicable in a DEMO reactor. • This work discusses the DEMO-physics challenges which require a different approach than ITER. • These concern: control of radiative instabilities, divertor detachment control, sawteeth control and adoption of ELM-free regimes. For electricity producing tokamak fusion reactors like EU-DEMO, it is prudent to choose a plasma scenario close to the ITER baseline, where the largest amount of experimental evidence is available. Nevertheless, there are some aspects in which ITER and EU-DEMO have to differ, as the simple exercise of up-scaling from ITER to a larger device is constrained both by physical nonlinearities and by technological limits. In this work, relevant differences between ITER and the current EU-DEMO baseline in terms of plasma scenario are discussed. Firstly, EU-DEMO is assumed to operate with a very large amount of radiative power originating both from the scrape-off layer and, markedly, from the core. This radiation level is obtained by means of seeded impurities, whose presence significantly affects many aspects of the scenario itself, especially in terms of transient control. Secondly, because of the need of breeding tritium, the EU-DEMO wall is less robust than the ITER one. This implies that every off-normal interruption of the plasma discharge, for example in presence of a divertor reattachment, cannot rely on fast-shutdown procedures finally triggering a loss of plasma control at high current, but other strategies need to be developed. Thirdly, the ITER method for the control of the so-called sawteeth (ST) has been shown to be too expensive in terms of auxiliary power requirements, thus other solutions have to be explored. Finally, the problem of actively mitigating, or suppressing, the Edge Localised Modes (ELMs) has recently increased the interest on naturally ELM-free regimes (like QH-mode, I-mode, and also negative triangularity) for EU-DEMO, thus increasing the needs for ELM mitigation or suppression with respect to the approach adopted in ITER. [ABSTRACT FROM AUTHOR]

Abstract: The upper port #3 in ITER will be used by the core Charge Exchange Recombination Spectroscopy (core CXRS) to channel out light from the inside of the vacuum vessel. Recent research about the lifetime of the first two mirrors and changes in the upper port plug geometry initiated further investigations into possible alternative system design concepts. Two new variants of the optical system were chosen for further investigation. The different sub-systems of core CXRS such as optical system, retractable tube and shutter are introduced together with their impact on the system design and their interactions. Space constraints originating from the envelope of the UPP and requirements emerging from the ITER environment such as remote handling and other maintenance considerations are also included in the investigation. Alternative system concepts taking the constraints into account are presented and discussed. Implications for further design work on the subsystems are derived from the results. [Copyright &y& Elsevier]

Abstract: Since the first feasibility studies of active beam spectroscopy on ITER in 1995 the proposed diagnostic has developed into a well advanced and mature system. Substantial progress has been achieved on the physics side including comprehensive performance studies based on an advanced predictive code, which simulates active and passive features of the expected spectral ranges. The simulation has enabled detailed specifications for an optimized instrumentation and has helped to specify suitable diagnostic neutral beam parameters. Four ITER partners share presently the task of developing a suite of ITER active beam diagnostics, which make use of the two 0.5MeV/amu 18MW heating neutral beams and a dedicated 0.1MeV/amu, 3.6MW diagnostic neutral beam. The IN ITER team is responsible for the DNB development and also for beam physics related aspects of the diagnostic. The RF will be responsible for edge CXRS system covering the outer region of the plasma (1>r/a>0.4) using an equatorial observation port, and the EU will develop the core CXRS system for the very core (0

Highlights: [•] We integrated a fluctuation beam emission measurement into the ITER CXRS prototype spectrometer. [•] The fluctuation BES measurement provided data at TEXTOR that agree well with the simulation based on the Simulation Of Spectra package. [•] The same simulation method has been used to evaluate the feasibility of a fluctuation BES measurement on the ITER DNB using the CXRS periscopes. [Copyright &y& Elsevier]

Abstract: Laser-based techniques in combination with spectroscopy are proposed for in situ characterization of the first wall in ITER. Three laser-based diagnostics, laser-induced desorption spectroscopy (LIDS), laser-induced ablation spectroscopy (LIAS) and laser-induced breakdown spectroscopy (LIBS) are under investigation in Forschungszentrum Jülich (FZJ) to determine the stored amount of tritium (“tritium retention”) and to characterize the layer deposition on the wall components in fusion devices (thickness, composition, growth rate). Demonstration experiments for LIDS, LIAS and LIBS were performed on TEXTOR and in the laboratory. An advanced ITER prototype version of these diagnostics is currently under preparation on TEXTOR based on coaxial laser beam injection and light detection with the possibility to scan certain wall areas in TEXTOR. It has been demonstrated that LIDS is a reliable diagnostic for the absolute determination of hydrogen isotopes retained on first wall components on the basis of a single laser shot in combination with local Hα spectroscopy. LIAS and LIBS are presently under investigation with respect to their capability to monitor reliably in situ the thickness and composition of deposited layers on the first wall during and between plasma pulses, respectively. A preliminary design and the main parameters for the application of these methods at ITER are discussed. [Copyright &y& Elsevier]