E. Veshchev

Influence of stray light on visible spectroscopy for the scrape-off layer in ITER

Since ITER will be a full metallic wall machine, scattered photons from the strong emission in the divertor may distort the emission from the scrape-off layer (SOL). The influence of stray light for visible spectroscopy of H? and Be?I emissions in ITER was investigated with a ray-tracing simulation. It was found that the stray light would be always more than one order of magnitude greater than the real signal intensity for H? emission from the SOL. For Be?I emission, although the situation was better than the cases of H? measurement, the stray light could be much larger than the real signal from the SOL. In ITER, it will inevitably reduce the stray light somehow for visible spectroscopy. The effect of optical dumps embedded on first walls was investigated with the ray-tracing analysis.

ITER diagnostic challenges

ITER will explore a plasma parameter envelope currently not available in tokamaks. This will require a set of diagnostics that can follow this envelope. To implement these diagnostics in a reliable and robust way requires development of current techniques in many areas to make them applicable to ITER: they need to be operable in the ITER environment and satisfy the physics and engineering requirements. In some cases, the exploitation of new techniques will be required. While much work has been carried out in this area, significant further work remains to bring the system to implementation.

Port-Based Plasma Diagnostic Infrastructure on ITER

Abstract The port-based plasma diagnostic infrastructure on ITER is described, including the port plugs, the interspace support structure and port cell structure. These systems are modular in nature with standardized dimensions. The design of the equatorial and upper port plugs and their modules is discussed, as well as the dominant loading mechanisms. The port infrastructure design has now matured to the point that port plugs are now being populated with multiple diagnostics supplied by a number of ITER partners - two port plug examples are given.

Conceptual design of the ITER fast-ion loss detector

A conceptual design of a reciprocating fast-ion loss detector for ITER has been developed and is presented here. Fast-ion orbit simulations in a 3D magnetic equilibrium and up-to-date first wall have been carried out to revise the measurement requirements for the lost alpha monitor in ITER. In agreement with recent observations, the simulations presented here suggest that a pitch-angle resolution of ∼5° might be necessary to identify the loss mechanisms. Synthetic measurements including realistic lost alpha-particle as well as neutron and gamma fluxes predict scintillator signal-to-noise levels measurable with standard light acquisition systems with the detector aperture at ∼11 cm outside of the diagnostic first wall. At measurement position, heat load on detector head is comparable to that in present devices.

Divertor stray light analysis in JET-ILW and implications for the H-α diagnostic in ITER

We report on the first results for the spectrum of divertor stray light (DSL) and the signal-to-background ratio for D-α light emitted from the far SOL and divertor in JET in the recent ITER-like wall (ILW) campaign. The results support the expectation of a strong impact of DSL upon the H-alpha (and Visible Light) Spectroscopy Diagnostic in ITER.

Assessment and Mitigation of Wall Light Reflection in ITER by Ray Tracing

Abstract In ITER, reflection of photons on vacuum vessel will make parasitic signals (stray light) for optical diagnostics. In this study, to estimate and mitigate the effect of the stray light in ITER in a systematic manner, a ray transfer matrix was constructed based on ray tracing calculations for a divertor impurity monitor and charge-exchange recombination spectroscopy (CXRS). It is shown that the allocation of the sources around the strike point and the X-point, where the emission is strong, is important for the model used to build the transfer matrix to effectively mitigate the stray light. The origin of the stray light for the core CXRS is investigated, and a case study to subtract the stray light is shown.

The impact of the fast ion fluxes and thermal plasma loads on the design of the ITER fast ion loss detector

Thermal plasma loads to the ITER Fast Ion Loss Detector are studied for QDT = 10 burning plasma equilibrium using the 3D field line tracing. The simulations are performed for a FILD insertion 9–13 cm past the port plasma facing surface, optimized for fast ion measurements, and include the worst-case perturbation of the plasma boundary and the error in the magnetic reconstruction. The FILD head is exposed to superimposed time-averaged ELM heat load, static inter-ELM heat flux and plasma radiation. The study includes the estimate of the instantaneous temperature rise due to individual 0.6 MJ controlled ELMs. The maximum time-averaged surface heat load is 12 MW/m2 and will lead to increase of the FILD surface temperature well below the melting temperature of the materials considered here, for the FILD insertion time of 0.2 s. The worst-case instantaneous temperature rise during controlled 0.6 MJ ELMs is also significantly smaller than the melting temperature of e.g. Tungsten or Molybdenum, foreseen for the FILD housing.

Integration of diagnostics on ITER

Diagnostics play a very important role in the modern Tokamak where optimum performance is essential. To achieve this, the device must be equipped with reliable and robust sensors and instrumentation that allow the operation envelope to be fully explored. Development of these diagnostics to maintain this reliability is necessary. Further to the development, the systems must be integrated in a way that maintains their performance while simultaneously satisfying the key requirements needed for safety and tokamak operation. ITER will have 50 diagnostics; almost all of which are utilized primarily for the real-time operation of the tokamak. While there is still much work to do, to date, significant progress has been made in the development of these systems. The work load for the developments is shared across all the ITER partners. This paper focuses on the challenges for the integration of the systems.