Development of a compact bolometer camera concept for investigation of radiation asymmetries at Wendelstein 7-X.

Power exhaust is one of the central challenges in magnetically confined fusion plasmas. Radiative detachment can be employed to reduce particle and heat fluxes to the divertor target, mitigating divertor damage and erosion. However, accomplishing this for a non-axisymmetric machine such as Wendelstein 7-X is a non-trivial task because of the complex role of transport and plasma-wall interaction in a three-dimensional magnetic field topology. We introduce a new bolometer camera design that can be easily installed in multiple toroidal locations and adapted to the required geometry, providing additional spatial coverage. This can be used to locally enhance tomographic capabilities or to resolve spatial variations of the plasma emissivity. By including these non-uniformities in the total radiated power estimate, global power balance measurements can be improved. We model each bolometer camera using ray tracing. We then analyze the forward-modeled detector response to several physically motivated synthetic emission phantoms with respect to its capability to quantify the local average emissivity. The results prove this concept as a promising asset for the investigation of poloidal and toroidal radiated power asymmetries in Wendelstein 7-X. The first CBC prototypes have undergone development and installation for the next experimental campaign.

Developing a robust sensor for infrared imaging bolometers.

A new type of large area sensor for infrared imaging bolometers has been developed. It replaces the thin and fragile free-standing metal foils, which typically have been used, with a multi-layer coated sapphire (or diamond) substrate. Sapphire is transparent to mid-infrared wavelengths, is robust against transients, and can be thick enough to even be the vacuum window. The primary radiation absorber is still a thin deposited metal layer, but now it is partially insulated from the supporting sapphire substrate by a black (carbon-based) layer, which also acts as a blackbody remitter. Test results indicate 6× more noise equivalent power density (estimated NEPD = 23 W/m2 at 5 ms camera exposure time, foil temperature decay time 60 ms) for a 2 µm gold-coated sapphire disk compared to estimated NEP = 4 W/m2 at 1.8 ms exposure time, with foil decay time 420 ms, for a nominal 2.5 µm thick platinum-free-standing foil.

2D core ion temperature and impurity density measurements with Coherence Imaging Charge Exchange Recombination Spectroscopy (CICERS) at Wendelstein 7-X (invited).

Coherence Imaging Charge Exchange Recombination Spectroscopy (CICERS) is an imaging diagnostic installed in Wendelstein 7-X from which 2D maps of ion temperature (Ti) and impurity density (nZ) are obtained. The improved spatial resolution and coverage, as compared to standard Charge eXchange Recombination Spectroscopy (CXRS), with which these parameters can be assessed, come at the expense of spectral resolution, requiring the development of new strategies to isolate the active charge exchange contribution from passive and Bremsstrahlung radiation. In this work, a new approach based on the modeling of background radiation is presented and applied to the derivation of 2D Ti maps. These are compared to the Ti profiles derived from standard CXRS, which found excellent agreement up to the edge (ρ > 0.8). The CICERS view is implemented in the pyFIDAsim code, which is used to provide further insight into the spatial localization of the radiation as measured by the diagnostic. Moreover, an absolute intensity calibration is carried out, and, coupled with pyFIDAsim, the first 2D nC maps are obtained and validated against CXRS data.

First Observation of a Stable Highly Dissipative Divertor Plasma Regime on the Wendelstein 7-X Stellarator.

For the first time, the optimized stellarator Wendelstein 7-X has operated with an island divertor. An operation regime in hydrogen was found in which the total plasma radiation approached the absorbed heating power without noticeable loss of stored energy. The divertor thermography recorded simultaneously a strong reduction of the heat load on all divertor targets, indicating almost complete power detachment. This operation regime was stably sustained over several energy confinement times until the preprogrammed end of the discharge. The plasma radiation is mainly due to oxygen and is located at the plasma edge. This plasma scenario is reproducible and robust at various heating powers, plasma densities, and gas fueling locations. These experimental results show that the island divertor concept actually works and displays good power dissipation potential, producing a promising exhaust concept for the stellarator reactor line.

Physically principled reflection models applied to filtered camera imaging inversions in metal walled fusion machines.

Ray-tracing techniques are applied to filtered divertor imaging, a diagnostic that has long suffered from artifacts due to the polluting effect of reflected light in metal walled fusion machines. Physically realistic surface reflections were modeled using a Cook-Torrance micro-facet bi-directional reflection distribution function applied to a high resolution mesh of the vessel geometry. In the absence of gonioreflectometer measurements, a technique was developed to fit the free parameters of the Cook-Torrance model against images of the JET in-vessel light sources. By coupling this model with high fidelity plasma fluid simulations, photo-realistic renderings of a number of tokamak plasma emission scenarios were generated. Finally, a sensitivity matrix describing the optical coupling of a JET divertor camera and the emission profile of the plasma was obtained, including full reflection effects. These matrices are used to perform inversions on measured data and shown to reduce the level of artifacts in inverted emission profiles.

Description of complex viewing geometries of fusion tomography diagnostics by ray-tracing.

Ray-tracing techniques are applied to bolometry, a diagnostic where the finite collection volume is particularly sensitive to the machine and detector configuration. A technique is presented that can handle arbitrarily complex aperture and collimator geometries, neglecting reflection effects. Sight lines from the ASDEX Upgrade bolometer foils were ray-traced with a path tracing algorithm, where the optical path is represented by a statistical bundle of ray paths connecting the foil surface with the slit geometry. By using the full 3D machine model for the detector box and first wall, effects such as occlusion and vignetting were included in the calculation of the bolometer's étendue. Inversion matrices calculated with the ray-tracing technique were compared with the more conventional single-ray approach and shown to be naturally more constrained, requiring less regularisation. The two models were tested on a sample radiation scenario, and the common single-ray approximation is shown to be insufficient. These results are particularly relevant for the divertor where strong emission gradients may be present. The technique developed generalises well to arbitrarily complex viewing geometries and collimators, opening up a new design space for bolometer configurations that might not normally have been considered.

Fibrogenic growth factors in encapsulating peritoneal sclerosis.

BACKGROUND: Increased local levels of fibrogenic growth hormones contribute substantially to the process of encapsulating peritoneal sclerosis (EPS) in animal models. METHODS: We analyzed probes from patients with normal kidney function (n = 10), with normal kidney function and inflammation (n = 10), on PD without (n = 10) and with EPS (n = 9). We investigated the degree of fibrosis and the number of vessels and vasculopathy. Additionally, we investigated the expression of NFkappaB, TGFbeta1, TGFbeta1 receptor, TGFbeta2, TGFbeta2 receptor, FGF-BP, CTGF and VEGF by immunohistochemistry. RESULTS: In EPS, we found an exclusive upregulation of VEGF (normal 0, appendicitis 1.0 +/- 1.2, PD 1.7 +/- 1.8 and EPS 5.7 +/- 4.4; p < 0.0001), whereas in PD, CTGF was significantly increased (normal 6.0 +/- 2.8, appendicitis 7.3 +/- 2.5, PD 10.0 +/- 1.8 and EPS 7.3 +/- 2.1; p = 0.0059). The results for the TGFbeta system and NFkappaB were not uniform, in EPS no increases were demonstrable. Vasculopathy was significantly more pronounced in EPS (normal 0.4 +/- 0.5, appendicitis 0.2 +/- 0.3, PD 1.0 +/- 0.7 and EPS 1.6 +/- 1.2; p < 0.0001) than in PD or inflammation (normal 30 +/- 16, appendicitis 82 +/- 48, PD 1,936 +/- 952 and EPS 2,613 +/- 1,209; p < 0.0001), whereas the density of vessels were decreased (normal 125 +/- 114, appendicitis 817 +/- 347, PD 81 +/- 57 and EPS 36 +/- 33; p < 0.0001). CONCLUSIONS: The process of EPS was associated with increased VEGF in the peritoneum. The reduced density of vessels compared with marked fibrosis could point to hypoxia as an inducer.

New facts about encapsulating peritoneal sclerosis as a sequel of long-term peritoneal dialysis - what can we do?

A long lasting peritoneal dialysis (PD) leads to a special disease, so-called encapsulating peritoneal sclerosis (EPS). The hallmarks of the latter stages of the disease are intestinal obstructions and, as a consequence, malnourishment. For the precise diagnosis radiology and pathology are essential. (Triad ''typical clinical picture- typical radiology- typical pathology''.) In the middle of the pathological process of EPS is proliferative fibrosis and sclerosis of the peritoneum that subsequently leads to the assembly of the typical ''cocoon'' and obstruction. In EPS we found in the peritoneum increased amounts of vascular endothelial growth factor (VEGF) fitting the hallmark of increased neoangiogenesis and blood exudates with fibrinous matrix on the peritoneum as a feeding ground for proliferation of fibroblasts. Additionally, the number of mast cells in EPS is decreased and therefore the chymase and other fibrinolytic enzymes. The ''plasma-leak'' hypothesis focuses on fibrin and our findings help to explain most of the pathophysiology. Since the mortality of EPS is still high, emphasis should be laid on preventive treatment. Since glucose and advanced glycation endproducts (AGEs), including glucose degradation products (GDPs), are responsible for fibrosis and sclerosis of the peritoneum, biocompatible peritoneal dialysis solutions with reduced amounts of AGEs and GDPs are recommended. Additionally, a careful monitoring of patients, especially after 5-8 years of PD is very important. In case of the first signs of EPS, cessation of the modality is necessary. Thanks to this approach, most end-stage EPS pictures can be avoided.