Demonstration of reduced neoclassical energy transport in Wendelstein 7-X.

Research on magnetic confinement of high-temperature plasmas has the ultimate goal of harnessing nuclear fusion for the production of electricity. Although the tokamak1 is the leading toroidal magnetic-confinement concept, it is not without shortcomings and the fusion community has therefore also pursued alternative concepts such as the stellarator. Unlike axisymmetric tokamaks, stellarators possess a three-dimensional (3D) magnetic field geometry. The availability of this additional dimension opens up an extensive configuration space for computational optimization of both the field geometry itself and the current-carrying coils that produce it. Such an optimization was undertaken in designing Wendelstein 7-X (W7-X)2, a large helical-axis advanced stellarator (HELIAS), which began operation in 2015 at Greifswald, Germany. A major drawback of 3D magnetic field geometry, however, is that it introduces a strong temperature dependence into the stellarator's non-turbulent 'neoclassical' energy transport. Indeed, such energy losses will become prohibitive in high-temperature reactor plasmas unless a strong reduction of the geometrical factor associated with this transport can be achieved; such a reduction was therefore a principal goal of the design of W7-X. In spite of the modest heating power currently available, W7-X has already been able to achieve high-temperature plasma conditions during its 2017 and 2018 experimental campaigns, producing record values of the fusion triple product for such stellarator plasmas3,4. The triple product of plasma density, ion temperature and energy confinement time is used in fusion research as a figure of merit, as it must attain a certain threshold value before net-energy-producing operation of a reactor becomes possible1,5. Here we demonstrate that such record values provide evidence for reduced neoclassical energy transport in W7-X, as the plasma profiles that produced these results could not have been obtained in stellarators lacking a comparably high level of neoclassical optimization.

An effective sub-quadratic scaling atomic-orbital reformulation of the scaled opposite-spin RI-CC2 ground-state model using Cholesky-decomposed densities and an attenuated Coulomb metric.

An atomic-orbital reformulation of the Laplace-transformed scaled opposite-spin (SOS) coupled cluster singles and doubles (CC2) model within the resolution of the identity (RI) approximation (SOS-RI-CC2) is presented that extends its applicability to molecules with several hundreds of atoms and triple-zeta basis sets. We exploit sparse linear algebra and an attenuated Coulomb metric to decrease the disk space demands and the computational efforts. In this way, an effective sub-quadratic computational scaling is achieved with our ω-SOS-CDD-RI-CC2 model. Moreover, Cholesky decomposition of the ground-state one-electron density matrix reduces the prefactor, allowing for an early crossover with the molecular orbital formulation. The accuracy and performance of the presented method are investigated for various molecular systems.

Impact of Magnetic Field Configuration on Heat Transport in Stellarators and Heliotrons.

We assess the magnetic field configuration in modern fusion devices by comparing experiments with the same heating power, between a stellarator and a heliotron. The key role of turbulence is evident in the optimized stellarator, while neoclassical processes largely determine the transport in the heliotron device. Gyrokinetic simulations elucidate the underlying mechanisms promoting stronger ion scale turbulence in the stellarator. Similar plasma performances in these experiments suggests that neoclassical and turbulent transport should both be optimized in next step reactor designs.

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.

Development of the 174 GHz collective Thomson scattering diagnostics at Wendelstein 7-X.

In this paper, we present the design and commissioning results of the upgraded collective Thomson scattering diagnostic at the Wendelstein 7-X stellarator. The diagnostic has a new radiometer designed to operate between the second and third harmonics of the electron cyclotron emission from the plasma at 171-177 GHz, where the emission background has a minimum and is of order 10-100 eV. It allows us to receive the scattered electromagnetic field with a significantly improved signal-to-noise ratio and extends the set of possible scattering geometries compared to the case of the original instrument operated at 140 GHz. The elements of the diagnostic are a narrowband notch filter and a frequency stabilized probing gyrotron that will allow measuring scattered radiation spectra very close to the probing frequency. Here, we characterize the microwave components applied to the radiometer and demonstrate the performance of the complete system that was achieved during the latest experimental campaign, OP2.1.

Development of the ion cyclotron emission diagnostic for the W7-X stellarator.

An ion cyclotron emission (ICE) diagnostic is prepared for installation into the W7-X stellarator, with the aim to be operated in the 2022 experimental campaign. The design is based on the successful ICE diagnostic on the ASDEX Upgrade tokamak. The new diagnostic consists of four B-dot probes, mounted about 72° toroidally away (one module) from the neutral beam injector, with an unobstructed plasma view. Two of the B-dot probes are oriented parallel to the local magnetic field, aimed to detect fast magnetosonic waves. The remaining two probes are oriented poloidally, with the aim to detect slow waves. The radio frequency (RF) signals picked up by the probes are transferred via 50 Ω vacuum-compatible coaxial cables to RF detectors. Narrow band notch filters are used to protect the detectors from possible RF waves launched by the W7-X antenna. The signal will be sampled with a four-channel fast analog-to-digital converter with 14 bit depth and 1 GSample/s sampling rate. The diagnostic's phase-frequency characteristic is properly measured in order to allow measuring the wave vectors of the picked up waves.

First results from the implementation of the ITER diagnostic residual gas analyzer prototype at Wendelstein 7-X.

Fusion reactors and long pulse fusion experiments heavily depend on a continuous fuel cycle, which requires detailed monitoring of exhaust gases. We have used a diagnostic residual gas analyzer (DRGA) built as a prototype for ITER and integrated it on the most advanced stellarator fusion experiment, Wendelstein 7-X (W7-X). The DRGA was equipped with a sampling tube and assessed for gas time of flight sample response, effects of magnetic field on gas detection and practical aspects of use in a state of the art fusion environment. The setup was successfully commissioned and operated and was used to observe the gas composition of W7-X exhaust gases. The measured time of flight gas response was found to be in the order of a second for a 7 m sample tube. High values of magnetic field were found to affect the partial pressure readings of the DRGA and suggest that additional shielding is necessary in future experimental campaigns.

Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation.

In this paper, we present a method for numerical computation of collective Thomson scattering (CTS). We developed a forward model, eCTS, in the electrostatic approximation and benchmarked it against a full electromagnetic model. Differences between the electrostatic and the electromagnetic models are discussed. The sensitivity of the results to the ion temperature and the plasma composition is demonstrated. We integrated the model into the Bayesian data analysis framework Minerva and used it for the analysis of noisy synthetic data sets produced by a full electromagnetic model. It is shown that eCTS can be used for the inference of the bulk ion temperature. The model has been used to infer the bulk ion temperature from the first CTS measurements on Wendelstein 7-X.

Collective Thomson scattering diagnostic at Wendelstein 7-X.

A Collective Thomson Scattering (CTS) diagnostic is installed at Wendelstein 7-X for ion temperature measurements in the plasma core. The diagnostic utilizes 140 GHz gyrotrons usually used for electron cyclotron resonance heating (ECRH) as a source of probing radiation. The CTS diagnostic uses a quasi-optical transmission line covering a distance of over 40 m. The transmission line is shared between the ECRH system and the CTS diagnostic. Here we elaborate on the design, installation, and alignment of the CTS diagnostic and present the first measurements at Wendelstein 7-X.

[Scleral buckling surgery and pneumatic retinopexy. Techniques, indications and results]. / Skleraeindellende Ablatiochirurgie und pneumatische Retinopexie. Techniken, Indikationen und Ergebnisse.

For many decades, conventional buckling surgery has been the gold standard for treating rhegmatogenous retinal detachment. The surgical technique has not changed markedly during this period; the three main buckling techniques currently used are the radial sponge, segmental sponge, and encircling band. With one of these options, an anatomic success rate of over 90% can be achieved in "simple" forms of retinal detachment. In pseudophakic eyes, however, the primary reattachment rate after buckling procedures is lower. Pneumatic retinopexy, because of its lower success rate, has not found general acceptance in Europe and is used only in selected cases. Concerning the results of the SPR study, many vitreoretinal surgeons were surprised that in the subgroup of phakic eyes, scleral buckling surgery achieved a comparable reattachment rate and better functional results even in this group of patients with complex hole configuration. This gives physicians reason to critically question the current trend of primary vitrectomy even in eyes with uncomplicated preoperative pathology and to reassess scleral buckling surgery. The longer learning curve to perform buckling surgery should be accepted. Because successful repair depends on careful preoperative examination, thorough training in binocular ophthalmoscopy skills with scleral depression should remain an essential part of the surgeon's education.

[Mutations of the frizzled-4 gene. Their impact on medical care of patients with autosomal dominant exudative vitreoretinopathy]. / Mutationen des frizzled-4-gens : ihre bedeutung in der betreuung von familien mit autosomal-dominanter exsudativer vitreoretinopathie.

PURPOSE: Autosomal dominant (familial) exudative vitreoretinopathy (adEVR) is a rare, congenital disease of the retinal vascular system, which may lead to blindness in severely affected eyes. One of the causative disease genes is located on chromosome 11q13-q23 and codes for "frizzled-4" (FZD4), a protein involved in vascular differentiation. METHOD: Examination of two families with adEVR over six and four generations and FZD4 mutation analysis. RESULTS: In family I, 18 examined affected members exhibited a heterozygous missense mutation (p.G492R) in the FZD4 gene. In family II, four examined family members were affected and carried a heterozygous deletion of five nucleotides (c.1286del5). Both mutations are novel and showed 100% penetrance and variable expressivity. CONCLUSIONS: With detection of the "family-specific" FZD4 gene mutation, carriers amongst offspring of affected family members can be identified at an early time. The complete penetrance of FZD4 mutations may justify abandoning repeated examinations of offspring of affected family members, if no mutations were detected in FZD4.

Detection of Treponema pallidum in the vitreous by PCR.

BACKGROUND: Ocular involvement of syphilis still poses a clinical challenge due to the chameleonic behaviour of the disease. As the serodiagnosis has significant limitations, the direct detection of Treponema pallidum (TP) in the vitreous represents a desirable diagnostic tool. METHODS: Real-time polymerase chain reaction (PCR) for the detection of TP was applied in diagnostic vitrectomies of two patients with acute chorioretinitis. Qualitative verification of TP by real-time PCR and melting point analysis according to a modified protocol was ruled out. Patients underwent complete ophthalmological examination with fundus photographs, fluorescein angiography, serological examination, antibiotic treatment and follow-up. RESULTS: In two cases of acute chorioretinitis of unknown origin, real-time PCR of vitreous specimens of both patients provided evidence of TP and was 100% specific. Initial diagnosis of presumed viral retinitis was ruled out by PCR of vitreous specimen. Patients were treated with systemic antibiotics and showed prompt improvement in visual function and resolution of fundus lesions. CONCLUSIONS: With real-time PCR, detection of TP in the vitreous was possible and delivered a sensitive, quick and inexpensive answer to a disease rather difficult to assess. In cases of acute chorioretinitis, the use of PCR-based assays of vitreous specimens in the diagnostic evaluation of patients is advisable. Although syphilitic chorioretinitis is a rare disease, PCR should include search for TP, as diagnostic dilemmas prolong definitive treatment in a sight-threatening disease.

Evaluation of cyclophotocoagulation effects with 1310-nm contact optical coherence tomography.

PURPOSE: The aim of this pilot study was to evaluate whether contact optical coherence tomography (OCT) allows visualization of the effects of cyclophotocoagulation. METHODS: In this pilot study, transscleral contact OCT images (1310-nm wavelength) were generated prior to and immediately after conventional transscleral diode laser cyclophotocoagulation in three eyes of three patients who were suffering from uncontrolled glaucoma. RESULTS: In the region of the ciliary body, transscleral contact OCT revealed two layers: (i) a superficial thick hyperreflective complex representing conjunctiva, the Tenon capsule, episclera, and sclera; and (ii) a thinner hyporeflective layer representing the ciliary body. The ciliary body could be differentiated from the overlying sclera by its marked drop in reflectivity. After cyclophotocoagulation, a marked increase of reflectivity in the treated area of the ciliary body was identifiable. After treatment, the distinct border between the hyperreflective scleral complex disappeared, and the region of the ciliary body appeared hyperreflective. The optical properties of the overlying sclera remained unchanged. On corresponding averaged A-scan images, scleral thickness appeared to be slightly increased, whereas ciliary body thickness remained unchanged. CONCLUSIONS: This pilot study demonstrates the capability of contact OCT for allowing visualization of changes in the ciliary body after transscleral cyclophotocoagulation (TSCPC). Further investigations are planned to clarify the complete significance of these data.

[Late needling with 5-fluorouracil when scarring of filtering bleb seems imminent]. / Late Needling mit 5-Fluorouracil bei drohender Sickerkissenvernarbung.

BACKGROUND: Evaluation of needling and 5-fluorouracil (5-FU) injections more than 4 months after preceding filtration surgery. PATIENTS AND METHOD: Retrospective analysis of 17 eyes in 14 patients who underwent needling of the filtering bleb and administration of 5-FU by injection at least 4 months after trabeculectomy (TE) with mitomycin C (MMC; same surgeon throughout). Complete success was defined as a reduction of intraocular pressure (IOP) by >30% from the baseline value without further medication and, in cases of primary open-angle glaucoma, IOP of 18 mmHg. The mean period of follow-up was 8.1 months (3-24 months). RESULTS: One to four needlings (Ø 1.6) with one to five injections (Ø 3.1) of 5-FU were performed as required according to clinical need an average of 31.3 months (4-108 m) after TE. The mean baseline IOP was 25 mmHg (+/-SD 6.02; median 25 mmHg). After needling and 5-FU injection the mean IOD at the last hospital visit was 13.64 mmHg (+/-SD 5.2, median 13 mmHg; p<0,001). Complete success was achieved in 82.4% of these cases. The mean reduction in IOP was 11.2 mmHg (0-22 mmHg). In the cases with successful outcome (14 of 17 eyes) the mean IOP reduction from baseline was 55%. Three eyes required further treatment. Complications encountered were hyphaema (2 cases), subconjunctival bleeding (1 case) and corneal erosion (3 cases). CONCLUSION: Late needling and injections of 5-FU can restore filtering bleb function even over 4 months after initial surgery. The high success rate and low incidence of complications together with the simple procedure justify regarding this approach as an alternative that can be used before passing on to more invasive interventions.

Secondary paracentral retinal holes following internal limiting membrane removal.

AIM: To report on a new postoperative finding after delamination of the internal limiting membrane (ILM) for the treatment of different macular pathologies. METHODS: Seven patients are described with paracentral retinal holes, all located temporally to the macula, which developed after pars plana vitrectomy and uncomplicated ILM removal for cystoid macular oedema (n = 3), macular pucker (n = 3), and macular hole (n = 1) with the use of indocyanine green (n = 4), trypan blue (n = 1), triamcinolone acetonide (n = 1), or without dye (n = 1). CONCLUSION: The use of dyes has been incriminated in causing iatrogenic damage to the retina. In this series, the new observation of retinal holes in the macular area is thought to be related to the removal of the ILM itself. The authors speculate that ILM delamination may cause a retinal weakening by Müller cell damage; this may be followed by a structural breakdown and, consequently, hole formation.

[Selective retina therapy in patients with diabetic maculopathy]. / Selektive Retina-Therapie bei Patienten mit diabetischer Makulopathie.

Selective Retina Therapy (SRT) is a new laser treatment that selectively targets the retinal pigmen epithelium (RPE). In this study, we treated 39 patients presenting with nonischemic, focal and focal-diffuse diabetic maculopathy with SRT. In the main. the results indicate that SRT had stabilizing effects on visual acuity, angiographic leakage, lipid exudation, and foveal retinal thickness. SRT is safe and is especially useful for treating pathologies that are located close to the fovea, which cannot be treated with conventional argon laser photocoagulation.

Absolute calibration of sniffer probes on Wendelstein 7-X.

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m(2) per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m(2) per MW injected beam power is measured.

A near infra-red video system as a protective diagnostic for electron cyclotron resonance heating operation in the Wendelstein 7-X stellarator.

The Wendelstein 7-X stellarator is a large nuclear fusion device based at Max-Planck-Institut für Plasmaphysik in Greifswald in Germany. The main plasma heating system for steady state operation in W7-X is electron cyclotron resonance heating (ECRH). During operation, part of plama facing components will be directly heated by the non-absorbed power of 1 MW rf beams of ECRH. In order to avoid damages of such components made of graphite tiles during the first operational phase, a near infra-red video system has been developed as a protective diagnostic for safe and secure ECRH operation. Both the mechanical design housing the camera and the optical system are very flexible and respect the requirements of steady state operation. The full system including data acquisition and control system has been successfully tested in the vacuum vessel, including on-line visualization and data storage of the four cameras equipping the ECRH equatorial launchers of W7-X.

N(epsilon)(carboxymethyl)lysin and the AGE receptor RAGE colocalize in age-related macular degeneration.

PURPOSE: To investigate whether glycoxidation products and the receptor for advanced glycation end products (RAGE) are present and colocalize in subfoveal membranes of patients with age-related macular degeneration (ARMD). METHODS: Surgically removed subfoveal fibrovascular membranes from 12 patients, 11 related to ARMD and 1 to an idiopathic membrane, were analyzed for the presence of the glycoxidation product N(epsilon)-(carboxymethyl)lysin (CML), one of the receptors for advanced glycation end products, RAGE, and the activation of NFkB, using immunohistochemistry. RESULTS: CML-like immunoreactivity was found in all ARMD specimens examined adjacent or colocalized with RAGE, but not in the idiopathic membrane. RAGE immunoreactive material was found in CD68-positive cells and in the fibrous matrix. CD68-positive cells and surrounding areas stained for p50, the activated form of NFkB. CONCLUSIONS: These results indicate that glycoxidation products are present in subretinal membranes of patients with ARMD. The concomitant expression of RAGE in these membranes and the finding of activated NFkB is suggestive of an implication of glycoxidation product formation in the pathogenesis of the disease.