Real-time Reflectometry Research Articles

Retinal pigment epithelial responses based on the irradiation density of selective retina therapy.

We evaluated the response of the retinal pigment epithelium (RPE) to high-density (HD) or low-density (LD)-selective retina therapy (SRT) with real-time feedback-controlled dosimetry (RFD) in rabbits. Sixteen eyes of 8 Chinchilla Bastard rabbits underwent SRT with RFD (527-nm wavelength, 1.7-μs pulse duration), using automatically titrated pulse energy, by using optoacoustic dosimetry or real-time reflectometry. Fifty-six 25-μJ SRT, including LD-SRT (1-spot or 2-spot-spacing) and HD-SRT (4-spot, 7-spot, or 9-spot-no-spacing), were applied per eye. Color fundus photography and fundus fluorescein angiography (FFA) were used to confirm SRT spots 1-h post-SRT. Light microscopy and scanning electron microscopy (SEM) were performed at 2-h, 3-day, 7-day, and 1-month post-treatment. We tested 896 spots irradiated by SRT with RFD and confirmed that SRT lesions were adequate, based on invisibility on fundoscopy and visibility on FFA. On SEM, at 2-h post-SRT, flattened RPE cells were observed in the center of the SRT lesion. While normal RPE cells were clearly observed between LD-SRT lesions, healthy RPE cells were rare in HD-SRT lesions at 2-h post-treatment. At 7-day post-SRT, SEM revealed completely restored LD-SRT lesions with small or large RPE cells with microvilli, whereas HD-SRT lesions were covered with RPE cells without microvilli. At 1-month post-SRT, SEM revealed restored RPE cells with microvilli in HD-SRT lesions. On light microscopy, both HD- and LD-SRT lesions were completely restored with adjacent RPE cells and spared photoreceptors at 1-month post-treatment. Although both HD- and LD-SRT lesions had recovered at 1-month post-SRT, LD-SRT lesions healed faster than HD-SRT lesions.

Relaxation of the magnetic state of a ferromagnetic–superconducting layered structure

We have proposed a real-time method of neutron reflectometry. The magnetic state of the Ta/V/FM/Nb/Si ferromagnetic–superconducting system has been analyzed. Relaxation of the inhomogeneous magnetic state with a characteristic time of several hours, which depends on the magnetic field magnitude and temperature, has been observed. The relaxation of the domain structure has changed upon a transition of the V and Nb layers to the superconducting state. It has been concluded that real-time reflectometry data for polarized neutrons are important for determining the origin of magnetism in ferromagnetic–superconducting layered structures.

Real-time reflectometry – An ASDEX Upgrade DCS plugin App for plasma position and shape feedback control

O-mode microwave reflectometry will be used, on ITER and foreseeably on DEMO, to complement the standard magnetic diagnostics for plasma position control. With the preliminary design of ITER's plasma position reflectometers (PPR) presently underway, it is of the utmost interest to test beforehand all possible aspects of this future control application. ASDEX Upgrade (AUG) features a modern, modular and easily adaptable control system, and the only O-mode reflectometry setup capable of probing the plasma at two of the four lines of sight of ITER's PPR (gaps g3 and g6). After the first successful demonstration of plasma position control using reflectometry [1], the diagnostic's hardware was updated to acquire a higher number of signals and to improve its real time (RT) data-processing capabilities. Meanwhile, the system's software was rewritten to implement a pipelined architecture to improve its performance and deterministic behavior. The last stage of this pipeline, used to calculate the relevant control parameters, and synchronize and communicate with the discharge control system (DCS), now uses the new DCS software framework, appearing to the control infrastructure as a modular plug-in RT diagnostic App Process. Herein are discussed the adopted synchronization strategies as well as the gains obtained with this new software implementation, namely in terms of performance, fault tolerance, and measurement rate. Experimental data from control discharges is presented to illustrate the system's operational performance.

Real-time reflectometry measurement validation in H-mode regimes for plasma position control

It has been shown that in H-mode regimes, reflectometry electron density profiles and an estimate for the density at the separatrix can be jointly used to track the separatrix within the precision required for plasma position control on ITER. We present a method to automatically remove, from the position estimation procedure, measurements performed during collapse and recovery phases of edge localized modes (ELMs). Based on the rejection mechanism, the method also produces an estimate confidence value to be fed to the position feedback controller. Preliminary results show that the method improves the real-time experimental separatrix tracking capabilities and has the potential to eliminate the need for an external online source of ELM event signaling during control feedback operation.

Study of optical properties of MoxC1−x films

Metallic optical mirrors are foreseen to be exploited in plasma diagnostic systems in ITER. They will suffer from deposition of impurities like carbon causing marked changes of the reflectivity. In this paper, we have focused on the co-deposition of MoxC1−x films (0⩽x⩽0.61) and have studied the influence of the deposited thin film composition on the optical properties. Deposits were performed by magnetron co-sputtering with argon as process gas in a high vacuum system. In-situ XPS measurements, real time reflectometry, ex-situ spectrophotometry and spectroscopic ellipsometry were used to characterize the resulting layers. Carbide formation was evidenced. As expected, optical constants of the films and reflectivity were found to depend strongly on the film composition. Simulations of the impact of thin film composition on the reflectivity of a molybdenum mirror show how a thin deposited layer can drastically degrade the reflectivity.