A field programmable gate array based Langmuir probe system for measurement of plasma parameters at 500 kHz in a high-power impulse magnetron sputtering plasma

By utilizing Field Programmable Gate Arrays in a configuration similar to that of the Mirror Langmuir Probe, it is possible to bias a single probe at three precise voltages in sequence. These voltages can be dynamically adjusted in real-time based on the measured plasma electron temperature to ensure the transition region is always sampled. The first results have been obtained by employing this method and have generated real-time outputs of electron temperature, ion saturation current, and floating potential on a low temperature pulsed-DC magnetron at 500 kHz. These results are in good agreement with the analysis of a conventionally swept Langmuir probe. This probe is designed with the intention of being implemented on MAST-U to aid in the study of exhaust physics and enable further investigation into filamentary behavior.

The digital mirror Langmuir probe: Field programmable gate array implementation of real-time Langmuir probe biasing

High bandwidth, high spatial resolution measurements of electron temperature, density, and plasma potential are valuable for resolving turbulence in the boundary plasma of tokamaks. While conventional Langmuir probes can provide such measurements, either their temporal or spatial resolution is limited: the former by the sweep rate necessary for obtaining I-V characteristics and the latter by the need to use multiple electrodes, as is the case in triple and double probe configurations. The Mirror Langmuir Probe (MLP) bias technique overcomes these limitations by rapidly switching the voltage on a single electrode cycling between three bias states, each dynamically optimized for the local plasma conditions. The MLP system on Alcator C-Mod used analog circuitry to perform this function, measuring T_e, V_F, and I_sat at 1.1 MSPS. Recently, a new prototype digital MLP controller has been implemented on a Red Pitaya Field Programmable Gate Array (FPGA) board which reproduces the functionality of the original controller and performs all data acquisition. There is also the potential to provide the plasma parameters externally for use with feedback control systems. The use of FPGA technology means the system is readily customizable at a fraction of the development time and implementation cost. A second Red Pitaya was used to test the MLP by simulating the current response of a physical probe using C-Mod experimental measurements. This project is available as a git repository to facilitate extensibility (e.g., real-time control outputs and more voltage states) and scalability through collaboration.

Differential modulation of Alzheimer's disease amyloid beta-peptide accumulation by diverse classes of metal ligands

Biometals have an important role in AD (Alzheimer's disease) and metal ligands have been investigated as potential therapeutic agents for treatment of AD. In recent studies the 8HQ (8-hydroxyquinoline) derivative CQ (clioquinol) has shown promising results in animal models and small clinical trials; however, the actual mode of action in vivo is still being investigated. We previously reported that CQ-metal complexes up-regulated MMP (matrix metalloprotease) activity in vitro by activating PI3K (phosphoinositide 3-kinase) and JNK (c-jun N-terminal kinase), and that the increased MMP activity resulted in enhanced degradation of secreted Abeta (amyloid beta) peptide. In the present study, we have further investigated the biochemical mechanisms by which metal ligands affect Abeta metabolism. To achieve this, we measured the effects of diverse metal ligands on cellular metal uptake and secreted Abeta levels in cell culture. We report that different classes of metal ligands including 8HQ and phenanthroline derivatives and the sulfur compound PDTC (pyrrolidine dithiocarbamate) elevated cellular metal levels (copper and zinc), and resulted in substantial loss of secreted Abeta. Generally, the ability to inhibit Abeta levels correlated with a higher lipid solubility of the ligands and their capacity to increase metal uptake. However, we also identified several ligands that potently inhibited Abeta levels while only inducing minimal change to cellular metal levels. Metal ligands that inhibited Abeta levels [e.g. CQ, 8HQ, NC (neocuproine), 1,10-phenanthroline and PDTC] induced metal-dependent activation of PI3K and JNK, resulting in JNK-mediated up-regulation of metalloprotease activity and subsequent loss of secreted Abeta. The findings in the present study show that diverse metal ligands with high lipid solubility can elevate cellular metal levels resulting in metalloprotease-dependent inhibition of Abeta. Given that a structurally diverse array of ligands was assessed, the results are consistent with the effects being due to metal transport rather than the chelating ligand interacting directly with a receptor.

Cryogenic wavefront correction using membrane deformable mirrors

Micro-machined membrane deformable mirrors (MMDMs) are being evaluated for their suitability as wavefront correctors at cryogenic temperatures. Presented here are experimental results for the change in the initial mirror figure of 37-channel MMDMs from OKO Technologies upon cooling to T=78K. The changes in the influence functions are also explored. Of the sample of 3 mirrors tested, one was found to have sufficiently small initial static aberrations to be useful as a wavefront corrector at this temperature. The influence functions at T=78K were found to be similar in shape to both those at room temperature and theoretical predictions of the MMDMs surface shape. The magnitude of the surface deflection at T=78K was reduced by around 20% compared with room temperature values.

Dual-conjugate wavefront generation for adaptive optics

We present results of the isoplanatic performance of an astronomical adaptive optics system in the laboratory, by using a dual layer turbulence simulator. We describe how the performance of adaptive correction degrades with off--axis angle. These experiments demonstrate that it is now possible to produce quantifiable multi-layer turbulence in the laboratory as a precursor to constructing multi-conjugate adaptive optics.

Binary adaptive optics: atmospheric wave-front correction with a half-wave phase shifter

We describe a binary approach to adaptive wave-front correction, especially suitable for narrow band applications, which would be simpler than conventional adaptive technology. Appropriate parts of the aberrant wave front are phase retarded by half a wavelength to ensure that none of the image-forming rays add together destructively. Simulations for monochromatic light show that the residual wave-front errors, in the absence of other errors, would result in Strehl ratios of ~40% with diffraction-limited widths at visible wavelengths. We simulate the imaging performance of such a system and describe a possible implementation that uses a ferroelectric liquid-crystal spatial light modulator.