Polymer Pellet Fabrication for Accurate THz-TDS Measurements

Quasi-optical design for the cross-polarization scattering diagnostic on the HL-3 tokamak

As the plasma beta (β) increases in high-performance tokamaks, electromagnetic turbulence becomes more significant, potentially constraining their operational range. To investigate this turbulence, a cross-polarization scattering (CPS) diagnostic system is being developed on the HL-3 tokamak for simultaneous measurements of density and magnetic fluctuations. In this work, a quasi-optical system has been designed and analyzed for the Q-band CPS diagnostic. The system includes a lens group for beam waist size optimization, a rotatable wire-grid polarizer for polarization adjustment, and a reflector group for measurement range regulation and system response enhancement. Laboratory tests demonstrated a beam radius of order 4 cm at the target measurement location (near the plasma pedestal), cross-polarization isolation exceeding 30 dB, and poloidal and toroidal angle adjustment ranges of ±40° and ±15°, respectively. These results verify the system's feasibility through laboratory evaluations. The quasi-optical system has been installed on the HL-3 tokamak during the 2023 experimental campaign to support the development of CPS diagnostics.

Semi-crystalline materials for pharmaceutical fused filament fabrication: Dissolution and porosity

A better understanding of crystallization kinetics and the effect on drug product quality characteristics is needed to exploit the use of semi-crystalline polymers in pharmaceutical fused filament fabrication. Filaments were prepared from polycaprolactone or polyethylene oxide loaded with a crystallization inhibitor or inducer, which was either 10% (w/w) ibuprofen or theophylline. A design-of-experiments approach was conducted to investigate the effect of nozzle temperature, bed temperature and print speed on the printed tablets' microstructure and dissolution kinetics. Helium pycnometry derived porosity proved an ideal technique to capture significant distortions in the tablets' microstructure. On the other hand, terahertz time domain spectroscopy (THz-TDS) analysis proved valuable to investigate additional enclosed pores of the tablets' microstructure. The surface roughness was analyzed using optical coherence tomography, showing the importance of extensional viscosity for printed drug products. Drug release occurred via erosion for tablets consisting of polyethylene oxide, which partly reduced the effect of the inner microstructure on the drug release kinetics. An initial burst release effect was noted for polycaprolactone tablets, after which drug release continued via diffusion. Both the pore and crystalline microstructure were deemed essential to steer drug release. In conclusion, this research provided guidelines for material and process choice when a specific microstructure has to be constructed from semi-crystalline materials. In addition, non-destructive tests for the characterization of printed products were evaluated.

Analysis of influencing factors in permittivity of oxidized lignite by FTIR, XRD, and THz-TDS based on orthogonal experiment

As an organic-rich and mineral-rich mixture, the permittivity of oxidized lignite is dependent on several factors in the terahertz (THz) band. In this study, thermogravimetric experiments were conducted to determine the characteristic temperatures of three types of lignite. The microstructural characteristics of lignite after treatment at 150, 300, and 450 °C were investigated by Fourier transform infrared spectroscopy and X-ray diffraction. The results show that the changes in the relative contents of CO and SiO are contrary to those of OH and CH₃/CH₂ with temperature variation. The relative content of CO is unpredictable at 300 °C. The aromaticity and crystallite diameter show a regular variation with temperature. The microcrystalline structure of coal tends to undergo graphitization with temperature. The variation of crystallite height is random at 450 °C. The uniform variation in microstructural characteristics of different types of lignite with oxidation temperature proves the feasibility of identifying oxidized lignite by THz spectroscopy. Based on orthogonal experiment results, the influence of the coal type, particle diameter, oxidation temperature, and moisture content on the permittivity of oxidized lignite in the THz band was arranged in an order. The order of the factors' sensitivity for real part of permittivity is oxidation temperature > moisture content > coal type > particle diameter. Similarly, the order of the factors' sensitivity for imaginary part of permittivity is oxidation temperature > moisture content > particle diameter > coal type. The results reveal the capability of THz technology to characterize the microstructure of oxidized lignite and provide guidance for minimizing error in THz technology.