Calibration and thermal test results of prototype bolometer sensors for ITER fusion reactor.

For over 10 years, several bolometer sensors with different properties have been tested in the IBOVAC facility. The aim has been to develop a bolometer sensor that can be operated in ITER and can withstand harsh operating conditions. For this purpose, important physical properties of the sensors, i.e., cooling time constant τ, normalized heat capacity κ, and normalized sensitivity sn, have been characterized in a vacuum condition and at various temperatures up to 300 °C. The calibration is achieved by ohmic heating of the sensor absorbers by applying a DC voltage and recording exponential current fall during heating. Recently, a Python program was developed to analyze the data and extract the above mentioned parameters including the uncertainties from recorded currents. In the present series of experiments, the latest prototype sensors developed for ITER are tested and evaluated. These include three different sensor types: two with Au absorbers on ZrO2 membranes (self-supporting substrate sensors) and one with Au absorbers on Si3N4 membranes supported by a Si frame (supported membrane sensors). Tests revealed that the sensor with ZrO2 substrate can only be operated up to 150 °C, while the supported membrane sensors passed the tests up to 300 °C successfully. These results will be used, together with other upcoming tests, such as irradiation testing, to select the most suitable sensors to be employed in ITER.

Spectral tunability of a plasmonic antenna with a dielectric nanocrystal.

We show that the positioning of a nanometer length scale dielectric object, such as a diamond nanocrystal, in the vicinity of a gold bowtie nanoantenna can be used to tune the plasmonic mode spectrum on the order of a linewidth. We further show that the intrinsic luminescence of gold enhanced in the presence of nanometer-scale roughness couples efficiently to the plasmon mode and carries the same polarization anisotropy. Our findings have direct implications for cavity quantum electrodynamics related applications of hybrid antenna-emitter complexes.

A time-resolved imaging system for the diagnosis of x-ray self-emission in high energy density physics experiments.

A diagnostic capable of recording spatially and temporally resolved x-ray self-emission data was developed to characterize experiments on the MAGPIE pulsed-power generator. The diagnostic used two separate imaging systems: a pinhole imaging system with two-dimensional spatial resolution and a slit imaging system with one-dimensional spatial resolution. The two-dimensional imaging system imaged light onto the image plate. The one-dimensional imaging system imaged light onto the same piece of image plate and a linear array of silicon photodiodes. This design allowed the cross-comparison of different images, allowing a picture of the spatial and temporal distribution of x-ray self-emission to be established. The design was tested in a series of pulsed-power-driven magnetic-reconnection experiments.

Enhanced X-ray emission arising from laser-plasma confinement by a strong transverse magnetic field.

We analyze, using experiments and 3D MHD numerical simulations, the dynamic and radiative properties of a plasma ablated by a laser (1 ns, 10[Formula: see text]-10[Formula: see text] W/cm[Formula: see text]) from a solid target as it expands into a homogeneous, strong magnetic field (up to 30 T) that is transverse to its main expansion axis. We find that as early as 2 ns after the start of the expansion, the plasma becomes constrained by the magnetic field. As the magnetic field strength is increased, more plasma is confined close to the target and is heated by magnetic compression. We also observe that after [Formula: see text] ns, the plasma is being overall shaped in a slab, with the plasma being compressed perpendicularly to the magnetic field, and being extended along the magnetic field direction. This dense slab rapidly expands into vacuum; however, it contains only [Formula: see text] of the total plasma. As a result of the higher density and increased heating of the plasma confined against the laser-irradiated solid target, there is a net enhancement of the total X-ray emissivity induced by the magnetization.