Showing papers in "Review of Scientific Instruments in 2021"

Entangled photon-pair sources based on three-wave mixing in bulk crystals.

Abstract: Entangled photon pairs are a critical resource in quantum communication protocols ranging from quantum key distribution to teleportation. The current workhorse technique for producing photon pairs is via spontaneous parametric down conversion (SPDC) in bulk nonlinear crystals. The increased prominence of quantum networks has led to a growing interest in deployable high performance entangled photon-pair sources. This manuscript provides a review of the state-of-the-art bulk-optics-based SPDC sources with continuous wave pump and discusses some of the main considerations when building for deployment.

Suppression of the vacuum space-charge effect in fs-photoemission by a retarding electrostatic front lens

Abstract: The performance of time-resolved photoemission experiments at fs-pulsed photon sources is ultimately limited by the e–e Coulomb interaction, downgrading energy and momentum resolution. Here, we present an approach to effectively suppress space-charge artifacts in momentum microscopes and photoemission microscopes. A retarding electrostatic field generated by a special objective lens repels slow electrons, retaining the k-image of the fast photoelectrons. The suppression of space-charge effects scales with the ratio of the photoelectron velocities of fast and slow electrons. Fields in the range from −20 to −1100 V/mm for Ekin = 100 eV to 4 keV direct secondaries and pump-induced slow electrons back to the sample surface. Ray tracing simulations reveal that this happens within the first 40 to 3 μm above the sample surface for Ekin = 100 eV to 4 keV. An optimized front-lens design allows switching between the conventional accelerating and the new retarding mode. Time-resolved experiments at Ekin = 107 eV using fs extreme ultraviolet probe pulses from the free-electron laser FLASH reveal that the width of the Fermi edge increases by just 30 meV at an incident pump fluence of 22 mJ/cm2 (retarding field −21 V/mm). For an accelerating field of +2 kV/mm and a pump fluence of only 5 mJ/cm2, it increases by 0.5 eV (pump wavelength 1030 nm). At the given conditions, the suppression mode permits increasing the slow-electron yield by three to four orders of magnitude. The feasibility of the method at high energies is demonstrated without a pump beam at Ekin = 3830 eV using hard x rays from the storage ring PETRA III. The approach opens up a previously inaccessible regime of pump fluences for photoemission experiments.

A scanning tunneling microscope capable of electron spin resonance and pump-probe spectroscopy at mK temperature and in vector magnetic field.

Abstract: In the last decade, detecting spin dynamics at the atomic scale has been enabled by combining techniques such as electron spin resonance (ESR) or pump–probe spectroscopy with scanning tunneling microscopy (STM). Here, we demonstrate an ultra-high vacuum STM operational at milliKelvin (mK) temperatures and in a vector magnetic field capable of both ESR and pump–probe spectroscopy. By implementing GHz compatible cabling, we achieve appreciable RF amplitudes at the junction while maintaining the mK base temperature and high energy resolution. We demonstrate the successful operation of our setup by utilizing two experimental ESR modes (frequency sweep and magnetic field sweep) on an individual TiH molecule on MgO/Ag(100) and extract the effective g-factor. We trace the ESR transitions down to MHz into an unprecedented low frequency band enabled by the mK base temperature. We also implement an all-electrical pump–probe scheme based on waveform sequencing suited for studying dynamics down to the nanoseconds range. We benchmark our system by detecting the spin relaxation time T1 of individual Fe atoms on MgO/Ag(100) and note a field strength and orientation dependent relaxation time.

High-power near-concentric Fabry–Perot cavity for phase contrast electron microscopy

Abstract: Transmission electron microscopy (TEM) of vitrified biological macromolecules (cryo-EM) is limited by the weak phase contrast signal that is available from such samples. Using a phase plate would thus substantially improve the signal-to-noise ratio. We have previously demonstrated the use of a high-power Fabry–Perot cavity as a phase plate for TEM. We now report improvements to our laser cavity that allow us to achieve record continuous wave intensities of over 450 GW/cm2, sufficient to produce the optimal 90° phase shift for 300 keV electrons. In addition, we have performed the first cryo-EM reconstruction using a laser phase plate, demonstrating that the stability of this laser phase plate is sufficient for use during standard cryo-EM data collection.

Low-voltage low-noise gate driven quasi-floating bulk self-cascode current mirror operational transconductance amplifier.

Abstract: A gate driven quasi-floating bulk self-cascode current mirror operational transconductance amplifier operable at ±0.9 V supply voltage with DC gain (70 dB), gain bandwidth (250 kHz), noise (2.8 µV/√Hz at 1 Hz), and power consumption (2.96 µW) simulated in 0.18 µm technology has been introduced. Results obtained are superior in comparison to gate driven self-cascode current mirror and regular current mirror OTAs, which can be utilized to improve the performance of analog-mixed signal circuits and systems.

Faster high-speed atomic force microscopy for imaging of biomolecular processes

Abstract: High-speed atomic force microscopy (HS-AFM) has enabled observing protein molecules during their functional activity at rates of 1–12.5 frames per second (fps), depending on the imaging conditions, sample height, and fragility. To meet the increasing demand for the great expansion of observable dynamic molecular processes, faster HS-AFM with less disturbance is imperatively needed. However, even a 50% improvement in the speed performance imposes tremendous challenges, as the optimization of major rate-limiting components for their fast response is nearly matured. This paper proposes an alternative method that can lower the feedback control error and thereby enhance the imaging rate. This method can be implemented in any HS-AFM system by minor modifications of the software and hardware. The resulting faster and less-disturbing imaging capabilities are demonstrated by the imaging of relatively fragile actin filaments and microtubules near the video rate, and of actin polymerization that occurs through weak intermolecular interactions, at ∼8 fps.

Rotational energy harvesting systems using piezoelectric materials: A review

Abstract: In the past few decades, rotary energy harvesting has received more and more attention and made great progress. The energy harvesting device aims to collect environmental energy around electronic equipment and convert it into usable electrical energy, developing self-powered equipment that does not require replaceable power supplies. This paper provides a holistic review of energy harvesting techniques from rotary motion using piezoelectric materials. It introduces the basic principles of piezoelectric energy harvesting, the vibrational modes of piezoelectric elements, and the materials of piezoelectric elements. There are four types of rotational energy harvesting technologies: inertial excitation, contact execution, magnetic coupling, and hybrid systems. An overview of each technology is made, and then, a detailed analysis is carried out. Different types of rotating energy harvesting technologies are compared, and the advantages and disadvantages of each technology are analyzed. Finally, this paper discusses the future direction and goals of improving energy harvesting technology. This Review will help researchers understand piezoelectric energy harvesting to effectively convert rotational energy into electrical energy.

Partial discharge detection with on-chip spiral inductor as a loop antenna.

Abstract: In this paper, a pioneer partial discharge (PD) loop antenna sensor is presented and examined. It is made of a 70-turn square planar inductor with a side length of 1.8 mm, which is fabricated on top of a silicon substrate in complementary metal oxide semiconductor technology. The microsensor ability to detect corona PD is demonstrated once connected in series with a 60 dB gain amplifier. The behavior is studied at different separation distances from the line through which the PD pulses flow. At 5 cm away, a damped sinusoidal induced voltage with an amplitude of about 100 mV has been measured. The output signal spectrum is highly concentrated around a central resonance frequency of ∼5 MHz. The microsensor response is compared with those of other industrial sensors from Techimp, i.e., horn antennas and high-frequency current transformer sensors. The presented on-chip sensor can be considered a non-intrusive competing solution compared with other heavy and expensive commercial sensors due to its lightweight, compact size, and low cost. In addition, it shows an acceptable signal to noise ratio compared with other commercial electromagnetic wave-based sensors.

Upgrades to the ion cyclotron emission diagnostic on the DIII-D tokamak.

Abstract: The ion cyclotron emission diagnostic on the DIII-D tokamak comprises seven single-turn loops that measure high-frequency (1–100 MHz) magnetic field fluctuations that are often excited by energetic particles in the plasma. The raw voltage signals induced in the loops in response to these fluctuations travel through a series of cables, isolation transformer DC blocks, low-pass filters, and finally a digitizer before being analyzed in frequency space. The diagnostic has been recently upgraded, most notably to include four additional graphite tile loops and a new eight-channel digitizer. The previous three loops are all on the low-field side of the tokamak. The measurement capabilities of the system have been expanded by the addition of a new horizontally oriented loop on the low-field side, an additional toroidal loop on the low-field side, and two toroidal loops on the high-field side. These loops will be used to provide approximate mode polarization, improved toroidal mode number calculations, and information on modes in inward-shifted plasmas, respectively.

Deep learning-based statistical noise reduction for multidimensional spectral data

Abstract: In spectroscopic experiments, data acquisition in multi-dimensional phase space may require long acquisition time, owing to the large phase space volume to be covered. In such a case, the limited time available for data acquisition can be a serious constraint for experiments in which multidimensional spectral data are acquired. Here, taking angle-resolved photoemission spectroscopy (ARPES) as an example, we demonstrate a denoising method that utilizes deep learning as an intelligent way to overcome the constraint. With readily available ARPES data and random generation of training datasets, we successfully trained the denoising neural network without overfitting. The denoising neural network can remove the noise in the data while preserving its intrinsic information. We show that the denoising neural network allows us to perform a similar level of second-derivative and line shape analysis on data taken with two orders of magnitude less acquisition time. The importance of our method lies in its applicability to any multidimensional spectral data that are susceptible to statistical noise.

Embedded heating, ventilation, and air-conditioning control systems: From traditional technologies toward radar advanced sensing.

Abstract: This paper comprehensively reviews the state of the art of Heating, Ventilation, and Air-Conditioning (HVAC) control sensing. The topic has broad impacts on society, by affecting energy consumption, Earth’s climate, and the environmental health. Great effort was taken by researchers to study and test new technologies and methodologies for improving HVAC energy efficiency, but this large amount of works is often fragmentary, and a complete and recent review paper does not yet exist. This paper aims at filling this gap by clarifying the key points of HVAC sensing, the main technologies, and their pros and cons. The advancement in this sector is fueled by the premium performance of the embedded systems exploited as sensors and their beneficial features. The state of the art of the available solutions has been summarized with the purpose of fueling and better organizing the research effort on this hot topic. Particular attention has been paid to investigate not only the performance and reliability of the current systems but also the advanced features that can be provided by the newly evolved and complex technologies, e.g., the radar technology that has been identified as the emerging one in this field.

A robust fiber-based quantum thermometer coupled with nitrogen-vacancy centers.

Abstract: The nitrogen-vacancy center in diamond has been broadly applied in quantum sensing since it is sensitive to different physical quantities. Meanwhile, it is difficult to isolate disturbances from unwanted physical quantities in practical applications. Here, we present a fiber-based quantum thermometer by tracking the sharp-dip in the zero-field optically detected magnetic resonance spectrum in a high-density nitrogen-vacancy ensemble. Such a scheme can not only significantly isolate the magnetic field and microwave power drift but also improve the temperature sensitivity. Thanks to its simplicity and compatibility in implementation and robustness, this quantum thermometer is then applied to the surface temperature imaging of an electronic chip with a sensitivity of 18mK/Hz. It thus paves the way to high sensitive temperature measurements in ambiguous environments.

High-energy x-ray nanotomography introducing an apodization Fresnel zone plate objective lens

Abstract: In this study, high-energy x-ray nanotomography (nano-computed tomography, nano-CT) based on full-field x-ray microscopy was developed. Fine two-dimensional and three-dimensional (3D) structures with linewidths of 75 nm–100 nm were successfully resolved in the x-ray energy range of 15 keV–37.7 keV. The effective field of view was ∼60 µm, and the typical measurement time for one tomographic scan was 30 min–60 min. The optical system was established at the 250-m-long beamline 20XU of SPring-8 to realize greater than 100× magnification images. An apodization Fresnel zone plate (A-FZP), specifically developed for high-energy x-ray imaging, was used as the objective lens. The design of the A-FZP for high-energy imaging is discussed, and its diffraction efficiency distribution is evaluated. The spatial resolutions of this system at energies of 15 keV, 20 keV, 30 keV, and 37.7 keV were examined using a test object, and the measured values are shown to be in good agreement with theoretical values. High-energy x-ray nano-CT in combination with x-ray micro-CT is applied for 3D multiscale imaging. The entire bodies of bulky samples, ∼1 mm in diameter, were measured with the micro-CT, and the nano-CT was used for nondestructive observation of regions of interest. Examples of multiscale CT measurements involving carbon steel, mouse bones, and a meteorite are discussed.

High-resolution inelastic x-ray scattering at the high energy density scientific instrument at the European X-Ray Free-Electron Laser

Abstract: We introduce a setup to measure high-resolution inelastic x-ray scattering at the High Energy Density scientific instrument at the European X-Ray Free-Electron Laser (XFEL). The setup uses the Si (533) reflection in a channel-cut monochromator and three spherical diced analyzer crystals in near-backscattering geometry to reach a high spectral resolution. An energy resolution of 44 meV is demonstrated for the experimental setup, close to the theoretically achievable minimum resolution. The analyzer crystals and detector are mounted on a curved-rail system, allowing quick and reliable changes in scattering angle without breaking vacuum. The entire setup is designed for operation at 10 Hz, the same repetition rate as the high-power lasers available at the instrument and the fundamental repetition rate of the European XFEL. Among other measurements, it is envisioned that this setup will allow studies of the dynamics of highly transient laser generated states of matter.

High voltage nanosecond pulse generator based on avalanche transistor Marx bank circuit and linear transformer driver.

Abstract: Avalanche transistor Marx bank circuits (MBCs) are widely used in high voltage repetitive nanosecond pulse generators, but problems exist with respect to increasing the output voltage due to the limited pulsed current. Accordingly, a novel topology based on an avalanche transistor MBC combined with a linear transformer driver is proposed, the latter of which exhibits advantageous stress distribution and modular structure. A four-module prototype with four units in each module is developed in the laboratory. The output characteristics are investigated by varying important parameters such as the main capacitance, the number of conducting units, the number of cascaded modules, and the trigger signal time delay. The test results verify the validity of the proposed topology. For a 50 Ω resistive load, the prototype can generate pulses with an amplitude of 10.9 kV, a rise time of 3.3 ns, and a voltage superposition efficiency of 89%. The topology proposed in this paper may help to provide a method to further improve the output performance of avalanche transistor MBCs.

Ultra-low-vibration closed-cycle cryogenic surface-electrode ion trap apparatus

Abstract: We describe the design, commissioning, and operation of an ultra-low-vibration closed-cycle cryogenic ion trap apparatus. One hundred lines for low-frequency signals and eight microwave/radio frequency coaxial feed-lines offer the possibility of implementing a small-scale ion-trap quantum processor or simulator. With all supply cables attached, more than 1.3 W of cooling power at 5 K is still available for absorbing energy from electrical pulses introduced to control ions. The trap itself is isolated from vibrations induced by the cold head using a helium exchange gas interface. The performance of the vibration isolation system has been characterized using a Michelson interferometer, finding residual vibration amplitudes on the order of 10 nm rms. Trapping of 9Be+ ions has been demonstrated using a combination of laser ablation and photoionization.

Resonant-type piezoelectric inertial drive mechanism with asymmetric inertial masses

Abstract: Resonant-type piezoelectric impact motors can improve the output capability effectively. A new construction of asymmetric inertial masses is proposed to synthesize approximate saw-tooth wave resonant vibration with matched anti-phase and in-phase modes. A prototype is designed, manufactured, and tested. With 40 Vp–p, 400 Hz exciting voltage for the anti-phase mode and 16 Vp–p, 800 Hz exciting voltage for the in-phase mode, the prototype provides a maximum no-load velocity of 17.2 mm/s and a maximum output power of 0.72 mW with 100 mN load. The velocity and output power of the prototype in the proposed resonant state are near three orders of magnitude higher than those in the traditional quasi-static state.

Performance and uniformity of a kilo-pixel array of Ti/Au transition-edge sensor microcalorimeters

Abstract: Uniform large transition-edge sensor (TES) arrays are fundamental for the next generation of x-ray space observatories. These arrays are required to achieve an energy resolution ΔE < 3 eV full width at half maximum (FWHM) in the soft x-ray energy range. We are currently developing x-ray microcalorimeter arrays for use in the future laboratory and space-based x-ray astrophysics experiments and ground-based spectrometers. In this contribution, we report on the development and the characterization of a uniform 32 × 32 pixel array with 140 × 30 μm2 Ti/Au TESs with the Au x-ray absorber. We report on extensive measurements on 60 pixels in order to show the uniformity of our large TES array. The averaged critical temperature is Tc = 89.5 ± 0.5 mK, and the variation across the array (∼1 cm) is less than 1.5 mK. We found a large region of detector’s bias points between 20% and 40% of the normal-state resistance where the energy resolution is constantly lower than 3 eV. In particular, results show a summed x-ray spectral resolution ΔEFWHM = 2.50 ± 0.04 eV at a photon energy of 5.9 keV, measured in a single-pixel mode using a frequency domain multiplexing readout system developed at SRON/VTT at bias frequencies ranging from 1 MHz to 5 MHz. Moreover, we compare the logarithmic resistance sensitivity with respect to temperature and current (α and β, respectively) and their correlation with the detector’s noise parameter M, showing a homogeneous behavior for all the measured pixels in the array.

Diagnosing plasma magnetization in inertial confinement fusion implosions using secondary deuterium-tritium reactions.

Abstract: Diagnosing plasma magnetization in inertial confinement fusion implosions is important for understanding how magnetic fields affect implosion dynamics and to assess plasma conditions in magnetized implosion experiments. Secondary deuterium–tritium (DT) reactions provide two diagnostic signatures to infer neutron-averaged magnetization. Magnetically confining fusion tritons from deuterium–deuterium (DD) reactions in the hot spot increases their path lengths and energy loss, leading to an increase in the secondary DT reaction yield. In addition, the distribution of magnetically confined DD-triton is anisotropic, and this drives anisotropy in the secondary DT neutron spectra along different lines of sight. Implosion parameter space as well as sensitivity to the applied B-field, fuel ρR, temperature, and hot-spot shape will be examined using Monte Carlo and 2D radiation-magnetohydrodynamic simulations.

A dual-magneto-optical-trap atom gravity gradiometer for determining the Newtonian gravitational constant.

Abstract: As part of a program to determine the gravitational constant G using multiple independent methods in the same laboratory, an atom gravity gradiometer is being developed. The gradiometer is designed with two magneto-optical traps to ensure both the fast simultaneous launch of two atomic clouds and an optimized configuration of source masses. Here, the design of the G measurement by atom interferometry is detailed, and the experimental setup of the atom gravity gradiometer is reported. A preliminary sensitivity of 3 × 10−9 g/Hz to differential gravity acceleration is obtained, which corresponds to 99 E/Hz (1 E = 10−9 s−2) for the gradiometer with a baseline of 0.3 m. This provides access to measuring G at the level of less than 200 parts per million in the first experimental stage.

CESAM-Coded excitation scanning acoustic microscope.

Abstract: Scanning acoustic microscopy (SAM) finds use across many disciplines, e.g., biology, industrial quality control, and materials science, thanks to its unique ability to quantify mechanical sample properties combined with its high resolution. However, such imaging is often slow, especially if averaging is necessary. We present a Coded Excitation Scanning Acoustic Microscope (CESAM) that employs coded signals and show that it produces images of higher signal-to-noise ratios (SNRs) than the classical SAM in a comparable measurement time. The CESAM employs coded signals instead of the short bursts used in traditional SAMs, and we employ both linear and non-linear frequency modulation. Our results show that compared to the SAM approach, this modulation increases the SNR by 16.3 dB (from 39.9 to 56.2 dB) and reduces the echo duration by 26.7% when we employ a linear chirp to the transducer with a nominal bandwidth of 130–370 MHz. Driving the transducer with a broader bandwidth signal using non-linear chirps (100–450 MHz), we obtained a SNR increase of 10.3 dB and a reduced echo duration of 70.5%. The shorter echo duration increases z-resolution, whereas the lateral resolution remains limited by the wavelength. Finally, we show that by using these coded signals, one can obtain enhanced image quality relative to the standard actuation of the same measurement time. Our results have potential to invigorate the field of acoustic microscopy, especially with samples where the enhanced SNR and/or contrast-to-noise ratio is crucial for image quality.

A sub-4 Kelvin radio frequency linear multipole wire trap.

Abstract: A linear cryogenic 16-pole wire ion trap has been developed and constructed for cryogenic ion spectroscopy at temperatures below 4 K. The trap is temperature-variable, can be operated with different buffer gases, and offers large optical access perpendicular to the ion beam direction. The housing geometry enables temperature measurement during radio frequency operation. The effective trapping potential of the wire-based radio frequency trap is described and compared to conventional multipole ion trap designs. Furthermore, time-of-flight mass spectra of multiple helium tagged protonated glycine ions that are extracted from the trap are presented, which prove very low ion temperatures and suitable conditions for sensitive spectroscopy.

A fast-reciprocating probe array for two-dimensional measurements in the divertor region of the Tokamak à configuration variable

Abstract: A detailed description of the construction and commissioning of the fast-moving reciprocating divertor Langmuir probe array on the Tokamak a Configuration Variable (TCV) is presented. A horizontal array of 24 Langmuir probes (12 Mach probes) combined with a fast vertical movement provides unprecedented two-dimensional measurements of the plasma properties across the entire divertor outer leg volume and up to the X-point. The L-shape probe arm has to be very compact to minimize plasma perturbations and, at the same time, has to house 24 coaxial transmission lines, withstand time-averaged heat fluxes of up to ≈30 MW/m2 and accelerations of up to 8 g, and be resilient to violent plasma disruptions. For the fast vertical motion of the probe arm, extending up to 38 cm into the TCV vacuum vessel, an assembly with a precise and powerful linear electric motor (up to 4000 N of force) was mounted in a 4 m high structure within the limited space below the TCV. The diagnostic has already performed measurements in ≈200 plasma discharges and has been hit by ≈20 disruptions without suffering any critical damage. The measurements are qualitatively and quantitatively consistent with other reference diagnostics, such as upstream electron Thomson scattering and downstream wall-embedded Langmuir probes, and are used extensively on the TCV for experimental divertor studies and for comparisons with edge transport and turbulence code results.

Collective optical Thomson scattering in pulsed-power driven high energy density physics experiments (invited).

Abstract: Optical collective Thomson scattering (TS) is used to diagnose magnetized high energy density physics experiments at the Magpie pulsed-power generator at Imperial College London. The system uses an amplified pulse from the second harmonic of a Nd:YAG laser (3 J, 8 ns, 532 nm) to probe a wide diversity of high-temperature plasma objects, with densities in the range of 1017–1019 cm−3 and temperatures between 10 eV and a few keV. The scattered light is collected from 100 μm-scale volumes within the plasmas, which are imaged onto optical fiber arrays. Multiple collection systems observe these volumes from different directions, providing simultaneous probing with different scattering K-vectors (and different associated α-parameters, typically in the range of 0.5–3), allowing independent measurements of separate velocity components of the bulk plasma flow. The fiber arrays are coupled to an imaging spectrometer with a gated intensified charge coupled device. The spectrometer is configured to view the ion-acoustic waves of the collective Thomson scattered spectrum. Fits to the spectra with the theoretical spectral density function S(K, ω) yield measurements of the local plasma temperatures and velocities. Fitting is constrained by independent measurements of the electron density from laser interferometry and the corresponding spectra for different scattering vectors. This TS diagnostic has been successfully implemented on a wide range of experiments, revealing temperature and flow velocity transitions across magnetized shocks, inside rotating plasma jets and imploding wire arrays, as well as providing direct measurements of drift velocities inside a magnetic reconnection current sheet.

Horizon: Microfluidic platform for the production of therapeutic microbubbles and nanobubbles

Abstract: Microbubbles (MBs) have a multitude of applications including as contrast agents in ultrasound imaging and as therapeutic drug delivery vehicles, with further scope for combining their diagnostic and therapeutic properties (known as theranostics). MBs used clinically are commonly made by mechanical agitation or sonication methods, which offer little control over population size and dispersity. Furthermore, clinically used MBs are yet to be used therapeutically and further research is needed to develop these theranostic agents. In this paper, we present our MB production instrument “Horizon,” which is a robust, portable, and user-friendly instrument, integrating the key components for producing MBs using microfluidic flow-focusing devices. In addition, we present the system design and specifications of Horizon and the optimized protocols that have so far been used to produce MBs with specific properties. These include MBs with tailored size and low dispersity (monodisperse); MBs with a diameter of ∼2 μm, which are more disperse but also produced in higher concentration; nanobubbles with diameters of 100–600 nm; and therapeutic MBs with drug payloads for targeted delivery. Multiplexed chips were able to improve production rates up to 16-fold while maintaining production stability. This work shows that Horizon is a versatile instrument with potential for mass production and use across many research facilities, which could begin to bridge the gap between therapeutic MB research and clinical use.

An x-ray penumbral imager for measurements of electron-temperature profiles in inertial confinement fusion implosions at OMEGA.

Abstract: Hot-spot shape and electron temperature (Te) are key performance metrics used to assess the efficiency of converting shell kinetic energy into hot-spot thermal energy in inertial confinement fusion implosions. X-ray penumbral imaging offers a means to diagnose hot-spot shape and Te, where the latter can be used as a surrogate measure of the ion temperature (Ti) in sufficiently equilibrated hot spots. We have implemented a new x-ray penumbral imager on OMEGA. We demonstrate minimal line-of-sight variations in the inferred Te for a set of implosions. Furthermore, we demonstrate spatially resolved Te measurements with an average uncertainty of 10% with 6 μm spatial resolution.

The Ice Chamber for Astrophysics-Astrochemistry (ICA): A new experimental facility for ion impact studies of astrophysical ice analogs.

Abstract: The Ice Chamber for Astrophysics–Astrochemistry (ICA) is a new laboratory end station located at the Institute for Nuclear Research (Atomki) in Debrecen, Hungary. The ICA has been specifically designed for the study of the physico-chemical properties of astrophysical ice analogs and their chemical evolution when subjected to ionizing radiation and thermal processing. The ICA is an ultra-high-vacuum compatible chamber containing a series of IR-transparent substrates mounted on a copper holder connected to a closed-cycle cryostat capable of being cooled down to 20 K, itself mounted on a 360° rotation stage and a z-linear manipulator. Ices are deposited onto the substrates via background deposition of dosed gases. The ice structure and chemical composition are monitored by means of FTIR absorbance spectroscopy in transmission mode, although the use of reflectance mode is possible by using metallic substrates. Pre-prepared ices may be processed in a variety of ways. A 2 MV Tandetron accelerator is capable of delivering a wide variety of high-energy ions into the ICA, which simulates ice processing by cosmic rays, solar wind, or magnetospheric ions. The ICA is also equipped with an electron gun that may be used for electron impact radiolysis of ices. Thermal processing of both deposited and processed ices may be monitored by means of both FTIR spectroscopy and quadrupole mass spectrometry. In this paper, we provide a detailed description of the ICA setup as well as an overview of the preliminary results obtained and future plans.

Development of small high-voltage AC power supply for a dielectric barrier discharge plasma actuator.

Abstract: A dielectric-barrier discharge plasma actuator (DBDPA) is a promising flow control device that can prevent flow separation around an airfoil using electrical discharges Miniaturizing the DBDPA power supply remains a crucial technological challenge because its size and weight determine the performance of fluid devices equipped with this type of actuator In this study, we propose a compact high-voltage AC power supply for a DBDPA intended for installation on small airplanes, including unmanned aerial vehicles The power supply, which consists of a power supply board, a main control board, and a DC/AC converter board, is ∼110 g in weight It can drive a 300-mm long DBDPA without any substantial voltage drop The power consumption in standby remains below 1 W, and the maximum consumption during discharge in burst mode at a burst ratio of 5% is 24 W The power supply uses a lithium-ion battery with a capacity of 1800 mA h, which allows continuous DBDPA operation for ∼15 h An experiment was conducted in a wind tunnel using an airfoil model whose cross-section corresponds to that of an airfoil from a commercial glider airplane Experimental results reveal that the surface pressure around the airfoil is modified by DBDPA operation, clearly demonstrating the effectiveness of the developed power supply for operating a DBDPA as a flow control device The size and weight of the proposed power supply can be established as a benchmark to further miniaturize and optimize DBDPA power supplies

Measuring the electron temperature and identifying plasma detachment using machine learning and spectroscopy.

Abstract: A machine learning approach has been implemented to measure the electron temperature directly from the emission spectra of a tokamak plasma. This approach utilized a neural network (NN) trained on a dataset of 1865 time slices from operation of the DIII-D tokamak using extreme ultraviolet/vacuum ultraviolet emission spectroscopy matched with high-accuracy divertor Thomson scattering measurements of the electron temperature, Te. This NN is shown to be particularly good at predicting Te at low temperatures (Te < 10 eV) where the NN demonstrated a mean average error of less than 1 eV. Trained to detect plasma detachment in the tokamak divertor, a NN classifier was able to correctly identify detached states (Te < 5 eV) with a 99% accuracy (an F1 score of 0.96) at an acquisition rate 10× faster than the Thomson scattering measurement. The performance of the model is understood by examining a set of 4800 theoretical spectra generated using collisional radiative modeling that was also used to predict the performance of a low-cost spectrometer viewing nitrogen emission in the visible wavelengths. These results provide a proof-of-principle that low-cost spectrometers leveraged with machine learning can be used to boost the performance of more expensive diagnostics on fusion devices and be used independently as a fast and accurate Te measurement and detachment classifier.

System-on-chip upgrade of millimeter-wave imaging diagnostics for fusion plasma

Abstract: Monolithic, millimeter wave “system-on-chip” technology has been employed in chip heterodyne radiometers in a newly developed Electron Cyclotron Emission Imaging (ECEI) system on the DIII-D tokamak for 2D electron temperature and fluctuation diagnostics. The system employs 20 horn-waveguide receiver modules each with customized W-band (75–110 GHz) monolithic microwave integrated circuit chips comprising a W-band low noise amplifier, a balanced mixer, a ×2 local oscillator (LO) frequency doubler, and two intermediate frequency amplifier stages in each module. Compared to previous quasi-optical ECEI arrays with Schottky mixer diodes mounted on planar antennas, the upgraded W-band array exhibits >30 dB additional gain and 20× improvement in noise temperature; an internal eight times multiplier chain is used to provide LO coupling, thereby eliminating the need for quasi-optical coupling. The horn-waveguide shielding housing avoids out-of-band noise interference on each module. The upgraded ECEI system plays an important role for absolute electron temperature and fluctuation measurements for edge and core region transport physics studies. An F-band receiver chip (up to 140 GHz) is under development for additional fusion facilities with a higher toroidal magnetic field. Visualization diagnostics provide multi-scale and multi-dimensional data in plasma profile evolution. A significant aspect of imaging measurement is focusing on artificial intelligence for science applications.