Segmented Anode Research Articles

Response of current distribution in a liter-scale microbial fuel cell to variable operating conditions

Microbial fuel cells (MFCs) are an emerging technology in renewable energy and waste treatment and the scale-up is crucial for practical applications. Undoubtedly, the analysis and comprehension of MFC operation necessitate essential information regarding the response of the current distribution to variable operating conditions, which stands as one of its significant dynamic characteristics. In this study, the dynamic responses of current distribution to external stimuli (external load, temperature, pH, and electrolyte concentration) were investigated by employing a segmented anode current collector in a liter-scale MFC. The results demonstrated that, with respect to the anodic segment close to the cathode, a major response of the segment current to changes in load, temperature and pH was observed while minor response to changes in ion concentration. It was also found that external stimuli-induced high current usually led to a worse current distribution while increasing electrolyte ion concentration could simultaneously improve the maximal power generation and current distribution. In addition, the response time of segment current to input stimulus followed the pattern of temperature ˃ pH ˃ ion concentration ˃ external load. The results and implication of this study would be helpful in enhancing the operational stability of scale-up MFCs in future practical application.

Coherent fluctuations in a partially magnetized small magnetron discharge operating on molecular nitrogen

We report experimental data on rotating plasma disturbances in a quasi-steady direct-current magnetron discharge operating with molecular nitrogen at pressures of 27, 40, 67, and 133 Pa. Experiments with a segmented anode measuring the local current flow reveal up to 12 coherent structures (“spokes”) propagating in the +E×B and −E×B azimuthal directions. The current–voltage characteristics are studied and found to follow a negative resistance profile at the lower discharge currents. The existence of coherent structures and the number of spokes observed depend on the discharge current and operating pressure. Lower pressures are more favorable to the retrograde −E×B spoke rotation, which is observed in the 27, 40, and 67 Pa discharges. The results are interpreted with a gradient-driven drift wave model, and using the dispersion relation, we show that the propagation direction depends on the orientation of the local electric field within the plasma. Using an electron fluid model, we show how experimental conditions can lead to field reversals that generate −E×B spoke rotation in the lower pressure discharges.

Characterizing the high-power-microwaves radiated by an axial output compact S-band A6 segmented magnetron fed by a split cathode and powered by a linear induction accelerator

In a recent publication [J. Appl. Phys. 131, 023301 (2022)], microwave generation by a segmented A6 S-band axial output relativistic magnetron (RM) fed by a split cathode and powered by a small pulsed power generator was demonstrated for the first time. In the present article, we add to the same RM a mode converter and an antenna and drive it by using a modified linear induction accelerator (LIA) (≤450 kV, ≤4 kA, ∼150 ns). It was found that the operation of the RM for a split cathode or a common explosive emission cathode differs significantly. For a split cathode, we optimize for the best microwave output, its geometrical parameters, the external magnetic field, and the LIA's charging voltages. For the optimal choice of these parameters, the RM generates ∼160 ns long microwave pulses of ∼130 MW, 1.78 GHz frequency with an electronic efficiency of ∼40%, without pulse shortening. On the other hand, a common solid cathode fed RM showed microwave pulse shortening. We demonstrated that the segmented anode allows using a μs-timescale magnetic field, making it possible for the RM to operate repetitively.

ATHENA: An active target detector for the measurement of total cross sections

Experimentally determined cross sections are a critical input for accurately modeling the nuclear processes that take place in a variety of astrophysical environments. A new detector has been designed and constructed to measure the total cross section of nuclear reactions relevant for astrophysics. The Active Target High Efficiency detector for Nuclear Astrophysics (ATHENA) has been constructed and commissioned by a measurement of the 12 C + 12 C fusion reaction. As an active target detector with a segmented anode, efficient measurements of total cross sections over a wide energy range are possible.

Electro-purification studies and first measurement of relative permittivity of TMBi

A new type of detector for positron-emission tomography (PET) has been proposed recently, using a heavy organo-metallic liquid — TriMethyl Bismuth (TMBi) — as target material. TMBi is a transparent liquid with the high Z element Bismuth contributing 82% of its mass. 511keV annihilation photons are converted efficiently into photo-electrons within the detector material producing both Cherenkov light and free charge carriers in the liquid. While the optical component enables a fast timing, a charge readout using a segmented anode can provide an accurate position reconstruction and energy determination. The charge measurement requires a high level of purification, as any electronegative contaminants cause signal degradation. In addition to the purity requirements, the reactive nature of TMBi poses many challenges that need to be met until a fully functioning detector for PET applications can be realized. The paper presents an experimental setup that aims to remove electronegative impurities by electrostatic filtering and to characterise the properties of TMBi, e.g. the relative permittivity, for its application as a detector medium for charge read out.

Concept and design of a hall-effect thruster with integrated thrust vector control

Hall-effect thrusters (HETs) are among the most commonly used propulsion systems for attitude and orbit control of satellites. As an arrangement in a cluster or individually, equipped with a mechanical suspension, thrust in all three spatial directions can be generated, but requires additional mechanisms and components. Therefore, the Technische Universität Dresden (TU Dresden) is currently working on a concept for developing a Hall-effect thruster with integrated thrust vector control, which would allow steering in all three spatial directions with just a single thruster. This new concept is intended to work solely by influencing the ion beam and should not have any additional mechanical components. The HET will come with a segmented anode to set different electrical potentials at the anode and cause an inhomogeneous distribution of the electric field within the discharge channel, which results in an inhomogeneous force vector distribution at the exit plane. It is assumed that this will generate turning moments around the center of gravity. Deliberately causing those turning moments can therefore be used for steering with just one thruster. This work presents the concept of the propulsion system, gives an outlook on the advantages of its technology and shows capabilities for space applications.

Simultaneous measurements of axial motion and azimuthal rotation of non-uniformities (“spokes”) in a Hall thruster

Low-frequency instabilities are often present in Hall thrusters and are associated with axial and/or azimuthal oscillations of plasma non-uniformities. The axial oscillations are related to the so-called breathing mode (periodic depletion of the neutral atom density due to ionization) and are associated with large amplitude current oscillations. The low-frequency azimuthal instabilities are characterized by local non-uniformities of the light emission rotating in the azimuthal direction and are generally called “rotating spokes.” The possibility of coexistence of these two modes has been discussed in the literature but without clear experimental evidence of their correlation. In this paper, we present for the first time simultaneous measurements of the axial and azimuthal positions of the spoke. These measurements have been obtained with a high-speed camera using a triangulation method based on parallax. This method has proven to be sufficiently sensitive to track the 3D position (r–θ–z) of local non-uniformities of the light emission. The optical method has been synchronized with measurements of the current on a segmented anode. The results show that under some conditions, breathing oscillations and spoke rotation in the E×B direction are coupled. During the current rise, the spoke moves from the anode region toward the channel exhaust region while rotating in the E×B direction and seems to follow the movement of the front of neutral atoms progressively filling the channel. About 60% ± 20% of the total anode current is carried by the spoke.

Long term neutron irradiation studies of square meter sized resistive strip micromegas detectors

Resistive strip Micromegas (MICRO-MEsh GAseous Structure) detectors provide even at square meter sizes a high spatial resolution for the reconstruction of Minimum Ionizing Particles (MIPs) like muons. Micromegas detectors consist of three parallel planar structures. A cathode, a grounded mesh and a segmented anode structure form the detector. Square meter sizes challenge the high-voltage stability during operation, especially when using the frequently used gas mixture of Ar:CO2 (93:7vol%) with low quencher content. To improve the HV-stability and to enhance the discharge quenching different gas mixtures have been investigated. A very promising one has an 2% admixture of isobutane forming the ternary gas Ar:CO2:iC4H10 (93:5:2vol%). Long term irradiation studies investigating both gas mixtures interrupted by cosmic muon tracking efficiency measurements have been performed by irradiation with neutrons and gammas from a 10 GBq Am–Be source for a period of two years. The comparison shows gain increase under Ar:CO2:iC4H10 and a considerably improved HV-stable operation of the detector. It is investigated for any performance deterioration for each of the two gas mixtures with focus on pulse-height and changes of efficiency.

New developments from the TORCH R&D project

TORCH is a large-area and high-precision time-of-flight detector, designed to provide charged particle identification over a 2–20GeV/c momentum range. The TORCH detector comprises a 10 mm thick quartz radiator, instrumented with photon detectors, which precisely time and measure the arrival positions of the Cherenkov photons. The photon detectors are micro-channel plate photo-multiplier tubes (MCP-PMTs) comprising a finely segmented anode of 64 × 64 anode pads, electronically ganged into 64 × 8 pixels, over a 53 × 53mm2 area, an excellent intrinsic time resolution of ∼ 30ps, and a long lifetime of up to ≳ 5C/cm2. The current version of the MCP-PMTs used by TORCH have been developed with an industrial partner, Photek Ltd, to satisfy the stringent requirements of the detector. The TORCH R&D programme has successfully demonstrated the detector concept through extensive laboratory and beam tests. A TORCH prototype has been constructed and has yielded encouraging results when exposed to low momentum charged hadrons. Characteristic patterns of Cherenkov photons have been recorded, illustrating the required spatial accuracy and timing resolution of 70 ps per photon. Both laboratory and beam test results are approaching the design goals of the TORCH detector.

Precise timing and recent advancements with segmented anode PICOSEC Micromegas prototypes

Timing information in current and future accelerator facilities is important for resolving objects (particle tracks, showers, etc.) in extreme large particles multiplicities on the detection systems. The PICOSEC Micromegas detector has demonstrated the ability to time 150 GeV muons with a sub-25 ps precision. Driven by detailed simulation studies and a phenomenological model which describes stochastically the dynamics of the signal formation, new PICOSEC designs were developed that significantly improve the timing performance of the detector. PICOSEC prototypes with reduced drift gap size (∼119 µm) achieved a resolution of 45 ps in timing single photons in laser beam tests (in comparison to 76 ps of the standard PICOSEC detector). Towards large area detectors, multi-pad PICOSEC prototypes with segmented anodes has been developed and studied. Extensive tests in particle beams revealed that the multi-pad PICOSEC technology provides also very precise timing, even when the induced signal is shared among several neighbouring pads. Furthermore, new signal processing algorithms have been developed, which can be applied during data acquisition and provide real time, precise timing.

Picosecond timing of charged particles using the TORCH detector

TORCH is a large-area, high-precision time-of-flight (ToF) detector designed to provide charged-particle identification in the 2–20 GeV/c momentum range. Prompt Cherenkov photons emitted by charged hadrons as they traverse a 10 mm quartz radiator are propagated to the periphery of the detector, where they are focused onto an array of micro-channel plate photomultiplier tubes (MCP-PMTs). The position and arrival times of the photons are used to infer the particles’ time of entry in the radiator, to identify hadrons based on their ToF. The MCP-PMTs were developed with an industrial partner to satisfy the stringent requirements of the TORCH detector. The requirements include a finely segmented anode, excellent time resolution, and a long lifetime. Over an approximately 10 m flight distance, the difference in ToF between a kaon and a pion with 10 GeV/c momentum is 35 ps, leading to a 10–15 ps per track timing resolution requirement. On average 30 photons per hadron are detected, which translates to a single-photon time resolution of 70 ps. The TORCH R&D program aims to demonstrate the validity of the detector concept through laboratory and beam tests, results from which are presented. A timing resolution of 70–100 ps was reached in beam tests, approaching the TORCH design goal. Laboratory timing tests consist of operating the MCP-PMTs coupled to the TORCH readout electronics. A time resolution of 50 ps was measured, meeting the TORCH target timing resolution.

Timing performance of a multi-pad PICOSEC-Micromegas detector prototype

The multi-pad PICOSEC-Micromegas is an improved detector prototype with a segmented anode, consisting of 19 hexagonal pads. Detailed studies are performed with data collected in a muon beam over four representative pads. We demonstrate that such a device, scalable to a larger area, provides excellent time resolution and detection efficiency. As expected from earlier single-cell device studies, we measure a time resolution of approximately 25 picoseconds for charged particles hitting near the anode pad centres, and up to 30 picoseconds at the pad edges. Here, we study in detail the effect of drift gap thickness non-uniformity on the timing performance and evaluate impact position based corrections to obtain a uniform timing response over the full detector coverage.

Benefits of Hydrogen in a Segmented-Anode Plasma Torch in Suspension Plasma Spraying

Suspension plasma spraying (SPS) enables the production of various coating microstructures with unique mechanical and thermal properties. Aeronautical manufacturers have been working for fifty years to improve the thermal barrier coating (TBC) performances in gas turbines. Commercial plasma torches with a segmented anode that are characterized by stable plasma jets should enable a better control of the TBC microstructure. The addition of diatomic gases such as hydrogen in the plasma-forming gas affects the plasma jet formation and causes some instabilities. However, it enhances the thermal conductivity of the gas flow, the plasma mass enthalpy and the heat transfer to particles. This study aims to characterise and describe the coating microstructure changes of yttria-stabilised zirconia when gradually adding hydrogen with argon into the plasma gas mixture. The effect of hydrogen is weighted out due to the gas mass enthalpy, mean velocity at the nozzle exit and “hot zone” length of the plasma jet. The coating microstructures, which depend on these plasma jet parameters, will be mapped from feathery and porous to dense and cracked deposits depending on the spraying conditions.

Design of the barrel and endcap DIRC detectors for particle identification in PANDA

The PANDA experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt/Germany aims to investigate fundamental questions of hadron physics. PANDA is designed as a fixed-target experiment for an antiproton beam with a momentum range of 1.5 GeV/[Formula: see text] to 15 GeV/[Formula: see text]. In order to obtain an excellent particle identification of pions and kaons, two independent DIRC detectors have been developed for two adjacent spatial regions. The Barrel DIRC covers polar angles from [Formula: see text]–[Formula: see text] and performs [Formula: see text] separation with [Formula: see text] or more for momenta from 0.5 to 3.5 GeV/[Formula: see text]. The novel Endcap Disc DIRC (EDD) detector will cover the forward polar angles between [Formula: see text] and [Formula: see text] and will provide a [Formula: see text] separation from 0.5 GeV/[Formula: see text] up to 4 GeV/[Formula: see text] with a separation power at least [Formula: see text]. The design of the Barrel DIRC is based on the successful BaBar DIRC and the SuperB FDIRC R&D with several improvements to optimize the performance for PANDA. Both PANDA DIRC detectors use synthetic fused silica as material for radiators and light guides and lifetime-enhance Microchannel Plate PMTs (MCP-PMTs) as sensors. The Barrel DIRC uses narrow bars as a radiator, a prism-shaped expansion volume and a complex multi-layer spherical lens as focusing system. The Cherenkov radiator for the EDD is a large, 2 cm thick fused silica plate that is divided into four identical quadrants. A combination of bars and cylindrical elements with aluminum coating focus the Cherenkov light on the MCP-PMTs with segmented anode plates. The technical design of the two DIRC detectors and the performance of prototypes, tested in a mixed hadron beam at CERN, will be discussed.

Micro-cathode arc thruster using segmented insulated anode with a slit for micro-satellite propulsion

Micro-cathode arc thruster (µCAT) is an electric propulsion device that uses metal cathode material as propellent to create plasma and ultimately produce thrust, which is suitable to serve as a propulsion system for microsatellites. In order to improve propulsion performance of the µCAT, a structure using a segmented insulated anode with a slit (SISA-µCAT), which mainly consists of a truncated-cone-shaped cathode, an insulating sleeve, a segmented anode including proximal anode and distant anode, and an anodic insulation layer with a slit, is proposed in this paper. We compare and analyze the differences in discharge characteristics, plasma generation characteristics and propulsion performance among the SISA-µCAT, a segmented exposed anode µCAT (SEA-µCAT) and the known non-segmented exposed anode µCAT (NSEA-µCAT). Study results show that when adopting the SISA-µCAT, plasma ejection performance is effectively improved by utilizing the special spatial electric field formed between segmented anode and the slit structure on the anodic insulation layer, thus improving the propulsion performance of the µCAT. During a single shot, compared with the NSEA-µCAT, peak values of generated thrust and thrust-to-power ratio are increased by 11.4 times and 10.4 times, respectively, by using the SISA-µCAT. Plasma parameters indicate that peak plasma density and propagation speed are increased by 8.2 times and 2.93 times, respectively.

The dynamics of coherent modes of gradient drift instabilities in a small magnetron discharge plasma

We report on the dynamic behavior of gradient-driven drift waves in a strongly obstructed magnetron discharge. The magnetron has a magnetic topology that results in a toroidal plasma within the gap and supports the development of very coherent modes of rotating plasma structures. The modes and their rotation are present over a wide range of conditions, and the rotation is retrograde to the usual externally imposed E×B direction. This feature seems to be unique to this device and is attributed to a field reversal due to the strong anode-directed electron diffusion that arises from large axial plasma density gradients. A multi-fluid model is proposed, and a Fourier analysis of the linearized equations results in the identification of conditions that support the growth of these instabilities and their transitions across mode symmetries, controlled experimentally by varying the discharge voltage. The model also provides insight on the possible mechanism driving cross-field particle transport. Experiments are carried out with a segmented anode to confirm the localized current flow concomitant with the presence of a coherent structure. These segment currents together with high speed videography unambiguously confirm the direction of plasma rotation and reveal the existence of a stochastic regime between voltage-controlled mode transitions. An analysis of the segment currents in this regime indicates that the lower frequency state decays into a spectrum of coherent higher frequency states that exhibit features consistent with a three-wave nonlinear parametric mixing process.

GRAAL: Gem Reconstruction And Analysis Library

Micro Pattern Gas Detectors (MPGD) are the new frontier in gas trackers. Among this kind of devices, the Gas Electron Multiplier (GEM) chambers are widely used. The experimental signals acquired with the detector must obviously be reconstructed and analysed. In this contribution, a new offline software to perform reconstruction, alignment and analysis on the data collected with APV-25 and TIGER ASICs will be presented. GRAAL (Gem Reconstruction And Analysis Library) is able to measure the performance of a MPGD detector with a strip segmented anode (presently). The code is divided in three parts: reconstruction, where the hits are digitized and clusterized; tracking, where a procedure fits the points from the tracking system and uses that information to align the chamber with rotations and shifts; analysis, where the performance is evaluated (e.g. efficiency, spatial resolution,etc.). The user must set the geometry of the setup and then the program returns automatically the analysis results, taking care of different conditions of gas mixture, electric field, magnetic field, geometries, strip orientation, dead strip, misalignment and many others.

Development of a novel segmented anode Frisch-grid ionisation chamber for fission measurements

A new method is presented to measure the emission angle of fission fragments in a double Frisch-grid ionisation chamber which is independent of the measured fragment energy. The emission axis measurement is dependent only on the relative timing of the charge-integrated signals from a triply radially-segmented anode, the geometry of the detector and the drift velocity of liberated electrons. The energy independence means that corrections for Frisch-grid inefficiency and gain matching of pre-amplifiers are not required. An isotropic 252Cf(sf) source has been used to test this method by comparing experimental data to a Monte-Carlo calculation of the angular efficiency of the detector. Agreement is found between the simulated and measured efficiencies. The method has also been compared to one of the established polar-angle measurement methods, where agreement is once again found.

The plasma morphology of an asymmetric electrode ablative pulsed plasma thruster

The ablative pulsed plasma thruster (APPT) is a typical form of electric propulsion that is highly suitable for micro-satellites. However, its low performance has been a main drawback. Recently, an asymmetric segmented anode schematic was shown to enhance the performance of APPTs. The improved thrust performance obtained with the use of a segmented anode can potentially enable promising applications in future space tasks. To further understand the physical processes behind a segmented anode APPT, experiments using an ultra-high-speed camera, narrow bandpass filters, and a magnetic probe were conducted with both normal parallel-plate electrodes and a segmented anode on an experimental APPT. Successive images of light emission from C+, neutral C2, and broadband emission reveal the evolution of the plasma morphology on an APPT with a segmented anode. The magnetic field strength profiles show that the inter-electrode plasma propagation velocity of a segmented anode APPT is approximately 19 km s−1, which is slightly lower than that of a normal APPT at 23 km s−1. However, the similar order of magnitude suggests a similar downstream acceleration mechanism between the two. The arc morphology observed in the high-speed images shows that the segmented anode APPT with asymmetric electrodes has a restricted arc attachment point, possibly resulting in stronger arc current density at the anode corner. This should result in higher ionization and ablation when compared with a normal anode APPT. Based on the results here, we hypothesize that the segmented anode APPT may be able to better utilize the restrike energy in the propellant ionization process. This fundamentally changes the physical process behind APPT operation, meaning that the improvements should also be applicable to other APPT designs. It can also be adopted as an additional step in the overall optimization of an APPT design.

Inter-electrode discharge of an ablative pulsed plasma thruster with asymmetric electrodes

Ablative pulsed plasma thrusters (APPTs) are a form of propulsion that have been widely used in space tasks. In a recent study, an asymmetric segmented anode schematic was shown to be able to enhance the thrust performance of APPTs. To further understand the physical processes behind a segmented anode APPT, various research campaigns were carried out in this work: the discharge characteristics were studied, measurements were made of the total discharge resistance and inductance, and mapping was performed for the current density (along the side-view plane). From the discharge parameters and fitted total resistance and inductance profiles, we found a 10% lower discharge resistance for the segmented anode APPT compared with a normal anode APPT, which indicates a more optimized discharge process in the segmented anode APPT. The time-resolved current density maps offer two clear indications that verify the better performance of a segmented anode APPT. The first indication is the stronger current density on the surface of PTFE of the segmented anode during the main discharge, which shows that the segmented anode increases the discharge arc current density, which can then improve the ablation and ionization processes. The other indication is the more intense current density distribution between the electrodes during the follow-up discharge period (re-strikes) on the segmented anode APPT. This phenomenon implies that the segmented anode APPT may be able to better utilize the restrike energy in the propellant ionization process.