Thermionic Effect Research Articles

Thermally Robust Aramid Triboelectric Materials Enabled by Heat‐Induced Cross‐Linking

AbstractThe rapid development of the Internet of Things has led to numerous functional electronic devices, making it a significant challenge to provide power for these distributed devices. Triboelectric self‐power technology is ideal for smart devices due to its material diversity and high energy efficiency. However, traditional triboelectric materials have weak electrostatic induction due to their low dielectric constant. Additionally, the thermionic emission effect reduces their electric output in high temperatures, limiting their applications. This study designes a thermally robust aramid triboelectric material with a high dielectric constant through heat‐induced cross‐linking heterogeneous interface engineering. This novel material not only achieves high triboelectric output but also maintains high performance across a wide temperature range. The heat‐induced cross‐linking process enhances the interaction between aramid nanofibers and Al2O3 nanosheets, significantly improving the electrical performance, and flame retardance of the material, and the relative dielectric constant increases 16‐fold. The triboelectric nanogenerator constructed with this material achieves a power density of 3.97 W m−2, and maintains high triboelectric output at 260 °C. Finally, a self‐powered detection system collects high‐temperature gas energy and drives sensors is designed. This research presents a novel strategy for high‐performance triboelectric materials, showing significant potential for self‐powered devices.

On the TCAD Modeling of Non-Permanent Gate Current Increase during Short-Circuit Test in SiC MOSFETs

Under short-circuit (SC) testing SiC MOSFETs exhibit an exceptional increase of gate current (100’s mA) which is not observed in their Si counterparts. Electro-thermal TCAD simulations are capable to accurately mimic all the details of measured gate current waveforms (iG) by capturing multiple physical mechanisms. One of these mechanisms is the thermionic or Schottky emission effect occurring at extreme temperatures (>1300K) for relatively thick gate oxides (>40nm). For the first time, it is proven that TCAD tunneling models, recommended for very thin oxides (<3nm), are suitable to reproduce the thermionic effect and predict iG in SiC MOSFETs under SC test.

Thermoradiative coupling graphene-based thermionic solar conversion

Thermionic conversion, due to its simple solid-state structure capable of converting heat to electricity directly, is promising for concentrated solar power. However, because of the extremely high cathode temperature, a large portion of the heat is lost to the environment. The paper introduces a novel concept of selective thermoradiative-graphene thermionic conversion (STR-GTI) that involving a combined control of photon and electron emission to modify the radiation dissipation. A detailed thermodynamic model is developed to evaluate the energy transfer irreversibility of STR-GTI solar conversion. The results demonstrate that the selective themoradiative photon emission and graphene thermionic electron emission effects synergistically reduce internal irreversible losses in the STR-GTI system, leading to a maximum energy efficiency of 34.34 % at a concentration ratio of 425, cathode work function of 1.8 eV and thermoradiative bandgap of 0.2 eV. The STR-GTI system outperforms both individual GTI and STR converters in terms of exergy efficiency and entropy production minimization. It exhibits a remarkable 102.03 % increase in exergy efficiency compared to the STR & GTI system at a thermoradiative voltage of −0.14 eV, accompanied by a 28.56 % reduction in exergy loss and a 37.83 % decrease in entropy production. The combination of narrowing the spectral radiation bandwidth and significant electron emission capabilities of graphene contribute to the system’s resilience against solar radiation fluctuations.

Reduced graphene oxide/TiO2 hybrid synergistically enhanced polyimide nanofibers with high triboelectric output and thermal charge stability

The output performance of triboelectric nanogenerators (TENGs) can drop dramatically in high temperature environments because of the thermionic emission effect. To enhance the thermal charge stability and expand the working temperature of TENG, polyimide nanofibers (PINF) were synergistically enhanced by the electron trapping mechanism of reduced graphene oxide (rGO) and interfacial polarization of TiO2. With the multiple enhancement effect of polyimide/rGO/TiO2 composite nanofibers (PRTNF) on triboelectric output, PRTNF-TENG generated an open circuit voltage of 228.26 V and a short circuit current of 5.22 μA, which were 3.80 and 3.48 times higher than those of PINF-TENG. The effective output of polymer-based TENG was investigated from 25 − 300 °C. Compared to room temperature, the PRTNF-TENG can maintain 19.45 % (44.39 V) and 18.20 % (0.95 μA) of the voltage and current at 300 °C, respectively, and still drive 50 commercial LEDs. Furthermore, PRTNF-TENGs were applied as self-powered sensors for firefighters to provide real-time motion monitoring and ambient temperature detection. This PRTNF-TENG has broad application prospects for energy harvesting and smart electronic monitor in harsh environments such as fire and space.

Simulation of dust grain charging under hypervelocity impact plasma environment

Dust plasma readily forms during hypervelocity impact, which serves as a source of plasma macroscopic charge separation and strong electromagnetic fields. In this study, we examine the dynamic evolution of surface charging of aluminum dust grains with micrometer or submicrometer sizes in a hypervelocity impact plasma environment based on the theory of orbital motion limited. As dust grains traverse the expanding plasma, plasma density and temperature decrease with increasing distance from the impact point. This leads to longer relaxation times for charging equilibrium (ranging from picoseconds to microseconds) and reduced equilibrium charges. The model incorporates thermionic and secondary electron emission effects on dust grain charging processes while also examining the impacts of five heating and cooling mechanisms on the thermal equilibrium temperatures of dust grains. Near the impact point, thermal equilibrium temperatures exceed aluminum's boiling point, which results in phase transition ablation processes. As dust grain temperatures increase, thermionic emission currents may dominate charging dynamics and influence final equilibrium charge numbers. High-temperature dust grains tend to acquire positive charges. Moreover, we observe that the radius of dust grains considerably affects charging processes, and smaller grain radii correspond to low equilibrium charges and longer relaxation times.

Cuprorivaite/hardystonite/alginate composite hydrogel with thermionic effect for the treatment of peri-implant lesion.

Peri-implant lesion is a grave condition afflicting numerous indi-viduals with dental implants. It results from persistent periodontal bacteria accumulation causing inflammation around the implant site, which can primarily lead to implant loosening and ultimately the implant loss. Early-stage peri-implant lesions exhibit symptoms akin to gum disease, including swelling, redness and bleeding of the gums surrounding the implant. These signs indicate infection and inflammation of the peri-implant tissues, which may result in bone loss and implant failure. To address this problem, a thermionic strategy was applied by designing a cuprorivaite-hardystonite bioceramic/alginate composite hydrogel with photothermal and Cu/Zn/Si multiple ions releasing property. This innovative approach creates a thermionic effect by the release of bioactive ions (Cu2+ and Zn2+ and ) from the composite hydrogel and the mild heat environment though the photothermal effect of the composite hydrogel induced by near-infrared light irradiation. The most distinctive advantage of this thermionic effect is to substantially eliminate periodontal pathogenic bacteria and inhibit inflammation, while simultaneously enhance peri-implant osseointegration. This unique attribute renders the use of this composite hydrogel highly effective in significantly improving the survival rate of implants after intervention in peri-implant lesions, which is a clinical challenge in periodontics. This study reveals application potential of a new biomaterial-based approach for peri-implant lesion, as it not only eliminates the infection and inflammation, but also enhances the osteointegration of the dental implant, which provides theoretical insights and practical guidance to prevent and manage early-stage peri-implant lesion using bioactive functional materials.

Multifunctional energy harvesting and storage textile technology based on thermionic effect

The development of effective dual-function energy harvesting/storage technologies is a milestone demand for the emerging generation of low-consumption autonomous electronics. This work reports the development of a multifunctional thermionic power textile device merging thermal energy harvesting and electrochemical energy storage for application in self-powered systems. An everyday cost-effective non-conductive natural fabric was transformed into an all-solid-state textile-based thermally-chargeable supercapacitor (T-TCSC) via dyeing with multiwalled carbon nanotubes and subsequent assembly with H3PO4-doped poly(vinyl alcohol) (PVA) solid-gel polyelectrolyte.When subjected to an out-of-plane temperature gradient, the T-TCSC was able to convert the thermal energy into electrical output and store the harvested energy. A Soret coefficient of 1.85 mV K−1 was obtained, which is the highest value achieved so far for TCSCs developed on non-conductive textile substrates reported in literature and ∼10× higher than those of conventional thermoelectric devices. Additionally, a maximum output potential of ∼30 mV was achieved for ΔT = 24.7 K. Concerning the energy storage performance, an energy density of 9.39 μW h cm−2 was obtained at 1.62 mW cm−2 power density.The smart T-TCSC outputs demonstrated its potentialities as a two-in-one self-chargeable textile device that can harvest the thermal energy generated by a temperature gradient, convert it into electrical energy and simultaneously store it.

A novel high-low-high Schottky barrier based bidirectional tunnel field effect transistor

In this work, we proposed a novel High-Low-High Schottky barrier bidirectional tunnel field effect transistor (HLHSB-BTFET). Compared with previous technology which is named as High Schottky barrier BTFET (HSB-BTFET), the proposed HLHSB-BTFET requires only one gate electrode with independent power supply. More importantly, take an N type HLHSB-BTFET as an example, different from the previously proposed HSB-BTFET, due to that the effective potential of the central metal is increased with the increasing of drain to source voltage (Vds), built-in barrier heights maintain at the same value when the Vds is increased. Therefore, there is no strong dependence between built-in barrier heights formed in the semiconductor region on the drain side and the Vds. Besides that low Schottky barrier formed on the interface between the conduction band of silicon regions on its both sides and the central metal (while high Schottky barrier formed between the valence band of silicon regions on its both sides and the central metal) have been designed for preventing the carriers in valence band from flowing into the central metal induced by thermionic emission effect. Thereafter, the proposed N type HLHSB-BTFET has a natural blocking effect on the carriers flowing in valence band, and this blocking effect is not significantly degraded with the increasing of Vds, which is a huge promotion from the previous technology. The comparison between the two technologies is carried out, which exactly agrees with the design assumptions.

Harsh Environmental-Tolerant and High-Performance Triboelectric Nanogenerator Based on Nanofiber/Microsphere Hybrid Membranes.

Triboelectric nanogenerator (TENG) can convert tiny mechanical energy into precious electrical energy. Constant improvements to the output performance of TENG is not only the driving force for its sustainable development, but also the key to expand its practical applicability in modern smart devices. However, most previous studies were conducted at room temperature, ignoring the influence of temperature on the output performance of TENG. Additionally, due to thermionic emission effect, the electrons transferred to a dielectric surface can be released into a vacuum after contact electrification. Therefore, TENG cannot maintain an effective electrical output under high-temperature conditions. Here, a series of high-temperature operatable flexible TENGs (HO-TENGs) based on nanofiber/microsphere hybrid membranes (FSHMs) was fabricated by electrospinning and electrospraying. The Voc of HO-TENG is 212 V, which is 2.33 times higher than that of control TENG. After 10,000 cycle stability tests, the HO-TENG shows excellent durability. Especially, this HO-TENG can maintain 77% electrical output at 70 °C compared to room temperature, showing excellent high-temperature operability. This study can not only provide a reference for the construction of advanced high-performance TENG, but also provide a certain experimental basis for efficient collection of mechanical energy in high-temperature environment and promote the application of TENG devices in harsh environments.

A novel thermionic crystal electron emission effect similar to Kikuchi lines

Kikuchi lines, known since 1928 [S. Kikuchi, Jpn. J. Phys. 5, 83 (1928)], are generated by irradiating a crystal with high-energy e-beam in SEM or TEM and observing backscattered electrons diffraction on crystalline planes. The Kikuchi line effect gave rise to several useful tools in electron microscopy of crystalline and nanocrystalline materials [K. Saruwatari, et al., J. Mineral. Petrol. Sci. 103, 16 (2007)]. We have discovered a similar diffraction effect but of the crystal’ own thermally emitted electrons.

Photo-thermo-electric modeling of photon-enhanced thermionic emission with concentrated solar power

Photon-enhanced thermionic emission (PETE) is an advanced technology that combines both the photoelectric and the thermionic effects synergistically into a single device for direct electricity generation. However, its industrial-level application is still missing partly due to the lack of advanced models to analyze its operating characteristics and to understand the synergistic mechanism. Herein, we develop a numerical model of PETE by fully considering the optical, the electrical and the thermodynamic aspects with one-dimensional steady-state continuity equations of carriers in the semiconductor cathode. A hybrid PETE-Stirling cycle system is also proposed to yield an output power density of 162.65 kW/m 2 with 32.8% conversion efficiency. The PETE conversion efficiency keeps ∼20% with the optimal electron affinity increases from 0.5 to 1.14 eV as solar concentration ratio varies from 100 to 500. The cathode thickness should be optimized by considering both solar absorption and photon enhancement, where the thickness range of 0.78–1.52 μm is obtained for 50–500 suns. The interelectrode gap is also found to significantly affect the PETE performance by regulating both the space-charge effect and near-field radiation, where the range of 0.5–2 μm is recommended. This work can serve as a foundation to understand the working mechanism of PETE converters and provide guidelines for the performance evaluation. • Numerical models are developed for photon-enhanced thermionic emission converters. • Coupled effects of optical, electrical and thermodynamic fields are fully considered. • Characteristics of the converter for various scenarios are analyzed in detail. • A hybrid system is proposed with a 162.65 kW/m 2 power density and a 32.8% efficiency.

SnO2 Nanofibers Network for Cold Cathode Applications in Vacuum Nanoelectronics

AbstractField‐emission cold cathodes are the key components of vacuum nanoelectronics that offer great advantages over other electron sources based on the thermionic or photoelectric effects. In the effort to realize new electron sources, a systematic investigation of the field emission (FE) properties of SnO2 nanofiber networks is performed. High‐purity SnO2 nanofibers, confirmed by X‐ray photoelectron spectroscopy, are prepared by electrospinning technique and then uniformly distributed over Si wafer. Field emission properties are investigated using a nanomanipulated tip‐shaped anode, inside a scanning electron microscope, for fine tuning the anode‐cathode separation distance. A field‐emission current is observed with an applied electric field as low as 25 V μm−1. Performance parameters such as turn‐on field and field enhancement factor are evaluated within the theoretical Fowler–Nordheim framework as a function of the anode–cathode separation distance, demonstrating that a maximum enhancement factor of about 150 is obtained at a separation of 200 nm. The emission from a single nanofiber is characterized by a current saturation at high voltages that can be explained in terms of electron supply limitation within conduction band. No evidence of field emission current contribution by electron tunneling from the valence band is observed in the experimental data.

Triboelectric Polymer with High Thermal Charge Stability for Harvesting Energy from 200 °C Flowing Air

AbstractDue to the thermionic emission effect, the electron transferred to dielectric surface can be released into vacuum after the contact electrification (CE). Therefore, triboelectric nanogenerator (TENG) cannot maintain effective electrical output under high temperature conditions. In order to obtain high thermal charge stability, polyimide is modified with strong electron withdrawing groups like trifluoromethyl (CF3) and sulfone group (SO2) in backbone. The fluorinated polyimides (F‐PI) with a big band gap can provide a tribocharge density of 170 µC m−2 (4 times of common Kapton film) and become more negative than polytetrafluoroethylene in triboelectric series. In addition, BaTiO3 nanoparticles are doped in F‐PI film for inducing deep traps and interfacial polarizations for CE, which can further enhance the charge density (200 µC m−2) and thermal charge stability. Finally, a flutter‐driven TENG (FD‐TENG) is designed based on this BaTiO3‐doped F‐PI film to harvest wind energy and sense wind velocity. This FD‐TENG can maintain 32% of its output performance at 200 °C in comparison with room temperature, which is the highest thermal charge stability reported for triboelectric polymers. Therefore, this BaTiO3‐doped F‐PI has great application prospects for energy generation and motion detection in hot wind tunnel and many other harsh environments.

Low work-function tether Deorbit Kit

This works presents a system level analysis of a Deorbit Kit (DK) based on electrodynamic tether technology. The analysis is focused on two relevant scenarios for deorbiting space debris: (i) Earth Observation (EO) satellites with mass in the range of 700 kg -1000 kg and initial orbital altitude of 800 km and 98° inclination, and (ii) Mega Constellation (MC) spacecraft in the order of 200 kg and initial orbit at 1200 km of altitude and 90° of inclination. The scenarios have been selected considering the orbits that are already suffering from the space debris problem or will suffer in the next future. The DK implements a bare electrodynamic tether for capturing electrons passively from the ambient plasma while three different methods are considered for emitting the electrons back to the plasma to reach a steady electrical current on the tether. The three studied options to close the electrical circuit are: (a) a hollow cathode, which has a high technological maturity but needs expellant and a little of power, (b) a thermionic emitter, which does not involve expellant but needs power, and (c) a Low Work-function Tether (LWT) that does not need neither expellant nor power because it has a segment coated with a special material that emits electrons passively through the thermionic and photoelectric effects. In order to provide a fully autonomous operation even in case of critical failure of the mother spacecraft, the DK includes a deployment mechanism, a telemetry and telecommand system, a complete Attitude Determination and Control System with attitude sensors (GNSS, sun sensors, magnetometer) and actuators (magneto torquers), solar panels and batteries. Upon activation, the DK autonomously de-tumbles the satellite, deploys a tether and carries out the satellite's de-orbiting. The study presents DK architectures, mass budgets and simulation results for the two scenarios. It is shown that a complete DK with mass below 6% the mass of the host spacecraft can deorbit EO and MC satellites in about 1.5 years and 10 years, respectively. The importance of the development of the LWT concept to enhance the simplicity and reduce the mass, power and volume budget is highlighted.

Trade-off analysis of C12A7:e− deposition techniques applied to Low Work Function Tethers

Due to its extraordinary properties, the C12A7:e− electride has been suggested in the past as one of the most promising materials for coating Low Work-function Tethers (LWTs). Such subclass of electrodynamic tether, made of a conductive substrate coated with materials that enhance the electron emission through the thermionic and photoelectric effects, would constitute a fully passive and consumable-free device for deorbiting space debris from Low Earth Orbit. This work presents experimental results on the manufacturing and testing of small tape-like LWT samples, which is the relevant geometry for electrodynamic tether applications. After preparing C12A7:e− targets under specific and controlled conditions, thin titanium foils have been coated with the C12A7:e− electride by using two different physical vapor deposition techniques: magnetron sputtering (MS) and pulsed laser deposition (PLD). In the case of MS, important difficulties and defects were found, including target damage, poor growth rate, and oxidation and changes in the composition of the coating. However, the performance on the PLD coating was radically different. First, Rutherford backscattering spectrometry confirmed that the composition of the thin film with the PLD coincides with that of the target. Second, X-ray photoelectron spectroscopy and thermionic emission experiments showed that the work function of the LWT sample is 2.6 ± 0.1 eV. Therefore, the trade-off analysis indicates that PLD can be used to manufacture LWT samples with work function close to the one of the bulk C12A7:e− (2.4 eV). Nevertheless, its application as passive cathode in electrodynamic tethers still requires further research activities.

First Evaluation of Coated Constantan Wires Incorporating Capuchin Knots to Increase Anomalous Heat and Reduce Input Power at High Temperatures

Anomalous Heat Effects (AHE) have been observed in wires of Cu55Ni44Mn1 (Constantan) exposed to H2 and D2 in multiple experiments during the last eight years. Improvements in the magnitude and reproducibility of AHE, and improvements in wire preparation and reactor design were reported by the authors in the present and previous papers. The oxidation of the wires by pulses of electrical current in air creates a rough surface featuring a sub-micrometric texture that proves particularly effective at inducing thermal anomalies when temperature exceeds 400◦C. This effect appears also to be increased substantially by deposing segments of the wire with a series of elements (such as Fe, Sr, Mn, K, via thermal decomposition of their nitrates applied from a water solution). Furthermore, an increase of AHE was observed after placing the treated wires inside a sheath made of borosilicate glass (B–Si–Ca; BSC), and even more after impregnating the sheath with the same elements used to coat the wires. The treated wire, comprised of knots and sheaths, was wound around a SS316 rod and inserted inside a thick wall glass reactor. The presence of thermal and chemical gradients is an important factor, especially when considering the noteworthy effect of knots on AHE. The ICCF21 Conference held in June 2018 marked a turning point, when the scientific community showed notable interest in the effects of knots and wire treatments, further increasing confidence in the approach. From that time on, attempts to further increase AHE focused on the introduction of different types of knots, leading to the choice of the “Capuchin” type. This knot design produces very hot spots along the wire and it features three areas characterized by a temperature difference up to several hundred degrees. Efforts were also made to better understand the thermionic effect of the wire, and the spontaneous voltage that arises when a second wire is introduced close by (anode). Eventually a large AHE rise was observed when an extra voltage was introduced between the active wire (cathode) and the second wire (anode) through an external power supply; a truly remarkable effect, despite its short duration due to the wire failure caused by an AHE runaway that melted the wire. This article summarizes the presentation given at the 13th International Workshop on Anomalies in Hydrogen Loaded Metals and reports the latest AHE results obtained from a new reactor design comprised of Capuchin knots and new custom manufactured, enhanced sheaths.

Ionospheric Experiment with a Low Work Function Tether Loop

An entirely passive and free of consumable ionospheric experiment, based on a low work function tether (LWT) loop with a control unit equipped with some basics sensors at its center, is presented. The loop has a torus shape and a hollow cross-section. It is made of an aluminum substrate coated with a low work function material to stimulate electron emission through thermionic and photoelectric effects. The work presents an electrodynamic model for the experiment and studies the current and voltage profiles developed in the anodic and cathodic segments of the LWT due to the motional electric field. Two modes of operation, with and without switches in the loop to interrupt the electric current, are considered. It is shown that the loop is deorbited by the Lorentz force exerted by the ambient magnetic field on the electric current. An analysis of the attitude dynamics in the presence of the gravity gradient and the Lorentz torques reveals that, for a circular equatorial orbit, the position of the loop with its symmetry axis normal to the orbital plane can be spin-stabilized easily. The required instruments and the scientific information that would be provided by the experiment are discussed.

Electrical model and optimal design scheme for low work-function tethers in thrust mode

A low work-function tether (LWT), a subclass of bare electrodynamic tether made of a conductor partially coated with a low work function material, can exchange momentum and energy with planetary magnetospheres without any consumable. If fed by an onboard power source to reverse the natural direction of the current given by the motional electric field, a LWT can produce an useful thrust in drag compensation and re-boost scenarios. In the considered scheme, the LWT has an anodic bare segment for passive electron collection, followed by an insulated segment, a power source, and a cathodic segment that emits electrons passively through thermionic and photoelectric effects. Current and voltage profiles along the LWT are obtained and used to compute the system efficiency, i.e. the electrical power to mechanical power conversion rate, and the minimum electrical power to avoid space-charge effects in the cathodic segment. The design conditions to reach a high-efficiency regime are presented. For a given orbit and required thrust, optimal values for the tether geometry, including the fractional lengths of all three tether segments, are found. The results are applied to the preliminary design of a LWT system that would compensate the aerodynamic drag on the International Space Station. The analysis shows that the mission can be performed by a LWT fed with a power source of 4.7 kW, length, width and thickness equal to 5.1 km, 2 cm and 30μm, work function 1.5 eV, and temperature 600 K.

Thermodynamic assessment of solar photon-enhanced thermionic conversion

Photon-enhanced thermionic conversion, an innovative solar power technology, combines photovoltaic and thermionic effects into a single process, and has the potential to surpass the Shockley–Queisser limit and conventional photo-thermal limit. However, there is little understanding about the energy conversion process from a thermodynamic point of view. A detailed thermodynamic model is proposed, encompassing energy and exergy balance, and entropy analysis to evaluate a process for solar photon-enhanced thermionic conversion. The correlation of photons, phonons and electrons is presented, as well as the energy transfer pathway in solar thermionic conversion. The total solar-to-electricity efficiency of energy and exergy are 54.32% and 58.42%, respectively, for a photon-enhanced thermionic converter combined with a Carnot engine, at a 1.20 eV bandgap with an electron affinity of 1.20 eV when the concentrated solar flux is 500 kW/m2. The combination of photoexcitation and thermalization facilitates the overall thermionic emission exergy ratio up to 62.36%, higher than that of conventional thermionic conversion by 10.92%. Temperature-entropy diagrams with quantitative analysis are proposed for the thermodynamic processes of thermionic and photon-enhanced thermionic conversion. The electron fluid cycles from the Fermi level of the anode back to the valance band of the cathode with a reduced entropy, while being thermalized from the conduction band in photon-enhanced thermionic conversion, contributing to the entire conversion of photoexcited energy to electricity.

Why do aged fluorescent tubes flicker?

Our everyday experience of aged and defective fluorescent tubes or bulbs informs us that they may flicker and emit a clicking sound while struggling to light up. In this article, the physical mechanisms controlling the initial illumination of a functioning fluorescent tube are investigated using a simple and affordable experimental setup. Thermionic emission from the electrodes of the tube controls the startup of fluorescent tubes. The origin of the faulty startup of aged fluorescent tubes is discussed and flickering regimes using functional tubes are artificially produced using a dedicated setup that decreases electron emission by the thermionic effect in a controlled manner. The physical parameters controlling the occurrence of flickering light are discussed, and their temporal statistics are reported.