The pseudospark switch a

gas-filled tube A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tubes exploit phenomena related to electric d ...

capable of high speed

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

ing. Pseudospark switches are functionally similar to

triggered spark gap A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conduct ...

s. Advantages of pseudospark switches include the ability to carry reverse currents (up to 100%), low pulse, high lifetime, and a high current rise of about 10¹² A/sec. In addition, since the cathode is not heated prior to switching, the

standby power Standby power, also called vampire power, vampire draw, phantom load, ghost load or leaking electricity ("phantom load" and " leaking electricity" are defined technical terms with other meanings, adopted for this different purpose), refers to ...

is approximately one

order of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...

lower than in thyratrons. However, pseudospark switches have undesired plasma phenomena at low peak currents. Issues such as current quenching, chopping, and impedance fluctuations occur at currents less than 2–3 kA while at very high peak currents (20–30 kA) a transition to a metal vapor arc occurs which leads to

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

of the

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

Construction

A pseudospark switch's electrodes (cathode and anode) have central holes approximately 3 to 5 mm in diameter. Behind the cathode and anode lie a hollow cathode and hollow anode, respectively. The electrodes are separated by an insulator. A low pressure (less than 50 Pa) "working gas" (typically

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

) is contained between the electrodes. While a pseudospark switch is generally fairly simple in construction, engineering a switch for higher lifetimes is more difficult. One method of extending the lifetime is to create a multichannel pseudospark switch to distribute the current and as a result, decrease the erosion. Another method is to simply use cathode materials more resistant to erosion. Typical electrode materials include

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...

rhenium Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

tantalum Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is ...

, and

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

materials. Tantalum, however, cannot be used with hydrogen due to chemical erosion affecting the lifetime adversely. Of the metals, tungsten and molybdenum are commonly used, though molybdenum electrodes show issues with reignition behavior. Several papers which compare electrode materials claim tungsten is the most suitable of the metal electrodes tested. Some ceramic materials such as

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...

and

boron carbide Boron carbide (chemical formula approximately B4C) is an extremely hard boron–carbon ceramic, a covalent material used in tank armor, bulletproof vests, engine sabotage powders, as well as numerous industrial applications. With a Vickers hard ...

have proven to be excellent electrode materials as well, with lower erosion rates than tungsten in certain cases.

Pseudospark discharge

In a pseudospark discharge a breakdown is first triggered between the electrodes by applying a voltage. The gas then breaks down as a function of the pressure, distance, and voltage. An " ionization avalanche" then occurs producing a homogeneous discharge

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

confined to the central regions of the electrodes. Pseudospark Switch

In the figure above, the various stages of the pseudospark discharge can be seen. Stage (I) is the triggering or low current phase. The discharges in both stage (II), the hollow cathode phase, and stage (III), the borehole phase, are capable of carrying currents of several hundred amps. The transition from the borehole phase to the high current phase (IV) is very fast, characterized by a sudden jump in switch impedance. The last phase (V) only occurs for currents of several 10 kA and is unwelcome as it results in high erosion rates.

References

External links

* * {{cite web , title=Cold-Cathode high-current low-pressure spark switches , url=https://www.hcei.tsc.ru/en/cat/technologies/tech15.html Gas-filled tubes Switching tubes Plasma physics Electrical breakdown

Construction

Pseudospark discharge

See also

References

Further reading

External links