Avalanche effect between two electrodes

The Townsend discharge is a gas ionization process where an initially very small amount of free electrons, accelerated by a sufficiently strong electric field, give rise to electrical conduction through a gas by avalanche multiplication: when the number of free charges drops or the electric field weakens, the phenomena ceases. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can It is a process characterized by very low current densities: in common gas filled tubes, typical magnitude of currents flowing during this process range from about 10 − 18A to about 10 - 5A, while applied voltages are almost constant. A gas-filled tube, also known as a discharge tube, is an arrangement of Electrodes in a Gas within an insulating, temperature-resistant Envelope Subsequent transition to ionisation processes of dark discharge, glow discharge, and finally to arc discharge are driven by increasing current densities: in all these discharge regimes, the basic mechanism of conduction is avalanche breakdown. Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials Townsend discharge is named after John Sealy Townsend. John Sealy Edward Townsend (7 June 1868 - 16 February 1957 was a Mathematical Physicist who conducted various studies concerning the Electrical conduction

## Quantitative description of the phenomenon

The basic setup of the experiments investigating ionization discharges in gases consist of a planar parallel plate capacitor filled with a gas and a continuous current high voltage source connected between its terminals: the terminal at the lower voltage potential is named cathode while the other is named anode. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors This page is about the physical properties of gas as a state of matter Direct current ( DC) is the unidirectional flow of Electric charge. A voltage source is any device or system that produces an Electromotive force between its terminals OR derives a secondary voltage from a primary A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An anode is an Electrode through which Electric current flows into a polarized electrical device Forcing the cathode to emit electrons (eg. by irradiating it with a X-ray source), Townsend found that the current I flowing into the capacitor depends on the electric field between the plates in such a way that gas ions seems to multilply as they moved between them. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. John Sealy Edward Townsend (7 June 1868 - 16 February 1957 was a Mathematical Physicist who conducted various studies concerning the Electrical conduction In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge He observed currents varying over ten or more orders of magnitude while the applied voltage was virtually constant: the experimental data obtained from his (and his school's) first experiments are described by the following formula

$\frac{I}{I_0}=e^{\alpha_n d},$

where

• $I\,$ is the current flowing in the device,
• $I_0\,$ is the photoelectric current generated at the cathode surface,
• e, is the
• $\alpha_n\,$ is the first Townsend ionisation coefficient, expressing the number of ion pairs generated per unit length (e. Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge g. meter) by a negative ion (anion) moving from cathode to anode,
• $d\,$ is the distance between the plates of the device. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An anode is an Electrode through which Electric current flows into a polarized electrical device Distance is a numerical description of how far apart objects are

The almost constant voltage between the plates is equal to the breakdown voltage needed to create a self-sustaining avalanche: it decreases when the current reaches the glow discharge regime. Breakdown Voltage of an Insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive. Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble Subsequent experiments revealed that the current I rises faster than predicted by the above formula as the distance d increases: two different effects were considered in order to explain the physics of the phenomenon and to be able to do a precise quantitative calculation.

### Gas ionisation caused by motion of positive ions

Townsend put forward the natural hypothesis that also positive ions produce ion pairs, introducing a coefficient αp expressing the number of ion pairs generated per unit length by a positive ion (cation) moving from cathode to anode. John Sealy Edward Townsend (7 June 1868 - 16 February 1957 was a Mathematical Physicist who conducted various studies concerning the Electrical conduction An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An anode is an Electrode through which Electric current flows into a polarized electrical device The following formula was found

$\frac{I}{I_0}=\frac{(\alpha_n-\alpha_p)e^{(\alpha_n-\alpha_p)d}}{\alpha_n-\alpha_p e^{(\alpha_n-\alpha_p)d}} \qquad\Longrightarrow\qquad \frac{I}{I_0}\cong\frac{e^{\alpha_n d}}{1 - {\alpha_p/\alpha_n} e^{\alpha_n d}}$

since β < < α, in very good agreement with experiments.

### Cathode emission caused by impact of ions

Townsend and Holst and Oosterhuis also put forward an alternative hypothesis, considering augmented emission of electrons by cathode caused by positive ions impact, introducing Townsends second ionization coefficient εi, the average number of electrons released from a surface by an incident positive ion, and working out the following formula:

$\frac{I}{I_0}=\frac{e^{\alpha_n d}}{1 - {\epsilon_i}\left(e^{\alpha_n d}-1\right)}.$

These two formulas may be thought as describing limiting cases of the effective behavior of the process: note that they can be used to well describe the same experimental results. John Sealy Edward Townsend (7 June 1868 - 16 February 1957 was a Mathematical Physicist who conducted various studies concerning the Electrical conduction A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. Other formulas describing, various intermediate behaviors, are found in the literature, particularly in reference 1 and citations therein.

## Applications

• Avalanche multiplication during Townsend discharge is naturally used in gas phototubes, to amplify the photoelectric charge generated by incident radiation (visible light or not) on the cathode: achievable current is typically 10~20 times greater respect to that generated by vacuum phototubes. Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials A phototube is a type of gas-filled or Vacuum tube that is extremely sensitive to light in the Ultraviolet, visible, and Near-infrared Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device A phototube is a type of gas-filled or Vacuum tube that is extremely sensitive to light in the Ultraviolet, visible, and Near-infrared
• The starting of Townsend discharge sets the upper limit to the blocking voltage a glow discharge gas filled tube can withstand : this limit is the Townsend discharge breakdown voltage also called ignition voltage of the tube. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble A gas-filled tube, also known as a discharge tube, is an arrangement of Electrodes in a Gas within an insulating, temperature-resistant Envelope Breakdown Voltage of an Insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive.
Neon lamp/cold-cathode gas diode relaxation oscillator
• The presence of Townsend discharge and glow discharge breakdown voltages shapes the VAIA characteristic of any gas diode or neon lamp in a way such that it has a negative differential resistance region of the S-type. A relaxation oscillator is an oscillator in which a Capacitor is charged gradually and then discharged rapidly Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical A neon lamp is a Gas discharge Lamp containing primarily Neon gas at low Pressure. Negative resistance (or negative differential resistance (NDR or differential negative resistance (DNR is a property of Electrical circuit elements composed This occurrence is typically used to generate electrical oscillations and waveforms, as in the relaxation oscillator whose schematic is shown in the picture on the right. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states waveformogg|right|a sine square and sawtooth wave at 440 hz]] Waveform means the shape and form of a signal such as a Wave moving in a solid liquid or gaseous A relaxation oscillator is an oscillator in which a Capacitor is charged gradually and then discharged rapidly The sawtooth shaped oscillation generated has frequency
$f\cong\frac{1}{R_1C_1\ln\frac{V_1-V_{GLOW}}{V_1-V_{TWN}}},$
where
• VGLOW is the glow discharge breakdown voltage,
• VTWN is the Townsend discharge breakdown voltage,
• C1, R1 and V1 are respectively the capacitance, the resistance and the supply voltage of the circuit. Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble Breakdown Voltage of an Insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive. Breakdown Voltage of an Insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive. Capacitance is a measure of the amount of Electric charge stored (or separated for a given Electric potential. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical
Since temperature and time stability of the characteristics of gas diodes and neon lamps is low, and also the statistical dispersion of breakdown voltages is high, the above formula can only give a qualitative indication of what the real frequency of oscillation is. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of A neon lamp is a Gas discharge Lamp containing primarily Neon gas at low Pressure. In Statistics, (statistical dispersion (also called statistical variability or variation) is variability or spread in a Variable or a Probability