{
  "id": "enwiki-001314537238",
  "slug": "townsend-unit",
  "title": "Townsend (unit)",
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  "lead": "The townsend (symbol Td) is a physical unit of the reduced electric field (ratio E/N), where E is electric field and N is concentration of neutral particles. It is named after John Sealy Townsend, who conducted early research into gas ionisation.",
  "body": "The townsend (symbol Td) is a physical unit of the reduced electric field (ratio E/N), where E is electric field and N is concentration of neutral particles. It is named after John Sealy Townsend, who conducted early research into gas ionisation. ==Definition== It is defined by the relation 1\\ \\text{Td} = 10^{-21}\\ \\text{V} \\cdot \\text{m}^2 = 10^{-17}\\ \\text{V} \\cdot \\text{cm}^2. For example, an electric field of E = 2.5 \\cdot 10^4\\ \\text{V}/\\text{m} in a medium with the density of an ideal gas at 1 atm and 0 °C, the Loschmidt constant n_0 = 2.6867811 \\cdot 10^{25}\\ \\text{m}^{-3} gives E/n_0 \\approx 10^{-21}\\ \\text{V} \\cdot \\text{m}^2, which corresponds to 1 Td. ==Uses== This unit is important in gas-discharge physics, where it serves as scaling parameter because the mean energy of electrons (and therefore many other properties of discharge) is typically a function of E/N over broad range of E and N . The concentration N , which is in ideal gas simply related to pressure and temperature, controls the mean free path and collision frequency. The electric field E governs the energy gained between two successive collisions. Reduced electric field being a scaling factor effectively means that increasing the electric field intensity E by some factor q has the same consequences as lowering gas density N by factor q. ==See also== Electric glow discharge Vacuum arc ==References==",
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    "title": "Townsend (unit)",
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      {
        "family": "Anticloud FZ LLE",
        "literal": "Anticloud FZ LLE"
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    ],
    "container-title": "encyclopegia.org",
    "publisher": "Anticloud FZ LLE",
    "publisher-place": "Dubai, United Arab Emirates",
    "URL": "https://encyclopegia.org/a/townsend-unit",
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      "date-parts": [
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          2026,
          11,
          15
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