Arthur Rudolph Berthold Wehnelt (April 4, 1871 – February 15, 1944) was a

German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

, noted for important contributions in the fields of

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

physics, gas discharges and

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

emission.

Life

Wehnelt's parents returned to Germany from Brazil when he was still a boy. He studied physics at the Technische Hochschule Charlottenburg, and from 1893 to 1897 at the Friedrich-Wilhelms University in

Berlin Berlin ( , ) is the capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's List of cities in the European Union by population within ci ...

. He received his PhD in 1898 in

Erlangen Erlangen (; East Franconian: ''Erlang'', Bavarian: ''Erlanga'') is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative district Erlangen), and with 116,062 inhab ...

. He taught as a lecturer from 1901 and associate professor of physics from 1904 at the Friedrich-Alexander University Erlangen-Nuremberg. He moved again in 1906 to the

University of Berlin Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative ...

, where he taught until his retirement in 1937 as a professor and research. In 1934 he was appointed director of the Physics Department.

Work

In 1899, he invented the Wehnelt

interrupter An interrupter in electrical engineering is a device used to interrupt the flow of a steady direct current for the purpose of converting a steady current into a changing one. Frequently, the interrupter is used in conjunction with an inductor (c ...

for induction coils. This device used a platinum electrode immersed in electrolyte. When current was passed through it the gas bubbles evolved caused repeated interruption in the current. It was able to develop higher voltages from induction coils, and was widely employed in the large induction coils that powered early

x-ray machine An X-ray machine is any machine that involves X-rays. It may consist of an X-ray generator and an X-ray detector. Examples include: *Machines for medical projectional radiography *Machines for computed tomography *Backscatter X-ray machines, used ...

s until the 1920s. Much of Wehnelt's research dealt with

thermionic emission Thermionic emission is the liberation of electrons from an electrode by virtue of its temperature (releasing of energy supplied by heat). This occurs because the thermal energy given to the charge carrier overcomes the work function of the mater ...

, the emission of

s in

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...

s. In this context, he developed in 1902/03 the

Wehnelt cylinder A Wehnelt cylinder (also known as ''Wehnelt cap'', ''grid cap'' or simply ''Wehnelt'') is an electrode in the electron gun assembly of some thermionic devices, used for focusing and control of the electron beam. It is named after Arthur Rudolph ...

, an electrode used in

electron gun An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...

s. In 1904 he developed what is arguably his most important invention, the Wehnelt or oxide

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...

for

s.Applied Surface Science Volume 251, Issues 1-4, 15 September 2005, Pages 24-30 He found that when the cathode in a vacuum tube is coated with an

alkaline earth metal The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are all ...

oxide, such as

calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ...

barium oxide Barium oxide, also known as baria, is a white hygroscopic non-flammable compound with the formula BaO. It has a cubic structure and is used in cathode ray tubes, crown glass, and catalysts. It is harmful to human skin and if swallowed in larg ...

, its

work function In solid-state physics, the work function (sometimes spelt workfunction) is the minimum thermodynamic work (i.e., energy) needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface. Here "immediately" ...

is reduced, causing it to emit electrons more rapidly. The oxide cathode became the standard type of cathode used in vacuum tubes to the present day.

Awards and honors

John Scott Medal John Scott Award, created in 1816 as the John Scott Legacy Medal and Premium, is presented to men and women whose inventions improved the "comfort, welfare, and happiness of human kind" in a significant way. "...the John Scott Medal Fund, establish ...

(1905)

References

External links

* {{DEFAULTSORT:Wehnelt, Arthur 1871 births 1944 deaths 20th-century German physicists