Arthur Wehnelt
Encyclopedia
Arthur Rudolph Berthold Wehnelt (born April 4, 1871 in Rio de Janeiro
, died February 15, 1944 in Berlin
) was a German
physicist
, noted for important contributions in the fields of X-ray
physics, gas discharges and electron
emission.
in Berlin
. He received his PhD in 1898 in Erlangen
. 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, where he taught until his retirement in 1937 as a professor and research. In 1934 he was appointed director of the Physics Department.
s. 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
s until the 1920s.
Much of Wehnelt's research dealt with thermionic emission
, the emission of electron
s in vacuum tube
s. In this context, he developed in 1902/03 the Wehnelt cylinder
, an electrode used in electron gun
s. In 1904 he developed what is arguably his most important invention, the Wehnelt or oxide
cathode
for vacuum tube
s. He found that when the cathode in a vacuum tube is coated with alkaline metal oxides, such as calcium oxide
or barium oxide
, its work function
is reduced, causing it to emit more electrons. The oxide cathode became the standard type of cathode used in vacuum tubes to the present day.
Rio de Janeiro
Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...
, died February 15, 1944 in Berlin
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...
) was a German
Germans
The Germans are a Germanic ethnic group native to Central Europe. The English term Germans has referred to the German-speaking population of the Holy Roman Empire since the Late Middle Ages....
physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
, noted for important contributions in the fields of X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
physics, gas discharges and electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
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 UniversityHumboldt University of Berlin
The Humboldt University of Berlin is Berlin's oldest university, founded in 1810 as the University of Berlin by the liberal Prussian educational reformer and linguist Wilhelm von Humboldt, whose university model has strongly influenced other European and Western universities...
in Berlin
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...
. He received his PhD in 1898 in Erlangen
Erlangen
Erlangen is a Middle Franconian city in Bavaria, Germany. It is located at the confluence of the river Regnitz and its large tributary, the Untere Schwabach.Erlangen has more than 100,000 inhabitants....
. 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, 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 for induction coilInduction coil
An induction coil or "spark coil" is a type of disruptive discharge coil. It is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current supply...
s. 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
X-ray machine
An X-ray generator is a device used to generate X-rays. These devices are commonly used by radiographers to acquire an x-ray image of the inside of an object but they are also used in sterilization or fluorescence....
s until the 1920s.
Much of Wehnelt's research dealt with thermionic emission
Thermionic emission
Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
, the emission of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s in vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s. In this context, he developed in 1902/03 the Wehnelt cylinder
Wehnelt cylinder
A Wehnelt cylinder 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 Berthold Wehnelt, a German physicist, who invented it during the years 1902 and 1903. A Wehnelt cylinder is also known as...
, an electrode used in electron gun
Electron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
s. In 1904 he developed what is arguably his most important invention, the Wehnelt or oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
for vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s. He found that when the cathode in a vacuum tube is coated with alkaline metal oxides, such as calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
or barium oxide
Barium oxide
Barium oxide, BaO, is a white hygroscopic compound formed by the burning of barium in oxygen, although it is often formed through the decomposition of other barium salts.It reacts with water to form barium hydroxide.-Uses:...
, its work function
Work function
In solid-state physics, the work function is the minimum energy needed to remove an electron from a solid to a point immediately outside the solid surface...
is reduced, causing it to emit more electrons. The oxide cathode became the standard type of cathode used in vacuum tubes to the present day.