Dictionary - Definition of HELICITY

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Specialty Definition: HELICITY

Domain	Definition
Physics	1: (from John Cobb) A measurement of the topological "tangledness" of magnetic field lines. It is formally defined as the scalar product of the magnetic vector potential with the magnetic field, K = A dot B. If the plasma is perfectly conducting, then helicity is a conserved quantity. (Without resistance, field lines cannot reconnect, and magnetic topology is conserved, so helicity is conserved). (See frozen-in flow). If the plasma has a small amount of resistivity, then Helicity is not exactly conserved. However, the total helicity inside of a given flux surface is often conserved to a good approximation. In that case, the dynamics of a plasma can be analyzed as an evolution toward a minimum energy state subject to the constraint of a conserved total helicity (See Taylor State, J.B. Taylor). This is often used in analyzing the equilibrium and relaxation of RFP's and other toroidal devices. (references)
	2: A measurement of the topological "tangledness" of magnetic field lines. It is formally defined as the scalar product of the magnetic vector potential with the magnetic field, K = A dot B. If the plasma is perfectly conducting, then helicity is a conserved quantity. (Without resistance, field lines cannot reconnect, and magnetic topology is conserved, so helicity is conserved). (See frozen-in flow). If the plasma has a small amount of resistivity, then Helicity is not exactly conserved. However, the total helicity inside of a given flux surface is often conserved to a good approximation. In that case, the dynamics of a plasma can be analyzed as an evolution toward a minimum energy state subject to the constraint of a conserved total helicity. This is often used in analyzing the equilibrium and relaxation of RFP's and other toroidal devices. - from John Cobb. (references)
Weather	1: A measure of low level wind shear, normally within the lowest 3 km of the atmosphere, relative to the movement of a thunderstorm (thus referred to as 0-3 km Storm Relative Helicity). This gives forecasters an indication of an environment that is favorable for supporting the development of thunderstorms with rotating updrafts, a precursor to supercell thunderstorms (the most violent of severe storms) and tornado development. Values of helicity greater than +150 are considered significant; however, like CAPE values, there is no magic value of (positive) helicity under which rotating thunderstorms will not develop. Helicity is only an index to determining thunderstorm rotation potential. (See also Shear). (references)
	2: A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve. Helicity is proportional to the strength of the flow, the amount of vertical wind shear, and the amount of turning in the flow (i.e. vorticity). (references)
Wikipedic	The term helicity has several meanings in physics, all referring (perhaps obliquely) to a phenomenon that resembles a helix. (references)
Source: compiled by the editor from various references; see credits.		Top

Common Expressions: HELICITY

Expressions	Definition
Helicity (fluid mechanics)	In fluid mechanics, helicity is the extent to which corkscrew-like motion occurs. If a parcel of fluid is moving, undergoing solid body motion rotating about an axis parallel to the direction of motion, it will have helicity. If the rotation is clockwise when viewed from ahead of the body, the helicity will be positive, if anticlockwise, it will be negative. (references)
Magnetic helicity	In plasma physics, magnetic helicity is the extent to which a magnetic field "wraps around itself". If magnetic field lines follow the strands of a twisted rope, this configuration would have nonzero magnetic helicity; left handed ropes would have negative values and right handed ropes would have positive values. (references)
Source: compiled by the editor from various references; see credits.		Top

Specialty Expressions: HELICITY

Expressions	Domain	Definition
Energy Helicity Index	Weather	An index that incorporates vertical shear and instability, designed for the purpose of forecasting supercell thunderstorms. It is related directly to storm-relative helicity in the lowest 2 km (SRH, in m2/s2) and CAPE (in j/kg) as follows: (or EHI). (references)
Helicity injection	Physics	A means of imparting a helical magnetic wave into a plasma to produce a driven current and is potentially valuable for sustaining toroidal and spherical devices. The helicity of a toroidal plasma is related to a linkage of toroidal and poloidal magnetic fields, and is approximately conserved throughout a discharge. If additional helicity can be injected, the plasma current can be sustained or even increased. (references)
Source: compiled by the editor from various references; see credits.			Top

Extended Definition: HELICITY

Helicity

The term helicity has several meanings in physics, all referring (perhaps obliquely) to a phenomenon that resembles a helix. See:

helicity (fluid mechanics)
helicity (particle physics)
magnetic helicity
circular dichroism

In biochemistry, helicity may also refer to the amount of alpha helix represented in the secondary structure of a protein.

In chemistry, helicity may refer to a type of planar chirality.

Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Helicity". Image Credit.
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Topics by Level of Interest: HELICITY
Topics sorted by level of Interest	Level (1=low, 600=high)	Topics sorted Alphabetically	Level (1=low, 600=high)
Helicity	16	Helicity	16
Helicity basis	10	Helicity (fluid mechanics)	9
Helicity (fluid mechanics)	9	Helicity (particle physics)	5
Helicity (particle physics)	5	Helicity basis	10
Magnetic helicity	5	Magnetic helicity	5
Source: the editor, created by/for EVE to gauge likely levels of human interest in linguistically triggered topics (compiled across various sources, such as Wikipedia and specialty expression glosses).

Translations: HELICITY

Language	Translations (or nearest inflections or synonyms, in parentheses)
Chinese Simplified	螺旋性 (helical, helicity). Additional references: Chinese Simplified, China, Brunei, helicity. (volunteer & more translations)
Chinese Traditional	螺旋性 (helicity). Additional references: Chinese Traditional, China, Brunei, helicity. (volunteer & more translations)
Français	hélicité (Helicity). Additional references: Français, France, Algeria, helicity. (volunteer & more translations)
French	hélicité (Helicity). Additional references: French, France, Algeria, helicity. (volunteer & more translations)
Hanguk Mal	〈물리〉 헬리시티 (helicity), 〈화학〉 나선 구조 (helicity), 헬리시티 (Helicity). Additional references: Hanguk Mal, Korea, South, Korea, helicity. (volunteer & more translations)
Hanguohua	〈물리〉 헬리시티 (helicity), 〈화학〉 나선 구조 (helicity), 헬리시티 (Helicity). Additional references: Hanguohua, Korea, South, Korea, helicity. (volunteer & more translations)
Italian	elicità (helicity). Additional references: Italian, Italy, Croatia, helicity. (volunteer & more translations)
Japanese	ヘリシティ (helicity). Additional references: Japanese, Japan, Taiwan, helicity. (volunteer & more translations)
Korean	〈물리〉 헬리시티 (helicity), 〈화학〉 나선 구조 (helicity), 헬리시티 (Helicity). Additional references: Korean, Korea, South, Korea, helicity. (volunteer & more translations)
Source: Eve, based on a combination of meta analysis and graph theory (for near and back translations).		Top

Language	Translations for “helicity” or closest synonym(s); back translations in parentheses.
Pig Latin	elicityhay (helicity). Additional references: Pig Latin, helicity. (volunteer)
Terran B	helicite (Helicity). Additional references: Terran B, helicity. (volunteer)
Source: compiled by the editor.		Top