An undulator is an insertion device from high-energy physics and usually part of a larger
installation, a synchrotron storage ring. It consists of a periodic structure of dipole magnets. A static magnetic field is alternating along the length of the undulator with a wavelength formula_1. Electrons traversing the periodic magnet structure are forced to undergo oscillations. So the electrons give off energy as electronmagnetic radiation. The radiation produced in an undulator is very intense and concentrated in narrow energy bands in the spectrum. The light beam is also collimated on the orbit plane of the electrons. This radiation is guided through beamlines for experiments in various scientific areas.
The important dimensionless parameter
formula_2
where "e" is the particle charge, "B" is the magnetic field, "formula_3", "formula_4" is the electron rest
mass and "c" is the speed of light, characterizes the nature of the electron motion. For
formula_5 the oscillation amplitude of the motion is small and the radiation displays interference patterns which lead to narrow energy bands. If formula_6 the oscillation amplitude is bigger and the radiation contributions from each field period sum up independently, leading to a broad energy spectrum. When K is much bigger than 1, the device is no longer called an "undulator"; it is called a wiggler.
Physicist think about undulators both using classical physics and relativity. This means that though the precision calculation is tedious the undulator can be seen as a black box. An electron enters this box and an electromagnetic pulse exits through a small exit slit. The slit should be small enough so that only the main cone passes, so that the side lobes may be ignored.
Undulators can provide hundreds of time more magnetic flux than a simple bending magnet and as such are in high demand at synchrotron radiation facilities. For an undulator that repeat N times (N periods), the brightness can be up to formula_7 more than a bending magnet. The intensity is enhanced up to a factor of N at harmonic wavelengths due to the constructive interference of the fields emitted during the N radiation periods. The usual pulse is a sine wave with some envelope. The second factor of N comes from the reduction of the emission angle associated with these harmonics, which is reduced in proportion to 1/N. When the electrons come with half the period, they interfere destructively. So, the undulator stays dark. The same is true if the electrons come as a bead chain. Because the bunch of electron spreads out the more times that they travel around the synchrotron, physicists want to design new machines that throw out the electron bunches before they have a chance to spread out. This change will produced more useful synchrotron radiation.
The polarization of the emitted radiation can be controlled by using permanent magnets to induce different periodic electron trajectories through the undulator. If the oscillations are confined to a plane the radiation will be linearly polarized. If the oscillation trajectory is helical, the radiation will be circularly polarized, with the handedness determined by the helix.
If the electrons follow the Poisson distribution, a partial interference leads to a linear increase in intensity.
In the free-electron laser the intensity increases exponentially with the number of electrons.
Physicists measure an undulator's effectiveness in terms of spectral radiance.
The first undulator was built by Hans Motz and his coworkers at Stanford in 1953. One of their undulators produced the first ever coherent infrared radiation. Their total frequency range was from visible light down to millimeter waves. The Russian physicist V.L. Ginzburg showed that undulators could be made in principle in a 1947 paper.
D. T. Attwood's page at Berkeley: Soft X-Rays and Extreme Ultraviolet Radiation . His lecture and viewgraphs are available online.
Storytime
"Storytime" is a song by Finnish symphonic metal band Nightwish. The song was written by keyboardist Tuomas Holopainen, who also created the band. It became the lead single from the band's seventh studio album "Imaginaerum" (2011). "Storytime" features vocals by the vocalist of Nightwish, Anette Olzon. The single was released on November 9, 2011 from Nuclear Blast with mostly positive reviews from music journalist.
The song is about human expressions through folklore tales such as Peter Pan and Alice's Adventures in Wonderland. It also talks about Gaia, a mythical Greek Earth goddess, in the song. A music video was released to promote "Storytime" in November 2011, it features the entire band playing their instruments in a "fantasy" world. After the single's release on radios, it peaked at number-one on the Finnish Singles Chart and peaked within the top 5 in Spain, Hungary, and the United Kingdom.
One day there was a really ugly thing called Lennie yeah and like he liked doin it doggy style yeah and like yeah
Imaginaerum
Imaginaerum is the seventh album by the Finnish symphonic metal group Nightwish. It is their second album with Swedish vocalist Anette Olzon. A movie of the same name was released in 2012. The movie has songs from the album in it. The album was No.1 in Finland.
Anette Olzon
Anette Ingegerd Olsson (born 21 June 1971) better known as Anette Olzon (married name Blyckert) is a Swedish singer. She is the current lead singer of the Finnish symphonic metal group Nightwish. She used to be the lead singer of Aylson Avenue.
Romania at the Olympics
Romania at the Olympics is a history which began in 1900.
The International Olympic Committee's official abbreviation for Romania was RUM. It is now ROU.
A team from Romania was first at the Olympic Games in 1900. They had only one participant. The National Olympic Committee for Romania is the "Romanian Olympic and Sports Committee". It was formed and recognized in 1914. The nation first sent a team to the Games in 1924. They have been to each of the Summer Olympic Games and Winter Olympic Games since then except for two times. Notably, Romania was the lone Eastern Bloc nation to participate at the 1984 Summer Olympics, which the other nations boycotted. That was also Romania's most successful Olympic Games: they won 20 gold medals and 53 medals total.
Romanian athletes have won a total of 293 medals, with gymnastics as the top medal-producing sport.
Serbia at the Olympics
Serbia was first at the Olympic Games in 1912. After 96 years, Serbia returned to the Olympics as an independent team at the 2008 Summer Olympics. From 1920 to the 1992 Winter Olympics Serbian athletes were part of the Yugoslavian team. At the 1992 Summer Olympics they took part as Independent Olympic Participants. This was because the United Nations was threatening to punish Serbia. Because of this, no Serbians were at the 1994 Winter Olympics. The threats stopped in 1995. From the 1996 Summer Olympics to the 2006 Winter Olympics they were part of the Serbia and Montenegro team.
Slovakia at the Olympics
Slovakia was first at the Olympic Games in 1994. They have been in every Games since then. Before Czechoslovakia broke up in 1993, Slovak athletes competed for Czechoslovakia at the Olympics.
Slovak athletes have won twenty medals altogether at the Summer Olympic Games. These were mostly for canoeing. The nation has also won four medals at the Winter Olympic Games.
The National Olympic Committee for Slovakia was made in 1992 and recognized in 1993.
Slovenia at the Olympics
Slovenia was first an independent nation at the Olympic Games in 1992. They have been in every Games since then. Prior to the breakup of Yugoslavia, Slovenian athletes were part of Yugoslavia at the Olympics.
The National Olympic Committee for Slovenia was formed in 1991 and recognized in 1993. Slovenian athletes have won a total of fifteen medals at the Summer Olympic Games and another seven at the Winter Olympic Games.
Sweden at the Olympics