Question: General Electric discovered synchrotron radiation when?
About the article "Electron", section "Particle accelerators".

Candidate passages:
With the development of the particle accelerator during the first half of the twentieth century, physicists began to delve deeper into the properties of subatomic particles.
The first successful attempt to accelerate electrons using electromagnetic induction was made in 1942 by Donald Kerst.
His initial betatron reached energies of 2.3 MeV, while subsequent betatrons achieved 300 MeV.
In 1947, synchrotron radiation was discovered with a 70 MeV electron synchrotron at General Electric.
This radiation was caused by the acceleration of electrons, moving near the speed of light, through a magnetic field.
With a beam energy of 1.5 GeV, the first high-energyparticle collider was ADONE, which began operations in 1968.
This device accelerated electrons and positrons in opposite directions, effectively doubling the energy of their collision when compared to striking a static target with an electron.
The Large Electron–Positron Collider (LEP) at CERN, which was operational from 1989 to 2000, achieved collision energies of 209 GeV and made important measurements for the Standard Model of particle physics.
Synchrotron radiation was named after its discovery in a General Electric synchrotron accelerator built in 1946 and announced in May 1947 by Frank Elder, Anatole Gurewitsch, Robert Langmuir, and Herb Pollock in a letter entitled "Radiation from Electrons in a Synchrotron".
Pollock recounts: "On April 24, Langmuir and I were running the machine and as usual were trying to push the electron gun and its associated pulse transformer to the limit.
Some intermittent sparking had occurred and we asked the technician to observe with a mirror around the protective concrete wall.
He immediately signaled to turn off the synchrotron as "he saw an arc in the tube."
The vacuum was still excellent, so Langmuir and I came to the end of the wall and observed.
At first we thought it might be due to Cherenkov radiation, but it soon became clearer that we were seeing Ivanenko and Pomeranchuk radiation."
If a charged particle such as an electron is accelerated, this can be acceleration in a straight line or motion in a curved path, electromagnetic radiation is emitted by the particle.
Within electron storage rings and circular particle accelerators known as synchrotrons, electrons are bent in a circular path and emit X-rays typically.
This radially emitted (formula_11) electromagnetic radiation when charged particles are accelerated is called synchrotron radiation.
It is produced in synchrotrons using bending magnets, undulators and/or wigglers.
The first observation came at the General Electric Research Laboratory in Schenectady, New York, on April 24, 1947 in the synchrotron built by a team of Herb Pollack to test the idea of phase-stability principle for RF accelerators.
When the technician was asked to look around the shielding with a large mirror to check for sparking in the tube, he saw a bright arc of light coming from the electron beam.
Robert Langmuir is credited as recognizing it as synchrotron radiation or, as he called it, "Schwinger radiation" after Julian Schwinger.
Classically, the radiated power "P" from an accelerated electron is: formula_12 this comes from the Larmor formula; where "K" is an electric permittivity constant, "e" is electron charge, "c" is the speed of light, and "a" is the acceleration.
Within a circular orbit such as a storage ring, the non-relativistic case is simply the centripetal acceleration.
However within a storage ring the acceleration is highly relitivistic, and can be obtained as follows: formula_13 where "v" is the circular velocity, "r" is the radius of the circular accelerator, "m" is the rest mass of the charged particle, "p" is the momentum, "τ" is the Proper time (t/γ), and "γ" is the Lorentz factor.
Radiated power then becomes: formula_14 For highly relativistic particles, such that velocity becomes nearly constant, the γ4 term becomes the dominate variable in determining loss rate.
This means that the loss scales as the fourth power of the particle energy γmc2; and the inverse dependence of synchrotron radiation loss on radius argues for building the accelerator as large as possible. 
The electromagnetic radiation emitted when charged particles are accelerated radially (formula_1) is called synchrotron radiation.
It is produced in synchrotrons using bending magnets, undulators and/or wigglers.
It is similar to cyclotron radiation except that synchrotron radiation is generated by the acceleration of ultrarelativistic charged particles through magnetic fields.
Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, or naturally by fast electrons moving through magnetic fields.
The radiation produced in this way has a characteristic polarization and the frequencies generated can range over the entire electromagnetic spectrum. 
 Cyclotron radiation Synchrotron light; see also synchrotron radiation High altitude nuclear explosion Bremsstrahlung Čerenkov radiation Radioluminescence Sonoluminescence