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.