Velocity bunching

Because of the velocity bunching effect due to initial acceleration the ion beam is nearly monokinetic, and the neutralisation does not effect the velocity distribution The details of the method can be found in [ KAUF 78 ], [ NUE 78] By neutralisation in an alkali vapour, the atomic metastable states are preferentially populated since their energies match the ionisation potential of the corresponding alkali atom Therefore this technic is ideally suited for laser spectroscopy of rare gas, and is recently successfully used to study the heaviest one, radon Fig. 

This means that the faster electrons contribute to the amplification of the incident laser wave, whereas the slower electrons attenuate it. This stimulated emission of the faster electrons and the absorption of photons by the slower electrons leads to a velocity bunching of the electrons toward the critical velocity Vc and enhances the coherent superposition of their contributions to the radiation field. The energy pumped by the electrons into the radiation field comes from their kinetic energy and has to be replaced by acceleration in RE cavities, if the same electrons in storage rings are to be used for multiple traversions through the wiggler. 

The klystron relies on the velocity bunching of the electrons from a heated cathode over a body length of 1 m or more. This is necessary to permit orderly physical spacing of the buncher cavities and the individual electron velocities to form properly. The superiority of the klystron over the gridded tube (typically a tetrode) is its output coupling, a cavity. 

There is no theoretical upper limit on m/z that can be examined, and TOF mass spectrometry is useful for substances having very high molecular mass. In practice, the current upper limit is about 350,000. Unfortunately, ions even of the same m/z value do have a spread of velocities after acceleration, so the resolution achievable with TOF is not very high because bunches of ions of one m/z value overlap those at the next m/z value. 

Clusters consist of from five to several hundred spherical particles attached to each other in a similar fashion to a bunch of grapes. They occur infrequently and appear to be a product of high power or high velocity. Flakes of smokeless powder are few in number and are occasionally seen in promptly collected residue. Unlike the other three types of particles, which are inorganic in nature, the flakes are organic although sometimes spherical particles are embedded in their surface. They range in size from about 50 to 1,000 pm. Clusters and powder flakes are rarely seen in casework as they are... 

Fast positrons are created by bremsstrahlung pair-production in an electron microtron accelerator. These are moderated and bunched into 25 ns packets at 30 Hz, each comprised of 2 x 104 slow positrons. The positrons are guided by a 150-G magnetic field and implanted at 1-2 keV kinetic energy onto an Al(lll) crystal heated to 576 5 K as shown in Figure 7a. About 30% of the incident positrons come off the surface as thermal positronium with a velocity distribution that is a beam Maxwellian. 

In vacuo, i.e., under space travel conditions, ions, which are atomic carriers of electric charges, can be accelerated by electric fields and bunched to give a single beam. The discharge velocity thus attained is of a higher order than that of gaseous products from chemical reactions. For this reason, very high values of specific impulse can be produced. 

Of special interest is the time structure of the particle current illustrated in Fig. 4. The duration of the puls Tp depends on the length and the velocity of the bunch. At the... 

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