Beam bunching

All ion gun optical columns are provided with deflection plates for scanning the ion beam over areas adjustable from a few square micrometers to many square millimeters. They have been adapted for pulsing by the introduction of additional deflection plates which rapidly sweep the beam across an aperture. By applying an ion beam bunching technique, ion pulses less than 1 ns wide can be produced. 

The Maestro beamed, bunching cheeks and very nearly showing his teeth. Identified and delivered, Your Serenity. Inquisitor Gritti has him locked up already. ... 

In addition, the primary ion analysis beam focusing/pulse sequencing can be tailored to optimize the specific information required. As an example, the pulse width, which defines the mass resolution, can be adjusted by pulsing the electrodynamic fields within the primary ion column such as to accelerate slower ions/decelerate faster ions within a specific pulse, such that they all arrive at the sample surface at the same time. This is referred to as beam bunching. The downside is that spatial resolution is lost when operating in the micro-probe mode. 

Because of the unique features of the x-ray radiation available at synchrotrons, many novel experiments ate being conducted at these sources. Some of these unique features are the very high intensity and the brightness (number of photons per unit area per second), the neatly parallel incident beam, the abihty to choose a narrow band of wavelengths from a broad spectmm, the pulsed nature of the radiation (the electrons or positrons travel in bunches), and the coherence of the beam (the x-ray photons in a pulse are in phase with one another). The appHcations are much more diverse than the appHcations described in this article. The reader may wish to read the articles in the Proceedings of the Materials Research Society Hsted in the bibhography. 

Biindel, n. bundle, bunch parcel, packet (of rays) pencil, beam (of waves) packet, biindeln, v.t. focus, concentrate bundle, bunch. Bundes-rat, tn. federal council. -tag, tn. federal diet. 

Bilschel, tn. tuft, bunch, cluster (Elec.) brush bundle, pencil, beam (of rays), -ent-ladung, /. (Elec.) brush discharge, buschelfdrmig, a. tuft-like, tufted, clustered. Buschholz, n. undergrowth, underwood. 

Other experiments reported the production of high-energy electrons with a similar set-up, and showed the suitability of such relativistic bunches for nuclear activation techniques. It has been showed that nuclear reactions could be efficiently triggered by electrons from thin CH foil targets [69], and also that nuclear reactions can be a useful tool to characterize the electron beam accelerated with similar targets [70]. This point will be further developed in Sect. 8.4. 

Recently, an interesting correlation between the laser pulse polarization and the ellipticity of the electron beam profile has been observed [71]. However, no major influence of laser polarization on the efficiency of the electron acceleration processes has been observed so far, nor this influence has been predicted by theory and simulations, differently from the proton acceleration. For proton acceleration, a great improvement on bunch charge and quality are expected by using circularly polarized laser pulses focused on thin foils at ultra-high intensities [72-74]. 

The electrons are bunched by the action of the RF accelerating field and therefore the emission occurs in sharp pulses, only tens of picoseconds in width, with frequency corresponding to the bunch spacing. For maximnm beam cnrrent many bnnches are used, giving a pulse frequency of typically 500 MHz. When only one bnnch is injected into the ring, the period drops to a few megahertz, while the pnlse width remains at a few picoseconds. This featnre has been used extensively for finorescence lifetime measnrements and may also be exploited in stroboscopic topography. 

The experiment was performed using a laser source, instead of a tested monoparticle source. It is known that even at low laser beam intensity, the probability of having only one single photon at a time is extremely weak because of to the bunching effect. 

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