Linear electron accelerators Linacs

The basis of the method is shown in Fig. 3.8. Pulsed radiation is usually generated by linear electron accelerators (Linacs) or by Van de Graaf accelerators, each having certain advantages. Both give nan-... 

There are seven types of electron accelerator available for industrial uses [41] (1) Van de Graaff generator (2) Cockcroft-Walton generator (3) insulated core transformer (4) parallel coupling, cascading rectifier accelerator (5) resonant beam transformer (6) Rhodetron (7) linear accelerator (LINAC). 

Schematic of a microwave linear accelerator or linac The three most common designs of industrial low-energy electron accelerators...

Fig. 3. Principle of linear accelerator (linac). Partially accelerated electrons from a source, such as a Cockcroft-Walton generator, arc further accelerated by stages as rhe electrons pass through radio-frequency cavities, powered by if oscillators. Each paiticle receives a small push as it passes from one cavity to the next until the final desired accelerated beam is produced Tile machine must be carefully synchronized CSG = Cockcroft-Walton generator, RFO = radio-frequency oscillator RFC = radio-frequency cavity...

Almost all the work in pulse radiolysis is based on the use of three types of electron accelerators linear accelerators (linacs). Van de Graaff accelerators, and Febetrons. The first accelerator used by Keene at Manchester was a 4-MeV linac with pulses of 0.2-2 ps duration [47a] this was replaced in 1967 with an 8-12-MeV linac capable of delivering pulses from 5 ns to 5 ps duration [93]. Further improvements made to the Manchester system up to 1989 have been documented [93]. Similarly, the 13-MeV linac used at Argonne in 1960 by Matheson and Dorfman produced pulses of 0.4 to 5 ps duration [46], whereas in 1989 the equipment comprised a 20-MeV linac, capable of producing pulses from 25 ps to 10 ps duration, and a 3-MeV Van de Graaff accelerator, which is dedicated to EPR and magnetic resonance studies (see below) [95, 98]. 

The third radiation facility is a linear accelerator Linac Saturne producing fast electrons at 18 MeV present at the Radiotherapy Department at S. Giovanni Hospital in Turin (Italy). 

The first experiments with the TOF method were accomplished on stationary reactors, obtaining a pulsed neutron beam by mechanical choppers. The real potential of the method was realized after the building of pulsed neutron sources, such as pulsed reactors, electron linear accelerators and proton synchrotrons - spallation sources. In electron linear accelerators (LINAC) and proton synchrotrons, targets from 239 j heavy atoms are used. Slowing-... 

Linear induction accelerators (induction linacs) Linear accelerators that operate by inducing an electromotive force in a cavity through a rapid change in the magnetic field strength. In effect, the electron beam acts as the analog of the secondary winding in a transformer. 

Radio-frequency linear accelerators (rf linacs) A linear accelerator that employs radio frequency (rf) cavities for electron acceleration. The particles are accelerated in cylindrical cavities that reqitire a high power soitrce for the rf fields. The rf fields in these cavities may be either traveling or standing waves. In the case of traveling wave conflguratiorts, which are most often employed for electron accelerators, the phase velocity if the rf fields must be synchronized with the desired electron velocity. 

During the last decade, a number of facilities have been built which use this so-called electroproduction of positrons. A review of the field has been given recently by Dahm et al. [3.14]. The large majority of the electron accelerators used for this purpose are linear machines (LINAC s), but it is also possible to use a microtron (Mills et al. [3.15]). All of the accelerators deliver pulsed electron beams, and their time structure is transferred to the resulting primary slow positron beam. Typical repetition rates are in the order of 100 s, while the pulse duration varies from a few ns to some (is. 

The insulated core transformer is another direct electron beam machine. It is similar to a three-phase power transformer in that a core and coils are used. One insulated core transformer will drive three accelerator tubes, which allows great flexibility and good power utilization. The Linac (linear accelerator) is an indirect electron beam ma-... 

At the Institute for the Organic Synthesis and Photoreactivity (ISOF) is operating a 12 MeV (maximum energy with no load) Vickers L-band (1.3 GHz) traveling wave electron linear accelerator. The LINAC was put in operation mainly to be used as energy source for pulse radiolysis studies. 

---