Laser Electron Accelerator

One kind of X-ray lasers is a subcase of the so-called free electron laser. Electrons, accelerated are forced, to almost the speed of light ("relativistic electrons") by klystrons and then bent or wiggled in special magnets called undulators are forced to emit some of their energy as synchrotron radiation inside the undulator, the synchrotron pulses can induce in-phase synchrotron emission by other electrons, thus producing a pulse at X-ray wavelengths. This was recently demonstrated as almost possible (2009). 

Pulse-probe studies using the Laser Electron Accelerator Facility (LEAF) at Brookhaven National Laboratory have revealed changes in optical absorption occurring on the picosecond time scale in rare gas fluids. In xenon, excimers are formed which absorb in the visible and near infra-red as shown in Fig. la. The absorption grows in during the first 50 picoseconds [see Fig. 1(b)].This growth is concomitant with ion recombination that leads first to excited atoms, reaction 1(a), which immediately form excimers, Xe, because of the high density of xenon. 

James R Wishart received a B.S. in Chemistry from the Massachusetts Institute of Technology in 1979 and a Ph.D. in Inorganic Chemistry from Stanford University in 1985 under the direction of Prof Henry Taube. After a postdoctoral appointment at Rutgers University, in 1987 he joined the Brookhaven National Laboratory Chemistry Department as a Staff Scientist in the Radiation Chemistry Group. He founded and presently supervises the BNL Laser-Electron Accelerator Facility for picosecond electron pulse radiolysis. His research interests include ionic liquids, radiation chemistry, electron transfer, and new technology and techniques for pulse radiolysis. He has authored over 90 papers and chapters, and is the co-editor of Advances in Chemistry Series o. 254, Photoehemistry and Radiation Chemistry. 

Figure 1 Schematic representation of the Laser-Electron Accelerator Facility at Brookhaven National Laboratory. The laser beam is split to generate both the electron pulse and the probe light (scheme courtesy of Dr. J. Wishart, Brookhaven National Laboratory).

To exploit the capabilities of fast lasers, a new picosecond Laser-Electron Accelerator Facility (LEAF) has been recently developed at Brookhaven National Laboratory. In this facility, schematically shown in Figure 1, laser light impinging on a photocathode inside a resonant cavity gun merely 30 cm in length produces the electron pulse. The emitted electrons are accelerated to energies of 9.2 MeV within that gun by a 15 MW pulse of RF power from a 2.9 GHz klystron. The laser pulse is synchronized with the RF power to produce the electron pulse near the peak field gradient (about 1 MeV/cm). Thus the pulse length and intensity are a function of the laser pulse properties, and electron... 

As mentioned above, a 3.5-cell RF photocathode gun is in operation as the accelerator for the Brookhaven National Laboratory Laser-Electron Accelerator Facility. Recently, 1.6-cell RF photocathode guns have replaced thermionic cathode systems as injectors for 30 MeV linear accelerators at Osaka University and the Nuclear Engineering Research Laboratory in Tokai-mura, Japan [6]. Another RF photocathode gun accelerator is under construction at the ELYSE facility at the Universite de Paris-Sud at Orsay, France. A magnesium cathode is in use at LEAF, copper is used at NERL, while the Orsay accelerator will use Cs Te. 

Brookhaven National Laboratory s Laser Electron Accelerator Facility (LEAF) uses a titanium-sapphire laser Ahv = 798 nm fwhm = 100 fs and energy per pulse is 0.01 J. 

This laser is a component of Brookhaven National Laboratory s Laser Electron Accelerator Facility (LEAF). 

High Field Photonics in Laser Plasmas Propagation Studies, Electron Acceleration, and Nuclear Activation With Ultrashort Intense Laser Pulses... 

Although this work is restricted to electron acceleration, it has to be mentioned here for completeness that an increasing amount of work is currently devoted (often in the same laboratories) to the study of proton and light ion acceleration with laser pulses, also in view of future medical applications. Among a number of recent works on this subject, see for example [9] and [10]. 

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]. 

With this experiment, laser-driven electron acceleration approaches the stage of suitability for medical uses, in particular for Intra-Operative Radiation Therapy (IORT) of tumors [78,79]. Comparison of the main parameters of electron bunches produced by two commercial RF Hospital accelerators for IORT treatment and those of this laser-driven accelerator is shown in the Table 8.1. Most of the performances of the experimental laser-driven electron accelerator set-up at CEA-Saclay are comparable with presently used conventional accelerators. Notice that, though the dose delivered for each shot is also comparable, the electron bunch duration is about six orders of... 

Laser-plasma accelerators represent a unique tool for investigating matter properties at a reduced laboratory scale, compared to large-scale facilities. Nowadays, efficient electron acceleration can be provided by such table-top accelerators and can be used to perform experiments in a variety of fields. 

Let us first review some experiments in which the laser-driven acceleration of electrons has been obtained in laser-solid interactions. 

A critical point in the retrieving of the number of nuclear reactions in laser-solid experiments is that there is no control on the spectrum of the electrons accelerated in the interaction, as well as the acceleration mechanism is uncertain and difficult to fit in a predictable scheme. In most cases, the electron energy distribution is assumed to be Boltzmann-like and deconvolutions are performed starting from this assumption. 

It should be noted that there is a limited number of works on classical relativistic dynamical chaos (Chernikov et.al., 1989 Drake and et.al., 1996 Matrasulov, 2001). However, the study of the relativistic systems is important both from fundamental as well as from practical viewpoints. Such systems as electrons accelerating in laser-plasma accelerators (Mora, 1993), heavy and superheavy atoms (Matrasulov, 2001) and many other systems in nuclear and particle physics are essentially relativistic systems which can exhibit chaotic dynamics and need to be treated by taking into account relativistic dynamics. Besides that interaction with magnetic field can also strengthen the role of the relativistic effects since the electron gains additional velocity in a magnetic field. 

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