The Turkish accelerator complex IR FEL project

Turkish accelerator complex (TAC) project was approved by State Planning Organization (DPT) of Turkey in 2006. The complex will contain a linac-ring type electron–positron collider as a particle factory and different accelerator based light sources. As a first step to the national center, the construction of an IR FEL facility is planned until 2011. It is also planned that the technical design report for TAC will be completed in 2010. The TAC IR FEL facility will consist of an electron linac in the range of 15–40 MeV energy to obtain FEL in 2–185 microns range. In this study, the preliminary parameters of TAC IR FEL facility were presented. The possible using of the obtained FEL in material science, nonlinear optics, semiconductors, biotechnology, medicine and photochemical processes were discussed.     

Analysis of FEL radiation in pulsed raman regime

Summary A direct numerical analysis, based on the Lienard-Wiechert potentials, is performed in the present paper, aiming to describe the relativistic interaction of the electrons composing a high-intensity beam (in Raman regime) both with each other and with the fields of an FEL structure and of an external resonant travelling electromagnetic wave. The different accelerations, due to the various forces acting on the charged particles, are seen to give different contributions to the total radiation field, which are separately considered here. The angular and frequency distributions of the obtained radiation are compared with the analytic ones deduced in the particular case of a single charge launched along the FEL structure. The interference effect between the fields of many bunches is seen to cause the shrinkage of the resulting radiation beam.     

THz radiation studies on biological systems at the ENEA FEL facility

Emerging technologies are considering the possible use of THz radiation in different fields, ranging from telecommunication to biology and biomedicine. The study of the potential effects of THz radiation on biological systems is then an important issue in order to safely develop a large number of applications. This task is being accomplished in the framework of the EU funded THz-BRIDGE project. Experiments on the effects of THz radiation on different biological samples with different techniques are being performed utilizing the compact free electron laser at the ENEA Research Center of Frascati. Experimental results, together with statistical analysis are reported.     

Pulsed ion hall accelerator for investigation of reactions between light nuclei in the astrophysical energy range

The factors defining the constraints on the current characteristics of the magnetically insulated ion diode (IDM) are considered. The specific current parameters close to the maximum possible ones are obtained for the particular IDM-40 design assigned for acceleration of light ions and investigation of nuclear reactions with small cross sections in the astrophysical energy range (2–40 keV) in the entrance channel. It is experimentally demonstrated that the chosen optimal operation conditions for IDM-40 units provide high stability of the parameters (energy distribution and composition of accelerated particle beams, degree of neutralization) of the accelerated particle flux, which increases during the working pulse.     

Compton scattering of the accelerator radiation in cylindrical cavity wall

Starting from the Klein-Nishina relations describing Compton scattering there was calculated the intensity distribution of the radiation incoming from the cylindrical cavity wall. The calculations were carried out at first - as completely incoherent and next - assuming the possibility of the caustics arising. Its results, compared with the experimental ones, confirm the above supposition.     

Investigations of ultrafast phenomena in high-energy density physics using X-ray FEL radiation

The advent of highly intense and ultrashort pulses of short-wavelength radiation in the vacuum-ultraviolet to X-ray regime provides for the first time the possibility to study plasmas at the time scale of equilibration or even electron thermalization. The emerging radiation sources are free-electron lasers (FEL) based on high-energy electron accelerators. FELs provide a peak brilliance nine orders of magnitude higher than the best performing X-rays sources today. The FEL radiation parameters will enable the creation of high-energy density states of matter and the development of new diagnostics tools to investigate dense plasmas. As the first of the new sources the VUV-FEL at DESY, Hamburg becomes operational for high-energy density physics experiments during 2005.     

Compact linear electron accelerator for radiation technologies

A prototype of a commercial compact continuous-beam linear electron accelerator has been designed and constructed. With its energy of 600 keV and a beam with 30 kW maximum power, the accelerator can be used in various radiation technologies. Its compact size, easy operation, reliability, wide adjustment range for the main parameters, and possible local shielding allow it to be integrated into the majority of radiation technology processes.     

Measurements of wave-breaking radiation from a laser-wakefield accelerator

Spectral analysis of radiation emitted transverse to laser propagation in laser-wakefield acceleration experiments shows broadband emission when electrons are accelerated to relativistic energies. The region over which emission occurs is short compared with the overall interaction length. The energy of the emission and location along the interaction length both vary with plasma density. A model for the radiation from self-trapped electrons indicates that the emission is a signature of the violent initial acceleration, and hence can be used as a diagnostic of the self-injection mechanism.     

Deducing the electron-beam diameter in a laser-plasma accelerator using x-ray betatron radiation

We investigate the properties of a laser-plasma electron accelerator as a bright source of keV x-ray radiation. During the interaction, the electrons undergo betatron oscillations and from the carefully measured x-ray spectrum the oscillation amplitude of the electrons can be deduced which decreases with increasing electron energies. From the oscillation amplitude and the independently measured x-ray source size of (1.8±0.3) μm we are able to estimate the electron bunch diameter to be (1.6±0.3) μm.     

工业辐照加速器扫描磁铁电源的研制

分析了工业辐照加速器扫描磁铁的三角波励磁电流的选取。介绍了一种输出电流峰 峰值20 A、扫描频率为20～50 Hz的连续三角波的工业辐照加速器扫描磁铁电源。阐述了三角波调制器的原理、三角波线性度、基于单片机的控制系统以及其在工业辐照环境下采取的抗干扰措施。理论和应用均表明该设计具有很好的辐照均匀度。     

工业辐照加速器扫描磁铁电源的研制

 分析了工业辐照加速器扫描磁铁的三角波励磁电流的选取。介绍了一种输出电流峰 峰值20 A、扫描频率为20～50 Hz的连续三角波的工业辐照加速器扫描磁铁电源。阐述了三角波调制器的原理、三角波线性度、基于单片机的控制系统以及其在工业辐照环境下采取的抗干扰措施。理论和应用均表明该设计具有很好的辐照均匀度。     

Giant fluctuations in the radiation intensity of two-dimensional electrons under quantum hall effect conditions

Giant fluctuations in the 2D-electron recombination radiation were studied in structures with a single or double GaAs quantum well under quantum Hall effect conditions. It is established that, if these conditions are exactly satisfied, the amplitude of the 2D-electron photoluminescence (PL) intensity is several orders of magnitude higher than the noise level, with the noise having a normal (Poisson) distribution. The fluctuations in the PL line intensity are accompanied by a jumpwise change in the line positions. Analogous jumps were also observed in the spectra of inelastic light scattering by 2D electrons in structures with a single GaAs quantum well. The fluctuation processes are correlated over macroscopic distances. The characteristic correlation length is 1–2 mm. The spectral density of giant fluctuations was found to exhibit narrow peaks. The ratios of the frequencies of these peaks are equal to those of Fibonacci numbers. The appearance of such frequencies in the fluctuation spectrum indicates that the fluctuations studied bear a resemblance to processes occurring in open dissipative dynamic systems. The methods developed in the theory of these systems can, in principle, be used to study giant fluctuations.     

Study on the radiation problem caused by electron beam loss in accelerator tubes

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20 MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5 MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.     

Transition radiation detector for relativistic particles at accelerator energies

Transition radiation (TR) has been investigated by using the arithmetic mean and the geometric mean of the pulses from 10 multiwire proportional chambers. The discrimination factor for different kinds of particles has been determined. Also the dependence of the intensity of TR on the Lorentz factor γ has been measured and compared with theoretical calculations.     

Study on the radiation problem caused by electron beam loss in accelerator tubes

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.     

A high-gradient accelerator based on a faster-than-light radiation source

A wide-band microwave generator using a faster-than-light source is proposed to be used as a charged particle accelerator. According to theoretical estimates, an electric field amplitude as high as ～10¹¹ V/m or more can be attained at the focus of a paraboloidal emitting surface with a focal parameter of ～1 m. These estimates are supported by numerical calculations. The schematic diagram of such an accelerator is suggested.     

Diagnostics of FEL and ILC ultrashort electron bunches based on undulator and synchrotron radiation

The diagnostics of ultrashort electron bunches developed basing on undulator and synchrotron radiation in the framework of the JINR-DESY collaboration is designated for the International Linear Collider (ILC) project, as well as for Free Electron Lasers (FELs) such as the FLASH and X ray XFEL laser. All these accelerator complexes require diagnostics of ultrashort electron bunches with lengths of 20–300 μm.     

A system for monitoring the radiation effects of a proton linear accelerator

The system for real-time monitoring of radioactivity of a high-current proton linear accelerator detects secondary neutron emission from proton beam losses in transport channels and measures the activity of radionuclides in gas and aerosol emissions and the radiation background in the environment affected by a linear accelerator. The data provided by gamma, beta, and neutron detectors are transferred over a computer network to the central server. The system allows one to monitor proton beam losses, the activity of gas and aerosol emissions, and the radiation emission level of a linear accelerator in operation.     

Terahertz radiation source using a high-power industrial electron linear accelerator

High-power (～ 100 kW) industrial electron linear accelerators (linacs) are used for irradiations, e.g., for pasteurization of food products, disinfection of medical waste, etc. We propose that high-power electron beam from such an industrial linac can first pass through an undulator to generate useful terahertz (THz) radiation, and the spent electron beam coming out of the undulator can still be used for the intended industrial applications. This will enhance the utilization of a high-power industrial linac. We have performed calculation of spontaneous emission in the undulator to show that for typical parameters, continuous terahertz radiation having power of the order of μW can be produced, which may be useful for many scientific applications such as multispectral imaging of biological samples, chemical samples etc.