Sinan Bilikmen

The nonlinear cold plasma-bunched beam interaction and the plasma wakefield accelerator case

In this paper, a nonlinear analytical solution for a cold plasma-bunched beam system based on the Hamiltonian formalism where α = nb/no and β = v/c have been taken as parameters matching between zero and unity is given. The oscillation limiting energies, frequencies and transformer ratios have been carried out in general for both the one-dimensional and the case where a small transverse component of motion is included. The plasma wakefield accelerator has been treated as a special case.

Longitudinally Pumped Ne-Like Titanium X-Ray Laser Simulation with a Post-Processor Code Coupled to EHYBRID

Longitudinal pumping with a grazing incidence scheme of Ne-like Ti has been modeled by using the EHYBRID and a post-processor code. The atomic data that are required in the simulation are obtained by using the Cowan code. The variation of the Ne-like Ti x-ray laser gain at 32.6 nm is calculated for a fixed delay time with a variation in the incidence angle and a fixed incidence angle with a variation in the delay time. The post processor code has been used to simulate the x-ray resonance lines between 17 and 29 A.

Small-power-pulsed and continuous longitudinal CO2 laser for material processing

A small average power CO2 laser for some industrial applications is presented. The laser might operate both in a continuous regime and in a pulsed one or in a combination of two. Average power up to 20 W and peak power of several hundreds of kW has been achieved. The advantages of the good optical quality bema of a longitudinal discharge laser and of a high peak power pulsed regime are simultaneously achieved. A high voltage capacitor, which is switched on by means of a rotary spark gap, sustains the pulsed regime. The commutation between the two regimes might be easily done and a mixed operation is obtainable. By superposition of the two regimes, a continuous heating of the materials by the continuous beam as well as an evaporation due to high peak power are obtainable. Drilling, cutting and marking of different types of glasses as well as different plastic materials were performed.

Monomode hybrid longitudinal CO2 laser for material processing

A hybrid with small average power CO2 laser is presented. The laser might operate both in a continuous regime and in a pulsed one. The advantages of the good optical quality beam of a longitudinal discharge laser and of a high power peak pulse are simultaneously achieved. A high voltage capacitor which is switched on by means of a rotary spark gap sustains the pulsed regime. The commutation between the two regimes might be easily done and a hybrid operation is also obtainable. Glass surface treatment using this laser was performed. Fine polishment of the irradiated surface was achieved. The fine structure of the surfaces which were irradiated have been studied using atomic force microscopy.

Radiative damping of whistlers in a dense magnetoactive plasma waveguide

The absorption of whistler waves in a magnetized cylindrical plasma due to coupling with oblique Langmuir waves is investigated. Two types of mechanisms exist for whistler absorption. The first one is related to the excitation of Langmuir waves in the volume of the dense plasma and their subsequent absorption due to the electron collisions. The second one is the emission of Langmuir waves outside of the cylindrical plasma when it is surrounded by the rare plasma. The relation between these whistler absorption mechanisms is discussed.

Chaotic electron trajectories in quadrupole wiggler free electron laser

The motion of an individual electron in a FEL in a field configuration consisting of an ideal quadrupole-wiggler field and uniform axial-guide field, is shown to be nonintegrable in Hamiltonian formulations and can become chaotic for certain initial conditions. The presence of chaos, which is induced by the transverse spatial inhomogenieties in the wiggler field; and the self-fields produced by the space charge and current, poses limits on the wiggler field amplitude and the beam size for beam propagation in Free-Electron Laser operation. Upon plotting Poincare surface-of-section maps, it is shown that the electron dynamics is chaotic.

Mode transitions in low-pressure nitrogen RF-CCP at different frequencies

Summary form only given. Low-pressure (p≈103-1Torr) capacitively coupled RF plasmas are mostly used in material processing [1]. Different parametrical conditions in the plasma are preferred by different applications. High density plasmas in gamma mode are ideal for etching applications while stabile plasmas in gamma mode are more convenient for sputtering applications [2]. Therefore, it is better to characterize the plasma before process to get more efficient results.This study reports mode transition points in low-pressure capacitively coupled pure nitrogen RF plasma driven at 13.56 MHz and 40.68 MHz. The plasma was ignited in a home-made (500 u 400 mm2) stainless steel cylindrical reactor. Distance between the identical (200 mm in diameter) electrodes was set to 40 mm [3, 4]. Moreover, L-type automatic matching network system was connected to the 40.68 MHz RF generator to get high accuracy while matching system of 13.56 MHz was perched in its generator. In addition, the pure (99.995 %) nitrogen was selected as an activation gas because there is not a strong work about mode characterization of nitrogen gas, although it has a remarkable impact in plasma processing applications. Mode transition analyses were done according to diagnostic results that were obtained by Impedans Langmuir single and double probe systems. Pressure and power dependence of electron conduction current density, electron density and electron energy (or temperature) were investigated to determine mode transition points. These investigations revealed that a smooth alpha to gamma transition was observed at 0.1 Torr pressure in 13.56 MHz nitrogen plasma at whereas a sharp one was seen at 0.3 Torr pressure in 40.68 MHz nitrogen plasma. Also, at these pressures, another transition point (from gamma to alpha) was noticed with 150 Watt critical RF power in both plasmas. In conclusion, heating mode transition pressure of the low frequency RF-CCP is lower than that of the high frequency RF-CCP. On the other hand, RF power shows the same effect in both RF plasmas.

The influence of annealing on fluorene-type thin film produced by biphenyl and methane RF plasma system

Fluorene (C13H10)-type thin films were produced under the capacitively coupled single radio frequency (rf) system by using the biphenyl (C12H10)/methane (CH4) plasma. The circular parallel plate electrodes were used; the upper electrode was connected to 13.56 MHz rf power while the lower electrode was grounded. To control the positive ion bombardment, a negative bias voltage was applied between the holder of the substrate and the wall of the chamber. The properties of the fluorene-type films were explored under the variable plasma parameters of input rf power (150, 200 W), CH4 flow rate (3, 5 sccm), negative bias voltage (-66 V), and deposition time (20, 30 min) at a constant pressure value of 0.3 mbar. The deposited films were annealed for 1 hour at different temperatures; 200, 300, 400, and 500 C̊. The changes of plasma chemistry during the deposition were investigated by optical emission spectroscopy (OES). The chemical structural properties were examined by fourier transform infrared (FTIR) spectroscopy. After annealing the sp3/sp2 ratio showed a decrease with increasing temperature due to the degassing of CHx from the surface and hydrogen release with temperature1. The reconfiguration of chemical bonds in the film structure with annealing caused the changes in the intensities of band peaks2. Additionally, the annealing increased the amount of sp1 carbon bonding (carbyne) in the deposited film and led to decrease in the degree of cross-linking. The morphology of the films was analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM). The crystallography of thin film was effectively changed at high rf power and the annealing caused a shifting in diffraction peaks. An increase was observed in crystalline size of the films after the annealing. The surface of thin film indicated significant nanostructures and peaks at high rf power and CH4 flow rate. After annealing, the intensity of peaks showed a decrease as a result of the decomposition and compaction of films as well as the reformation of the amorphous covalent network that is occurring smoother surfaces2,3. The thickness was measured by ellipsometer, and since the annealing temperature caused to an effective thermal decay and a disruption of microvoids in the films2, the thickness of thin films had a decrease as increased the temperature. The contact angle measurement was used for the determination of hydrophobic behavior of the thin films.

Optical Characterization of Amorphous Hydrogenated Carbon (a-C:H) Thin Films Prepared by Single RF Plasma Method

Methane (CH4) plasma was used to produce amorphous hydrogenated carbon (a- C:H) fllms by a single capacitively coupled radio frequency (RF) powered plasma system. The system consists of two parallel electrodes: the upper electrode is connected to 13.56 MHz RF power and the lower one is connected to the ground. Thin fllms were deposited on glass slides with difierent sizes and on silicon wafers. The in∞uence of the plasma species on fllm characteristics was studied by changing the plasma parameters. The changes of plasma species during the deposition were investigated by optical emission spectroscopy (OES). The structural and optical properties were analyzed via Fourier transform infrared (FTIR) spectroscopy, X-ray difiraction (XRD) and UV-visible spectroscopy, and the thicknesses of the samples were measured by a profllometer. The sp 3 /sp 2 ratio and the existing H atoms play a signiflcant role in the determination of the chemical properties of thin fllms in the plasma. The fllm quality and deposition rate were both increased by raising the power and the ∞ow rate.

Conversion Efficiency Calculations for Soft X-Rays Emitted from Tin Plasma for Lithography Applications

Laser-produced plasmas can be used as extreme ultraviolet (EUV) sources for lithography, operating in the 13.5 nm range. Soft X-rays emitted from laser-produced tin plasma were simulated using the EHYBRID code. Required atomic data for tin ions were calculated using the Cowan code. In the EHYBRID simulations tin slab target is assumed to be irradiated by 1064 nm wavelength Nd:YAG laser. Simulations were performed for different driving laser parameters.