Alexandr Jancarek

Study of Pinching Capillary Discharge for Nitrogen H-like Recombination Laser

A computer model of EUV nitrogen laser pumped by pinching capillary discharge is presented. The model consists of magneto‐hydrodynamics plasma description and subsequent ion kinetic evaluation. Quick changes of electron temperature during the pinch decay lead to ionisation and excitation non‐equilibrium and result in inversion population on Balmer alpha transition. Validity of our model was proved via comparison of measured and evaluated spectra of our device with 15.5 kA peak current. High gain lasing system is predicted for 2 mm diam. capillary filled by 0.2 kPa nitrogen if 80 kA peak current and 30 ns pulse duration are taken into account.

Soft X-ray radiation of fast-capillary-discharge CAPEX 2

The paper reports on technological modifications of the capillary discharge experiment CAPEX, especially in capillary region. A temporal evolution of axial soft X-ray radiation and a spectroscopic measurement in the soft X-ray region on the modified capillary are presented as well. The strong spectral line at the wavelength of laser transition (Ne-like Ar, γ=46.9 nm) was observed.

Porosity Measurement Method by X-Ray Computed Tomography

This paper describes a new nondestructive approach for porosity measurement developed in response to a need for a more accurate porosity measuring method for solid samples. The conventional methods in X-ray CT imaging are based on image segmentation where a threshold is applied at a user-defined value. As a result, the uncertainty in the porosity measurement is introduced. Therefore, the new method, called the grey level method, which reflects the phenomenon of image processing and computation of ration between the volume of voids and the total volume of the entire sample, was considered and improved in term of image noise and artifacts. The volumes of 2D CT image as a surface are achieved by means of integrating the surface with operations relating to image histogram. The porosity value is given from the curve of a porosity distribution. Subsequently, the properties of individual pores were measured and comparison with conventional destructive method of porosity computation was carried out. Also limitations of industrial X-ray CT as well as their accuracy are discussed.

Time-resolved XUV radiation diagnostics from nitrogen discharge Z-pinch plasma

XUV radiation from nitrogen filled capillary discharge plasma was diagnosed using a 104 grooves/mm SiNx free-standing transmission grating. The resolution bandwidth of 0.3 nm was achieved. Time dependence of 13.4 nm line emitted power was recorded by photomultiplier in order to verify inherence of resonant radiation emission corresponding to NVII 2-3 laser transition. An increase of emitted power is expected during the pinch decay caused by recombination processes. We report here results obtained with 90 mm long capillary discharge supplied by a current pulse with maximum amplitude of 50kA and quarter-period of 80 ns. This high-current pulse was generated by a 1.5 ohm water line high-voltage generator which is used for underwater wire explosion experiments and which was adjusted for capillary discharge design using results of PSPICE simulations. Initial nitrogen pressures were varied in the range of 20 ÷ 500 Pa. MHD and kinetic simulations of the discharge plasma were performed and compared with experimental data. Simulations were performed with presumption of wall ablation. The capillary wall and electrodes material emission lines were also identified in measured spectra.

EUV Emission Spectra and Gain in Polyacetal Capillary Discharge

Experimental and computer studies of polyacetal capillary discharge are reported. Time resolved spectra in the wavelength region 3 – 25 nm are measured. Space‐time dependences of plasma electron density and temperature are calculated by means of MHD code. Time profiles of selected lithium‐, helium‐ and hydrogen‐like carbon and oxygen ion populations and time resolved spectra are evaluated by means of the FLY code. Gain factors for a capillary initially either evacuated or filled by polyacetal vapors are calculated.

Table-top water-window soft X-ray microscope using a Z-pinching capillary discharge source

The development and demonstration of a table-top transmission soft X-ray (SXR) microscope, using a laboratory incoherent capillary discharge source has been carried out. This Z-pinching capillary discharge water-window SXR source, is a first of its kind to be used for high spatial resolution microscopy at λ = 2.88 nm (430 eV) . A grazing incidence ellipsoidal condenser mirror is used for focusing of the SXR radiation at the sample plane. The Fresnel zone plate objective lens is used for imaging of the sample onto a back-illuminated (BI) CCD camera. The achieved half-pitch spatial resolution of the microscope approaches 100 nm, as demonstrated by the knife-edge test. Details about the source, and the construction of the microscope are presented and discussed. Additionally, the SXR images of various samples, proving applicability of such microscope for observation of objects in the nanoscale, are shown.

Focusing and photon flux measurements of the 2.88-nm radiation at the sample plane of the soft x-ray microscope, based on capillary discharge source

Feasibility measurements leading to the development of a Soft X-ray (SXR) microscopy setup, based on capillary discharge XUV source is presented. Here the Z-pinching plasma is acting as a source of XUV radiation, emitting incoherent radiation in the “water-window” (λ = 2.3 – 4.4 nm) region of interest (natural contrast between the carbon and oxygen edges).This soft X-ray microscopy setup will realize imaging of the biological objects with high spatial resolution. The 2.88 nm radiation line is filtered out from the water-window band, and is focused by an axi-symmetric ellipsoidal mirror, coated with nickle. The focussed spot size is measured and reported. Flux measurements for the available number of photons (photons/pulse) at the sample plane has been carried out with AXUV PIN diode at the sample plane (slightly out of focus). For imaging, a fresnel zone plate lens will be used as an objective. The overall compact transmission SXR microscopy setup design is presented.

Discharge driver for 13.4 nm XUV laser

During adiabatic expansion of Z-pinching plasma column can arise conditions suitable for amplified spontaneous emission (ASE) pumped by 3-body recombination. MHD and kinetic simulations had shown1, that capillary discharge with current amplitude I > 60 kA and slope dI/dt > 2 × 1012 As-1 can produce plasma condition for ASE of H-like nitrogen Balmer-alpha line at 13.4 nm. Discharge driver capable to deliver up to 90 kA with rise-time ~25 ns into 22 cm long capillary was designed. Driver is based on water slab capacitor pulse compression stages switched by spark-gap. Capillary is charged symmetrically with voltage up to ±160 kV. -100 A high-frequency current pulse is used to pre-ionize gas in the capillary. The driver will be used primarily as an experimental device to study capillary plasma for ASE by 3-body recombination, and secondarily as a source of high intensity incoherent XUV radiation in water-window region.

Axial particle and soft X-ray emission from the fast capillary discharge

Measurements with a pair of deflecting electrodes and solid-state track detector indicated highly collimated intense particle stream from the fast capillary discharge. Also positively biased collector behind the deflecting electrodes registered some peaks belonging to ions. On the other hand, measurements with Faraday cup were not successful due to giant photoemission. Amplified soft X-ray spontaneous emission has not yet been found.

Single-Shot near Edge X-ray Fine Structure (NEXAFS) Spectroscopy Using a Laboratory Laser-Plasma Light Source

We present a proof of principle experiment on single-shot near edge soft X-ray fine structure (NEXAFS) spectroscopy with the use of a laboratory laser-plasma light source. The source is based on a plasma created as a result of the interaction of a nanosecond laser pulse with a double stream gas puff target. The laser-plasma source was optimized for efficient soft X-ray (SXR) emission from the krypton/helium target in the wavelength range from 2 nm to 5 nm. This emission was used to acquire simultaneously emission and absorption spectra of soft X-ray light from the source and from the investigated sample using a grazing incidence grating spectrometer. NEXAFS measurements in a transmission mode revealed the spectral features near the carbon K-α absorption edge of thin polyethylene terephthalate (PET) film and L-ascorbic acid in a single-shot. From these features, the composition of the PET sample was successfully obtained. The NEXAFS spectrum of the L-ascorbic acid obtained in a single-shot exposure was also compared to the spectrum obtained a multi-shot exposure and to numerical simulations showing good agreement. In the paper, the detailed information about the source, the spectroscopy system, the absorption spectra measurements and the results of the studies are presented and discussed.