Fluctuation of femtosecond X-ray pulses generated by a laser-Compton scheme

A short-pulse X-ray-generation experiment was performed by Compton scattering through interaction between a 3-ps electron beam and 100-fs laser photons in a 90° scattering configuration. The observed X-ray intensity was typically 3×10⁴ photons/pulse and roughly matched the theoretically expected intensity. The X-ray energy and pulse duration were estimated theoretically to be 2.3 keV and 280 fs from the observed electron- and laser-beam parameters. The fluctuation of the X-ray output was measured as 25% (rms) during a 30-min operation. The fluctuation was expressed as a function of the fluctuation of the timing between the electron and laser beams. The measured fluctuation of the X-rays was approximately consistent with that caused by the fluctuation of the timing between the beams. Received: 19 November 2001 / Revised version: 23 January 2002 / Published online: 14 March 2002     

Dust diagnostics on an inertial electrostatic confinement discharge

Micron size dust particles were used to diagnose the direction of ion flow in an inertial electrostatic confinement discharge. Particles were dropped onto a one-dimensional device and were shown to deflect away from the center. The deflection of the dust particles was then accounted for by ion drag. It is concluded that ions are created at the cathode center and flow outwards. This supports recent work that has reached the same conclusion using Doppler spectroscopy. Moreover, estimates of the ion density from the deflection of dust particles was in agreement with Langmuir probe measurements.     

Enhancement of X-ray emission in the side on direction in a Mather-type plasma focus

A 1.8 kJ Mather-type plasma focus (PF) for argon and hydrogen filling is examined. Two anode configurations are used. One is tapered towards the anode face, and the other is cylindrical but the face is cut at different angles. At optimum conditions, the system is found to emit Cu–Kα X-rays of about 1.6±0.1 J/sr in the side-on direction for argon filling, which is about 32% of the total X-ray emission. In 4π-geometry, maximum total X-ray yield and wall plug efficiency found are 26.4±1.3 J and 1.5± 0.1% respectively. The modified geometry may help to use the PF as a radiation source for X-ray diffraction.     

Time resolved studies on X-rays and charged particles emission from a low energy plasma focus device

The time resolved studies on soft X-ray, hard X-ray, electron beam and ion beam emissions from a low energy plasma focus device are carried out simultaneously by employing a photodiode X-ray spectrometer, a scintillator photomultiplier tube, a combination of Faraday cup and Rogowski coil assembly and a biased Faraday cup, respectively. The soft X-ray is seen to be emitted in short multiple pulses corresponding to different pinch stages where as it is a single for hard X-ray, which corresponds to only maximum pinch stage. Similarly, multiple pulses of electron beam is found, which also corresponds to different pinch stages and these pulses are analogous with the soft X-ray pulses. The effective hard X-ray photon energy is estimated by foil absorption technique and found to be around 110 keV, which is consistent with the observed electron beam energy distribution. The simultaneous investigation of the electron and ion beam shows that both are accelerated by the same local field generated during the pinching process. The detailed results of time resolved studies on various radiations are incorporated in this Letter.     

Spatial beam profiles of femtosecond X-ray pulses generated by laser Compton scattering from a low-emittance electron beam

Polarization-dependent spatial beam profiles of femtosecond X-ray pulses generated by a laser Compton scheme were measured. The X-ray pulses were generated by the interaction at an angle of 90° between 100-fs laser light and a 3-ps, 3π-mm mrad electron beam. The polarization of the laser light was linear in two different directions, either parallel or perpendicular to the electron beam axis. The measured profiles showed good agreement with theoretical results. Received: 5 July 2002 / Revised version: 17 October 2002 / Published online: 5 February 2003 RID="*" ID="*"Corresponding author. Fax: +81-424/684477, E-mail: msf_yorozu@shi.co.jp     

Effect of high energy ion irradiation on silicon substrate in a pulsed plasma device

We have performed an experimental analysis on the investigation of high energy ion beam irradiation on Si(1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beams are characterized using standard surface science diagnostic tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive X-ray (EDX) analysis and atomic force microscope (AFM) and the results are reported. In particular, it has been found that with silicon targets, the application of PF carbon ion beams results in the formation of a surface layer of hexagonal (6H) silicon carbide, with embedded self-organized step/terrace structures.     

Crystallization of amorphous zirconium thin film using ion implantation by a plasma focus of 1 kJ

In this work preliminary results of amorphous zirconium crystallization using ion beam pulses are presented. Energetic argon- and oxygen-ion beams generated by a plasma focus device were used to promote crystallization on amorphous ZrO₂-2.5 mol% Y₂O₃ film deposited by chemical solution deposition onto silica glass substrate. The films were burnt at 370 °C for 1 h in normal atmosphere previous to plasma irradiation. The irradiation was performed by means of successive pulses of ion beams. The evolution of the surface morphology and crystallization was followed by AFM and X-rays diffraction in a grazing incidence asymmetric Bragg geometry (GIAB), respectively. Argon-irradiated films showed highly nucleated cubic zirconia after 10 pulses. On the other hand, oxygen-irradiated films showed a delayed and less extensive cubic nucleation, but a more ordered structure and well-defined grains.     

Relativistic electron beams detection in a dense plasma focus

Fast electron beams into a hollow anode of a small plasma focus machine (2 kJ, 4 μF) were measured. The diagnostic method designed for this purpose is founded in a small Rogowski coil introduced into a cavity performed in the anode. By means of this, electron beam pulses of about 10 ns width generated in the plasma focus are detected. Simultaneously, hard X-ray signals obtained from a scintillator-photomultiplier system are registered. The electron beam energy was measured through the time-of-flight of the electrons between probe and anode top. The beams are found to be relativistic and its energy is into the range of hard X-rays energy. An analysis of signal intensities and relative delays for three hundred shots are here presented. Received 28 February 2002 / Received in final form 7 May 2002 Published online 24 September 2002     

Avalanche Phenomenon of Superthermal Electrons Measured by SDD with New SPHA during ECRH

Two high performance silicon drift detectors （SDD） are installed at the equatorial port with z = 0 and z = -16.4 cm on HL-2A tokamak, respectively. These SDDs combine with the new and non-conventional software pulse height analyser （SPHA ） successfully developed more recently by us to measure the time evolution of soft x-rays spectra, the thermal and superthermal electron temperatures. The high-quality three-dimensional figure of time evolution for soft x-rays energy spectra is easily obtained by combination of a new SPHA and computer. Therefore, the measurement accuracies and the time resolutions of thermal and superthermal electron temperatures are also improved. The enhancement phenomenon of superthermal electron during electron cyclotron resonance heating （ECRH） can be explained by the combination of superthermal electron avalanche theory and experimental parameters.     

Absolute intensity of a sodium-like resonance line for temperature diagnosis of neon-like X-ray laser plasmas

Nine different neon-like ions with atomic numbers ranging from 28 to 42 have exhibited gain in various 3p—3s transitions. The temperature of the lasing plasma is critical in determining the state of ionization and the relative importance of collisional excitation and recombination pumping. In this paper we demonstrate a potentially useful new temperature diagnostic for these plasmas that works in the density range of interest for X-ray lasing: the absolute intensity of 3p—3s sodium-like lines. Due to their large collisional couplings and high optical depths, their brightness temperature approaches the actual kinetic temperature of the plasma in temperature and density regimes of importance for achieving optimal X-ray laser performance.     

Effect of electron emission and potential perturbations of a hot filament in high voltage pulsed glow discharge

The high voltage dc pulsed glow discharge can be ignited earlier by putting an electron emitting filament in the plasma chamber. The electrons emitted from the filament act as a seed and can cause earlier ignition. The potential of the hot filament shows some periodic positive perturbations (electron loss signals) when it is kept floating in the plasma chamber. It is observed that the positive perturbations disappear as potential difference between the plasma and the filament is made smaller by directly connecting the filament to the grounded chamber.     

Self-organized transformation to polyaniline nanowires by pulsed energetic electron irradiation in a plasma focus device

An ingenious method for fabricating network of polyaniline nanowires at room temperature in microsecond timescale is demonstrated by using the pulsed electron beam of a plasma focus device. The electron beam of the plasma focus device having a wide range of energies (10-200 keV) was irradiated on to the freestanding polyaniline film. The growth of polyaniline nanowires on the surface of film sample is confirmed by field emission scanning electron microscope images showing nanowires of about 50-80 nm in diameter and up to few tens of micrometers in length.     

Radiographic method for measuring the continuum hard X-ray output spectrum of a Plasma Focus device

A radiographic method is proposed and then applied to infer the continuum part of the hard X-ray spectrum of a 4.7 kJ Plasma Focus from differential absorption measurements on metals. Copper, nickel, titanium and silver samples with thicknesses spanning between 0.1 and 10 mm were employed as filters. The X-ray radiation was detected using a standard radiographic screen-film system. The results show the presence of a dominant peak around 75 keV with significant spectral components in the range of 40 to 200 keV. The method is easy to follow, inexpensive, and allows for calibrated, single shot, spectral measurements.     

Effect of cathode structure on neutron yield performance of a miniature plasma focus device

In this Letter we report the effect of two different cathode structures - tubular and squirrel cage, on neutron output from a miniature plasma focus device. The squirrel cage cathode is typical of most DPF sources, with an outer, tubular envelope that serves as a vacuum housing, but does not carry current. The tubular cathode carries the return current and also serves as the vacuum envelope, thereby minimizing the size of the DPF head. The maximum average neutron yield of (1.82±0.52)×¹⁰⁵ n/shot for the tubular cathode at 4 mbar was enhanced to (1.15±0.2)×¹⁰⁶ n/shot with squirrel cage cathode at 6 mbar operation. These results are explained on the basis of a current sheath loading/mass choking effect. The penalty for using a non-transparent cathode negates the advantage of the smaller size of the DPF head.     

Majority carrier transistor based on voltage-controlled thermionic emission

A new type of transistor is proposed based on gate-controlled charge injection in unipolar semiconductor structures. Its design has some similarity with the recently fabricated triangular barrier diodes but contains an additional input circuit which allows an independent control of the barrier height for thermionic emission. This circuit is provided by a MOS gate on the semiconductor surface. In the proposed device the current flows perpendicular to the semiconductor surface over a planar potential barrier controlled by the gate. The static transconductance characteristics and dynamical response are analyzed. The characteristic response time is limited by the time of flight of electrons across the structure and can be in the picosecond range. The gate voltage required to switch the output current at room temperature is of order 0.2 V.     

Analysis of new electrical signals in respect to quantification of radio frequency glow discharge emission spectrometry

Radio frequency glow discharge optical emission spectroscopy (RF-GD-OES) is routinely used for the chemical analysis of solid samples. For quantification two independent electrical signals of the discharge are required. These are provided in real time by the glow discharge source with integrated voltage and current sensors. The available time-dependent voltage and current must be reduced. For this purpose a plasma equivalent circuit is used. It is shown that the cathode voltage and active cathode current describe the sputtering and excitation well. Measuring standard reference materials at constant cathode voltage and cathode current results in linear calibration curves.     

VUV-spectroscopy of the plasma light emission generated by the pulsed arc cluster ion source (PACIS)

A pinhole grid spectrometer is used to measure the light emission from the plasma of the pulsed arc cluster ion source (PACIS). Spectra of various metals and carbon have been measured between 20 and 100 nm. In the case of carbon the average electron temperature is estimated to about 0.69 eV. Higher temperatures up to 0.79 eV are measured when inserting seeding gas which flushes the discharge volume with approx. one atmosphere of helium. An operation under this source conditions leads to the generation of an intense charged cluster beam. The application of the source as a bright light source in the VUV region is discussed. Received: 26 February 1998 / Revised: 12 May 1998 / Accepted: 14 May 1998     

Application of a newly developed CCD for spectral-width measurements of a 53 eV germanium laser

We report the application of a soft X-ray CCD for X-ray laser experiments. A newly developed CCD which has a thinned protection layer (SiO₂) of about 0.2 m was attached to a grazing incidence spectrometer with a resolving power of 16000 in order to measure high-resolution spectra of a germanium soft X-ray laser. Clear spectra have been recorded with a high sensitivity in the energy range between 51 eV (240 Å) and 55 eV (225 Å). In addition to the two strong lasing lines at 236 Å and 232 Å, more than 20 weak spontaneous emission lines have been recorded in this energy range. The spectral width of the 236 Å lasing line is approximately 20.5 mÅ at the full width at half maximum. It is shown that this direct X-ray detection system has a spatial resolution of about 1/10 of the CCD pixel size in this spectral measurement.     

Diagnostics for first plasma study on EAST tokamak

The first plasma was obtained in the EAST on September 26th, 2006. Single-null (SN) and double-null (DN) diverted plasmas were achieved successfully in the EAST tokamak on January 22nd, 2007. The employed plasma diagnostics for first plasma study of EAST are as follows: a vertical one-channel far-infrared (FIR) hydrogen cyanide (HCN) laser interferometer for measuring the line average density, a 10-channel soft X-ray array for intensity measurement, a 16-channel heterodyne Electron Cyclotron Emission (ECE) for measuring the electron temperature profile, a 8-channel XUV bolometer array to measure plasma radiation losses, a 3-channel hard X-ray array for intensity measurement, an electromagnetic measurement system, a 35-channel Hα radiation array, 20 probes for divertor plasma, a one-channel visible bremsstrahlung emission, an impurity optical spectrum measurement system and two optical spectroscopic multi-channel analyzers (OMA). The first experimental results of diagnostic systems are summarized in this Letter.     

Thermoluminescence glow curves of CaF2: Dy crystals irradiated by soft X-rays

Applying a deconvolution of the thermoluminescence glow curves, parameters of single glow peaks of CaF₂: Dy TLD 200 dosemeters irradiated by soft X-rays were determined. A dependence of the height ratio of low temperature (T393, 413 and 473 K) single peaks on energy of absorbed photons was measured in a region of 1–22.2 keV. Standard radionuclides¹⁰⁹Cd,²³⁸Pu,⁵⁵Fe and iodine laser produced aluminium plasma (T _e 500 eV) were used as soft X-ray sources. The ratios of the heights of different single peaks are discussed with respect to high local doses. The decreasing ratio of the heights of the first and third and/or second and third peak with increasing photon energy allows to determine reversely a mean photon energy of absorbed soft X-ray radiation.