A three-channel polarointerferometer for diagnostics of magnetic fields in high-temperature plasma

A polarointerferometer designed for studying magnetic fields in high-temperature laser or electricdischarge plasma with the method of measuring the Faraday rotation of the plane of polarization of a probing laser beam is described. The instrument’s optical system allows three—shadow, polarization, and interference—images of an object to be formed in a single diagnostic channel, thereby making it possible to record plasma images using only one digital camera.     

Calibration of a flat field soft x-ray grating spectrometer for laser produced plasmas

We have calibrated the x-ray response of a variable line spaced grating spectrometer, known as the VSG, at the Fusion and Astrophysics Data and Diagnostic Calibration Facility at the Lawrence Livermore National Laboratory (LLNL). The VSG has been developed to diagnose laser produced plasmas, such as those created at the Jupiter Laser Facility and the National Ignition Facility at LLNL and at both the Omega and Omega EP lasers at the University of Rochester's Laboratory for Laser Energetics. The bandwidth of the VSG spans the range of ～6-60?A?. The calibration results presented here include the VSG's dispersion and quantum efficiency. The dispersion is determined by measuring the x rays emitted from the hydrogenlike and heliumlike ions of carbon, nitrogen, oxygen, neon, and aluminum. The quantum efficiency is calibrated to an accuracy of 30% or better by normalizing the x-ray intensities recorded by the VSG to those simultaneously recorded by an x-ray microcalorimeter spectrometer.     

Thrust bearing using a magnetic fluid lubricant under magnetic fields

This paper describes a thrust bearing using a magnetic fluid lubricant under a magnetic field. The critical pressures of the bearing versus the magnitude of the magnetic flux densities have been investigated experimentally. It is shown that the critical pressures of the proposed bearing are larger than those of the normal lubricated bearing under high speeds.     

Measurement of magnetic susceptibility in pulsed magnetic fields using a proximity detector oscillator

We present a novel susceptometer with a particularly small spatial footprint and no moving parts. The susceptometer is suitable for use in systems with limited space where magnetic measurements may not have been previously possible, such as in pressure cells and rotators, as well as in extremely high pulsed fields. The susceptometer is based on the proximity detector oscillator, which has a broad dynamic resonant frequency range and has so far been used predominantly for transport measurements. We show that for insulating samples, the resonance frequency behavior as a function of field consists of a magnetoresistive and an inductive component, originating, respectively, from the sensor coil and the sample. The response of the coil is modeled, and upon subtraction of the magnetoresistive component the dynamic magnetic susceptibility and magnetization can be extracted. We successfully measure the magnetization of the organic molecular magnets Cu(H(2)O)(5)(VOF(4))(H(2)O) and [Cu(HF(2))(pyz)(2)]BF(4) in pulsed magnetic fields and by comparing the results to that from a traditional extraction susceptometer confirm that the new system can be used to measure and observe magnetic susceptibilities and phase transitions.     

Thomson-scattering measurements in the collective and noncollective regimes in laser produced plasmas (invited)

We present simultaneous Thomson-scattering measurements of light scattered from ion-acoustic and electron-plasma fluctuations in a N(2) gas jet plasma. By varying the plasma density from 1.5×10(18) to 4.0×10(19)?cm(-3) and the temperature from 100 to 600 eV, we observe the transition from the collective regime to the noncollective regime in the high-frequency Thomson-scattering spectrum. These measurements allow an accurate local measurement of fundamental plasma parameters: electron temperature, density, and ion temperature. Furthermore, experiments performed in the high densities typically found in laser produced plasmas result in scattering from electrons moving near the phase velocity of the relativistic plasma waves. Therefore, it is shown that even at low temperatures relativistic corrections to the scattered power must be included.     

Compression and focusing a laser produced plasma using a plasma optical system

Axi-symmetric compression and focusing of a low temperature laser produced copper plasma with an electrostatic plasma optical system was investigated for the first time. The degree of plasma concentration was quantified using Langmuir ion measurements of the ion flow and optical measurements of the thickness distributions of copper depositions on glass substrates. Both the ion flow and the deposition measurements showed strong concentration of the ion-plasma flow towards the axis. The ion current density at the focus was compressed by a factor up to 9. The on-axis deposition rate was increased by about the same factor.     

The possibility of measuring magnetic fields of flaws by using magnetic-powder suspensions

It is known that magnetic-powder testing is an indicator technique; a flaw in an article is inferred by the deposition of a magnetic suspension within flaw regions (segments) when articles are magnetized. Thus, the magnetic suspension does not allow quantitative evaluation of the field and, therefore, the parameters of the detected flaw. We have conducted some experiments allowing direct measurement of the magnetic field of a flaw by magnetic-powder suspensions. The resistivity was used as a characteristic proportional to the value of the field measured.     

Characterization of microplastic deformation produced in 6061-T6 by using laser shock processing

High dislocation densities are formed in the irradiated region of the workpiece during the laser shock processing; in which case, surface hardening is resulted. The process involves with recoil pressure loading at the workpiece surface with the minimum heating effects in the irradiated region. This favors the process to be a good candidate for the surface treatment of metallic materials. Therefore, in the present study, laser shock processing of 6061-T6 aluminum alloy is carried out and the influence of a number of laser pulses and irradiated spot diameter on the treated layer characteristics, including morphology and hardness, are investigated. It is found that the number of laser pulses has significant influence on the resulting surface characteristics such as surface roughness, crystallite size, micro-strain, and microhardness of the alloy. In this case, surface roughness is deteriorated by increasing number of laser pulses and pulse intensity. In addition, fine crystallite structure takes place in the laser-treated region.     

Generation of quasistatic magnetic fields

A prototype switching system has been developed which can switch 20 kA at 230 V furnished by low-voltage dc generators at the National Magnet Laboratory. The energy is used to generate quasistatic magnetic fields in liquid-nitrogen-cooled copper coils for times approaching 1 s. The present arrangement is limited to fields up to 40 T. The silicon-controlled rectifier switching system, protective devices, circuit operation, and magnet structures are discussed.     

Active cancellation of stray magnetic fields in a Bose-Einstein condensation experiment

A method of active field cancellation is described, which greatly reduces the stray magnetic field within the trap region of a Bose-Einstein condensation experiment. An array of six single-axis magnetic sensors is used to interpolate the field at the trap center, thus avoiding the impractical requirement of placing the sensor within the trap. The system actively suppresses all frequencies from dc to approximately 3000 Hz, and the performance is superior to conventional active Helmholtz cancellation systems. A method of reducing the field gradient, by driving the six Helmholtz coils independently, is also investigated.     

Quantitative phase imaging of nanoscale electrostatic and magnetic fields using off-axis electron holography

Off-axis electron holography in the transmission electron microscope is a powerful interferometric technique that enables electrostatic and magnetic fields to be imaged and quantified with spatial resolution often approaching the nanometer scale. Here, we demonstrate the capabilities of the technique for phase quantification at the nanoscale by briefly reviewing some of our recent studies of nanostructured materials. Examples that are described include determination of the electrostatic potential profiles associated with doped Si- and GaAs-based semiconductor devices, measurement of hole accumulation in Ge quantum dots, mapping of polarization fields in III-nitride heterostructures, and observation of the remanent states and reversal mechanisms of lithographically patterned magnetic nanorings. Some issues associated with sample preparation for doped semiconductor heterostructures are also briefly discussed.     

On developing a magnetorheological transformer that operates in orthogonal magnetic fields

The operation of a magnetorheological transformer in which choke channels are replaced with a cylindrical clearance between two coaxial cylinders is considered. The cylindrical clearance, as well as the working and compensation chambers, are filled with a magnetorheological fluid. It has been shown that this design of the magnetorheological transformer is preferable for damping impact loads.     

Plasma enclosed in a magnetic field produced by flexible surface magnets

A homogeneous steady state plasma with a usable volume of approximately 200 l and with an electron temperature of 1-2 eV and a plasma density of approximately 10(9)-10(10) cm(-3) is produced in a discharge chamber the outside of whose walls is covered with flexible magnetic strips. This magnet arrangement can be built at a fraction of the cost of a conventional system using rigid surface magnets. The magnetic multipole field leads to an increase of the plasma density by one to two orders of magnitude and it is also found to cause trapping of high energy electrons originating from the discharge region.     

Studies of acoustic fields excited by a turn-type transmitter in a constant magnetic field

Rigorous mathematical calculations are used to construct graphical dependences that characterize excitation of acoustic vibrations via the electrodynamic effect, which is one of the effects of the electromagnetic-acoustic (EMA) transformation. The calculations were performed using fundamental mathematical expressions, which were obtained in [1], and the plots were constructed for the diametrical plane with respect to the transmitter. A turn above the half-space in a constant magnetic field was chosen as the transmitter. Materials with sharply different electrophysical properties were considered. Calculations were performed for transducers of different dimensions (two limiting cases) and different values of the working gaps. It is shown that the displacement value consists of three summands: a force that is directed along the x axis, a force that is directed along the z axis, and a socalled electromagnetic-like wave. On the basis of the analysis of the obtained plots, it is shown that in all the considered cases, acoustic vibrations propagate as a narrow beam along the normal and the beam width increases as the gap increases.     

Using magnetic hysteresis for testing electroconductive objects in pulsed magnetic fields

The distributions of the electric voltage U(t) that is read from an induction magnetic head as it scans a discrete magnetic medium with residual magnetic field records that were obtained under the action of a pulsed magnetic field with different-polarity surges on a magnetic medium with a tested object are given. The onset of ordered distributions of the residual magnetic fields on the magnetic medium due to the sequential action on it by pulses of the magnetic field is called the hysteresis interference of a pulsed magnetic field (HI). The scheme of an experimental device for studying propagations of pulsed magnetic fields and methods of testing objects made of electroconductive and magnetic materials, which increase the accuracy of the determination of their specific conductivity σ, permeability μ, distribution uniformity of σ and μ, thickness, and parameters of continuous defects in them, are described.     

Development of laser scanning microscopy using a near ultraviolet laser

We have developed a legitimate fluorescence con-focal scanning microscope (CLSM) using a near ultraviolet (UV) laser. This system has almost no chromatic aberration from the near UV region to the visible region (350–600 nm), and the objectives are designed as water-immersion type. Therefore this system provides the high-quality fluorescence image excited by the near UV laser, and high-quality image of deep points in a sample.     

Development of a time-resolved soft x-ray spectrometer for laser produced plasma experiments

A 2400 lines/mm variable-spaced grating spectrometer has been used to measure soft x-ray emission (8-22 A?) from laser-produced plasma experiments at Lawrence Livermore National Laboratory's Compact Multipulse Terrawatt (COMET) Laser Facility. The spectrometer was coupled to a Kentech x-ray streak camera to study the temporal evolution of soft x rays emitted from the back of the Mylar and the copper foils irradiated at 10(15)?W/cm(2). The instrument demonstrated a resolving power of ～120 at 19 A? with a time resolution of 31 ps. The time-resolved copper emission spectrum was consistent with a photodiode monitoring the laser temporal pulse shape and indicated that the soft x-ray emission follows the laser heating of the target. The time and spectral resolutions of this diagnostic make it useful for studies of high temperature plasmas.