摘要:

We describe a diagnostic suitable for the investigation of strong coupling effects in a plasma. The diagnostic is based on x-ray scattering of kilovolt x rays from a plasma and the determination of total x-ray scattering cross sections. The first experimental results of the total scattering cross sections from a strongly coupled plasma measured with kilovolt x rays are presented. The scattering plasma is formed by radiatively heating an Al foil with soft x rays created by Au laser-conversion foil; the plasma is probed with Ti XXII1s2–1s2pline x rays emitted from a second laser produced plasma. A detailed description of the scattering technique is presented and the potential of x-ray scattering as a diagnostic of strongly coupled plasmas is explored. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148675

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new method of plasma density profile reconstruction in microwave reflectometry is proposed and implemented on anX-mode broadband reflectometer of the GAMMA 10 mirror device with an ultrafast sweep rate of 10–20 &mgr;s. The proposed method makes use of the wavelet transform of the detected signal. Excellent resolution in the time-frequency domain, inherent to wavelet analysis, allows one to obtain a radial electron density profile for every frequency sweep. The electron density reconstruction algorithm, besides the wavelet transform of the reflectometer signal, also includes the calibration, profile initialization, and the solution of an integral equation, ultimately yielding the local values of the electron density. Calibration of the measured signal phase and profile initialization is performed using the independent results of microwave interferometry. Inversion of the integral equation is implemented utilizing the gradient method, numerically stable even for plasma regions with steep density gradients and density profile plateaus. A wavelet-based profile reconstruction algorithm is especially advantageous for monitoring transient plasma phenomena and fast processes, such as in pellet injection, ultrafast swept reflectometry, and short pulsed reflectometry. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148676

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A mutual inductance bridge which may be used for automatic measurement of ac magnetic susceptibilities from 4 K to room temperature at frequencies up to 1 kHz is described. An alternative and new arrangement of the probe is described in details. The coil set is kept at room temperature and moves in such a way to place the sample in the center of each of the secondary coils. The sample, motionless, has its temperature controlled by a helium flow refrigerator. Use of a magnetic shield minimizes coupling of the probe with nearby magnetic materials. The movement of the probe and the operation of the bridge are fully controlled by a personal computer. This probe has a sensitivity of10−7 emuin an ac magnetic field of 8 G rms and frequency of 100 Hz. The frequency range employed can easily be extended to 10 kHz without seriously affecting the accuracy of the measurements. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148677

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A two-step chemical etching procedure has been developed for fabricating probes used by scanning near-field optical microscopy. These probes have two tapered regions which can be reproducibly constructed with a wide range of cone angles. The shape of the probe allows it to be used over sample surfaces with deep and narrow regions. Furthermore, our method can be applied to silica glass fibers which are commercially available. To demonstrate, we used these tips to acquire the near-field optical image of a thin layer of polystyrene spheres. Intensity interference patterns were observed. The demonstrated in-plane resolution was estimated to be about 250 nm. This is mainly limited by the diameter of the metal-coated tip. The transmission efficiency of the tip is better than10−4.©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148678

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe an ultrahigh vacuum instrument for transmission electron microscopy and reflection electron microscopy for the study of surfaces and thin film growth. The focus of previous experiments was on the high spatial resolution (<3 Å) generally associated with microscopy, at the cost of controlled growth and characterization. We have taken a different approach. It has been shown that most experiments using diffraction and diffraction contrast imaging can be performed well at poorer resolution (∼20 Å), including the imaging of monatomic steps and monolayer coverages. The instrument is designed for best control of growth and vacuum, with sacrifices in optical resolution, which is theoretically ∼2 nm. The instrument is called SHEBA (surface high-energy electron beam apparatus). We can examine a∼1 cm2sample in both transmission electron microscopy and reflection electron microscopy,in situwith well-controlled molecular beam epitaxy (MBE) growth capabilities, well characterized vacuum, and surface characterization by Auger spectroscopy and low-energy electron diffraction. Preliminary experiments of cobalt on silicon have shown MBE growth rates ranging from 1.5 monolayers per hour to 18.3 monolayers per hour depending on the temperature of the evaporation source. Using SHEBA for a reactive MBE experiment has provided the first direct evidence of the formation of aluminum nitride by nitridation of basal plane sapphire. The most serious design problems were stray magnetic fields and mechanical vibrations. These have been overcome and allow a spatial resolution of <10 nm. The instrument is expected to be very valuable in studies of film growth. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148679

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Magnetic resonance microscopy (MRM) depends on the use of high field, superconducting magnet systems for its operation. The magnets that are conventionally used are those that were initially designed for chemical structural analysis work. A novel, compact magnet designed specifically for MRM is presented here, and while preserving high field, high homogeneity conditions, has a length less than one-third that of conventional systems. This enables much better access to samples, an important consideration in many MRM experiments. As the homogeneity of a magnet is strongly dependent on its length, novel geometries and optimization techniques are required to meet the requirements of MRM in a compact system. An important outcome of the stochastic optimization performed in this work, is that the use used of a thin superconducting solenoid surrounded by counterwound disk windings provides a mechanism for drastic length reductions over conventional magnet designs. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148680

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A noncontacting method for measuring mechanical strain between two fiducial marks has been developed for use where environmental conditions would be disruptive to methods utilizing optical light. A silicon 111 Johansson crystal is used for this application where MoK&agr;radiation is used to fluoresce fiducial markers made of yittria-stabilized zirconia. This substance is used for a thermal barrier coating in gas turbine engines and the technology for applying this material to withstand long term high temperature exposure is highly developed. The current system has a displacement repeatability of better than 0.1 &mgr;m which is not limited by counting statistics, but rather determined by mechanical considerations. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148681

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Broad band direct sensing of the transient dynamic normal velocity of an object surface and evaluating its absolute value were realized by using a sensor fabricated with a piezoelectric polyvinylidene fluoride film and a polyvinyl chloride (PVC) back load and a PVC wear plate. The transient output signal from the sensor obtained by a test employing a well-defined steplike force, at the epicenter of a steel plate, showed very good agreement with the dynamic normal velocity calculated by using a Green’s function and a simulated source function. The output was proportional to the dynamic normal velocity of the surface, and the frequency-dependent sensitivity for the velocity was flat within a deviation of±3.8 dBfor the average in the frequency range up to 2 MHz. The transient dynamic normal velocity of the surface could be absolutely determined by using a sensor calibrated by theoretical one. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148682

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate an optical two-beam deflection setup forin situstress measurements in thin films. By using improved position sensitive photodetectors we reach a resolution of better than10−4 m−1for substrate curvature measurement at a bandwidth of 1 kHz, with a relatively short optical path of 0.53 m and without employing a lock-in technique. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148721

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An economical and easily constructed tensile stage to study thin polymer films in an environmental scanning electron microscope has been developed. Surface features of the film and the morphology in the vicinity of a crack tip while under stress may be studied using this stage. The construction, sample mounting technique, and some of the photomicrographs obtained using this tensile stage have been illustrated and described. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148720

出版商:AIP    

年代:1998

数据来源: AIP