摘要:

Collective Thomson scattering on alpha density fluctuations in ignited plasma regimes is investigated with reference to a promising candidate source as the mm‐wave gyrotron and a representative ITER‐like plasma regime. It is shown that a number of intrinsic limitations characterize each of the equatorial scattering geometries selected as more promising, namely a backscattering geometry atf0=80 GHz and two similar quasiorthogonal geometries atf0=180 GHz. A lack of spatial resolution typical of the former geometry has to be contrasted with a significant limitation in plasma access typical of the remaining geometries. Other relevant differences concern the requirements in terms of gyrotron power, acceptable stray radiation levels, etc. Special emphasis is given in the work to a discussion of ECE noise, on which the feasibility itself of the alpha collective scattering diagnostics at mm‐waves largely depends in the plasma regimes considered. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147286

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A comparison is made between the statistical properties of phase and power signals from a homodyne reflectometer on the STOR‐M tokamak and simulated signals from a two‐dimensional distorted surface model. Experimental results from edge density fluctuations show phase fluctuations of less than half a fringe with a Gaussian distribution and no phase ramping. Reflected power fluctuations are substantial (up to 45%) and are non‐Gaussian distributed. Both phase and power signals display broadband turbulent frequency spectra with spectral indexes of −3.5. Fluctuations in the scattered electric field are calculated in the model using physical optics principles with a Gaussian reflectometer incident beam profile and structured surface distortions to replicate variations in the plasma cutoff layer. Simulation results display a wide range of features depending on three parameters, surface fluctuation amplitude, transverse wavenumber spectrum, and incident beam width. With the beam width fixed by the experiment (50 mm) and (realistic) fitted values of 1–2 mm for the root mean square fluctuation depth and 2 cm−1for thek‐spectral width—good agreement is found with the experiment. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147287

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An imaging vacuum‐ultraviolet monochromator has been developed to provide the space‐resolved impurity line emissions from magnetically confined plasmas. With minor modifications of a commercial normal incidence monochromator, a pinhole entrance slit and a microchannel plate detector displaced away from the exit slit, the instrument performs two‐dimensional spectroscopic observations in the wavelength range from 400 to 2000 A˚. Ray tracing has been performed to understand the spatial imaging properties in the practical geometric configuration. The measured spatial resolution is about 0.5 and 1 mrad in dispersion and vertical plane, respectively, with the entrance slit of 0.1 mm width and height. The results of the testing experiments and the measurements carried out on the JIPP T‐IIU tokamak plasma are presented and discussed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147515

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Temperature stabilization by inertial feedback control has proven a powerful tool to create the ultrastable environment essential for high resolution calorimetry. A thermally insulated mass, connected to a base through Seebeck effect sensors (thermopiles) is used as a reference to control the base temperature. The thermopile signal is proportional to both the heat capacity of the reference mass and the derivative &THgr;˙ of the base temperature &THgr;. Using vacuum insulation and bismuth telluride thermopiles, we designed and tested temperature derivative sensors (TDSs) with sensitivities up to 3300 V s K−1. Standard industrial controllers with approximately ±1 &mgr;V input noise and stability, permit control of temperature derivatives to ±3×10−10K s−1. Single‐cup thermoelectric calorimeters coupled to the TDS‐controlled base permitted measurement of heat flow from samples in a power range from 3 &mgr;W to 10 W with high accuracy (±100 ppm), resolution (±0.2 &mgr;W), and reproducibility (±1 &mgr;W). The design of two instruments is described in detail. Their performance is demonstrated on a variety of measurements, e.g., the determination of sample heat capacities with temperature ramp rates &THgr;˙=±5×10−6K s−1, the half‐life of a 3 g tritium sample in a uranium getter bed, the decay heat of depleted uranium, and the heat evolution of epoxy resin. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147306

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We consider a new approximation ofT=f(R) andR=g(T) functions for germanium (GRT) and platinum (PRT) cryogenic resistance thermometers from 1.2 to 85 K and from 14 to 325 K, respectively, using the weighted orthonormal polynomial expansion method (OPEM). The main aspect in this description is an evolving new type of weighting function referred to the specific material characteristics of the investigated cryogenic resistance temperature sensors. The OPEM fitting errors for GRT and PRT characteristics in the considered approximation within the whole useful temperature ranges determine the perspectives of our method in cryogenic thermometry. The proposed OPEM description ofRandTfunctions of the investigated thermoresistors defines the hopefulness of our algorithm with respect to both the calibration of GRT and PRT sensors and the automation of thermal measurements at low temperatures. The demonstrated values of the OPEM fitting errors with theRfunction approximation as well as the evaluation of the first derivativedR/dTallow the OPEM to be successfully used for a generation of the interpolation tables with the resistance thermometer calibration. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147288

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Near‐field imaging is a means of exceeding the diffraction limit in optical microscopy to yield subwavelength resolution optical images of a sample surface. In order to achieve such high resolution, it is necessary to scan the measurement probe above the surface at a height of only a few nanometers which requires careful control of the separation between tip and sample. In the implementation of the near‐field optical microscope (NFOM) reported here, the distance regulation scheme is based on an inverted noncontact atomic force microscope (AFM) in which a cantilever is used as the sample substrate and imaging is performed with a fiber optic tip. In this way, both the benefits of AFM and NFOM are realized simultaneously. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147289

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We successfully developed an atomic force microscope (AFM) with a batch‐fabricated silicon cantilever with a pyramidal stylus. The high quality lead zirconate titanate (PZT) piezoelectric thin film allows simultaneously displacement sensing and actuating. The PZT thin film with a dielectric constant of 1000, a remanent polarization of 30 &mgr;C/cm2, and a piezoelectric constant of −100 pC/N, which are as high as those of bulk ceramics PZT, has been formed by sputtering at 400 °C and subsequent annealing at 650 °C. A Si(111) mono‐atomic step whose height is 4 A˚ has been observed clearly in an AFM cyclic contact mode by a PZT‐AFM lever as a displacement sensor. A PZT‐AFM lever has been used as an actuator forzfeedback positioning for AFM imaging of a compact disk pit. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147290

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The electric fields of the helical resonator, both of the fundamental frequency and the odd harmonics up to the eleventh, have been probed using metallic copper and heavily doped Si:P disks by measuring the relative frequency shift &Dgr;f/fand the change in quality factor &Dgr;(1/Q) with a network analyzer after insertion of the disk as a probe mounted on a dielectric support rod which could be translated along thezaxis of the helix with a micrometer drive. The magnetic field componentHzwas probed using the paramagnetic free radical DPPH and a simple transmission electron spin resonance (ESR) spectrometer. The &Dgr;f/fresults were compared with calculated results using the Bethe–Schwinger expression and the plasma result for the change in dielectric response, while the &Dgr;(1/Q) results were compared with a standard loss expression. The results, except for the role of the short but including the metallic disk thickness and diameter dependence, agree with the fields given by Pierce for an infinite helical current sheet, when adapted to the standing wave form. The ESR results demonstrate the optimum position for a paramagnetic sample. The ESR amplitude versus probe insertion depth is in qualitative agreement with an expression by Wilmshurstetal., but also exhibits an unexplained sign change. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147291

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A numerical method for obtaining the vibrating sample magnetometer (VSM) sensitivity functions due to a uniformly magnetized sample in the shape of ellipsoid, cuboid or cylinder, and then calculating the induced voltage in a VSM detection coil systems is presented. The induced voltage, which depends on the equilibrium position and amplitude of the sample in three‐dimensional space, and depends on the geometric parameters of both sample and detection coils, is calculated from the viewpoint of magnetic charges. This numerical method is more accurate than others, which use dipole moment approximation without taking into consideration the sample shape and size. By using this method, the induced voltage, for which the shape and size effects of the sample must be taken into account, can be calculated if there is knowledge of geometric parameters of the sample and coils. The formulas for calculating the correction coefficient are also given for samples whose shape errors should be considered. Our results provide rigorous theoretical guidance for the exhaustive study of the VSM working principle, for accurate measurement of the sample magnetic moment, and for optimum design of configuration, position, and orientation of VSM pickup coils. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147292

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This article presents a new, automated Raman scattering experiment to measure the orientation in nematic liquid crystals. The automated experiment utilizes phase modulation to alter the polarization state of light unlike conventional, polarized Raman experiments which require the manual manipulation of polarizers and multiple measurements. Polarization modulation imparts the ability to quantify the second and fourth moments of the orientation distribution function with a single measurement. The feasibility of the new experiment is demonstrated through orientation measure‐ ments of a well characterized nematic liquid crystal, 4‐pentyl‐(4‐cyanophenyl)‐cyclohexane. Additionally, since the results of the polarization‐modulated technique are in excellent agreement with conventional Raman measurements, this study supports the validity of the theory describing Raman scattering from birefringent materials. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147293

出版商:AIP    

年代:1996

数据来源: AIP