摘要:

A technique is described whereby an estimate of the false coincidence signal, suitable for background correction of data acquired in a coincidence experiment, is obtained by using a pseudorandom pulser to generate a stream of “false” start events. The statistical properties of this simulated source are adjusted to mimic those of the real source of electron start events. False ion coincidences with the simulated starts are measured concurrently with the real coincidence signal, with the mean count rate of the pseudorandom pulse source automatically tracking that of the true electron start events. In this manner any long term instrumental drifts during the course of an extended experimental measurement will similarly affect both the real and simulated coincidence data. Subtraction of the simulated background of false coincidences from the real coincidence data then yields an improved estimate of the true coincidence signal. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149074

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The time dependence of the polarization of a stored proton beam was measured near an induced depolarizing resonance. The resonance was created by a magnetic field which oscillated along the beam axis. The distance to the resonance was varied by changing the frequency of the oscillating field. The resonance was approached from either side and the time dependence of the polarization was found to be symmetric with respect to the resonance, and in agreement with an earlier measurement that involved an intrinsic depolarizing resonance. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149075

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The plasma of a high-current hydrogen–cesium glow discharge of planotron and PenningH−ion sources was studied with the use of spectroscopic methods. The elemental and charge compositions of the plasma were determined. The temperature of hydrogen atoms was determined and the electron density was estimated. The density variation of hydrogen atoms, cesium atoms, and molybdenum atoms (electrode material) and cesium ions during the discharge pulse with the space resolution along two coordinates was observed. Blocking up of cesium atoms and ions and molybdenum atoms near the cathode surface was found. The radiation energy of the discharge plasma was measured within the visible spectral range. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149076

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In experiments on positronium annihilation in three photons, the background rate of triple-coincident events is usually measured by performing a separate counting run, in which one of the detectors is moved out of the three quanta annihilation plane. A thorough analysis shows that this approach can entail systematic errors and we suggest an alternative procedure. By employing a few auxiliary coincidence modules, the new approach avoids the necessity of a further dedicated counting run with modified detector geometry. Experimental results confirm the viability and accuracy of the method. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149077

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This work aims to show a selection process for natural crystals that considers the major characteristics and performance as gratings for neutron monochromators using the neutron diffraction technique. A total of 19 crystals have been selected and classified regarding their adequacy for use as neutron diffraction devices. Applying special criteria, method and the rocking curve technique, the measurements have been performed and the theoretically available values compared with the experimental results, obtained directly from a neutron diffractometer in operation at the IEA-R1 (5 MW) nuclear research reactor. The choice for natural crystals, expanding the operational range of the neutron diffraction instruments, is related with the purpose of getting monochromatic neutron sources suitable for the applications. The neutron has proved to be the most powerful microscopic testing particle in condensed matter studies and in many other areas of application. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149078

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Weakly collisional ions trapped in the toroidal field ripples at the outer plasma edge of a Tokamak can be prevented from escaping the plasma due to gradBdrift by a counteracting radial electric field. This leads to an increase in the density of ripple-trapped ions, which can be monitored by the analysis of charge exchange neutrals. The minimum radial electric fieldErnecessary to confine ions with energyEand chargeq(q=−1:charge of the electron) isEr=−E/(q×R),whereRis the major radius at the measuring point. Slowing-down ions from neutral injection are usually in the right energy range to be sufficiently collisionless in the plasma edge and show confinement by radial electric fields in the range of tens of kV/m. The density of banana ions is almost unaffected by the radial electric field indicating that the change in the fluxes of ripple-trapped ions is, indeed, caused by the radial electric field and not by direct changes in plasma parameters. Single particle calculations for real ASDEX Upgrade geometry and magnetic fields but with an assumed electric field profile give a rule of thumb estimate of the electric field strength. They also make plausible the reason why the charge exchange flux may react in less than 100 &mgr;s to an abrupt onset of a radial electric field with a halfwidth of at least the Larmor diameter of the particles in question and thus make this measurement an interesting tool for the investigation of the edge radial electric field. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149079

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A novel electro-optical probe (EOP) has been developed to characterize the spatial uniformity of various plasma parameters. Spatially resolved electron density and energy distribution function, neutral and charged particle densities, as well as ion flow velocity are determined by the EOP. The design of the EOP combines a Mach probe, back-to-back charge collectors, and a collimated optical fiber. The light collection angle of the optical fiber is limited by recessing the fiber in a ceramic tube. The line-of-sight integration length of the plasma emission is bounded by the charge collector disk. A spatial resolution of 2.4 cm is obtained by the present design of the EOP. The ion flow velocity perpendicular to the charge collector surface is determined by the ratio of the ion saturation currents of the two counter facing charge collectors. Localized actinometry, that combines spatially resolved optical emission spectra and electron energy distribution functions, is used to determine the density of atomic chlorine and fluorine radicals. The spatial distribution is obtained by scanning the EOP across the plasma volume. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149080

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A millimeter-wave interferometer having a capability of concomitant electron temperature measurement, based on the electron cyclotron absorption (ECA) technique, has been developed for divertor diagnostics in JT-60U. Three lines of sight, which pass through theXpoint horizontally, the inboard divertor and the outboard divertor, are chosen. Two transmitter/receiver units with frequencies of 217 and 183 GHz are employed in order to eliminate the spurious vibration effect using a two color scheme. The two independent units are also arranged to enable two sight line measurements without the vibration compensation. Furthermore, these units allow us to apply the simultaneous ECA diagnostic. Due to the complexity of the transmission line inside the tokamak, the insertion loss is as large as 65 dB. However, the interferometer system can be operated with the signal-to-noise (S/N) ratio of about 20 dB due to the low equivalent input noise of −90 dB m. The measurements performed for several types of the JT-60U discharges indicate the feasibility of the system and the rapid reduction of the electron density near theXpoint at the high confinement mode transition is first demonstrated. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149081

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

X-ray imaging of plasmas with a resolution on the order of 1 &mgr;m could not be achieved with pinholes because the light flux on the detector would be too low. We tested two different types of diffractive lenses derived from the circular grating based on the Fresnel zones. Compared to pinholes, they can have an equivalent diameter of about 100 &mgr;m with a resolution of about 1 &mgr;m. The two kinds of devices tested were: (1) a transmission phase Fresnel zone lens (PFZL) associated with a multilayer mirror; (2) a reflective Bragg–Fresnel lens (BFL) which combines a multilayer mirror and the grating. The PFZL works at normal incidence by transmission; an additional mirror is used to reflect only a small bandwidth within the spectrum; the angle of reflection of the multilayer of the imaging beam on the mirror is set as to adjust the center of the useful bandwidth. The BFL works at fixed grazing incidence and we only use an off-axis part of the BFL in order to avoid the illumination of the detector by zeroth order diffracted light. We computed the spatial response of both devices and found that the aberrations were very low within an object field of 100 &mgr;m for the BFL device and 1 mm for the PFZL device. Their theoretical resolution is given by the width of their last zone: below 0.1 &mgr;m for the BFL device and 0.4 &mgr;m for the PFZL device. We also made images of plasma with both devices and using back-lighted grids, we obtained a resolution on the order of 4–5 &mgr;m. In the discussion, we try to explain the difference between the theoretical and experimental results. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149082

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new method for producing a tracer-encapsulated solid pellet (TESPEL) has been developed for a local deposition of the tracer ions in the core plasma and an accurate measurement of the particle transport. The method allows manufacturing of TESPELs in the form of polystyrene shells containing lithium hydride inside as a tracer. The TESPEL acceleration has been successfully performed and photos of the pellets in flight confirmed the TESPEL integrity. For the pellets with diameter 300–400&mgr;m and wall thickness 40–50&mgr;m the pellet fragility becomes insignificant. Calculation of the TESPEL ablation rate has showed that the achieved pellet velocities and sizes are appropriate for the injection into a medium size plasma. It was proposed to fractionate the tracer contents in order to provide better localization of the deposited tracer ions in the plasma. The data obtained in these experiments have proved that injection of the TESPEL made from the plastic shells can be a promising tool for the particle transport diagnostics.©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149083

出版商:AIP    

年代:1998

数据来源: AIP