摘要:

A bellows assembly with a radio frequency (rf) shield has been designed and developed for the KEK B factory (KEKB). The rf shield is the usual finger type but has a special spring finger to press contact fingers onto the beam tube. A test of the mechanical performance using a trial model shows good results. Further experimental studies are focused on the two key points of the finger‐type rf shield, that is, the contact force of fingers and the length of slits between adjacent fingers. First, to reduce the excess abrasion at contact points, the necessary contact force is studied experimentally utilizing microwaves. Abnormal heating is checked by transmitting a 508 MHz cw microwave through a trial model in a coaxial line. Arcing at the contact point in vacuum is observed by transmitting a 2856 MHz pulse microwave in a rectangular waveguide equipped with a model piece of the rf shield. A contact force of 50 g/finger is found to be necessary. Second, the optimum slit length is studied with a strategy to minimize the higher order mode (HOM) power leaked from the beam tube into the inside of the bellows while keeping a sufficient sliding stroke. The coupling coefficient, &bgr;, of the rf shield is measured experimentally from theQvalue of a TE mode resonance in a cylindrical cavity connected to the bellows assembly. Using the measured dependence of &bgr; on the slit length, a rough estimation of leaked HOM power is tried for the KEKB. The expected leaked power is about 6–18 W for a slit length of 20 mm, which is in the allowable range. The results obtained through these experiments are reflected to the design for the KEKB: the contact force of 80–100 g/finger will be adopted finally considering the manufacturing error of typically ±10 g/finger in our test and leaving a margin for higher frequencies. The nominal slit length will be set to be 20 mm, keeping the expansion/contraction of ±10 mm. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147110

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A technique for measuring ion transport using laser‐induced fluorescence has been developed and tested in an argon plasma. It uses only one broadband beam thus being simpler than some previous techniques because no detection beam is required. First, a 5 &mgr;s laser pulse centered on 611 nm stimulates a transition from the metastable state in Ar(II) 3d 2G9/2to 4p 2F7/20. A 4p 2F7/20to 4s2D5/2transition rapidly results with emission at 461 nm. Upon cessation of the laser pulse, the 461 nm light in the detection volume does not return to its background level immediately because the 3d 2G9/2level is partially depleted. The time history of the 461 nm signal in returning to steady‐state background intensity provides a means of determining ion transport because the recovery signal is due to processes including ion excitation, diffusion, convection, and thermal motion. Measurements of the ion velocity distribution yield the contributions of thermal and convective effects to ion transport. By varying the laser beam diameter and the detection volume the plasma ion spatial diffusion coefficientD, and the time, &tgr;pit takes for processes other than transport to bring the 461 nm emission back to the steady‐state background level are determined. For example, in one set of plasma conditionsD=0.58±0.16 m2/s and &tgr;p=59±7 &mgr;s were found. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147111

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A retarding field energy analyzer has been developed for diagnosing 300 &mgr;s duration, 60 cm×60 cm negative glow, sheet plasmas immersed in a 150–250 G axial magnetic field. The electron density in these 4.5 kV, 13 A, 120 mTorr discharges in air and other gases, is high enough to reflectX‐band microwaves. The presence of the magnetic field makes the suppression of secondary electrons from the Faraday collector surface more difficult. The approach taken here is to bias the entire collection circuit and the amplifiers 90 V positive with respect to the data acquisition room. The differentially pumped analyzer is designed to accept electrons with a large range of perpendicular velocities, and it measures the parallel velocity distribution function of the discharge electrons entering a 0.64‐mm‐diam hole in the anode plate. It gives valuable information about the energy spectrum of the energetic beam electrons emitted from the cathode, and the effect of energy loss and scattering processes on this propagating beam component. Additionally, since the analyzer sampling hole is offset from the anode‐cathode axis, the current density profile can be measured for different bias voltages on the retarding grid, by rotating the linear cathode about the vertical anode‐cathode axis. These profiles give the sheet thickness for the beam and plasma components of the negative glow discharge. It also gives useful information about the scattering induced beam spreading and its effects on the plasma sheet thickness and electron density. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147088

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

For absolute soft‐x‐ray line intensity measurements to deduce elemental concentrations and parameters of magnetically confined plasmas large‐area x‐ray sources are developed and investigated. These calibration sources useK,L, andMtransitions in different elements and cover a wide photon energy (and wavelength) range. From the measured absolute line intensities of these sources the quantum efficiency values of numerous elements forK‐,L‐, andM‐line emission per incident electron are deduced. They represent the basis of simple soft‐x‐ray monitors for impurities in fusion plasmas. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147112

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This article describes a technique that uses a piezoelectric quartz crystal microbalance (QCM) for determining the diffusion coefficient of naphthalene into air. The QCM is placed onto the open top of a closed Stefan tube and its active surface is covered with a thin layer of solid naphthalene. Due to the markedly enhanced QCM resolution of 10−9g/cm2over that of the conventional digital electronic balance, the QCM in this study requires much less time than previous studies using digital electronic balances for measuring the diffusion coefficient in a binary gas system. AtP=0.1013 MPa and in a temperature range from 278.25 to 315.15 K, the empirical correlations to evaluate both the diffusion coefficient of naphthalene into air at 1 atm pressure and the Schmidt number of naphthalene at various temperatures are presented. The measurement uncertainty of the diffusion coefficient of naphthalene into air with the present system is less than 3%. In addition, measured results verify that the measurement of the diffusion coefficient of naphthalene into air is only slightly affected by the length of the diffusion tube if the QCM is used in the closed Stefan tube for measuring the mass flux in the diffusion tube. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147113

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

As part of a mixing test, an instrument to measure transient concentration of several different binary gas mixtures was required. A combination sonic nozzle/hot film instrument was selected for this measurement, but for certain gas mixtures the output from this device was unexpectedly small. A study of the dynamics of the instrument reveals that this is caused by the compensatory nature of the two principal contributors to convection: change in constant velocity convection coefficient and change in sonic velocity. The problem is addressed by introducing a physical delay line between the hot film element and the sonic nozzle. Results show that a finite interval of constant velocity thermal convection data can be taken before sonic velocity effects are introduced. A second variation is proposed where the hot film sensor is replaced by a simple orifice flowmeter. Orifice pressure drop and sonic velocity effects, normally strongly compensatory, are also separated by a delay line such that nearly constant velocity orifice discharge coefficient data can be taken over a finite time interval. Results show that this instrument design has higher sensitivity and lower cost than the hot film variant, albeit with slower time response. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147114

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A method is described to acquire x‐ray absorption fine structure (XAFS) spectra of high‐pressure liquid and supercritical fluid solutions. The technique employs a short length of fused‐silica capillary tubing that has an inner diameter of 250 &mgr;m and an outer diameter of 360 &mgr;m. A hairpin bend is formed near the center of the capillary and the bend is then placed end‐on directly in the focused x‐ray beam. Fluorescence spectra were acquired in a 90° geometry using a 13 element Ge detector. Demonstration XAFS spectra are reported for a Mn organometallic complex dissolved in subcritical and supercritical CO2. Although the maximum pressure of these studies was 160 bar, with slight modification, the method will be applicable to studies requiring pressures as high as 4 kbar. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147115

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present the design of a machine which allows us to measure the surface tension of a free standing smectic film with an accuracy of 0.1 mN/m absolute and 0.01 mN/m relative. Our design makes it possible to measure the surface tension over a wide range of temperatures with minimal drift in the detector itself. The response time of our detector can be as small as 0.01 s which allows us to study dynamic processes involving the interaction between the film and the meniscus around the frame that supports the film. Our design is based on a rigid frame with a movable side suspended as a pendulum. The surface tension force on the movable side is opposed by a feedback system to stabilize the position of the movable side. The stabilizing force then is a measure of the surface tension. An optical system detects deflection of the movable side due to the surface tension force, and applies a restoring force by generating electric current in a coil which applies force to a permanent magnet attached to the pendulum arm. The feedback control includes an integrator stage to achieve finite force with negligible error in position. The device can be calibrated with a simple lever and weight scheme to simulate a surface tension force. The design elements that determine the stability and accuracy of the system are discussed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147116

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A sessile drop tensiometer enhanced by video‐image digitization is designed for the experimental measurement of dynamic/advancing/receding contact angle. A collimated light beam passes through the sessile drop of liquid and a silhouette of the drop is created. The equipment video images the silhouette, digitizes the image, and locates the edge coordinates of the drop. A new technique, replacing the classical selected plane method, is developed to obtain the values of capillary constant and the radius of curvature at apex from the edge coordinates of digitized drop profile. Four parameters (location of apex, radius of curvature at apex, and the capillary constant) are calculated from the best fit between the edge coordinates and the theoretical curve obtained from the Laplace equation. The contact angle is then obtained from the location of the air/solid interface and the best‐fitted sessile drop profile. By controlling the humidity of air phase surrounding the drop, this technique can measure the advancing and receding contact angles and monitor the rate of advancing and receding of the three‐phase line simultaneously. This technique works well on contact angle measurement for sessile drops with or without an equator. Preliminary studies on the dynamic contact angle have been made for water drops on paraffin, polymethylmethecrylate, and glass. The technique is capable of giving contact angle of 0.2° precision. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147117

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A fitting method using parallel beam x‐ray diffraction (XRD) for profiling phase content changing with depth is presented. This method depends on measurements of XRD intensity at various incident angles, and numerical procedures are employed for obtaining the true depth profiles quantitatively. The procedures were then applied to a nitrided steel sample without preferred orientation and a thin‐film sample with preferred orientation. Both model‐independent and model‐dependent ways were used in fitting. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147124

出版商:AIP    

年代:1996

数据来源: AIP