摘要:

We report a modified procedure to fabricate electrochemically etched scanning tunneling microscopy tips under ac voltage. By both confining the etching action to a small region and controlling the etching current on a tungsten wire, we produce ultrasharp tips with low‐aspect ratio. No electronic shut‐off control is required. Atomic resolution images are routinely obtained. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145612

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new instrument constructed at the high‐pressure facility at CHESS provides a simple mechanism to group MCA data on the basis of a rapidly varying sample temperature. This system allows powder diffraction from samples at simultaneous high pressures and high temperatures in a diamond‐anvil cell. The instrument consists of a laser beam delivery system and incandescent light collection optics to analyze the resulting graybody spectra. A portion of the incandescent light controls into which multichannel analyzer group the x‐ray‐diffraction pattern accumulates. We illustrate the performance of the system with recent experiments. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146449

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A mock‐up has been constructed to test the functioning and performance of the Advanced Photon Source (APS) front ends. The mock‐up consists of all components of the APS insertion‐device beamline front end with a differential pumping system. Primary vacuum tests have been performed and compared with finite element vacuum calculations. Pressure distribution measurements using controlled leaks demonstrate a better than four decades of pressure difference between the two ends of the mock‐up. The measured pressure profiles are consistent with results of finite element analyses of the system. The safety‐control systems are also being tested. A closing time of ∼20 ms for the photon shutter and ∼7 ms for the fast closing valve have been obtained. Experiments on vacuum protection systems indicate that the front end is well protected in case of a vacuum breach. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145613

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The initial operation of the first three insertion devices in ELETTRA is described, including the effects on the electron beam and analysis of the first spectral measurements. Some details are also given about compensation of the ID effects, and operation of the ID control system and vacuum chamber protection system. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145614

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this paper, the results of a series of thermal and distortion finite element analyses performed on room‐temperature silicon for the three standard APS sources, namely, the bending magnet, wiggler A, and undulator A, are reported. The modeling was performed with the silicon cooled directly with water or liquid gallium through rectangular channels. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145615

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The transformation of ray coordinates through a complete beamline is described via a single matrix. This transformation matrix can be used either for conventional ray tracing or for phase space transformation. The matrix elements represent the optical aberrations of the complete system. An optimization program is described that minimizes a weighted sum of the matrix elements. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145616

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The vertical divergence of a photon beam impinging onto a double‐crystal monochromator with asymmetric crystals, and the horizontal divergence in an inclined double‐crystal monochromator, cause an optical distortion of the exit beam. The consequence of this distortion is that a real point‐like source is transformed into a virtual source which has a finite vertical dimension. This may manifest itself on the size of the focus when using conventional focusing optics after the monochromator. For some real sources the height of the corresponding virtual sources are estimated, and it is shown that this effect is more serious in the case of the inclined monochromator. The beam distortions are confirmed also by raytracing simulations. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145617

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A modular system of techniques and software has been developed for the calibration and correction of intensity linearity, uniformity of response, spatial distortion, and image plate decay. With calibration the Molecular DynamicsTMImaging Plate scanner system has been shown to give comparable results to the MarResearchTMscanner. The ESRF x‐ray image intensifier/charge‐coupled device detectors inherently cause large spatial and uniformity of response distortions, and successful data analysis depends on calibration and correction. Results of synchrotron radiation experiments are presented. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145618

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new type of valve is introduced, thesquare‐rootvalve, in which the valve stem radius is machined to vary as the square root of the turn numberN. The open area then varies in direct proportion to the turn number, and the measured flow rateQs(N) was found to be adequate to allow this valve to be used in an automatic feedback control system. As the flow‐rate function will generally depend on the source and load impedances, a systematic method to empirically obtain precise linear (or other) flow‐rate functions is outlined. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145619

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Repeating pneumatic pellet injectors developed at the Oak Ridge National Laboratory (ORNL) were used for plasma fueling experiments on the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET). For plasma fueling on the DIII–D tokamak, a small‐bore (1.8‐mm) injector has been developed and tested in the laboratory at pellet rates of up to 10 Hz and speeds of ≤1 km/s (for pulse lengths of up to 15 s). This performance represents the smallest pellet size and highest repetition rate demonstrated with an ORNL repeating pneumatic pellet injector. The design has been incorporated in the three‐barrel injector that was previously used on JET; the injection system, equipped with nominal pellet sizes of 1.8‐, 2.7‐, and 4.0‐mm diameter, has been installed on DIII–D and will be used in future plasma fueling experiments. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145620

出版商:AIP    

年代:1995

数据来源: AIP