摘要:

We have developed a new compact retarding-potential Mott spin polarimeter and achieved an efficiency of1.9×10−4for gold target operating in 25 keV. A novel design of the retarding field electron optics with 0.59 sr collection solid angle for scattered electrons was adopted based on Monte Carlo calculations for the spin-dependent electron scattering process and electron beam ray-tracing calculations. We have combined the new spin polarimeter with an angle-resolved photoelectron spectrometer and measured the spin- and angle-resolved photoelectron spectra and studied the spin-dependent electronic structure of Ni(110) along the&Ggr;¯S¯line of its surface Brilluoin zone. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148401

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe in detail the procedures used for the preparation of ultrathin (∼10 nm) free-standing membranes for(e,2e)spectroscopy. Such a thin target is needed to minimize electron multiple scattering before and after an(e,2e)event. The development of a rf plasma source which allowsin situthinning and thickness monitoring is of key importance to the success of the target preparation. Materials (C, Si, Ni, Cu, Al2O3,SiO2,CuO) with different properties and structures are usually prepared in different ways. For insulating targets it is important to have a conducting sublayer to avoid the charging problem. A well prepared target usually has a thin area larger than the(e,2e)beam size(∼0.2 mm in diameter) and yields high quality(e,2e)data from which the electron energy-momentum density in a chosen direction is determined. Efforts demonstrated in this article indicate that the preparation of ultrathin free-standing films is a challenging area where significant technical development is needed.©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148402

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A multistage electron collector has been designed for an electron-beam energy recovery system. The electrodes of the collector are cylindrical and partially conical or spiky near the axis in order to maintain a continuous field effect on the beam. The field effect of these electrodes is so efficient that a magnetic field is not necessary between the deceleration and collection gap to confine the beam on the axis. The energy recovery efficiency, 99.8&percent;, of the collector was calculated by using a computer code with about 10 mA beam current and−75 keV.To test the performance of the collector, it has been assembled with a laser-heated electron gun and electrically connected to its power supply. The potentials of each electrode have been provided through a voltage divider of several hundred megaohms. Experimentally, the efficiency obtained was 73&percent;–98&percent; with a beam current of 0.67 mA. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148403

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article presents an analytical expression of the first, the third, and the fifth harmonic component for axial field of magnetic deflectors made of straight or tapered saddle coils or straight toroidal coils in air. In particular, the expressions for the tapered saddle coils and also for the fifth components for straight saddle and toroidal coils have not been derived so far. The existence of the analytical expressions for the simple but important problems of magnetic deflectors in free space is quite advantageous for the check of the correct mesh layout for the more general problems. The axial field functions are compared with those computed with the first order finite element method for the same geometry, with very good agreement of the results. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148404

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The design and operation of a gas-discharge neutralizer of positive ion beams is presented. It is based on the discharge with crossed electric and magnetic fields initiated by the ion beam, which travels through the device, without an additional energy source. Depending on the pressure, there are two types of the discharge inside the neutralizer: high-voltage (at a low pressurep<3×10−4 Torr) and magnetron (at a high pressurep>3×10−4 Torr). In the high-voltage regime, the ion beam is partially neutralized. Full ion beam compensation is achieved in the magnetron regime. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148405

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

To improve the turbulence characterization and the estimation of the transport processes at the plasma edge, we designed and installed, in the Brazilian tokamak (TBR), a complex probe that consisted of five single Langmuir probes, a four-channel triple probe, and magnetic probes. In this work, we describe in detail this diagnostic system and present experimental examples of simultaneously measured plasma parameters and electrostatic and magnetic turbulent fluctuations in the TBR tokamak. This procedure permits to investigate any coupling between these two kinds of oscillations. Furthermore, our results confirmed that corrections due to electron temperature fluctuations are relevant for turbulence characterization. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148406

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Waveguide windows are major components of a transmission line used in microwave plasma devices. The function of the waveguide window is to provide vacuum isolation of the source side from the plasma chamber while transmitting microwaves with minimum attenuation. Commonly a single thin dielectric plate is sandwiched between a choke type flange and a flat flange and is used as a waveguide window. To arrive at a better window configuration in terms of the low power reflection coefficient, the voltage standing wave ratio calculation is carried out for different window configurations (single window and double window) and for various window thicknesses. It is found that the power reflection is the minimum in the case of double window configuration. The minimum power reflection is as low as 0.8&percent; for a combination of alumina and a quartz plate each of 1 cm thickness in the double window configuration. Also, it is more advantageous to use radial microwave coupling than axial coupling in order to increase the life time of the microwave waveguide window. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148407

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An electric-field sensor was developed using both piezoelectric and converse piezoelectric resonances. Composed of no metallic parts, this probe minimizes field disturbance. The most distinguishing feature of this probe is that a signal is transmitted neither electrically nor optically, but mechanically. To demonstrate the field sensing capability of this probe, we measured both the capacitive and inductive fields inside empty and plasma-filled solenoidal coils. The result shows that the capacitive field is dominant in an empty solenoid, although it is almost completely shielded by inductively excited plasma. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148408

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of a broadband wave number(k)and frequency (&ohgr;) spectrumS(k,&ohgr;),on particle flux due to electrostatic fluctuations in a plasma is examined. Effect of the broadband spectrum on density-potential coherence is also calculated. Particle flux results are compared with a standard quasilinear transport estimate that has been used to interpret heavy ion beam probe and Langmuir probe measurements in fusion plasmas. Situations in which the quasilinear estimate is probably inaccurate are illustrated, including edge shear layer measurements and interior measurements from the TEXT tokamak. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148409

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The efficient confinement of the energetic charged fusion products and the complete transfer of their kinetic energy to the plasma is of great importance for the realization of a fusion reactor which will depend on alpha-particle heating. In todays fusion experiments with deuterium plasmas, this aspect can be investigated using the 1 MeV tritons from thed(d,p)treaction. The slowing down behavior of these tritons can be studied by measuring the 14 MeV neutrons from thet(d,&agr;)nreaction (triton burnup). At ASDEX Upgrade a time-resolved diagnostic based on a silicon barrier detector has been installed to measure the time evolution of the 14 MeV neutron rate. Using the Si(n,p)Al and Si(n,&agr;)Mg reactions the high energy neutrons, with an energy above the 6 MeV threshold, are converted to charged particles directly inside the semiconductor diode. The complete functionality of the detector system is demonstrated by the successful measurement of the complex spectrum of the charged reaction products in silicon triggered by fusion neutrons during plasma discharges. As an integral component of this diagnostic a time dependent burnup code based on classical slowing-down theory has been developed for the use at ASDEX Upgrade to analyze the complex time evolution of the 14 MeV neutron rate. First measurements are compared to the results of the code. A new application for such detectors is proposed, as in conjunction with the materials of the tokamak structure it can be operated simultaneously as anin situactivation system. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148410

出版商:AIP    

年代:1997

数据来源: AIP