摘要:

In the proposed pulsed ion source, a steady-state sputtering avalanche sustained by secondary ions locked in phase with an ac voltage applied between plates creates high current bunches with energy monochromaticity and ion purity. In a two-surface cascade, the average current exhibits a Child–Langmuir-like scaling, due to the dynamical constraints on the normalized ac voltage. A single-surface cascade, using a bending magnetic field, operates with unconstrained voltage and exhibits much lower heat load for given current, as well as the ability for average current in excess of the Child–Langmuir limit. The pulsed source is particularly attractive for ion beams of solid materials with high vaporization temperature. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148480

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new technique for trapping of fast (keV) ion beams is presented. The trap, which is electrostatic, works on a principle similar to that of optical resonators. The main advantages of the trap are the possibility to trap fast beams without need of deceleration, the well-defined beam direction, the easy access to the trapped beam by various probes, and the simple requirement in terms of external beam injection. Results of preliminary experiments related to the radiative cooling of molecular ions are also reported. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148481

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The aberrations coefficients are derived for electrostatic systems that are axially symmetric except for the presence of a localized potential defect (i.e., a patch field). The near-axis aberrations caused by such a defect near the edge of an aperture are then investigated. When a beam fills the aperture the resulting aberrations cannot be characterized in terms of coefficients, and so a new characterization of the aberrations is defined. Numerical evaluations are carried out for representative types of potential defect. Relationships are presented that enable the increase in spot size of a focused beam to be deduced from the measured or estimated mean deflection of the spot. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148482

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This article describes the optimization procedure to design a compact scintillator which has a maximum secondary electron collection efficiency without the need of a bias voltage for a focused ion beam (FIB) system. The optimized scintillator design was proven to be very effective for focused ion beam systems. By doing design optimization theoretically and experimentally, a 100&percent; collection was realized for a simple, compact and robust scintillator structure without the bias voltage. So far our experimental study is within the scope of FIB imaging, but we have reasons to believe that the optimized designs or the optimization methodology discussed in this article should be useful in other charged particle applications such as scanning electron microscopy or wherever a scintillator is used to collect secondary electrons. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148483

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The gain of windowless electron multipliers 226EM and EMI 9643/2B with BeCu dynodes was measured forTaq+ions(12⩽q⩽49)with kinetic energies ranging from 8 to164 keV/q.A Faraday cup was used as a standard ion-current detector. The comparison of the anode current of an electron multiplier (EM) with the Faraday cup current initiated by impact of ions indicates effects of their charge state as well as the velocity for response of both the EMs. The current gain of both the EMs has been found to monotonously increase with increasing charge state for ion energy per charge up to24 keV/qbut has a minimum for higher energy. The analog particle gain derived from the measured current gain increases with increasing charge state for all the accelerating voltages applied. The analog particle gain of 226EM increases with increasing ion energy per charge forqless than∼27but decreases with ion energy for higherq.For EMI 9643/2B the particle gain increases with increasing velocity up to charge state 49 where it becomes approximately independent of its velocity. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148521

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A high power rf transformer has been developed and implemented for the purpose of plasma production in a toroidal plasma source, PLADEPUS (plasma deposition at the University of Sydney), which is designed for plasma processing experiments. The plasma can be generated, either in a pulsed or a continuous mode, at electron densities up to about1013cm−3. The results show that rf power can be efficiently transferred to the plasma through the magnetic coupling of the transformer ferrite core. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148484

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A simpler and faster method for determining the total radiated power emitted from a tokamak plasma in real-time has been developed. This quantity is normally calculated after the discharge by a deconvolution of line integrals from a bolometer camera. This time-consuming algorithm assumes constant emissivity on closed flux surfaces and therefore needs the exact magnetic equilibrium information. Thus, it is highly desirable to have a different, simpler way to determine the total radiated power in real-time without additional magnetic equilibrium information. The real-time calculation of the total radiated power is done by a summation over ten or 18 lines of sight selected out of a bolometer camera with 40 channels. The number of channels is restricted by the summation hardware. A new selection scheme, which uses a singular value decomposition, has been developed to select the required subset of line integrals from the camera. With this subset, a linear regression analysis was done against the radiated power calculated by the conventional algorithm. The selected channels are finally used with the regression coefficients as weighting factors to determine an estimation of the radiated power for subsequent discharges. This selection and the corresponding weighting factors can only be applied to discharges with a similar plasma shape, e.g., in our case the typical ASDEX upgrade elliptical divertor plasma. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148485

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electron attachment mass spectrometry (EAMS) has been developed to study mixtures of electronegative gases and plasmas. A quadrupole mass spectrometer (QMS) has been used to detect negative ions, formed from sampled species by attachment of low energy electrons. Varying the electron energy allows to collect the attachment cross section of the considered species. EAMS appears to be a very powerful technique to study the chemistry of electronegative gases. Unlike ionization mass spectrometry, where cross sections are low at the threshold and rather flat over a broad range of electron energies, attachment resonances are sharp and distinct. Also very limited fragmentation of the parent negative ion occurs, so a given molecule yields only a few different negative ions. This facilitates identification of components in a gas mixture. It is particularly advantageous for detection of large, fragile molecules, which break up after ionization, but can be easily transformed into large negative ions. Moreover, sensitive detection of active species is possible due to their relatively high attachment cross sections. A particularly important application of EAMS is the determination of an effective attachment cross section in a plasma. Recording this cross section allows to decide on the actual negative ion formation mechanism in the plasma environment, where active products of plasma conversion can significantly alter the negative ion production channels and consequently the whole balance of charged particles. Examples of EAMS applications to fluorocarbon gases and low-pressure radio-frequency plasmas are discussed. In aCF4discharge conversion of the parent gas into species likeC2F6andC3F8is easily visualized. The dominant mechanism of negative ion formation in the plasma is electron attachment to these minority species and not to the parent gas. Also larger polymers are readily formed in fluorocarbon plasmas. In aC2F6discharge molecules with up to ten carbon atoms (the mass limit of our apparatus) have been detected using EAMS. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148486

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Two different systems for noise cancellation (first order gradiometers) have been developed using two similar high temperature superconducting quantum interference devices (SQUIDs). “Analog” gradiometry is accomplished in hardware by either (1) subtracting the signals from the sensor and background SQUIDs at a summing amplifier (parallel technique) or (2) converting the inverted background SQUID signal to a magnetic field at the sensor SQUID (series technique). Balance levels (ability to reject a uniform background magnetic field) achieved are2×103and1×103at 20 Hz for the parallel and series methods, respectively. The balance level as a function of frequency is also presented. The effects which time delays (phase differences) in the two sets of SQUID electronics have on these balance levels are presented and discussed. It is shown that these delays, along with geometrical considerations, are the limiting factor for balance level for any electronic gradiometer system using two (or more) SQUIDs, a very different situation from the case with wire-wound gradiometers. Results using a dipole field to study the performance of both the parallel and series devices functioning as gradiometers in an unshielded laboratory are presented and compared with theory. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148524

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A technique for high temperature sound velocity measurement using piezoelectric transducers, that avoids the existence of the usual high temperature bond between the sample and the buffer, was developed. This bond is frequently responsible for a large attenuation and distortion of the sound field, with a consequent inaccuracy in the experimental results. This technique was successfully used by the authors to make good quality measurements of sound velocity in iron–silicon single crystals from room temperature toT≈1000 °C,unlike other authors who report strong attenuation in different regions of this temperature range for similar samples. The furnace, which is only 35 mm wide, allows work under magnetic field and a controlled atmosphere up to 1300 °C. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148487

出版商:AIP    

年代:1998

数据来源: AIP