摘要:

A series of systematic tests have been carried out on the superconducting electron cyclotron resonance ion source SCECRIS at the Michigan State University National Superconducting Cyclotron Laboratory in order to better understand the role of different parameters which determine the performance of these sources. A relevant part of these tests has been focused on the role of magnetic field and microwave frequency, with the goal of demonstrating the capability of low frequency electron cyclotron resonance ion sources to produce high ion charge states, in spite of their relative low plasma density. This goal can be achieved using a very high magnetic confining field, according to the concept of a high B mode. A comparison of the source performance at 2.45 and 6.4 GHz for different levels of magnetic field is described in this article. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147556

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We developed and evaluated a new partially ionized beam (PIB) source to deposit high quality Cu films. The novelty of the PIB source lies in the fact that the crucible and ionization parts are spaced in one cylindrical shell to make its structure compact and to get a uniform beam profile, but their electric circuits are not separated. In this article, we report the characteristics of the PIB source, such as voltage‐ampere characteristics of the crucible and ionization parts, Cu+ion beam uniformity with a change of the ionization currents, and deposition rate. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147578

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this article, we present a multichannel source with cold electrodes generating spatially combined ion and electron beams with homogeneous profile of current density on 100 mm diam. The source was designed on the basis of a modified Penning cell. The anode configuration provides high current efficiency, reaching 50% under certain conditions. The source has two operating modes: ion beam generation and synthesized ion‐electron flow. High current densities 0.5–5 mA/cm2of ion and electron beams with energies in the range of 0.5–7 keV under low working pressure (1–10)×10−5Torr are the advantage of this source. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147548

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We developed a simple current mode preamplifier for the microchannel plate (MCP) with the anode biased to high voltage. It uses a capacitor to block dc high voltage and measures the MCP current through the capacitor. Then it compensates exactly the distortion caused by the capacitor so the amplifier can measure any length of signals without distortion. It is much less expensive and simpler than using the phosphor screen system to isolate the dc high voltage. We derived a formula for that compensation and implemented it by using an op‐amp’s circuit. It gives an approximate time resolution of 10 &mgr;s which is restricted by the op‐amp’s characteristics. So, it may be improved by using fast op‐amp’s. This can also be used for channeltron and other electron multipliers. For the test of the preamplifier, we measured the photoelectron currents induced by the soft x rays radiated from the KT‐1 tokamak of which the pulse length was 20 ms. The data revealed well, without distortion, the time evolution of the line radiation. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147557

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A low pressure discharge plasma, with magnetic multipolar confinement, is produced in a cylindrical ultrahigh vacuum device. The device has been specially designed to allow both moving Langmuir probe measurements and laser induced fluorescence diagnostic for the plasma ions. It is well suited to explore the sheaths region in a bounded plasma and to study wave and turbulence in a laboratory plasma. The main characteristics of the experimental setup and of the produced plasma are described. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147558

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The characteristics of emissive probes in unmagnetized high pressure (≤1 Torr) argon and helium plasmas, produced by inductively coupled 13.56 MHz rf power, are studied. A procedure is given for interpreting emissive probe current–voltage (I–V) characteristics. TheI–Vcurves indicate the amplitude of the rf fluctuation of the plasma potential. They also show ionization near the emissive probe when the potential drop between the emissive probe and the plasma potential is more than the ionization potential. Experiments show that when the temperature of the emissive probe wire and/or the neutral pressure is increased, ionization becomes significant. An increase in the local ion density due to the additional ionization was demonstrated by theI–Vcurves of an emissive probe and a nearby Langmuir probe. A simple procedure is presented for interpreting these results. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147559

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A reflectometry system has been developed for ASDEX Upgrade to measure the plasma profile from the scrape‐off layer until the bulk plasma, simultaneously at the high and low field sides. Unique features of the system are the ultrafast broadband frequency modulation of a continuous wave using solid state stable hyper abrupt tuned oscillators (down to 10 &mgr;s), high and low field side channels and fully remote control operation, via optical fiber links. Due to the special design of the transmission line, with decoupled in going and out going lines and one‐antenna configuration, the system is optimized for reception and spurious reflections are eliminated. The ultrafast operation guarantees that the effect of plasma turbulence is greatly reduced. Both features determine the high performance of the diagnostic. A dedicated data acquisition system handles the large amounts of data generated by the broadband operation. Recent developments include the operation of new channels and an automatic and accurate frequency calibration circuit. Also, advanced digital signal processing techniques were applied to obtain density profiles with high spatial and temporal (20 &mgr;s) resolutions under turbulent plasma regions, e.g., the scrape‐off layer. Experimental results are presented showing the great sensitivity of the diagnostic to plasma radial movements and its tolerance to vertical movements of the plasma. Density profiles measured in ELMy regimes illustrate the capabilities of the diagnostic to detect fast profile changes. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147517

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Basic design requirements are presented for pyroelectric detectors to be used effectively when the radiation source emits part or all of its power in the vacuum ultraviolet range, as is the case for a typical plasma in magnetic confinement fusion research. The difficulty associated with the VUV wavelength range lies in the high photoelectric yield of the associated energetic photons. A relatively inexpensive, commercially available detector was modified to eliminate the spurious currents resulting from photoelectrons. The modifications have little effect on the basic characteristics of the commercial detector (time response, sensitivity, etc). ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147560

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe a new liquid‐target system for low‐debris laser‐plasma soft x‐ray sources. The system is based on a microscopic liquid jet and is experimentally evaluated for 0.7–1 keV proximity lithography and water‐window x‐ray microscopy applications. Compared to an existing liquid‐droplet target, this target system has the same low debris emission, high x‐ray photon flux, and narrow spectral bandwidth. The advantages of the liquid‐jet target include improved x‐ray flux stability, increased range of suitable target liquids, and elimination of the need for temporal synchronization, thereby allowing less complex laser systems to be used. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147561

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

At present, data requirements of hundreds of Mbytes/discharge are typical in devices such as JET, TFTR, DIII‐D, etc., and these requirements continue to increase. With these rates, the amount of storage required to maintain discharge information is enormous. Compaction techniques are now essential to reduce storage. However, general compression techniques may distort signals, but this is undesirable for fusion diagnostics. We have developed a general technique for data compression which is described here. The technique, which is based on delta compression, does not require an examination of the data as in delayed methods. Delta values are compacted according to general encoding forms which satisfy a prefix code property and which are defined prior to data capture. Several prefix codes, which are bit oriented and which have variable code lengths, have been developed. These encoding methods are independent of the signal analog characteristics and enable one to store undistorted signals. The technique has been applied to databases of the TJ‐I tokamak and the TJ‐IU torsatron. Compaction rates of over 80% with negligible computational effort were achieved. Computer programs were written in ANSI C, thus ensuring portability and easy maintenance. We also present an interpretation, based on information theory, of the high compression rates achieved without signal distortion. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147544

出版商:AIP    

年代:1996

数据来源: AIP