摘要:

The measurement of low‐temperature specific heat (LTSH) (0.1 K<T<60 K) has seen a number of breakthroughs both in design concepts and instrumentation in the last 15 years—particularly in small sample calorimetry. This review attempts to provide an overview of both large and small sample calorimetry techniques at temperatures below 60 K, with sufficient references to enable more detailed study. A comprehensive review is made of the most reliable measurements of the LTSH of 84 of the elements to illustrate briefly some of the problems of measurements and analysis, as well as to provide additional references. More detail is devoted to three special areas of low‐temperature calorimetry that have seen rapid development recently—(1) measurement of the specific heat of highly radioactive samples, (2) measurement of the specific heat of materials in high magnetic fields (18 T), and (3) measurement of the specific heat of very small (100 &mgr;g) samples. The review ends with a brief discussion of the frontier research currently underway on microcalorimetry for nanogram sample weights.

ISSN:0034-6748    

DOI:10.1063/1.1137207

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A procedure has been developed to measure the attenuation of second sound in liquid helium at temperatures nearT&lgr;. The decay rate of a second‐sound resonance in a high‐Qcavity is determined, and data for more than one harmonic is obtained allowing the separation of the attenuation due to bulk fluid from losses at the cavity walls. This method has proven particularly successful nearT&lgr;, where the second‐sound velocity is strongly dependent on temperature and a high degree of temperature stability is needed. Results are given for the temperature range 40 &mgr;K<T&lgr;‐T<40 mK at saturated vapor pressure. With minor modifications the apparatus can be used for measurements at elevated pressure and over a much wider range of temperatures.

ISSN:0034-6748    

DOI:10.1063/1.1137226

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A technique and a particular apparatus for an inductive measurement of critical currents as a function of temperature and magnetic field in thin‐film superconductors are described. The technique has been found to be particularly useful for high‐field A‐15 compounds 2 to 3 &mgr;m thick. Samples with lower critical current densities would have to be correspondingly thicker to measure over the same broad range of temperature and field. The design of the apparatus is detailed showing that the film can be taken directly from the deposition chamber and mounted without electrical contacts so samples can be changed easily. The principles of operation are developed based on the Critical State Model. These principles are tested by measurements which verify that the measured value of critical curent is independent of the amplitudes and frequency of the small ac magnetic field which is added to a much larger quasistatic field. The inductive measurements are compared with results of transport current measurements on a film which had been etched in a four‐point bridge pattern. The two techniques give the same values when a 1‐&mgr;V criterion is used to define the critical transport current.

ISSN:0034-6748    

DOI:10.1063/1.1137206

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An apparatus and procedures to determine the critical parameters and the vapor–liquid coexistence curve in the critical region by observing the disappearance of the vapor–liquid interface are described. The apparatus has the advantage of measuring the saturated vapor and liquid densities with only a single filling of the sample, and the procedures are applicable not only to pure fluids but also to mixtures. Three densities of liquid and eight of vapor on the coexistence curve for trifluoromethane are obtained, and the critical temperature, density, and pressure are also determined.

ISSN:0034-6748    

DOI:10.1063/1.1137208

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A novel method for measuring the thermal conductivity of an electrical conductor is described. The heat flow is radial, giving important advantages for high‐temperature studies. It is an electrical method and is, therefore, most suited to resistive materials which have a high temperature coefficient of resistance, such as semiconductors. Since the outside temperature of the sample need not be determined directly, and the sample is best kept thin, the method holds promise for studies of liquids, especially where convection problems have occurred in the past. In many of these aspects, the proposed method works best where the conventional axial guarded heat flow method fails.

ISSN:0034-6748    

DOI:10.1063/1.1137209

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A high‐density magnetized plasma is seen to heat small diameter tungsten wire probes to electron emission. The use of these self‐emissive probes to determine the plasma potential in a tandem mirror plasma is investigated. A simplified model is presented and comparison is made with conventional emissive probe behavior.

ISSN:0034-6748    

DOI:10.1063/1.1137210

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A new detector system for single shot measurement of electron temperature and density profiles in a magnetically confined plasma has been developed. Preliminary results have been obtained with this multipoint Thomson scattering diagnostic on Torus II, a high beta tokamak. It has a density range of 2×1013cm−3≲ne≲5×1014cm−3in the preionization phase and 5×1014cm−3≲ne≲2×1015cm−3in the tokamak phase. Electron temperatures range fromTe≳6 eV in the preionization phase toTe≲80 eV in the tokamak phase. The detector used is a multianode microchannel plate (MCP) with a 25‐mm‐diam multialkali photocathode. A 10×10 array of anodes collects the current, which has been amplified by as much as 106. Each anode is independent, so the MCP can be viewed as a parallel array of 100 independent photomultiplier tubes.

ISSN:0034-6748    

DOI:10.1063/1.1137211

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The ion‐beam extraction performance of the 30‐kV–35‐A circular magnetic‐multipole bucket ion source applied for the neutral beam injection system of the Heliotron E fusion machine has been investigated with special reference to ion‐beam optics. By using the numerical simulation code for the cylindrical ion‐extraction system, the computational beam‐divergence angles have been compared with the experimental data. The experiments show that the applied three‐electrode beam optics are satisfactorily stable against source‐plasma variation and that the minimum beam‐divergence angle is less than 1.15 deg. The obtained optimal perveance of the ion source is nearly 6.3×10−6(A/V3/2), and the experimental optics behavior is in reasonable agreement with the numerical prediction. On the basis of the experiments, the effect of the edge angle of the first beam‐forming, high‐potential electrode is also discussed. The experiment suggests that the obtuse angle (∼73°) for that edge is preferable to the acute angle (∼30°).

ISSN:0034-6748    

DOI:10.1063/1.1137212

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The design and operation of an electron beam probe for ion beam diagnostics is described. Advantages of this method for the analysis of space‐charge neutralization studies are discussed and examples of its applications to heavy ion beams are shown.

ISSN:0034-6748    

DOI:10.1063/1.1137213

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An effort was made to measure and reduce the impurity content of an intense hydrogen beam used for neutral injection heating of a stellarator plasma. Originally, the hydrogen ion beam contained 5% water and water‐like ions. A simple and very useful method to reduce the contamination turned out to be evaporation of titanium on the inner surfaces of the ion source, which reduced the low‐Z impurity content to 0.6%.

ISSN:0034-6748    

DOI:10.1063/1.1137214

出版商:AIP    

年代:1983

数据来源: AIP