摘要:

Nuclear activation techniques have been used to measure the fluence of high‐energy deuterons in a plasma‐focus device. Substantial activation of carbon and aluminum targets was observed on most shots where the deuterium pressure was less than 3 Torr. Carbon activation indicates more than 1015deuterons above 330 keV on some high‐intensity shots. These deuterons are strongly forward directed with 0° to 90° ratios exceeding 104on high‐yield shots. Ratios of13N to28Al, foil‐stack activation measurements, and neutron time of flight all consistently show some deuterons have energies above 2 MeV. Measured13N/28Al ratios also indicate more than 1012deuterons of energy greater than 5 MeV, but this result has not been verified by an independent threshold‐activation measurement. These measurements illustrate that the plasma‐focus device can be operated in two distinctly different modes, with low‐pressure operation resulting in the acceleration of ions and electrons to many times the capacitor‐bank charging voltage. Most of the neutron emission in low‐pressure operation may come from beam‐target reactions.

ISSN:0021-8979    

DOI:10.1063/1.325045

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Glass microspheres filled with D2and3He were imploded using the LLL 1.06 &mgr;m Argus laser. The energetic 14.7‐MeV protons from the D‐3He reactions were measured. By taking the ratio of the number of D‐3He reactions to the D‐D reactions, ion temperatures were calculated. The results were compared with numerical modeling of the experiments.

ISSN:0021-8979    

DOI:10.1063/1.325046

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A model for the formation of the fireball arc or spark discharge, sometimes called a fireball plasma, is developed based on the nonlinearity of the voltage‐current characteristics of a high‐current arc discharge. A nonlinear transmission line equation for the discharge current is obtained which is solved in terms of the Jacobi elliptic functions. Under certain prescribed conditions the current field collapses into a small region. This collapse of the current field is taken to be the fireball. It is additionally pointed out that nonlinearities other than the voltage‐current characteristics of the high‐current arc could produce similar results. Finally, it is suggested that Ball Lightning may have the same origin.

ISSN:0021-8979    

DOI:10.1063/1.325047

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

This paper presents a study of the self‐focusing of a high‐power non‐Gaussian laser beam operating in TEM01mode in a strongly ionized plasma. The nonlinearity in the dielectric constant is caused by the nonuniform redistribution of carriers due to their inhomogeneous heating by the laser beam having transverse variation of intensity along its wave front. It is found that when the power of the beam exceeds the critical power, focusing effects are observed in theYdirection, whereas divergence of the beam takes place in theXdirection. In the reverse case (whenP<Pcr) the normalized beam‐width parameterf2first increases in theYdirection, after penetrating a certain depth it reaches a broadened maxima and then starts decreasing with the distance of propagation inside the medium. The beam continues diverging in theXdirection. It has also been found that absorption brings about a reduction in the extent of self‐focusing. When the absorption length is less than the self‐focusing length appreciable self‐focusing does not take place.

ISSN:0021-8979    

DOI:10.1063/1.325048

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The transformation of silicon to the amorphous state by implanted ions was studied both experimentally and theoretically. Experimentally, the amount of transformed silicon and the critical ion dose necessary to amorphize the entire implanted layer were determined by ESR. How the critical dose varies with ion mass (Li, N, Ne, Ar, and Kr), ion energy (20–180 keV), and implant temperature (77–475 K) was determined. Theoretically, several phenomenological models were used to analyze these data. The overlap‐damage model was used to determine the critical dose from the data, the size of the amorphous region around the ion track, and the degree of overlap damage required for amorphization. For all implants, the first ion created only predamage, while the second or third ion into the same region caused the amorphous transformation. The critical‐energy‐density model was in good agreement with the measured critical doses. This model assumed that a region would become amorphous if the energy density deposited into atomic processes by the ions exceeded the critical energy density of 6×1023eV/cm3. For high‐temperature implantations, out‐diffusion models can explain the temperature dependence of the critical dose. Although the analysis is not completely definitive, the critical‐energy‐density model may also be valid at high temperature if diffusion of the damage energy is taken into account. This out‐diffusion of energy from around the ion track occurs via a thermally activated process. Probably, the energy moves with the out‐diffusion of the vacancies from the ion track.

ISSN:0021-8979    

DOI:10.1063/1.325049

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

From measurements of the sheet conductivity and the Hall effect in combination with layer stripping by chemical etching, we have evaluated the doping profiles of ion‐implanted PbTe. By using thin films grown epitaxially on insulating substrates, we avoided difficulties with the formation of an insulatingp‐njunction. The carrier profiles of samples implanted in a random direction are deeper and broader than those of the LSS theory. The charge‐carrier profiles associated with the implantation damage show a constant value of the maximum concentration largely independent of the implantation dose and the ions used.

ISSN:0021-8979    

DOI:10.1063/1.325050

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Field‐effect devices with evaporated silicon monoxide coatings for liquid‐crystal alignment exhibit rectification under dc and ac excitation when the coatings are asymmetric. The rectification mechanism is a polarity‐ and electrode‐dependent depletion of residual ionic carriers from the bulk. Polarity reversal transients offer a novel means of studying the electrode double‐layer charging and demonstrate hydrodynamic contributions to the mobility. The threshold conditions for rectification under ac excitation are outlined.

ISSN:0021-8979    

DOI:10.1063/1.325051

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A twisted nematic structure is induced by an electric field. The distortion of the structure and the optical activity of the cell is computed for both static and dynamic behavior. Experimental results are given and followed by a tentative interpretation.

ISSN:0021-8979    

DOI:10.1063/1.325052

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Threee new phases of the alloy Nb3Si have been produced by a relatively low‐temperature (∼800 °C) recrystallization anneal under pressures of up to 100 kbars. The new phases are apparently formed only when the Nb3Si starting material has a metastable body‐centered‐cubic structure which is prepared by sputtering. They are not formed when the Nb3Si starting material has the Ti3P‐type structure. One of the new high‐pressure phases has a superconducting transition temperatureTcof 5.45 K, but its crystal structure has not yet been identified. The phase formed at 60 and 100 kbars has a tetragonal Ni3P‐type structure, but the structure of the 80‐kbar phase is not known.

ISSN:0021-8979    

DOI:10.1063/1.325053

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

General expressions for the changes in resistivity and conductivity around 60°, edge, and screw dislocations as a consequence of the piezoresistance effect were calculated for III‐V compounds. These expressions are discussed with reference to the symmetry of the crystal. The specific case ofn‐type GaSb is considered and it is shown that 60° and edge dislocations are surrounded by regions of increased and decreased conductivity parallel to the lines of the dislocations. It is also shown that the conductivity parallel to the line of a screw dislocation is increased irrespective of the sign of the Burgers vector. The results indicate that the dislocations can alter the bulk conductivity parallel to their lines and that they can play an important role in the threshold behavior of laser devices. Finally, it is shown that there are charging effects associated with the dislocations during device operation.

ISSN:0021-8979    

DOI:10.1063/1.325054

出版商:AIP    

年代:1978

数据来源: AIP