摘要:

A standard passive dissipative resistor in a photodiode circuit is replaced by a low‐noise active artificial resistor. A room‐temperature artificial resistor acts on a signal current from the photodiode in the same manner as the resistor, but the self‐generated noise of the artificial resistor is that of a resistor at cryogenic temperatures. Because of its low noise, the artificial resistor can produce an improvement in the signal to noise of the photodetector system with minimum effect on the bandwidth. Analysis shows that the system signal to noise can approach that of the photodiode itself. An experiment designed to demonstrate the effect produced an improvement of 2.8 dB in a photoamplifier circuit.

ISSN:0021-8979    

DOI:10.1063/1.331177

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The drift orbit cyclotron was investigated both theoretically and experimentally. A drift orbit cyclotron was designed and constructed, and acceleration experiments using electrons in high vacuum were performed. Theoretical calculations using the guiding center approximation match the experimental results. Improvement of the acceleration efficiency was observed by using the stochastic acceleration technique.

ISSN:0021-8979    

DOI:10.1063/1.331178

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Several experiments proposed to detect parity non‐conserving effects in atomic hydrogen study radio‐frequency transitions induced in a resonance cavity. We point out that characteristics of the transition amplitudes, such as the resonance line shape and possible interference terms, can be affected substantially by the spatial variation of the fields in the cavity.

ISSN:0021-8979    

DOI:10.1063/1.331179

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A beam source of atomic hydrogen is described which produces metastable atoms in the 2S1/2state by optical pumping. A beam flux of 1016atoms/s is generated in the ground state. The atoms in the beam pass in front of a lamp producing Lyman‐&bgr; (1026 A˚) radiation, where some of them are excited to the 3Plevel and cascade with a branching ratio of 12% to the 2S1/2state. The number of metastable atoms produced is measured by quenching them with an electric field and detecting the emitted Lyman‐&agr; (1216 A˚) radiation. Beams of 106metastable atoms/s were obtained. Using the Bethe‐Lamb theory for the quenching process, a metastable beam effective temperature of 100 K was measured.

ISSN:0021-8979    

DOI:10.1063/1.331180

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An experimental basis is provided for the theoretical expressions associated with theE&rgr;lateral‐wave field due to a horizontal dipole in a conducting half‐space of sea water. Both perturbed and unperturbed fields are studied in detail in a laboratory model of the lithosphere. It is found that rectilinear and wedge‐shaped discontinuities at the air‐water interface comprise effective perturbations ofE&rgr;, while submerged metallic cylinders do not. The effective perturbations, localized in their effect on the overall propagation of the lateral wave over several wavelengths, have geometries chosen to characterize the broad plateaus and mountains of a real lithosphere.

ISSN:0021-8979    

DOI:10.1063/1.331181

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Inertial‐confinement fusion reactors with light ion‐beam drivers will require that several intense ion beams propagate a few meters from separate diodes to a single target. Each beam would be confined and guided by a laser‐initiatedzdischarge in a background gas. In this experiment we have studied the transport of a proton beam in such a laser channel. A pulsed, line‐tuned, CO2laser triggers the discharge in 4–20 Torr of ammonia gas. When the discharge current reaches peak value, an ion beam is injected from a pinch‐reflex ion diode on the Hydra accelerator. The transported proton beam is detected by nuclear activation of carbon targets. Total current transport efficiencies of up to 50% were achieved in 13–45 kA, one‐meter‐long discharges. The most reproducible results were found for discharge currents of less than 30 kA; framing photography shows that the channel is unstable for kink modes at higher currents. Conditions in the discharge which led to this kink instability are examined, and the implications for reactor studies are considered. Operational data for the pinch‐reflex diode operating in a high‐impedance mode are also presented.

ISSN:0021-8979    

DOI:10.1063/1.331182

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The focusing properties of an Inverse Reflex Tetrode (IRT) used for ion beam generation have been investigated experimentally. Focusing is achieved by replacing the planar (0°) electrodes of a standard IRT with moderately inwardly tapered electrodes (7.5, 10, and 15°). The greatest degree of focusing is obtained with the 15° electrodes as determined by beam profile measurements using streak photography and nuclear activation techniques at various axial target positions. A scissoring effect is observed, due to temporal variations in generator voltage and current, that is manifested by an axial variation in the focal point with time. Calculations of proton trajectories confirm the experimental results and demonstrate the importance of self‐fields within theA‐Kgap in determining the characteristics of an ion beam generated by an IRT.

ISSN:0021-8979    

DOI:10.1063/1.331183

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Discharge parameters have been investigated experimentally and theoretically for a high‐pressure, ultraviolet‐preionized, transversely excited CO2laser. The theoretical model including the excitation circuitry is presented which predicts the discharge performance at pressure ranges of 2–10 atm in a satisfactory manner. The operatingE/Nand discharge impedance in a quasi‐steady field were studied by accurately measuring the voltage‐current waveforms;Eis the electric field strength andNthe gas number density. The electron transport coefficients have been found to be a function of the pressure versus the change of the measured voltage waveforms relating to that pressure. The theoretical results treating the transport coefficient as a function of the pressure were in very good agreement with the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.331184

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

In this work a dilute fluorine plasma pumped by the ion‐ion recombination of H+2and F−has been operated as a pulsed amplifier. Two synchronously excited plasmas were produced by preionized discharges in an atmospheric electrical avalanche device switched by hydrogen thyratrons. Two principal outputs having wavelengths of 745 and 635 nm were obtained from the tube serving as an oscillator. These were dispersed so that they could be individually threaded through the second discharge. Calibrated attenuation of the beam from the oscillator subsequently injected into the amplifier provided data on the overall amplification ratio. From these data effective saturation intensities of 1.2 and 4.5 kW/cm2were found for the transitions at 745 and 635 nm, originating on the 3p4P05/2and 3p4S03/2states of F*, respectively. Corresponding small signal gains were found to be extremely high, reaching 0.44 and 0.31 cm−1, for the two transitions, respectively.

ISSN:0021-8979    

DOI:10.1063/1.331158

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A computer model of a CO chemical laser produced by supersonic mixing of CS/S with O2is presented. The model has been shown to accurately predict measured gain coefficients of P7(14) and P5(18) lines, hence it was utilized for further parametric studies leading to a better understanding of the processes involved in laser operation. The model predicts high gain and high specific available energy inv= 1→0 tov= 20→19 transitions. A maximum gain was obtained for each of the parameters investigated. For certain operational conditions, complete population inversion was observed.

ISSN:0021-8979    

DOI:10.1063/1.331159

出版商:AIP    

年代:1982

数据来源: AIP