摘要:

The design criteria of electrical current shims for high resolution nuclear magnetic resonance magnets are discussed. Specific current configurations are given for various corrections to magnetic field gradients of the first, second, third, and fourth orders.

ISSN:0034-6748    

DOI:10.1063/1.1717338

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A description is given of the construction and operation of a device which is capable of producing multiple layers of evaporated films. Uniform strands of a metal and of a dielectric are alternately cut into bits, which are evaporated completely, the size of each bit determining the thickness of the corresponding layer. Each layer of metal may be continuous, or divided quite uniformly into small particles, depending on the conditions of the experiment. In the latter instance, the result may be a rather concentrated monodispersed colloid. The preparation of a specimen containing 60 000 layers of tin, approximately 40 A thick, and constituting 10% of the total volume, is described. Evaporated nylon has been found to be a satisfactory insulator between the layers of metal; Mylar film, 0.00025 in. thick, works very well as a substrate. Several other uses for the evaporating machine are suggested.

ISSN:0034-6748    

DOI:10.1063/1.1717339

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A calculation is made of the interaction of a beam of particles in an accelerator with the radio‐frequency cavity that provides the accelerating mechanism of the machine. A Hamiltonian for synchrotron motion is employed that makes possible the simultaneous solution of Maxwell's equations and the Vlasov equation, so that a self‐consistent distribution of particles in synchrotron phase space is determined. The effective voltage on the cavity due to the beam of charged particles is of the order of magnitude of the product of the total circulating current in the accelerator and the shunt impedance of the rf cavity. It has the net effect of producing a total voltage on the cavity which is both less than the applied voltage, and shifted in phase with respect to it. The increase in the stable phase angle required so the particles will remain in phase with the accelerating radio frequency is calculated. The decrease in total voltage and increase in stable phase angle result in a decrease in stable phase space available for acceleration, and convenient expressions are given for these quantities in terms of parameters of the accelerator. It is shown that the consequences of the induced voltage may be alleviated by increasing the voltage applied to the cavity. Non‐resonant interaction between the beam and cavity is not considered.

ISSN:0034-6748    

DOI:10.1063/1.1717340

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Coherent electromagnetic fields arising from an azimuthally modulated beam are considered. The beam is completely enclosed in a toroidal vacuum tank of rectangular cross section and highly conducting walls. Expressions are given for the image currents arising from low harmonics of the beam circulation frequency. These expressions are then used to evaluate resistive losses in the walls of the chamber. Expressions are given for fields arising from harmonics of the revolution frequency high enough that the beam may be in resonance with a characteristic mode of the vacuum chamber. The results are generalized to provide a description of the electric field in the neighborhood of a resonance. Numerical examples of resistive losses are given, indicating that these effects will not be serious for circulating currents of the order of 1 amp. Some properties of high‐order Bessel functions, required for a description of the resonant chamber modes and the energy lost in their excitation, are developed in an appendix.

ISSN:0034-6748    

DOI:10.1063/1.1717341

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The electromagnetic interaction of an intense relativistic coasting beam with itself, including the effect of a nonperfectly conducting vacuum tank, or a quiescent rf cavity, is investigated theoretically. It is shown that the resonances that may occur between harmonics of the particle circulation frequencies and the electromagnetic modes of the cavities can lead to a longitudinal instability of the beam. A criterion for stability of the beam against such longitudinal bunching is obtained as a restriction on the shunt impedance of the rf cavity, or theQof the vacuum tank. This criterion contains the energy spread and intensity of the coasting beam, as well as the parameters of the accelerator. Numerical examples are given which indicate that, in general, the resonances with the vacuum tank will not cause instabilities, while those with an rf cavity can be prevented from causing instabilities by choosing the shunt impedance at a sufficiently low but still convenient value.

ISSN:0034-6748    

DOI:10.1063/1.1717342

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The detector described consists of a block of plastic scintillator covered by a 4&pgr; anticoincidence shield of scintillation plastic sheets. By means of optical filters, the light emitted by the shield is distinguished from the light arising from the core scintillator.

ISSN:0034-6748    

DOI:10.1063/1.1717343

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Apparatus has been constructed in which plasma, ionized by 144‐Mc radio‐frequency excitation, is subjected to repeated submicrosecond voltage pulses immediately after excitation is removed. It is expected that observed variation of resulting current pulses may be correlated with quantitative aspects of the plasma decay.

ISSN:0034-6748    

DOI:10.1063/1.1717344

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The absolute absorption coefficient of a commercial plastic scintillator was measured as a function of wavelength over the region of its luminescence. The absorption coefficient was found to be quite small (∼10−3cm−1) through most of the visible spectrum with strong absorption beginning at about 4000 A. The details of the experimental apparatus and the procedure are described. Some interpretations of the absorption properties are offered.

ISSN:0034-6748    

DOI:10.1063/1.1717345

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A voltage‐tuned low frequency solar spectrum analyser has been developed. This analyser tunes over the range 15 to 30 Mc at rates up to 10/sec. A description is given of the voltage‐controlled tuner device which employs silicon capacitors.

ISSN:0034-6748    

DOI:10.1063/1.1717346

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

An optical method for the quantitative study of the density distribution behind shock waves has been developed. The method, which uses a photoelectric recording, is based upon the integrated schlieren method originally devised by Resler and Scheibe. A detailed theoretical analysis is given. Excellent agreement with predicted performance was found in measurements of the density profiles behind shock waves in CO2. The method is very accurate and retains its high sensitivity for weak shocks. The pictures obtained show a nearly exponential approach to equilibrium of the density behind shock waves.

ISSN:0034-6748    

DOI:10.1063/1.1717347

出版商:AIP    

年代:1961

数据来源: AIP