Effects of perturbing magnetic fields on the performance of photoelectronic sensors

Abstract

Photoelectronic sensors are all susceptible, to a greater or lesser degree, to the influence of perturbing ambient magnetic fields. Theoretical and experimental results are presented for the effects of axial and transverse magnetic fields on the various types of image intensifiers (including microchannel plate devices), TV camera tubes, and photomultipliers. The most immediately apparent effects are image displacement and loss of focus; additionally, changes in gain and certain other more subtle effects may be encountered. Numerical and graphical or nomographic methods for determining the magnitudes of the major effects in the different electron-optical systems at various voltages are provided, and electrode supply tolerances may be obtained therefrom. The nomographs can also be used to derive the focus conditions for magnetically focused systems. Interpretations of previously unexplained phenomena in the behavior of microchannel plates are also presented.

Analysis of uncertainty of electron density and temperature using laser Thomson scattering in helicon plasmas

“…In the presence of a magnetic field, some experimental equipment can be affected by the magnetic field and can cause noticeable uncertainty in the experimental result. 26,28) A significant error of the ICCD and the optics elements might be induced by the external magnetic field as described in the previous study. 26) To avoid or minimize this magnetic field effect on the measurement, the experiment was performed in a relatively low magnetic field regime less than 600 G where the effect of the magnetic field on the measurement signal was less than 2%, the uncertainty of magnetic field effect is around 1% (see Fig.…”

MCP-PMT studies at the High-B test facility at Jefferson Lab

“…Both methods yield consistent results. 11,19, and 21 bins, respectively, for the calculation of the total anode charge collected for that event. The limits and the width of the integration range were varied for systematic purposes.…”

“…The studies of gain performance of small-pore-size microchannel-plate photomultipliers (MCP PMTs) in magnetic fields up to 5 T presented here, aim to identify the operational limits of commercially available sensors and, eventually, to support the optimization of MCP-PMT design and operational parameters for implementation in the EIC DIRC, as MCP PMTs offer good timing and a large number of pixels over a small area. Previously, MCP-PMT performance in magnetic fields has been studied experimentally [5][6][7][8][9][10] in fields up to 2 T. Theoretical calculations have been only done for axial magnetic fields [11,12]. Our measurements are the first in fields above 2 T.…”

Sensitivity degradation of an anger camera operated in SPECT-like mode under the influence of a strong external magnetic field

“…The problem is especially pernicious at the first dynode in front window type PMTs employed in nuclear imaging equipment, since the electron path from the photocathode to the first dynode is long. Coleman PMTs -of the type typically employed in PET and SPECT equipment -are especially susceptible to this effect [1]. Kuroda and collaborators reported a loss of gain of up to 50% in external fields as low as 3 mT [2].…”