Determination Of Space Charge Distributions Research Articles

Determination of space charge distributions in highly segmented large volume HPGe detectors from capacitance–voltage measurements

The space charge distribution of a large volume highly segmented HPGe detector was determined by a non-destructive capacitance–voltage measurement. The capacitances between the 36 segments and the core were measured simultaneously with a precision pulser which was implemented in the core preamplifier. The pulser measurement was compared to and validated by direct capacitance measurements. The three-dimensional doping profile was reconstructed using analytical and numerical methods. Consistent values for the impurity concentration in the range of 0.5 and 1.5×10 10 cm −3 were obtained.

Thermal step method for space charge measurements under applied dc field

The thermal step method (TSM) is a nondestructive technique which measures the distribution of the electric field and space charge density across solid insulating materials. This work first reviews the principle and the basic equations of the TSM when used on a short circuited flat insulating structure (film or plate). An evolution of the method, which allows the determination of space charge distribution in an insulator while submitted to an external dc field, is then described. The fundamentals, the experimental setup and the validation of this technique on flat samples and on power cables are presented and discussed.

A finite element method for the determination of space charge distributions in complex geometry

Electrical breakdown in insulators very often initiate near high field regions of the structure, as found near small-radius impurities or at electrode defects. This is attributed to the development of localized space charges. For this reason many efforts have been made to determine such charge. Various techniques are now available, but they are not directly applicable to complex geometries where it is difficult to determine analytically the field configuration and thus the relation between the measured variables and the space charge distribution. To solve this problem, we propose to use a numerical simulation using a finite element method (FEM). In this paper we describe how it can be implemented in the case of the pressure wave propagation (PWP) method. It is shown that measured signals in insulating samples with divergent electric field regions are well fitted by simulations. We show that this allows for the determination of space charge distribution in such samples.

Exploration of the space charge behaviour of polyethylene using measurements of thermally stimulated discharge currents coupled with the determination of space charge distributions by the thermal step method in hydrogenated poly(vinyl chloride)

By using the thermally stimulated discharge currents (TSDC) technique and coupling it with the thermal step (TS) method, which allows accurate measurement of the space charge distribution (an outstanding electrical property), both the relaxation and the relative contribution of the intrinsic polarization charges and the extrinsic trapped charges have been analysed for a series of poly(vinyl chloride) (PVC) materials after partial hydrogenation as a precursor structure of polyethylene (PE). The α relaxation related to the release of frozen-in dipole orientation, and the ρ relaxation which is due to the trapping of extrinsic charges have been found to vary, both in intensity and in temperature, with the percentage of ethylene units. On the other hand, the TS measurement of the space charge distribution prior to and after destroying the polarization charges according to the TSDC behaviour, allows one to correlate, as a first approximation, those types of space charge with the molecular microstructure, of either PVC or PE parts. Even if further work remains to be done, the results, as discussed in the light of earlier work on tacticity-driven microstructure–PVC property relationships and on space charge distribution of PVC after hydrogenation, studied by the TS method, provide an original although still tentative interpretation of the space charge behaviour of PE.

Determination of space charge distributions in polyethylene samples submitted to 120 kV DC voltage

The measurements of charge distribution evolutions in polyethylene samples subjected to an applied voltage of <or=120 kV are discussed. To apply significant voltage gradients to plates or cables having an insulator thicknesses ranging from 5 to 10 mm, the large applied voltage was necessary. The possibilities offered by this equipment are illustrated by results obtained with 6-mm-thick plates. A comparison of the behaviors of 2-mm-thick plates and 6 mm thick plates made of the same materials and submitted to the same field is presented. The results indicate that increasing the thickness of the insulator does not increase the charge densities which develop under the applied field and that the observed space charge is localized at the vicinity of the electrodes, in a region extending over 0.7 mm, in which the diffusion of impurities from the semiconducting electrodes is very important.<<ETX>>

Determination of space charge distribution in thick dielectric samples

A method for determining the space charge distribution on thick samples of dielectrics is presented. The method is based on measurements of the effective surface charge density on one side of a plane parallel sample, when the other side is simultaneously dissolved (or etched) in conducting or dielectric solvent. The space charge distribution can be obtained by differentiation of the surface charge density as a function of sample thickness. An important advantage of the method is the simplicity of the measuring circuit and its relatively high resolution. A possible application of the method was checked on wax electrets and a good agreement with literature data was obtained.