Radiation induced conductivity in space dielectric materials

Abstract

International audienceThe radiation-induced conductivity of some polymers was described mainly in literature by a competition between ionization, trapping/detrapping, and recombination processes or by radiation assisted ageing mechanisms. Our aim is to revise the effect of the aforementioned mechanisms on the complex evolution of Teflon® FEP under space representative ionizing radiation. Through the definition of a new experimental protocol, revealing the effect of radiation dose and relaxation time, we have been able to demonstrate that the trapping/recombination model devised in this study agrees correctly with the observed experimental phenomenology at qualitative level and allows describing very well the evolution of radiation induced conductivity with irradiation time (or received radiation dose). According to this model, the complex behavior observed on Teflon® FEP may be basically ascribed to the competition between electron/hole pairs generation and recombination: electrons are deeply trapped and act as recombination centers for free holes. Relaxation effects have been characterized through successive irradiations steps and have been again well described with the defined model at qualitative level: recombination centers created by the irradiation induce long term alteration on the electric properties, especially the effective bulk conductivity. One-month relaxation does not allow a complete recovery of the material initial charging behavior

Radiation-Induced Conductivity of Space Used Polymers Under High Energy Electron Irradiation

“…If this trend is not surprising on Teflon® (since we demonstrated in a previous study that RIC of Teflon steeply drops down with the increasing radiation dose [7]), it is however much more questionable for Kapton® since we demonstrated in previous studies that RIC steadily soars up with the increasing radiation dose [8]. Other mechanisms, than those taken into account by several authors [1][2][3][4][5][6][7][8], might therefore prevail during the stimulated relaxation. Applying these basic models for stimulated relaxation does not indeed induce any RIC decline but follows the same trend as those described above (RIC rises for Kapton®, as we can see in .…”

“…RIC and the experimental features are described through a basic 0D numerical model, initially developed by Rose [2] and Fowler [1] and adapted further on by different research teams [3][4][5][6][7][8]. In our study, this model has been amended for a better numerical prediction.…”

“…We assume as well that a free charge recombines with a localized charge with opposite sign. Based on the above assumptions and introducing charge detrapping process in the model, the equations describing the 0D RIC model are: dn/dt =g(E)- 1 n(p t1 +p t2 )-n/ n1 -n/ n2 +n t1 / nt1 +n t2 / nt2 (5) dp/dt =g(E)- 1 p(n t1 +n t2 )-p/ p1 -p/ p2 +p t1 / pt1 +p t2 / pt2 (6) dn t1 /dt =n/ n1 -n t1 / nt1 - 2 pn t1 (7) dn t2 /dt =n/ n2 -n t2 / nt2 - 2 pn t2 (8) dp t1 /dt =p/ p1 -p t1 / pt1 - 1 np t1 (9) dp t2 /dt =p/ p2 -p t2 / pt2 - 1 np t2 (10) for which g(E) is the electron / hole pairs generation rate which varies with the applied electric field, α 1 and α 2 are the recombination rates, n, n t1 and n t2 are densities of free and trapped electrons, p, p t1 et p t2 are densities of free and trapped holes, τ n1 , τ n2 , τ p1 and τ p2 are trapping time for free electrons and holes, τn t1 , τn t2 , τp t1 and τp t2 detrapping time for trapped electrons and holes. We can then assess densities of free electrons and holes that are used in (11) for surface potential assessment:…”

Time-Resolved Radiation-Induced Conductivity of Polyimide and Its Description Using the Multiple Trapping Formalism

“…As already mentioned, a two-trap quasi-band model proved very popular in studies of the electron charging of polymer slabs with non-penetrating beams [16,17]. Recently, it found a new lease on life for the interpretation of charging polymer films (used or intended for use) in spacecrafts by electron beams closely imitating the spectra of plasma electrons in Earth orbits [15,37]. The ONERA researchers employed the surface potential decay method sometimes in the presence of fully penetrating electrons with a current density close to real values in orbit.…”

“…All this time, leading research groups (Gross et al [13,14], and currently French researchers [15]) adhered to the two-trap RIC model whose parameters were retrieved from experiments which were not intended to directly measure the RIC itself (this last approach was again first proposed by Gross [16,17]).…”