**7. Polyimide for space application**

Polyimide (PI) is also used for the materials of multilayer insulators (MLIs) of spacecraft. Many researchers studied space charge characteristics in PI irradiated by electron [8, 9]. And recently, the space charge behavior in PI irradiated by proton is also focused. It is because that many satellite had operation anomaly due to charging by radiation and discharging [10]. In this chapter, few examples of charge accumulation behavior in PI irradiated by radio-active rays are explained.

### **7.1 Negative charge accumulation in PI irradiated by an electron**

The space charge [8] distributions in Kapton®500H (Dupont-Toray Co.Ltd., nominal thickness is 125 μm, a surface with Al evaluation layer) are irradiated by an electron are discussed. The electron beam irradiation condition is 40 and 60 keV, with 40 nA/cm<sup>2</sup> current density in 10−5 Pa order vacuum chamber. The insite space charge measurements were carried out using PIPWP method [1, 8, 11]. Charge distributions and integrated charge amount in the bulk are shown in **Figures 12** and **13**, respectively. The measurement interval is 30 s.

In the **Figure 12**, the charge profile waveform is the data of maximum negative charge accumulation in the bulk during 20 min irradiation. From the figure, we can see the negative charge accumulation in the bulk. Such negative charges distributed from the irradiation surface to depth of 34, 60 μm (with the broken perpendicular line). Those accumulated positions have a good correlation with the calculated penetration depth using Karz and Penfold's experimental equation.

**Figure 12.** *Negative charge accumulation in PI under electron irradiation.*

### **Figure 13.**

*Total negative charge amount in the bulk of PI under And after electron irradiation.*

Form **Figure 13**, those negative charges were saturated during the irradiation time progress. And in the case of 60 keV irradiation, those negative charges were decreased in spite of irradiation progressing. The total accumulated charge amount

### *Space Charge Accumulation Phenomena in PI under Various Practicable Environment DOI: http://dx.doi.org/10.5772/intechopen.96786*

in the bulk is decided due to the balance between the amount of charges supplied by the irradiation and the amount of charges released due to change of the bulk conductivity. Therefore, in this case, it is considered that the amount of accumulated charges was reduced because the amount of change in conductivity inside the bulk became largely dominant.
