Difference in threshold voltage of arc inception between electron beam and ultraviolet environment

Abstract

As a charging method in ground experiments, an electron beam is often used to simulate high energy particles. In addition to this, a charging method using ultraviolet has been devised because charging by sunlight also occur in the space environment. Accordingly, ultraviolet were used for the discharge threshold measurement experiment of the solar cell, but the large difference of the threshold voltage was seen in two charging methods. The purpose of this research is to find out the cause of this large difference and to apply ultraviolet to charging and discharge experiment of space solar cell. We assumed that the charging potential of the cover glass edge of the solar cell was different in two charging methods and it caused the difference of the discharge threshold voltage. Therefore, we measured the surface potential focusing on the cover glass edge. In the experiment, a sample simulating the structure of the space solar cell was prepared and irradiated with ultraviolet or electron beam until the potential of the cover glass surface did not change overall. The surface potential of the cover glass edge at this time was measured with a contactless surface electrometer, and the results by two charging methods were compared. As a result, it was found that the surface potential at the cover glass edge was different in two charging methods. On the other hand, it was also found that measurement accuracy was low. We devised measurement method using Pockels effect which can measure potential directly or plan to improve measurement accuracy by improving sample because higher measurement accuracy is required to clarify the difference in charging.