| Popis: |
The phenomena of electron field emission and breakdowns still contain many unknowns,but affect many applications across science and industry. For instance, controlling the breakdown rate is essential for the effectiveness of accelerators operating at high electric fields. Copper has been chosen as one of the suitable materials for the accelerating structures of the future Compact Linear Collider (CLIC). This study aims at investigating the properties of electrode surfaces of soft copper when exposed to high electric fields at cryogenic temperatures. First, the sample underwent conditioning, with pulses of increasing voltage. When the electric field had reached its maximum without surpassing a breakdown rate of 1×10−5 breakdowns per pulse, the copper was exposed to pulses of fixed voltage to test the number of pulses between each breakdown. Finally the field emission was measured by supplying steady increasing voltage, and studying the current between the electrodes. These experiments showed that the cryogenic environment improved the possible maximum electric field, although longer time was required to reach the maximum field. The enhancement factor β, that describes how many times the local electric field is amplified by surface protrusions, was found to be β = 302 ± 90 after conditioning at room temperature. After cryogenic cooling to 30 K, we found that β = 70.5 ± 9 before additional conditioning, and β = 92.4 ± 2 after additional conditioning. We observed a trend of increasing β during the following warm-up phase from 45 K up to 100 K. The number of pulses between each breakdown seemed to follow a power law decay, similarly to recent studies at CERN and at the University of Helsinki. Examinator: Andreas Korn |
