Fighting arcing and field emission in medical X-ray tubes

Vacuum breakdown induced by field emission is limiting the performance of modern X-ray tubes. To reduce the probability of arcing, a combination of design and controlled production processes such as cleaning and degassing is necessary. Outgassing rates of various materials have been measured at temperatures up to 1300 K together with mass spectrometrical data. Also given are mass spectrometrical data of various tubes during pumping and conditioning. This has led to standardized processes. Field emission currents have been measured in dependence of polishing methods, showing that mechanical polishing is well suited for most electrode surfaces. Results of different pretreatments are discussed by qualitative means.