MULTIPACTOR DISCHARGES IN GAPS OF THE ACCELERATION CHANNEL AND OTHER AREAS OF RESONATOR STRUCTURE OF THE LINEAR ION ACCELERATOR

摘要

Multipactor discharges, accompanied by electron reproduction of secondary electron emission (SEE) and reaching electron close of electrodes in linear ion accelerator (LIA) are undesirable phenomena that must be eliminated. In the scientific literature there is no information on disruption of the accelerator characteristics, distorted by discharges in its different areas. In such cases, discharge areas outside the acceleration channel can be visually identified and eliminated. In this study, a modern accelerator excitation circuit is used, consisting of two identical HF-sources with independent positive feedbacks. They operation together on the same resonant load (primary or perturbed frequency) which allows to provide both sustainable HF excitation voltages and suppression of multipactor processes and discharges. Examination of the internal structure LIA showed that there are intense glow discharges in other areas of the accelerator. At the entrance it is a gap of 1.353 cm with sections of parallel end surfaces of the first drift tubes. In the periphery it is a spurious slot of ～ 0.1...0.2 mm (measured with the vacuum jacket open), formed by the surface structure and the end of the copper plate (patch that closes the unnecessary through hole); the tin solder between them was partially sublimated. From the analysis of pulse distortion of the reference voltages and total currents of SEE, it became clear that the basic rules relevant to the research subject are observed. Visual observation of the radiant emittance of the discharge area and the analysis of time dynamics of these distortions of voltage puke shapes and electronic currents allowed to characterize unambiguously both discharges as multipactor ones, which greatly facilitates their research and selection of methods for their elimination. The investigation allowed us to better understand the conditions of development and control of multipactor processes and discharges in high-Q (Q_0＞＞1) resonator structures, which is essential to provide time-constant characteristics of a linear ion accelerator.