Physics

Postgraduate research

Sihui Wang

Photo of  Sihui Wang

PhD research student

Research areas

Date of start of studies: 1 April 2012
Country: China
Supervisors: Dr Mike Cropper & Dr Oleg Malyshev (ASTeC) & Dr Reza Valizadeh (ASTeC)

A resonant motion of electrons generated by residual gas ionization, photoemission or secondary electron emission from the vacuum chamber walls will cause beam-induced multipacting. These electrons move resonantly within the vacuum chamber and collide both with the circulating ion beam and walls. Electrons form a cloud along the beam path and cause an unwanted growth in emmitance, which is one of the main limitations for particle accelerators with high intensity positively charged beams and short bunch spacing. The electron cloud density depends not only on the characteristics of the positively charged beam including bunch length, charge and spacing, but also on the Secondary Electron Yield (SEY) of the surface of the vacuum chamber. As a result, the SEY of the surface of the vacuum chamber is one of the main parameters that governs the electron cloud phenomenon. Secondary electron emission, as a surface process, is influenced by different surface modifications such as surface morphology, surface composition and cleaning processes.

My project is to synthesise anti-multipacting coatings (with low secondary electron yield) using Physical Vapour Deposition (PVD) methods on basic accelerator internal surface materials such as stainless steel, copper and aluminium alloys. These will be analysed by X-ray Photo-emission Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) to provide detailed information on surface properties such as chemical bonding, morphology, roughness and structure. The SEY is measured as a function of both primary- and secondary-electron energy using a dedicated facility.