[Eng-div] ODU CAS seminar- March 26th

[Gayle Sundeen]

We will have our next CAS seminar on Thursday Mar. 26 at 1:30 at ODU in the CAS building (see below). There will also be a video link for the talk at Jefferson Lab in the ARC building in room 728 and in the MCC Conference Room (bldg 85). Refreshments will be available at ODU at 1 pm. The schedule for future talks is listed at the end of this message. If you want to be added to this email distribution list, please let me know. 


Plasma Processing of SRF Cavities 
Janardan Upadhyay 
Old Dominion University 

When: Thursday March 26, 2015; 1:30 pm ( Refreshments at 1 pm ) 
Where: CAS Building at ODU (1021 W. 47th St.) 
Video: Jefferson Lab ARC 728 
Video: MCC Conference Room (bldg 85) 

Abstract: 


The first results of plasma processed Niobium (Nb) SRF cavities using cylindrical coaxial capacitively coupled radio frequency (rf) plasma will be presented. The research was focused on the transition of plasma etching from two-dimensional flat surfaces to inner surfaces of three-dimensional (3D) structures. The results could be applicable to a variety of inner surface of 3D structures other than SRF cavities. Understanding the Ar/Cl 2 plasma etching mechanism is crucial for achieving the desired modification of Nb SRF cavities. An apparatus was built and a method was developed to plasma etch a single cell Pill Box cavity. The plasma characterization was done with the help of optical emission spectroscopy. The Nb etch rate at various points of this cavity was measured before processing the SRF cavity. Cylindrical ring-type samples of Nb placed on the inner surface of the outer wall were used to measure dependence of the process parameters on plasma etching. The measured etch rate dependence on pressure, rf power, dc bias, temperature, Cl 2 concentration and diameter of the inner electrode was determined. The etch rate mechanism was studied by varying the temperature of the outer wall, the dc bias on the inner electrode and gas conditions. In a coaxial plasma reactor, uniform plasma etching along the cylindrical structure is a challenging task due to depletion of the active radicals along the gas flow direction. The dependence of etch rate uniformity along the cylindrical axis was determined as a function of process parameters. The formation of dc self-biases due to surface area asymmetry in this type of plasma and its variation on pressure, rf power and gas composition was measured. Enhancing the surface area of inner electrode to reduce the asymmetry was studied by changing the contour of the inner electrode. The optimized contour of the electrode based on these measurements was chosen for SRF cavity processing. 

__________________________________________________________ 
Future Speakers: 
April 2: Joe Grames 
April 23: Vasiliy Morozov 


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Gail Dodge 
Department of Physics 
Old Dominion University 
Norfolk, VA 23529 

gdodge at odu.edu 
office: (757) 683-5854 
fax: (757) 683-3038 







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