Author: Popovic, S.     [Popović, S.]
Paper Title Page
WEPPC104 Tomography as a Diagnostic Tool for Plasma Etching of SRF Cavities 2459
  • M. Nikolić, A.L. Godunov, S. Popović, A. Samolov, L. Vušković
    ODU, Norfolk, Virginia, USA
  • F. Čučkov
    Old Dominion University, Norfolk, USA
  Plasma based surface modification is a promising alternative for etching of superconductive radio frequency (SRF) cavities. A plasma processed SRF cavity presents a plasma reactor with limited or distorted symmetry. We are developing a tomographic reconstruction of local plasma parameters, as a diagnostic tool in the plasma etching setting of SRF cavities. The method is non-invasive and provides deep insight into the fundamental processes and phenomena during the plasma treatment of SRF cavities’ surfaces. Here we report on our progress in developing tomographic numerical method, based on 2D inverse Radon formula. We tested it on supersonic flowing microwave discharge maintained in the cylindrical quartz tube. Due to the model’s sensitivity to the noise signal in the experiment, an automated measurement system has been built with the aim to increase the overall precision of data acquisition as well as to stream line the measurement process.  
WEPPC105 Study of Etching Rate Uniformity in SRF Cavities 2462
  • J. Upadhyay, S. Popović, L. Vušković
    ODU, Norfolk, Virginia, USA
  • H.L. Phillips, A-M. Valente-Feliciano
    JLAB, Newport News, Virginia, USA
  Plasma based surface modification is a promising alternative to wet etching of superconducting radio frequency (SRF) cavities. The crucial aspect of the technology development is dependence of the etching rate and surface roughness on the frequency of the power supply, pressure, power level, driven electrode shape and chlorine concentration in gas mixture during plasma processing. To optimize the plasma parameters, we are using a single cell cavity with 20 sample holders symmetrically distributed over the cell. These holders are used as diagnostic ports for the measurement of the plasma parameters and as holders for the samples to be etched. The plasma properties are highly correlated with the shape of the driven electrode and the percentage of chlorine concentration in Argon/chlorine gas mixtures. The effect of the plasma parameters and chlorine gas concentration are investigated at RF (100 MHz) and microwave (2.45 GHz) frequencies.  
WEPPR094 Large Volume Resonant Microwave Discharge for Plasma Cleaning of a CEBAF 5-Cell Srf Cavity 3156
  • S. Ahmed, K. Macha, J.D. Mammosser
    JLAB, Newport News, Virginia, USA
  • M. Nikolić, S. Popović, J. Upadhyay, L. Vušković
    ODU, Norfolk, Virginia, USA
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The U.S.
We report preliminary results on plasma generation in a 5-cell CEBAF SRF cavity for the application of cavity interior surface cleaning. CEBAF currently has ~300 of these five cell cavities installed in the JLab accelerator which are mostly limited by cavity surface contamination. The development of an in-situ cavity surface cleaning method utilizing a resonant microwave discharge could lead to significant performance improvement. This microwave discharge is currently being used for set of plasma cleaning procedures targeted to the removal of various organic, metal and metal oxide impurities. These contaminants are responsible for the increase of surface resistance and the reduction of RF performance in installed cavities. CEBAF five cell cavity volume is ~ 0.5 m2, which places the discharge in the category of large-volume plasmas. Our preliminary study includes microwave breakdown and optical spectroscopy, which was used to define the operating pressure range and the rate of removal of organic impurities.