1. David Seebacher, AEC’09, CERN, Switzerland 13.10.20091 Impedance of Coatings

2.  Motivation  Method  Results 13.10.20092 David Seebacher, AEC’09, CERN, Switzerland

3.  Electromagnetic Properties of NEG coatings  different statements about the influence of NEG coatings on the impedance of machines exist  to check possible influences of the coatings, the impedance in the microwave range was measured  additionally carbon coatings were tested 13.10.20093 David Seebacher, AEC’09, CERN, Switzerland

4.  Cavity perturbation method was used to measure the properties  a frequency range of 2-4Ghz was chosen 13.10.20094 David Seebacher, AEC’09, CERN, Switzerland

5.  Glass rods with a 4mm diameter were chosen as „sample holders“  a non conducting material eases the determination of electromagnetic properties  coatings with different thicknesses were measured 13.10.20095 David Seebacher, AEC’09, CERN, Switzerland

6.  permittivity and permeability can be determined in the microwave range  magnetic and/or electric field in the resonator, influenced by the insertion of a sample  NEG measurement  sample was inserted horizontally in the center of the resonator  therefore it only interacts with the odd resonance peaks and the electric field 13.10.20096 David Seebacher, AEC’09, CERN, Switzerland

7.  inserted sample detunes the cavity  the permittivity and the sample size determine the amount of detuning dielectricconductor losses 13.10.20097 David Seebacher, AEC’09, CERN, Switzerland

8.  The upward shifted and damped odd peaks of NEG show resistive behavior  as cross check a brass rod of the same size was measured and simulated  The results of the brass rod are very similar to the of NEG this is due to similar thickness/skindepth and conductivity 13.10.20098 David Seebacher, AEC’09, CERN, Switzerland

9. 13.10.20099  no significant changes in frequency and only slight damping of the peaks  Such small changes in frequency can also be caused by temperature dependence of the resonator  conductivity was determined by the difference of the Q-factors David Seebacher, AEC’09, CERN, Switzerland

10. 13.10.200910  average square conductivity is ~4000S/m (~1kΩ/square for a 0,25µm coating) at DC  conductivity of ~600S/m (~6.6kΩ/square) was measured within the variation of different coatings  ~1E5 smaller than copper  The variation of the conductance is caused by reaching the validity of the method (it has to be a small sample) David Seebacher, AEC’09, CERN, Switzerland

11.  all odd peaks up to the 9th resonance have been considered  relative large deviation between the different resonance peaks sample is not a „small“ perturbation any more (condition for the evaluation formulas)  imaginary part shows negative values, corresponding to negative losses! 13.10.200911 David Seebacher, AEC’09, CERN, Switzerland

12.  both coatings show resistive behavior major impact on the impedance can be excluded  dielectric constant can’t be determined  changes were too small  detuning already highly influenced by temperature at such small changes  the measured data was cross checked with simulations 13.10.200912 David Seebacher, AEC’09, CERN, Switzerland