David Seebacher, AEC’09, CERN, Switzerland

1. ImpedanceofCoatings David Seebacher, AEC’09, CERN, Switzerland

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

3. Motivation • 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 David Seebacher, AEC’09, CERN, Switzerland

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

5. Samples 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 David Seebacher, AEC’09, CERN, Switzerland

6. Cavity Perturbation Method • 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 David Seebacher, AEC’09, CERN, Switzerland

7. Cavity Perturbation Method dielectric conductor losses inserted sample detunes the cavity the permittivity and the sample size determine the amount of detuning David Seebacher, AEC’09, CERN, Switzerland

8. Results NEG Coating 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 David Seebacher, AEC’09, CERN, Switzerland

9. Results Carbon Coating • 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. Results Carbon Coating • 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. Results Glass Rods 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! David Seebacher, AEC’09, CERN, Switzerland

12. Measurement Results • 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 David Seebacher, AEC’09, CERN, Switzerland