Impedance of Coatings David Seebacher AEC 09 CERN

Impedance of Coatings David Seebacher, AEC’ 09, CERN, Switzerland 13. 10. 2009 1

Outline Ø Motivation Ø Method Ø Results 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 2

Motivation Ø Electromagnetic Properties of NEG coatings Ø different statements about the influence of NEG coatings on the impedance of machines exist Ø to check possible influences of the coatings, the impedance in the microwave range was measured Ø additionally carbon coatings were tested 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 3

Cavity Perturbation Method Ø Cavity perturbation method was used to measure the properties Ø a frequency range of 2 -4 Ghz was chosen 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 4

Samples Ø Glass rods with a 4 mm diameter were chosen as „sample holders“ Ø a non conducting material eases the determination of electromagnetic properties Ø coatings with different thicknesses were measured 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 5

Cavity Perturbation Method Ø permittivity and permeability can be determined in the microwave range Ø magnetic and/or electric field in the resonator, influenced by the insertion of a sample Ø NEG measurement Ø sample was inserted horizontally in the center of the resonator Ø therefore it only interacts with the odd resonance peaks and the electric field 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 6

Cavity Perturbation Method Ø inserted sample detunes the cavity Ø the permittivity and the sample size determine the amount of detuning dielectric conductor losses 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 7

Results NEG Coating Ø The upward shifted and damped odd peaks of NEG show resistive behavior Ø as cross check a brass rod of the same size was measured and simulated Ø The results of the brass rod are very similar to the of NEG this is due to similar thickness/skindepth and conductivity 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 8

Results Carbon Coating Ø no significant changes in frequency and only slight damping of the peaks Ø Such small changes in frequency can also be caused by temperature dependence of the resonator Ø conductivity was determined by the difference of the Q-factors 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 9

Results Carbon Coating Ø average square conductivity is ~4000 S/m (~1 kΩ/square for a 0, 25µm coating) at DC Ø conductivity of ~600 S/m (~6. 6 kΩ/square) was measured within the variation of different coatings Ø ~1 E 5 smaller than copper Ø The variation of the conductance is caused by reaching the validity of the method (it has to be a small sample) 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 10

Results Glass Rods Ø all odd peaks up to the 9 th resonance have been considered Ø relative large deviation between the different resonance peaks sample is not a „small“ perturbation any more (condition for the evaluation formulas) Ø imaginary part shows negative values, corresponding to negative losses! 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 11

Measurement Results Ø both coatings show resistive behavior major impact on the impedance can be excluded Ø dielectric constant can’t be determined Ø changes were too small Ø detuning already highly influenced by temperature at such small changes Ø the measured data was cross checked with simulations 13. 10. 2009 David Seebacher, AEC’ 09, CERN, Switzerland 12