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Impedance of Coatings. David Seebacher, AEC’09, CERN, Switzerland. Outline. Motivation Method Results. Motivation. Electromagnetic Properties of NEG coatings different statements about the influence of NEG coatings on the impedance of machines exist

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Presentation Transcript
slide1

ImpedanceofCoatings

David Seebacher, AEC’09, CERN, Switzerland

outline
Outline

Motivation

Method

Results

David Seebacher, AEC’09, CERN, Switzerland

motivation
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

cavity perturbation method
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

samples
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

cavity perturbation method1
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

cavity perturbation method2
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

results neg coating
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

results carbon coating
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

results carbon coating1
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

results glass rods
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

measurement results
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

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