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David Seebacher, AEC’09, CERN, Switzerland

13.10.2009

Impedance of Coatings

Outline

Motivation

Method

Results

13.10.2009 2David Seebacher, AEC’09, CERN, Switzerland

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

13.10.2009 3David Seebacher, AEC’09, CERN, Switzerland

Cavity Perturbation Method

Cavity perturbation method was used to measure the properties

a frequency range of 2-4Ghz was chosen

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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

13.10.2009

Samples

David Seebacher, AEC’09, CERN, Switzerland

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

13.10.2009 6David Seebacher, AEC’09, CERN, Switzerland

inserted sample detunes the cavity the permittivity and the sample size

determine the amount of detuning

Cavity Perturbation Method

dielectric

conductor

losses

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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 conductivity13.10.2009

Results NEG Coating

David Seebacher, AEC’09, CERN, Switzerland

913.10.2009

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

1013.10.2009

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 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!

13.10.2009 11David Seebacher, AEC’09, CERN, Switzerland

Measurement Results

both coatings show resistive behaviormajor impact on the impedance can be

excluded

dielectric constant can’t be determinedchanges were too small detuning already highly influenced by

temperature at such small changes

the measured data was cross checked with simulations

13.10.2009 12David Seebacher, AEC’09, CERN, Switzerland