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Field Emission Measurements From Cesiated Titanium and Stainless Steel Electrodes

Field Emission Measurements From Cesiated Titanium and Stainless Steel Electrodes . K.Surles-law, P.Adderley, J.Brittian, D.Charles, J.Clark, J.Grames, J.Hansknecht, M.Poelker, M.Stutzman. Field Emission from 25deg Electrodes. POISSON model of 25deg electrode E-fields shown are for

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Field Emission Measurements From Cesiated Titanium and Stainless Steel Electrodes

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  1. Field Emission Measurements From Cesiated Titanium and Stainless Steel Electrodes K.Surles-law, P.Adderley, J.Brittian, D.Charles, J.Clark, J.Grames, J.Hansknecht, M.Poelker, M.Stutzman

  2. Field Emission from 25deg Electrodes POISSON model of 25deg electrode E-fields shown are for V = -100kV

  3. Field Emission • Electrons are confined in a metal by a potential well • Energy of electron insufficient to escape from metal • Electron must be given extra energy to escape (thermal, photoemission) • QM demonstrates the electron wavefunction attenuates rapidly outside potential barrier

  4. Field Emission • Application of external fields lowers and thins the potential barrier • Fowler- Nordheim used quantum mechanics to demonstrate that some electrons can tunnel through the potential barrier and escape into the vacuum

  5. Field Emission: Fowler-Nordheim Equation This is the Fowler-Nordheim expression for field emission E is the electric field (MV/m) F is the work function of the material (eV) b is the field enhancement factor A is the effective emitting area

  6. Field Emission: Fowler-Nordheim Equation Plot of Fowler-Nordheim equation with b = 200. The electric field gradients were generated from POISSON model of the 25 degree electrode. The potential varied from 10 to 125kV

  7. Field Emission: Fowler-Nordheim Equation • One can use exponential form of FN to compare field emission from Ti and SS

  8. Field Emission: Fowler-Nordheim Plot 210min of Cs for Ti and SS

  9. Field Emission: Fowler-Nordheim Plot • More interesting to plot ln(I/V^2) vs. 1/V • The slope of the fitted data is proportional to the work function to the 3/2 power • If work function changes, the slope of FN plot changes

  10. Field Emission: Fowler-Nordheim Plot

  11. Field Emission: Fowler-Nordheim Plot • Now let’s observe FN plots for Ti and SS with no Cs and 210min of Cs

  12. Field Emission: Fowler-Nordheim Plot

  13. Field Emission: Fowler-Nordheim Plot

  14. Field Emission: Fowler-Nordheim Plot

  15. Field Emission: Fowler-Nordheim Equation • Next, decrease cathode-anode spacing • Take FE data for Ti and SS with no Cs • Compare FE vs. spacing: Is Ti or SS better, or same?

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