1. Numerical Calculations of Field Enhancements due to Small Grooves
Tetsuo ABE (KEK)
5th Collaboration Meeting on
X-band Accelerator Structure Design and Test Program 
@SLAC, USA

2. Computation of RF Fields by CST-MWS ~ Geometry and Definition ~
(v )
e.g. Gap=20mm, D=30mm
Rectangular Waveguide with fcutoff(TE10) = 10 GHz
1.0mm
15.0mm
3 Parameters to Describe the Groove
Gap ~ D
Simulating:
- Chamfer of the Quadrants
- etc.
R=50mm (fixed)

3. Meshing Parameters and Mesh-Size Dependence
FDSolver.Method "Hexahedral Mesh"
Mesh.MeshType "PBA" ‘(Perfect Boundary Approx.)
Mesh.LinesPerWavelength “300"
Mesh.AutomeshRefineAtPecLines "True", “RAPL"
FDSolver.AccuracyHex "1e-6"
RAPL=2 (default)
RAPL=5
R=50mm

4. RAPL=2 (default) (PEC) (Vac) X (X<0 ) 0 (X>0)
Using a function: “GetFieldVectorSurface()”
 Better field interpolation scheme on PEC surfaces
RAPL=2 (default)
(PEC)
(Vac) X
(X<0 ) (X>0)

5. RAPL=5(Adopted)
(PEC)
(Vac)
Emax X
(X<0 ) (X>0)

6. Results
Gap D
R=50mm

7. Check the Results(1): E-Static Fields by CST-EMS
(v )
10.0mm
1.0mm
3 Parameters to describe the groove
Gap ~ D
R=50mm (fixed)

8. Meshing Parameters and Mesh-Size Dependence
EStaticSolver.Method "Hexahedral Mesh"
Mesh.MeshType "PBA" ‘(Perfect Boundary Approx.)
Mesh. MinimumStepNumber “100"
Mesh.AutomeshRefineAtPecLines "True", “RAPL"
EStaticSolver.Accuracy "1e-9"
RAPL=2(default)
RAPL=5
R=50mm

9. RAPL=5(Adopted)
(PEC)
(Vac)
Emax

10. Comparison of the Results ~Cross-Check of the Computations~
Good Agreements as expected

11. Simulation using Omega3P (by Zenghai Li) CST-MWS (T. Abe) (update)
Check the Results(2):
Simulation using Omega3P (by Zenghai Li)
CST-MWS (T. Abe) (update)
Gap (micron)
D (micron)
Emax / Enominal
1.21 20
1.36 10
1.37 D
SLAC Omega3P (Z. Li)
Gap (micron) D
(micron)
Emax / Enominal
1.23 20
1.40 10
1.44
Fairly Good Agreements

12. Magnetic Field Enhancement
e.g. R=50mm, Gap=20mm, D=30mm
TE10-like
Mode

14. Conclusions
Field enhancements due to small grooves with round chamfers have been computed by using CST-MWS/EMS.
At least 20% enhancement for R=50mm round chamfers.
Increases to 40% enhancement
as the D size increases to 25mm.
More simulation studies to be done
Conductor surfaces damaged by BD/discharge
Etc.

15. End of the Slides