| Paper | Title | Page |
|---|
| TUP62 | Hydrodynamic Thermal Modeling of 9-cell ILC Cavity Electropolishing and Implications for Improving the EP Process | 275 |
| | - C. E. Reece, J. Mammosser
JLab - J. Ortega
Blue Ridge Numerics
| |
| | Multi-cell niobium cavities often obtain the highest
performance levels after having been subjected to an
electropolishing (EP) process. The horizontal EP process
first developed at KEK/Nomura Plating for TRISTAN[1]
cavities is being applied to TESLA-style cavities and
other structures for the XFEL and ILC R&D. Jefferson
Lab is presently carrying this activity in the US. Because
the local electropolishing current density is highly
temperature dependent, we have created using
CFDesign?? a full-scale hydrodynamic model which
simulates the various thermal conditions present during
9-cell cavity electropolishing. The results of these
simulations are compared with exterior surface
temperature data gathered during ILC cavity EP at JLab.
Having benchmarked the simulation, we explore the
affect of altered boundary conditions in order to evaluate
potentially beneficial modifications to the current
standard process. | |
| WEP28 | Latest Results of ILC High-Gradient R&D 9-cell Cavities at JLAB | 525 |
| | - R. L. Geng, R. Afanador, A. C. Crawford, G. K. Davis, D. Forehand, C. Dreyfus, C. Grenoble, B. Golden, R. Johnson, P. Kushnick, K. Macha, J. Mammosser, J. Saunders, A. Wu
JLab - D. Bice, D. A. Sergatskov
Fermilab
| |
| | It has been over a year since JLAB started processing
and testing ILC 9-cell cavities in the frame work of
ILC high-gradient cavity R&D, aiming at the goal of a
35 MV/m gradient at a Q0 of 1E10 with a yield of 90%.
The necessary cavity processing steps include field flatness
tuning, electropolishing (EP), hydrogen out-gassing under
vacuum, high-pressure water rinsing, clean room assembly,
and low temperature bake. These are followed by RF
test at 2 Kelvin. Ultrasonic cleaning with Micro-90, an effective
post-EP rinsing recipe discovered at JLAB, is routinely
used. Seven industry manufactured 9-cell TESLAshape
cavities are processed and tested repeatedly. So far,
33 EP cycles are accumulated, corresponding to more than
65 hours of active EP time. An emphasis put on RF testing
is to discern cavity quench characteristics, including its nature
and its location. Often times, the cavity performance is
limited by thermal-magnetic quench instead of field emission.
The quench field in some cavities is lower than 20
MV/m and remains unchanged despite repeated EP, implying
material and/or fabrication defects. The quench field
in some other cavities is high but changes unpredictably
after repeated EP, suggesting processing induced defects.
Based on our experience and results, several areas are identified
where improvement is needed to improve cavity performance
as well as yield. | |