FEL Cryomodule Final Review 19 February, 1997



A combined presentation of the FEL 1/4 Cryomodule test results and FEL Cryomodule final design changes were presented. Topics included:
Cavity Performance Waveguide Thermal Performance HOM Thermal Performance HOM Load Status and Design Microphonics with Shield Flow Performance Tuner Performance Beam Line Design Warm Window Status
Presentation materials are available upon request to Joe Preble.
Cavity System Performance

Q. Peter Kneisel

Was the off resonance power dissipation , normally attributed to window losses, measured?

A. Joe Preble

Yes it was. Results as follows.
IA328, cavity 7
Off resonance Forward Power 5.5 kW -> Dissipated Power 5 W
On resonance Forward Power 5.3 kW -> Dissipated Power 47 W

IA , cavity 8
Off resonance Forward Power 1.7 kW -> Dissipated Power 0.6W
On resonance Forward Power 1.6 kW -> Dissipated Power 7 W

C. Peter Kneisel

The slope of IA328 Q0, cavity 7, is pronounced.

C. John Mammosser, Ganapati Myneni

This may be a good candidate for Helium Processing. The current level of experience with that process is enough to minimize the risk and make it worth while.

Q. Have you ever kept high power rf on during a cooldown?

A. Joe Preble


C. Peter Kneisel

We could try this with the upcoming Motivation cryomodule test.


Q. Jean Delayen

Is this representative of the traveling wave power that will be seen in FEL operation?

C. Peter Kneisel

This is a standing wave condition.

C. Larry Phillips

The length of the wave guide with the standing wave provides a reasonable similarity to the traveling wave condition.
Q. Court Bohn

Is it conceivable that the standing wave condition is significantly different than the travel wave condition during operations.

A. Group

The final answer will only come with true traveling wave power in the wave guide.

C. Mark Wiseman

I believe there is the potential for needing to change the wave guide interlock levels, IR interlock in particular, when running 50 kW rf power. The answer to this will come with commissioning testing.


C. Jean Delayen

The performance of the magnetostrictive materials is strongly dependent on the stress on the material. The initial coarse tuning conditions could change the fine tuner performance.

C. Mark Wiseman

We can reduce the stress in the tuner with a thicker wall nickel tube, or even a solid rod. Both are compatible with the existing design.

C. Larry Phillips

You can also use a "folded tube" design to increase the active length of the nickel tube.

Q. Court Bohn

What is the highest risk item in the 1/4 cryomodule or the cryomodule?

A. Ganapati Myneni

The 1/4 cryomodule HOM load ceramics falling off.

Q. Court Bohn

What is the impact of that happening?

A. Joe Preble

Repair would require a complete rework of the 1/4 cryomodule. The Higher Order Mode Loads installed in the 1/4 cryomodule have been qualified prior to installation. This included several tests to ensure mechanical integrity. Each load was thermally cycled to LN2 temperature ~50 times, the ceramics were mechanically stressed in the warm state, and the installed loads were transported while in the cavity pair to simulate assembly and operational handling. The cavity pair was tested after these qualifications and performed as reported here. Indeed the load design a concern for mechanical stability, and has changed as a result, but the installed loads have been tested and passed.

The 1/4 cryomodule is acceptable for supporting ITS and FEL operations. The performance of the cavities may be enhanced with helium processing and should be considered for implementation during the commissioning work. The commissioning of the 1/4 Cryomodule will be the first time the hardware has operated with a 50 kW rf source and commissioning should include a characterization of the input coupler under these conditions.

The final designs presented for the FEL cryomodule are accepted as sound. The FEL cryomodule will have a small amount of instrumentation incorporated to characterize these designs.