# Presentation: 143747

## 201-MHz RF Cavity Construction (Plan) for MICE 

**Derun Li**
**Center for Beam Physics**
**Lawrence Berkeley National Laboratory**
**NFMCC Meeting**
**March 17, 2008**

## Outline

**MICE Cavity Design**
**Based on the design of 201-MHz cavity for MUCOOL**
**Cavity body**
**Ports for power coupler, vacuum and probes**
**RF power loop coupler and ceramic RF window**
**Curved Beryllium window**
**Tuners**
**Interface and integration with RFCC module **
**Summary**
**Status and fabrication plan**
**Techniques developed for MUCOOL cavity**
**Spinning, port extruding, curved Be windows, RF couplers**

## MICE Cooling Channel

- Courtesy of S. Q. Yang, Oxford Univ.

**LH****2**** absorbers**

**Eight**** 201-MHz RF cavities**

## MICE RF Cavity

**Eight 201-MHz cavities + with materials for two more spares**
**Baseline design: 201-MHz for MUCOOL, but**
**Cavity body profile needs to be modified**
**Resonant frequency**
**Better estimation of spring back after spinning**
**Port extruding**
**Port interface is different from the MUCOOL cavity**
**RF coupler and ceramic window**
**Same as the MUCOOL cavity with Toshiba ceramic windows for SNS**
**Curved Beryllium windows**
**Modified design to better control silver alloy flow during the brazing**
**Tuners and interface with RFCC module**
**Post-processing: Water cooling pipes, cleaning (EP & water rinsing), low power measurement, tuning, assembly and shipping  **

## Cavity Design Parameters

** ****The cavity design parameters**** **
- Frequency: 201.25 MHz
-  β = 0.87
- Shunt impedance (VT2/P): ~ 22 MΩ/m
- Quality factor (Q0): ~ 53,500
- Be window radius and thickness: 21-cm and 0.38-mm
**  ****Nominal parameters for cooling channels in a muon**
**      ****collider  or a neutrino factory and ****MICE**
- ~ 16 MV/m (~ **8 MV/m**) peak accelerating field
- Peak input RF power ~ **4.6 MW** (~ **1 MW**) per cavity (85% of Q0, 3 filling)
- Average power dissipation per cavity ~ **8.4 kW ****(~ 1 kW at 1 Hz repetition rate and 1 ms pulse length)**
- Average power dissipation per Be window
-    ~ **100 watts** **(~ 12 watts)**

## MUCOOL Cavity Review

-  Design and engineering at LBNL
-  Half shells spun at Acme in Minnesota
-  Parts made in Univ. of Mississippi and LBNL
-  E-beam welding & port-pulling, cleaning and
-   EP at J-Lab, NASA
-  Coupler tests at SNS, Oak Ridge National Lab
-  Final assembly and high power tests at MTA,
-   FNAL (March-2006) and reached 16-MV/m
-   without external magnetic field

## The Cavity Body Profile

**De-mountable ****pre-curved Be windows**** **
**pointing in the same direction to **
**terminate RF fields at the iris**

**2****o ****tilt angle**

**Spherical section at the equator to **
**ease addition of ports (± ~ 6****o****)**
**Elliptical-like (two circles) nose to **
**reduce peak surface field**

**6-mm Cu sheet permits spinning **
**technique and mechanical tuners **
**similar to SCRF ones **

**Stiffener ring**

**Bolted Be window**

**Low peak surface field and easy fabrication**

**E-beam joints**

## Cavity Body

**MUCOOL cavity frequency is slightly lower than 200-MHz, but within the bandwidth of RF source**
**Mechanical (fixed) tuners available and tested in air**
**MICE cavities  **
**Target frequency is 201.250-MHz**
**One RF source (tube) powers more than one cavity**
**Each cavity will be made (spinning) to frequency very close to 201-MHz **
**Modifying the existing mold used for MUCOOL cavity**
**A new mold (could be new materials)**
**3D simulations to predict the frequency shifts by ports, curved Be windows and thermal contraction (LN operation)**
**Conceptual tuner designs (fine tuning)**

## Ports Extruding and Flanges

**	**

**Local annealing of ports**

**Finished cavity port**

**Port flange e-beam weld**

**Extruded port**

**Cavity ports being extruded (pulled)**

**Vacuum leak!**

**Development of the technique**

## Fabrication of the Coupler 

** ****The coupling can be **
**   ****adjusted by rotating the**
**   ****loop**
** ****Water cooling line goes**
**  ****around the loop**
** ****RF ceramic windows from**
**  ****Toshiba Company**

**RF window**

**Loop coupler**** **

## RF Coupling Loop Design

**	**

**Prototype coupling loop design uses standard off-the-shelf copper co-ax**
**Parts to be joined by torch brazing**
**Coupling loop has integrated cooling**
**    ****(Possible off-shelf components?)**
**Two SNS style RF windows mfg. by Toshiba received (no cost!)**
**Bellows connection required on MICE for thermal and dimensional reasons**
**Need to integrate with MICE layout**

**MUCOOL**

**MICE**

## Curved Be Windows

**We have made two windows available so far**
- 21-cm and 0.38-mm thick
***Good*** braze (between annular frames and foil)
- Achieved ~ 95 % of the designed profile
- Thin Ti-N coatings
**The windows were HP tested at MTA, Fermilab**
** **

## Beryllium Window Update

**Improved design for better brazing (based on suggestions from Brush-Wellman Company)**

- Be foil

## Tuners for MICE Cavities

**Clocking of tuner position between adjacent cavities avoids interference**
**Actuators offset from cavity center plane due to width of coupling coil**
**Soft connection only (bellows) between tuner/actuators and vacuum vessel shell**

**Four 201-MHz cavities in each RFCC module; one tuner assembly **
**(six sets of tuners) on each cavity.**

## Tuner Section View

- Ball contact only

- Dual bellows
- feedthrough

- Tuner actuator
- (likely air)

- Pivot point

- Fixed (bolted)
- connection

## MUCOOL Cavity Tuners

## Integration to RFCC Module

**RF couplers, vacuum, RF probes, tuners, water cooling pipes**

## Post-Processing

**Cavity cleaning and assembly**
**Low power RF measurements and shipping**

## Summary

**Status  **
**Cavity design modifications have started**
**Cavity body profile and analysis (RF, thermal [watering cool + possible LN operation], mechanical, vacuum, ...)**
**Modified Be window designs, ready to place PO**
**Tuners and interface with RFCC module**
**Apply successful techniques developed from MUCOOL cavity R&D and look for possible simplifications**
**Spinning, port extruding and post-processing**
**Re-qualify venders (spinning, e-beam welding, port extruding and post-processing) with our supervision**
**US vendors: NIOWAVE, ...**
**HIT in China**
**Brush-Wellman for Be windows**
**Toshiba for ceramic RF windows**
**Design and Fabrication Plan**
**Design review ~ June 2008 (MICE CM21 at DL)**
**Schedule has been developed (~ by early 2010)**

## Slide 20