Status of the 201 MHz Cavity and
Coupling Coil Module
Steve Virostek
Lawrence Berkeley National Laboratory
MICE Video Conference
March 10, 2004
201 MHz Cavity Concept
Extruding ports
Spinning of half
shells using thin Cu
sheets and e-beam
welding to join the
shells
Water cooling
channels
Cavity design accommodates
different windows
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 2
The Cavity Body Profile
Spherical section at the equator to
ease addition of ports (± ~ 6o)
Elliptical-like (two circles) nose to
reduce peak surface field
Stiffener ring
2o tilt angle
6-mm Cu sheet permits spinning
technique and mechanical tuners
similar to SCRF ones
De-mountable pre-curved
Be windows to terminate
RF fields at the iris
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
Bolted Be window
LBNL Page 3
The Cavity Parameters
The cavity design parameters
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Frequency: 201.25 MHz
β = 0.87
Shunt impedance (VT2/P): ~ 22 M/m
Quality factor (Q0): ~ 53,000
Be window radius and thickness: 21-cm and 0.38-mm
Nominal parameters for cooling channel in a neutrino factory
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Up to 17 MV/m peak accelerating field
Peak input RF power ~ 4.6 MW per cavity (85% of Q0, 3τ filling)
Average power dissipation per cavity ~ 8.4 kW
Average power dissipation per Be window ~ 100 watts
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 4
Spinning @ ACME
An example of the spinning technique!
Spinning tools
Spinning a bowl
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 5
RF & CMM Measurements at LBNL
3 CMM scans per half shell conducted
at 0o, 45o, 90o, respectively.
Measured frequency: 196.97 MHz
(simulated frequency: 197.32 MHz)
201 MHz Muon Cavity Shell #1 CMM Profiles
20
CMM scans, RF frequency and
Q measurements of half shells;
Cu tape for better RF contacts.
Axial Dimension (cm)
16
12
8
4
0
0
10
20
30
40
50
60
Radial Dimension (cm)
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 6
E-Beam Welding
Stiffener ring
Preparation for e-beam welding of the
stiffener ring (left); after the e-beam
Welding (above)
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 7
Extruding Tests at JLab
Extruding tests on a flat Cu plate
going through e-beam joint
Successful extruding recently!
Possible improvement:
Anneal around the extruding area or
Combination between pilot hole
dimensions and lid heights, …
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 8
Be Windows R&D
• Ideal windows
– Transparent to muon beams
– Perfect electric boundary to RF field
– No detuning of cavity frequency
Window
profile
evolutions
• Engineering solutions
– Pre-stressed flat Be (low-Z) windows
– Pre-curved Be windows
– Grids
A pre-curved Be window:
0.25 mm thick and 21 cm
in radius
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 9
Curved S.S. Windows
Succeeded in the S.S. window with Cu frame for 805 MHz cavity
(scaled version of the window for 201 MHz cavity)
Pre-formed at room temperature by
holding foil edge then brazing the Cu frames
March 10, 2004
MICE Video Conference
A finished curved S.S. window with
brazed Cu frame
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 10
Curved Be Window
Failed in forming Be window at room temperature
The curved Be windows can be formed at higher temperature by the BrushWellman Company. Order was placed for two 805 MHz windows.
The Be foil cracked during forming at
room temperature (LBNL)
March 10, 2004
MICE Video Conference
A successfully formed Be foil
(Feb. 5th 2004 at Brush-Wellman)
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 11
Curved Be Windows
Brush-Wellman recently succeeded in making two curved Be
windows with Cu frames for the 805 MHz cavity
Fabrication Methodology
•Fabricated dies in the shape
of the windows
•Press Be into shape at high
temperature
•Braze Cu frames to curved
Be in a separate process
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 12
201 MHz Cavity Status
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Four half shells have been formed by spinning
Cu stiffener rings were e-beam welded to two half shells
The shells were mechanically cleaned at JLab
Shells are being machined prior to e –beam welding of equator joint
Equator weld fixturing has been fabricated at LBNL
Cavity nose piece rings (fab. By U. Miss.) have been brazed at LBNL
Conceptual design of RF loop coupler is complete
Prototype pre-curved Be windows complete (805 MHz size)
E-beam welding of equator joint and nose rings
Extruding of four ports (2 RF, 2 vacuum)
Brazing of cooling lines to cavity exterior
Chemical cleaning and electro-polishing of the cavity
Design and fabrication of tuner system
Final design and fabrication of RF coupling loops
The cavity should be ready for test in MTA at Fermilab this fall
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 13
MICE RF Module Layout Status
New layout has several changes and additions:
 New coupling coil design incorporated
 RF coupling loops modified
 Vacuum system for cavities and vessel added
 AFC module vessel flanges extended 62 mm
on downstream ends to make flanges
symmetric to coils
 Various vessel joint concepts being explored
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 14
MICE RF Module Layout
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 15
MICE RF Module Coupling Loops
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 16
MICE RF Module Vacuum System
March 10, 2004
MICE Video Conference
Status of 201 MHz Cavity and Coupling Coil
S. Virostek
LBNL Page 17