201 mhz nc rf cavity r&d
DESCRIPTION
201 MHz NC RF Cavity R&D. Derun Li Center for Beam Physics Lawrence Berkeley National Laboratory. WG3 at NuFact 2004 July 28, 2004. Collaborators. R. MacGill, J. Staples, S. Virostek, M. Zisman Lawrence Berkeley National Laboratory R. Rimmer, L. Philips, G. Wu - PowerPoint PPT PresentationTRANSCRIPT
201 MHz NC RF Cavity R&D
Derun Li
Center for Beam Physics
Lawrence Berkeley National Laboratory
WG3 at NuFact 2004July 28, 2004
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 2
Collaborators
R. MacGill, J. Staples, S. Virostek, M. Zisman
Lawrence Berkeley National Laboratory
R. Rimmer, L. Philips, G. Wu
Jefferson National Laboratory
D. Summers
University of Mississippi
W. Lau, S. Yang
Oxford University, UK
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 3
Outline• Introduction• 201 MHz cavity
– Cavity design– Fabrication status– Progress on curved Be windows
• FEA modeling and prototype for 805 MHz cavity
– 21-cm curved Be windows
• Experimental study at 805 MHzExperimental study at 805 MHz– Pillbox cavity with demountable windowsPillbox cavity with demountable windows– Cavity iris termination: foils and gridsCavity iris termination: foils and grids– Surface damage study with a button in the cavitySurface damage study with a button in the cavity
• Summary
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 4
IntroductionMuon cooling channels call for normal conducting RF cavities with
highest possible accelerating gradients– Muon beam: secondary, unstable and has short decay
time (~ 2 s at rest)
• Created with LARGE 6-D phase space → High gradient with large beam aperture (iris)
• Strong external magnetic field needed to confine muon beams
→ Normal conducting • Muon beam decays, manipulation must be done quickly,
including cooling→ High accelerating gradient
– Goal: design and engineering for • RF cavity with high shunt impedance, large beam aperture
and withstand high peak RF field→ Higher gradient for the same input RF power (less RF
power)→ No surface breakdown
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 5
Introduction (cont’d)
• Shunt impedance of an RF cavity
• High peak RF field: Kilpatrick number
• Required gradient at 201 MHz: ~ 16 MV/m
– Kilpatrick: 15 MV/m
• Required gradient at 805 MHz: ~ 30 MV/m
– Kilpatrick: 26 MV/m
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WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 6
Choice of NC RF Cavity
• Conventional approach: NC “Ω” cavity with open iris– “High” shunt impedance for open iris cavities
– high peak surface field (high Epk/Eacc ~ 2)
– Shunt impedance reduces with the increase of iris
→ Very difficult (if not possible) to achieve the gradient required
for a muon cooling channel
• Taking advantage of muon beam’s penetration property, we choose a RF cavity with irises terminated by windows or grids– Pillbox like cavity
– Lower peak surface field (low Epk/Eacc ~ 1)
– Independent phase control, higher transit factor– High shunt impedance, but with large windows
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WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 7
201 MHz Cavity R&D
• Prototype of 201 MHz cavity with curved Be windows– Cavity design
• Body profile• Be windows, grids• Ports• Coupler• RF (ceramic) windows• Tuners
– Cavity fabrication going reasonably well • Cu sheets + spinning techniques• E-beam welding• Ports extruding• Cleaning, …
– Progress and status of cavity fabrication – Placed purchase order of 21-cm radius of curved Be
windows
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 8
201 MHz Cavity Concept
Spinning of half shells and e-beam welding
Water coolingchannels
Cavity design accommodatesdifferent windows
At NuFact 2003 !
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 9
201 MHz Cavity Design
Spinning of half shells using thin Cu sheets and e-beam welding to join the shells. Four ports across the e-beam joint at equator.
Cavity design uses pre-curved Bewindows, but also accommodatesdifferent windows or grids.
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 10
Cavity Body Profile
De-mountable pre-curved Be windows pointing in the same direction to terminate RF fields at the iris
2o tilt angle
Spherical section at the equator to facilitate fabrication of ports (± ~ 6o)Elliptical-like nose shape to furtherreduce peak surface field
6-mm Cu sheet permits spinning technique and mechanical tuners similar to SCRF ones
Stiffener ring
Bolted Be window
Spinning
E-Beam welding
Port extruding
Curved Be windows
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 11
The cavity parameters
The cavity design parameters (~1.2 m diameter, 0.43 m long)– Frequency: 201.25 MHz– β = 0.87
– Shunt impedance (Vacc2/Pw): ~ 22 M/m
– Quality factor (Q0): ~ 53,000
– Curved Be window radius and thickness: 21-cm and 0.38-mm (better performance with significant savings, compared to pre-tensioned flat Be windows)
Nominal parameters for a cooling channel in neutrino factory
– 16 ~ 17 MV/m 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
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 12
Spun half shells + RF & CMM measurements
CMM scans, RF frequency andQ measurements of half shells;Cu tape for better RF contacts.
201 MHz Muon Cavity Shell #1 CMM Profiles
0
4
8
12
16
20
0 10 20 30 40 50 60
Radial Dimension (cm)
Axi
al D
imen
sio
n (
cm)
3 CMM scans per half shell conducted at 0o, 45o, 90o, respectively.
Measured frequency: 196.97 MHz
(simulated frequency: 197.32 MHz)
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 13
E-Beam welding at JLab
Preparation for e-beam welding of thestiffener ring (left); after the e-beam Welding (above)
Stiffener ring
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 14
Recent progress for the welding
fmeasured = 200.88 MHz
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 15
Recent Progress
Po
rt extrud
ing
We have successfully developed techniques to extrude ports across e-beam welded joints.
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 16
What’s Next?
Cavity has been cleaned and ready for nosewelding and ports annealing in next two weeks
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 17
Status
• Cavity cleaning at J-Lab• 2~3 Months delay for using NASA e-beam welder
– Extruding ports– Cosmetic welding
• Continue engineering designs– Loop coupler: conceptual → engineering design – Supporting structure (vacuum): developed– RF windows (SNS type 4” coaxial window)– Tuner: mechanical
• Cavity test at MTA this year
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 18
Window for muon RF cavity
• Performance for an ideal window– Transparent to muon beams
Low-Z material
– Perfect electric boundary to RF field Good electrical conductivity
– Mechanical strength and stability No detuning of cavity frequency under RF heating
• Beryllium is a good material for windows– High electrical & thermal conductivity with strong mechanical
strength and low-Z
• Engineering solutions being explored so far– Thin, flat Be foils (pre-tensioned)– Curved Be foils– Grids (Ph.D thesis of M. Alshaor’a at IIT)
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 19
Curved Be window R&D– Designed, fabricated and tested pre-tensioned flat Be windows
• They work, but expensive; balance between thickness & RF gradient – Progress on FEA modeling and engineering design of all approaches
– Fabricated pre-curved windows of S.S. and Be for 805 MHz cavity
– Cu frames + curved Be foils: better performance with BIG savings
ANSYS simulations: mechanical vibration modesFabricated pre-curved Be window:
16-cm in diameter and 0.254 mm thick
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 20
More on Be Windows
• Model validation– Preliminary measurements on mechanical
vibration frequency of curved Be windows for 805 MHz cavity agree with FEA modeling
• Ti-N coatings at LBNL recently– Curved Be windows– Pre-tensioned Be windows
• Placed purchase order of 3 curved Be windows for 201 MHz cavity (21-cm radius, 0.38-mm thick)
• Baseline design for MICE cavities
WG3 at NuFact 2004 July 28, 2004
201 MHz NC RF Cavity R&DDerun Li
Osaka University, Osaka, Japan Page 21
Summary
• Good progress on NC RF R&D programs – Experimental study at 805 MHzExperimental study at 805 MHz
• Tests of Ti-N coated curved and pre-tensioned Be windows at MTA
• Tests on grids
– 201 MHz cavity prototype – Be window: FEA modeling and prototype
• Progress on 201 MHz test cavity fabrication; ready for testing this year (2004)
• Test plans are being developed• The 201 MHz cavity has been used as baseline design
for MICE