Transcript 201 MHz Cavity Studies MuCool RF Workshop (Fermilab) July 7 and 8, 2009 Derun Li Lawrence Berkeley National Laboratory.

201 MHz Cavity Studies
MuCool RF Workshop
(Fermilab)
July 7 and 8, 2009
Derun Li
Lawrence Berkeley National Laboratory
Outline
• Brief review and progresses of the 201-MHz test
program
– RF tests with flat Cu and curved thin Be windows
• Curved Be windows installed
• Cavity retuned to 200-MHz
• Tested up to ~ 19 MV/m
– RF tests with stray magnetic fields of Lab-G magnet
•
•
•
•
Move the cavity next to Lab-G magnet
New transmission line
New Vacuum pump
Preliminary test results
– Simulation study of RF cavity in strong magnetic field
• 201-MHz cavity fabrication for MICE
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 2
Primary Goals
• Development of normal conducting 201-MHz cavity that can
operate at a gradient of ~ 16 MV/m in a few Tesla magnetic
fields environment
– Prototype: exploring engineering solutions (challenges)
– RF conditioning and operation without and with B fields
• Operating a NC RF cavity (with thin and curved Be windows)
at ~ 16 MV/m in strong B field could be very challenging, but
to be confirmed experimentally
– Test with stronger magnetic fields
• SC coupling coil for MUCOOL: being fabricated at ICST, Harbin
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 3
201-MHz Prototype Cavity
•
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: 21cm and 0.38-mm
•
Nominal parameters for cooling
channels in a muon collider or a
neutrino factory
– ~ 16 MV/m peak accelerating field
– Peak input RF power ~ 4.6 MW per
cavity (85% of Q0, 3 filling time)
– Average power dissipation per cavity
~ 8.4 kW
– Average power dissipation per Be
window ~ 100 watts
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National LabThe
– July 201-MHz
7, 2009
cavity
Page at
4 MTA
Test Setup at MTA
The 805-MHz and 201-MHz cavities at MTA, FNAL for RF
breakdown studies with external magnetic fields.
201 MHz cavity
805 MHz pillbox cavity
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 5
RF Tests of curved thin Be Windows
• The cavity reached to ~ 19 MV/m
– Cavity frequency had to be retuned
– Cavity frequency was stable during the operation, however,
we did observe frequency shift due to RF heating on the
windows
• Frequency shift of ~ 125 kHz (from 0 to ~ 19 MV/m, 150-micro-second
pulse, 10-Hz repetition rate) in ~ 10 minutes, well within the tuning
range ( ~ 110 kHz/mm,  4 mm range)
• With low external magnetic field
– Cavity can be operated at ~ 19 MV/m with a few hundred
Gauss stray field from Lab-G magnet
• Tests with stronger external magnetic fields
– SC coupling coil for MuCool
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 6
Tests with Magnetic Fields
The 100-cm long coaxial
section was replaced by
20-cm one
Lab-G magnet
Separation of the nearest
curved Be window from
the face of Lab-G magnet
is 10-cm (before was 110cm)
Maximum magnetic field
near the Be window ~ 1.5
Tesla (5 Tesla in magnet)
The 201-MHz cavity
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 7
Tests at external field B = 0
Radiation (mRem/hr)
Radiation data compared with a fitting with to
gradient to ~ 14th power
Cavity Gradient (MV/m)
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 8
Radiation at B = 0.5-T Field
Radiation (mRem/hr)
Radiation data compared with a fitting with to
gradient to ~ 14th power
0.5-T B field to the
nearest Be window
Cavity Gradient (MV/m)
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 9
Test Results We have so far
 Multi-pactoring was observed at the entire magnetic field
range up to 3.75-T (~ 1.1-T at nearest Be window)
 A strong correlationship exists between cavity vacuum and
radiation levels
 We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the
nearest curved thin Be window) {~ 19 MV/m without B}
 The test results are very encouraging
 We may need to commission (condition)
the 201-MHz cavity longer to reduce the
multi-pactoring before we can properly
measure and study the magnetic field
effects in the stray field
 Numerical studies with external
magnetic fields and SC coupling coil
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 10
Numerical Study with B Field (Bob’s Talk)
• Physics models and numerical simulations (BNL, SLAC, …)
– Cavity with flat windows: 5 MV/m on axis; 2-T uniform
external magnetic field; scan of a few points from one cavity
side
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 11
201-MHz Cavity for MICE
• Eight 201-MHz cavities + with materials for two more spare
cavities
• Baseline design: 201-MHz for MUCOOL, but
– Cavity body profile has been modified
• Raise resonant frequency
– Port extruding
• Port interface is different from the MUCOOL cavity
– RF coupler and ceramic window
• The same window as for the MUCOOL cavity
– Curved Beryllium windows
• Improved 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
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 12
Four RF Cavities in each RFCC Module
Curved
Be window
SC coupling Coil
201-MHz cavity
Vacuum Pump
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 13
Update on MICE RF Cavity Design
• 3-Dimensional RF cavity parameterized model
to study frequency shifts from RF ports and
curved Be windows and Epeak
• Frequencies variation between cavities should
be within  100 kHz
• Fabrication
– Modification of the mold for prototype
cavity
• Reduction in diameter to raise the MICE
cavity frequency
– Tune cavities close to design frequency by
deformation of cavity body (if needed)
– Fine tuners operate in the push-and-pull
mode  230 kHz
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 14
Visit to ACME Spinning in April 2009 (1/2)
•Machined the MuCool mold to the new profile
•Re-spun the two half spare shells to new profile
• Measured frequency shifts before and after spinning
Expected frequency shift ~ 1 MHz
Measurements:
Shell #1:
197.275 MHz (before)
198.180 MHz (after)
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 15
Visit to ACME Spinning in 04-2009 (2/2)
• Spun and measured a new half shell (frequency: 198.415 MHz)
• Developed a fabrication procedure
• Pre-polishing copper sheets
• Inspecting the surface
• Polishing visible scratches locally if necessary (before and after)
• Handling and shipping
Polished surface
Local polishing to remove
deeper scratches
Surface inspection during
the spinning
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 16
Cavity Inspection at LBNL (1/2)
• 12 spun half shells arrived LBNL in May 2009
• CMM scans to pair best matches of two half shells in diameters, all
of them have been measured
Center hole for
handling & spinning
Polished cavity
surface
Labeling each
shell
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 17
Cavity Inspection at LBNL (2/2)
• CMM scans to pair best matches of two half shells (diameters)
• Over 1,500 points along the cavity perimeter
• Find the best match of average radii, radius deviations and the
location of the deviation angles
Radius deviations are
magnified by a factor of 55 here
• Examples of two shells
1.5
1
0.05
Shell 4B (blue)
and 6B (yellow)
0.04
0.03
0.5
0
0.02
-1.5
-1
-0.5
0
0.5
1
1.5
0.01
0
-0.01 0
500
1000
\
-0.5
1500
2000
-0.02
-1
-0.03
-0.04
-0.05
-1.5
Rotating Shell 4B
Shell Nominal
Rotating Shell 6B
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 18
Fabrication Status at Applied Fusion (1/3)
• Fixtures used for the MuCool prototype shipped to Applied Fusion
• Two re-spun half shells arrived Applied Fusion in early May for
fabrication test/practice
• E-beam welding tests
• Stiffener rings
• Equator
• Port extruding
• Water cooling pipes
E-beam welding of
the stiffener ring
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 19
Fabrication Status at Applied Fusion (2/3)
Port extruding and flange
welding testing
E-beam strength testing
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 20
Fabrication Status at Applied Fusion (3/3)
Applied Fusion
June 9, 2009
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 21
Current Plan at Applied Fusion
• June – September 2009:
― Machine the shells and prep for EB
― EBW stiffener rings
― Equator welding
― Port extruding (4 in each cavity)
― Machine and weld port flanges
― Machine-finish and EBW of the nose rings
― Machine-finish and EBW of the nose rings
― Tig-weld water cooling pipes
― Vacuum check of the cavity and water cooling pipes
Integration of cavities, coupling coils and other module
components will take place at LBNL
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 22
Schedule Summary (Presented at CM23 & 24)
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 23
Summary
• 201-MHz RF cavity tests
– MP was observed at the entire magnetic field range up to 3.75T (~ 1.1-T at nearest Be window)
– A strong correlation exists between cavity vacuum and
radiation levels
– We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the nearest
curved thin Be window) {~ 19 MV/m without B}
– More careful systematic RF conditioning studies
– MuCool SC coupling coil
– Study of cavity frequency stability with thin Be window from 0
to high power (~ 5 MW) for a given duty factor (information is
important to MICE cavity tuner designs)
– Study MP of the RF (co-axial) coupler with B fields
• MICE cavity fabrications: first 4 cavities by 2010
MuCool RF Workshop: 201-MHz RF Cavity Studies
Derun Li - Lawrence Berkeley National Lab – July 7, 2009
Page 24