Transcript 805 MHz Pillbox Cavity (IIT, Chicago, IL, Feb. 7th, 2002) Derun Li Center for Beam Physics Lawrence Berkeley National Laboratory.

805 MHz Pillbox Cavity
(IIT, Chicago, IL, Feb. 7th, 2002)
Derun Li
Center for Beam Physics
Lawrence Berkeley National Laboratory
Collaborators
J. Corlett, A. Ladran, R. MacGill, R. Rimmer,
J. Wallig, M. Zisman
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
D. Summers, M. Reep
University of Mississippi, Oxford, MS
A. Moretti, A. Rowe, Z.B. Qian, V. Wu
Fermi National Accelerator Laboratory
Batavia, IL
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 2
Introduction & Review
•
•
Development of the 805 MHz Pillbox cavity
– High shunt impedance and high acceleration gradient at order
of 30 MV/m
– Allow for testing of Be windows with different thickness,
coatings and as well as other windows
– Study RF cavity operation issues under the influence of
strong magnetic fields at both the solenoid and gradient
modes
The cavity: design and status
– The 805 MHz pillbox cavity design should allow for testing of
different windows  demountable windows to cover the beam
irises (we have five Be windows, four Cu windows ...)
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 3
Cavity Design & status
Coupler
Waveguide + window
Thermo-couples
or view ports
Be (or Cu) windows
Three more view ports on the equator
Pillbox cavity
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 4
Cavity Design Parameters
• Frequency: 805 MHz
• Shunt Impedance:
– 38 M/m (Z0); 32 M/m (ZT2); {Z = V{0,T}2/P}
• Quality factor: Q0 = 18,800
• Coupling Constant:
– c = 1.0 at critical coupling; <E> = 30 MV/m requires
2 MW peak power, 350 watts average, 52 watts on
windows (Cu, 66 watts for Be) at duty factor of
1.8x10-4 (12 [FNAL=19] us pulse length and 15 Hz
repetition rate).
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 5
Manufacturing of the cavity
The cavity was fabricated at University of
Mississippi, brazed at Alpha Braze Comp.
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 6
Cavity and coupler tuning
• The cavity was ready for final tuning for the
frequency and coupling in June, 2001.
(June 24-27, 2001 in University of Mississippi)
– Before tuning: f = 803.198 MHz, c = 0.12
– After tuning: f = 805.486 MHz, Qext = 12,800
– After final brazing:
Measurements done in November 14, 2001 at LBNL
before shipping to Lab G at Fermilab:
f = 804.946 MHz, c = 1.3, Q0 = 15, 000
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 7
Cavity Tuning (continued)
Michael and Daniel
assembling the cavity
Cavity halves, coupler
and Cu windows
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 8
Cavity Tuning (Continued)
– Frequency tuning (shortening the gap)
– Coupler tuning (widening coupling slot and shortening the
transition waveguide)
Coupling slot
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 9
Coupler Tuning (continued)
•The couple slot angle
was widened from
400 to 500 (two cuts)
in order to get close
to critical coupling.
• Measurements of
the coupling agree
well with time domain
MAFIA simulations
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 10
Vacuum issues
• After final brazing at Alpha-Braze Comp.
• Vacuum leaking was detected at the coupler.
• Cu coating on the big transition waveguide was
stripped and re-coated at LBNL.
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 11
Modification to coupler
O-Ring Grove
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 12
Vacuum issues (continued)
• Old flanges were removed, and welded with new ones
• UHV cleaning, RGA scan
• Test setup at LBNL
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 13
Vacuum issues (continued)
– After many failures, an O-ring at the transition
of the coupler + guard vacuum were employed
– Cold and hot N2 gas was used to flush and bake
the system
– Before shipping to Lab G at Fermilab:
• Leak tight with base pressure (after a few days
baking): 3x10-8 Torr and a clean RGA scan
• Shipped to Fermilab under pressured N2 gas.
– Lesson learned:
DON’T MACHINE A BRAZED JOINT  IT MAY LEAK !
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 14
Diagnostics
– Three view ports on the equator of the cavity
– Three RF probes (adjusted to about -52 dB gain from the
standard waveguide port) available for E & M field
measurement
– An optic bore-scope can be used to inspect the windows
and inner surface of the cavity ( need lighting and TV/VCR
for viewing and recording)
– Maximum six thermo-couples can be attached to monitor
temperature distribution on windows
– Two compartments behind the cavity can be used to
measure window deflection by frequency shift
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 15
Diagnostics (continued)
– Equipment available
at Lab G:
x-ray, dark current
+ spectrum, forward
+ reflected RF power
and arc detector
– Lab G layout 
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 16
Be windows
• Pre-stress study of the Be windows
– Received two more Be windows (10,20 mills)
– Two new copper windows with coatings
– Halogen lamp heating measurements on two failed
Be windows
– Accelerometer measurements
– Acoustic measurements
– FEA (ANSYS code) modeling
• Magnetic and E & M forces on windows
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 17
Be windows (continued)
Acoustic Measurement
Setup for accelerometer
measurement
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 18
Current Status
• Cavity with Cu windows is now at Lab G
– Leak tight at pressure of 2x10-7 Torr (1/22/02)
– Braces are being made at Fermilab
– Leak checking is underway
– Waiting for vacuum parts to be made for final
assembling of the vacuum and waveguide system
• LBNL personnel (with test plan) will be at Lab G in
Fermilab before turning on the RF power
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 19
Test Plan
• A complete microwave measurement:
– Resonant frequency
– Coupling constant
– Q factor
– Verify calibration of the RF probes
• Final assembling of the vacuum/waveguide systems
• Bake with N2 flow at 100 oC for two days
preferably with RGA scans
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 20
Test Plan (continued)
• Continue baking at vacuum for two days
• RF conditioning slowly starting at low power
• Push for high gradient
– 2.5 MW peak power  34 MV/m accelerating
gradient and ~ 500 watts at 1.8x10-4 duty factor
• Turn on superconducting magnet in solenoid mode to
repeat above studies
• Replace two Cu windows with the ones with TiN
coatings
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 21
Test Plan (continued)
• Should we test Be windows? NO!
– EH&S issues need to be addressed first
– may contaminate the vacuum system …
• Future test plan depends on the upcoming
test results and inputs from MUCOOL
collaboration.
Feb. 7th, 2002
MUCOOL, IIT
805 MHz Pillbox Cavity
Derun Li
Center for Beam Physics
LBNL Page 22