Transcript HPRF - International Muon Ionization Cooling Experiment

Progress of High Pressure Hydrogen Gas Filled
RF Cavity Test
Katsuya Yonehara
Accelerator Physics Center, Fermilab
MTA RF workshop
Fermilab, November 15-16, 2010
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Prospect of HPRF cavity project
Short term (~ FY12)
• Demonstrate cavity under high radiation condition
• Investigate beam induced plasma in the cavity
• Figure out beam loading effect and suppress it
• Make a new cavity to test the modification technology
• Provide information to high level management group
for RF technology selection (including with safety issue)
Long term (FY13 ~)
If the HPRF cavity is chosen as the RF technology
• Make a realistic RF cavity
- Test in cryogenic condition
- Test in cooling channel fields
- Test gas regulation system
- etc…
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Time table of HPRF beam test
Time duration: 3~4 months
Nov, 2010
Dec, 2010
Jan, 2011
RF modification, assemble
& calibration
Wave Guide & Circulator
Beam line
Detector & DAQ
Timing Calibration
RF test without beam
RF beam test
805 MHz button cavity test
• MTA Radiation Shielding Assessment has been passed in
the local radiation safety committee at Fermilab
• Beam will be available in January
• Maximum rate 60 pulse/hr
November 15-16, 2010
MTA RF workshop – HPRF R&D
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MTA beam line
Final beam absorber
Beam profile:
MTA experimental hall
• Deliver 400 MeV H- beam in the MTA exp. hall
• 1012 to 1013 H-/pulse
• Tune beam intensity by collimator and triplet
• Reduce factor from full linac int. down to 1/40 or less
MTA solenoid
magnet
400 MeV
H- beam
MTA exp hall
400 MeV
H- beam
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Apparatus for beam test
• No energized device within 15 feet from HP cavity due to
hydrogen safety issue
• Beam must be stopped in the magnet due to radiation safety
Elastic scattered proton from
vacuum window (100~1000 events/pulse)
400 MeV
H- beam
New apparatus:
(Ti)
• New HPRF cavity
• Beam extension line
• Collimator+Beam absorber
• Luminescence screen+CCD
• Beam counter
• RF circulator + damper
• etc…
MTA RF workshop – HPRF R&D
Bound electrons of negative Hydrogen will be
fully stripped in the vacuum window
Ex) Thickness = 4.5 g/cm3 × 0.1 = 0.45 g/cm2
Stripping cross section ~ 10-18 cm2
0.45/47.9 × 6.0 1023 = 5.6 1021
5.6 1021 10-18 = 5600
November 15-16, 2010
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RF modification & collimator
RF coax line
HPRF cell
Collimator
RF
inlet
beam
Luminescence
screen
Gas
inlet
beam
Support rail
Current status (11/15/2010)
• New RF test cell has been delivered
• Now Cu plating
• New rail system has been delivered
• New collimator has been delivered
• Waiting for Cu electrode & Thread rod
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Waveguide & circulator
New 800 MHz Waveguide
HPRF (1540 psi, 11/13/09)
5-T solenoid magnet
HPRF cavity
400 MeV proton beam
RF Circulator + Damper
Solenoid magnet stage
Schematic picture from
Al Moretti’s hand drawing
Current status (11/15/2010)
RF modulation due to reflected RF power
• Al has a hand drawing of new wave guide system
• Order pieces to extend wave guide
• Al found the RF power damper and tested
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Beam extension line
Elastic scattered proton
from vacuum window
400 MeV
H- beam
(Ti)
Current status (11/15/2010)
• Discussed with engineer
• Final drawing will come out soon
• They expected two weeks of construction period
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Detector system
Elastic scattered proton
from vacuum window
400 MeV
H- beam
(Ti)
Current status (11/15/2010)
• Luminescence screen+ CCD have been delivered
• We will use a telescope counter for beam monitor by using
existing plastic counters
• Also use toroid coil for beam intensity monitor
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Data acquisition system
Name
Diagnostic
signal
ADC input
SiPM/PMT1
Top plate
Light trig.
Fast Osc1
SiPM/PMT2
Top plate
Spectroscopic
Fast Osc1
3
SiPM/PMT3
Topl plate
TPB/spare
4
SiPM/PMT4
Side wall
Light trig.
5
SiPM/PMT5
Side wall
Spectroscopic
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SiPM/PMT6
Side wall
TPB/spare
RF Pickup1
Electric signal
Fast Osc1
RF Pickup2
Magnetic signal
Slow Osc
RF Forward1
Upstream of
Circulator
RF Return1
Upstream of
Circulator
RF Forward2
Between
Circulator&cavity
RF Return2
Between
Circulator&cavity
Slow Osc
Toroid1
In front of cavity
Fast Osc1
Toroid2
MTA beamline
Fast Osc2
Beam counter
Telescope
Fast Osc2
RF Klystron
TTL From MCR
Fast Osc2
SiPM/PMT 1
2
RF Pickup 1
2
RF Forward 1
RF Return 1
Beam counter
System
trigger
RF Klystron trigger
November 15-16, 2010
Gate
MTA RF workshop – HPRF R&D
Slow Osc
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Fine timing calibration
HPRF
Digital Oscilloscope
Optical feedthrough
Acceptable polar angle ~ 45 mrad
SiPM/PMT
ps Laser
½” Heliax for
RF pickup signal
½” Heliax for
Optical signal
Goal: Timing calibration < 100 ps
Current status (11/15/2010)
• Ordered optical feedthrough
• Preparing SiPM and optical fiber
• ps Laser is ready
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Study delay & distortion of signal in
long cable
• Giulia Collura (Summer student) made a fast laser circuit
by using avalanche trangister
• Realize 0.6 ns timing resolution system
• Laser diode was located in parallel to R3
• Similar test is planed by using < 10 ps Laser system
Initial RF pickup signal
Final signal after 300 ft ½’’ Heliax cable
• She also investigated the distortion of signal in cable
• No big signal distortion is observed
• Phase shift due to dispersion was observed
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Physics in HPRF plasma
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Expected beam loading effect in
HPRF cavity
Simulated RF pickup signal in HPRF cavity with high
intensity proton beam passing though the cavity
Beam loading effect:
• Beam-induced ionized-electrons are
produced and shaken by RF field and
consume large amount of RF power
• Such a loading effect was estimated as a
function of beam intensity
• Recombination rate, 10-8 cm3/s are chosen
for this simulation
Scientific goals:
RF field must be recovered in few
nano seconds
• Measure RF Q reduction to test
beam loading model
• Study recombination process in
pure hydrogen gas
• Study attachment process with
electronegative dopant gas
• Study how long does heavy ions
become remain in the cavity
M. Chung et al., Proceedings of IPAC’10, WEPE067
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Electronegative dopant gas
Damaged Cu electrode
November 15-16, 2010
• SF6 and other Fluorine base gas has a large attachment
cross section
• However, SF6 is dissociated and forms F- that damages
the cavity surface
• Besides, cavity cannot operate in cryogenic temperature
lower than the boiling point of SF6 (209 K in STP)
• NH3 has 1/1000 lower attachment cross section than SF6
but it
forms in H2 + N2 mixture gas due to beam energy
deposition
RF workshop
R&D of N2 need
• QuestionMTA
is how
much– HPRF
amount
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Diagnostic of plasma dynamics
RF pickup signal in breakdown process
Equivalent resonance circuit
• Resonance circuit of normal RF
cavity consists of L and C
• Breakdown makes streamer
• It produces additional L and R
• Resonance frequency is shifted
by them
November 15-16, 2010
Spontaneous emission:
• Solid line is a least square fitting of Lorentz
function by taking into account all points
• Timing delay due to lifetime of de-excitation
• Broadened Balmer line is observed
• Stark effect well-explains resonance broadening
• Plasma density 1018~1019 electrons/cm3
MTA RF workshop – HPRF R&D
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Breakdown event in HPRF
and vacuum (box) cavities
Box cavity (0T, 0degree, 10/08/10)
RF pickup
B= 0T
Trig light
B= 3T
X-ray
Spec light (515.3 nm)
3 T, 0 degree (2010, 0820)
• X-ray disappears in strong B fields
RF pickup
• Trig light (white light) intensity is generally lower
Trig light
in stronger field
• Decay shape of RF pickup signal is modulated
by external fields
• Spectroscopic measurement sometimes failed
due to human error, not physics
X-ray
Spec light (515.3 nm)
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Decay constants in HPRF and box cavity
Breakdown τ in HPRF (various gas pressures)
Low pressure
Breakdown τ in box cavity
High pressure
09/24/2008
• Time constant in HPRF cavity is 10 times faster than the box (vacuum) cavity
(Please be aware that the RF decay function in box cavity in strong fields are not really
exponential)
• Clear RF frequency shifts are observed in the HPRF but not in the box cavity
• Both indicate the plasma density in HPRF cavity is much denser than the box cavity
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Critical issues for down selection
RF field must be recovered in few nano seconds
1. DC to 800 MHz, Hydrogen breaks down at E/P = 14. It indicates we can
use DC data as a framework to explain results.
Need higher frequency measurements to test frequency dependence
2. Electrons move with a velocity, v  E rf . Current J nev.
Power dissipation due to electrons in phase with RF and dissipate
energy through inelastic collisions = j  Erf  (neErf )Erf
Measurements with beam verify mobility numbers and verify our loss


calculation
3. Electrons recombine with positive ions and removed. If this is very fast
 cause trouble
they don’t load cavity, if slow
Beam measurement will give the recombination rate
4. Solution: use electronegative gas(es) to capture electrons and form
negative ions
Beam measurement will verify attachment rate
5. A+e →A- heavy negative ions. How long do these hang around and do
they cause the breakdown voltage of the cavity to be lowered
Beam measurement will give necessary answers
Feasibility including with hydrogen safety analysis also need to be answered
November 15-16, 2010
MTA RF workshop – HPRF R&D
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Collaborators
Alan Bross, Al Moretti, David Neuffer, Milorad Popovic, Gennady Romanov,
Vladimir Shiltsev, Alvin Tollestrup, Katsuya Yonehara (Fermilab)
Chuck Ankenbrandt, Gene Flanagan, Rolland Johnson, Grigory Kazakevitch,
James Maloney, Masa Notani (Muons, Inc)
Ben Freemire, Pierrick Hanlet, Daniel Kaplan, Yagmur Torun (IIT)
Moses Chung (Handong Global Univ.)
Giulia Collura (Politecnico di Torino)
Andreas Jansson (European Spallation Source)
Leo Jenner (Univ. College London)
Ajit Kurup (Imperial College)
Giovanni Pauletta (Univ. of Udine)
November 15-16, 2010
MTA RF workshop – HPRF R&D
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