Powerpoint file

Report
Novel Beam Diagnostics on PXIE
Vic Scarpine, FNAL
2nd Annual PASI Meeting
April 3-5, 2013
Scope of PXIE*
Build an integrated systems test of the first ~ 30 MeV of Project X
– Validate front-end concept to minimize technical risk elements
– Demonstrate wideband chopper
– Low-b superconducting acceleration
Integrated systems test goals:
– 1 mA average current with 80% chopping of beam in MEBT
– Efficient acceleration with minimal emittance dilution
The scope of beam diagnostics are to identify and provide the
instrumentation systems necessary to successful commission,
characterize and operate PXIE and to validate the system test goals.
* See Steve Holmes talk later in this session
2013 PASI Meeting, Vic Scarpine
2
Project X Injector
Experiment: PXIE
HLEBT
5 mA
30 keV
RFQ
HWR-CM
MEBT
5 mA
~ 2.1 MeV
1 mA
~ 2.1 MeV
SSR1-CM
HEBT/
Dump
1 mA
~ 25 MeV
~ 40 m long
•
•
•
•
•
•
•
CW H- source delivering 5 mA at 30 keV
LEBT with beam pre-chopping
CW RFQ operating at 162.5 MHz and delivering 5 mA at 2.1 MeV
MEBT with integrated wide-band chopper and beam absorbers capable of
generating arbitrary bunch patterns at 162.5 MHz, and disposing of 4 mA
average beam current
Low beta superconducting cryomodules: 1 mA to ~25 MeV
Beam dump capable of accommodating 2 mA at 25 MeV (50 kW) for extended
periods.
Associated beam diagnostics, utilities and shielding
2013 PASI Meeting, Vic Scarpine
Page 3
PXIE Measurement Goals
• Beam current
•
– DCCTs, Toroids, HighBandwidth Resistive Wall
Current Monitors (RWCM)
•
– Warm and cold BPMs
•
• Beam position and phase
• Beam energy and energy spread
– Time-of-flight from BPM phase,
spectrometer magnet
• Beam transverse profiles
– Wire scanners, multi-wires,
laser wires
•
•
Beam transverse emittance
– Allison scanner, slit-wire
scanners, laser emittance monitor
Beam longitudinal profiles
– Wire-based bunch shape monitor,
picosecond laser wires
Beam halo
– Vibrating wire, high-gain wires,
laser wire, apertures, diamond
detectors
Beam loss monitoring
– Ion chambers, neutron detectors
Chopped beam extinction
efficiency
– High-Bandwidth RWCM, single
(few) particle detection
List of ~ 15 unique instruments needed for PXIE
2013 PASI Meeting, Vic Scarpine
4
Source-LEBT
Instrumentation
Allison Emittance Scanner
LEBT
Beam Current
– Unchopped Beam Current
• DCCT
– Chopped Beam Current
• Toroid pickup
Beam Emittance
– Water-cooled Allison Scanner
• Measurement at ion source
• Collaboration with SNS
2013 PASI Meeting, Vic Scarpine
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MEBT Instrumentation
RF
Dump
RF
Kick1
RF
Kick2
MEBT Operational Beam Measurements: (red = CW)
• Transverse position - BPMs
• Bunch Phase – BPMs  time-of-flight  beam energy
• Beam Current – DCCT, Toroids, RWCM (resistive wall current monitor)
• Extinction – RWCM with fast scope
• Transverse shape – wire scanners, laser wires
• Transverse emittance – slit/multiwire (low-res), double slit/Faraday cup (hi-res), Quad scans
• Longitudinal shape – laser wires, chopper, wire bunch shape monitor
• Absorber Profiler – OTR Imager or IR imager
2013 PASI Meeting, Vic Scarpine
6
Current HEBT concept
From Dave Johnson’s talk
R
W
C
M
Extinction Monitor
Multi-port
Diagnostics
Box
Thin foil
Dump dipole
H0
Laser
wire
/Wire
Scanner
combo
H-
H+ H0 Profile
Monitor*
A
b
s
o
r
b
e
r
BPM (4 button warm)
Quad doublet
MEBT design
With X&Y corr.
*H0 profile monitor:
neutralization monitor
emittance measurement
Multi-port diagnostics Box: (similar to
SNS MEBT 6-pack)
• Extinction monitor - tbd
• Transverse emittance - slit/detector
• wire scanner and/or laser wire (if
needed)
• halo monitor – tbd
• Longitudinal bunch shape monitor
• future “unknown” diagnostics
2013 PASI Meeting, Vic Scarpine
Sweeping dipole
Transverse Beam Position and
Longitudinal Phase - Warm BPMs
• Same as MEBT BPM design
and functionality
Beam Current Monitor
•
Two RWCM – like MEBT
Profiles in dump line to measure
energy spread
7
“Novel” Beam Diagnostic
Issues and Instruments
nov·el 1 (nvl) n.
1. A fictional prose narrative of considerable
length, typically having a plot
2. Strikingly new, unusual, or different.
Warm and Cold BPMs
MEBT/HEBT
Quadrupole Block
Requirements:
Transverse resolution
• 0.03 mm (for a single ~1 μs macro-pulse)
• 0.01 mm (CW)
Phase resolution - 0.1 deg (> 10 ms pulses)
Bunch-by-bunch measurements in MEBT chopper region
Synchronize signal detection
•
Allows for lock-in detection for laser wire
Mechanical Issues:
• Warm BPMs embedded in Quads
• Cold BPM stability in CM
Signal Processing Issues:
• Arbitrary beam pattern from MEBT chopper
• Multiple paths through MEBT chopper
HWR/SSR1
Cold BPM
Four
button
Warm
BPM
Chopped
Beam
Patterns
2013 PASI Meeting, Vic Scarpine
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MEBT Chopper Extinction
Measurement
Use upstream and downstream
Resistive Wall Current Monitors
(RWCM)
• Extinction -> ‘SBD-like’ monitor
–
–
–
–
2013 PASI Meeting, Vic Scarpine
Average over many bunches
< 1 Hz BW
Fits to bunch shape
Measure impact on adjacent bunches
10
Combined Wire Scanner Laser Wire Unit
Transverse 3-wire wire scanner plus laser
wire module
•
•
•
•
Hybrid wire scanner with laser ports
–
Modified version of SNS design
Wire scanner in pulsed beam operation only
Laser wire in either pulsed or CW beam
operation
Laser wire intended to measure transverse and
longitudinal profiles
– Will different lasers be required for
transverse versus longitudinal
measurements?
• Can wires or lasers measure profile
tails/halo?
– Transverse halo measurements with wire
suffer from cross-talk
– Halo measurement with laser suffer from
scattered light effects
Locations: MEBT, between SC cryomodules, HEBT
2013 PASI Meeting, Vic Scarpine
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Low-Power Transverse and
Longitudinal Laser Wire
Mode-locked psec laser used to measure
both transverse and longitudinal profiles
• Laser rep-rate is locked to accelerator RF
• Distribute modulated laser pulses via fibers
•
Narrow-band lock-in amp detects modulated
signal
• Measure profiles by either:
• Collection of electrons
• Use BPM as notched-beam pickup would
allow laser monitor to fit between cryomodules
Questions:
• What is the photodissociation efficiency?
• What are the noise issues?
• What are the nonlinear limits to power in the fiber?
• What signal-to-noise ratios and averaging times are
practical?
Fall back laser wire option is to use high-power laser
technique similar to SNS
R. Wilcox, LBNL
2013 PASI Meeting, Vic Scarpine
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Laser Wire Emittance
Monitor
Preliminary SNS Measurements (Y. Liu)
Horizontal
Laser Wire Emittance Monitor
– Laser acts like slit  x
• Generates H0
– H0 profiler measure H0 divergence  x’
• Background from beam neutralization
– Demonstrated at SNS
Vertical
Operate at the end HEBT
2013 PASI Meeting, Vic Scarpine
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Vibrating Wire Halo Monitor
Beampipe
Temperature change affects the tension of sensitive wire and results in the shift
of resonance frequency of the vibrating wire in permanent dipole magnets.
Beam
Sensitive wire
heated by beam
Frequency of vibrating wire (Hz)
2200
Preliminary
measurements
made at HINS
2400
2600
2800
3000
Moses Chung,
FNAL
3200
3400
3600
-4200 -4000 -3800 -3600 -3400 -3200 -3000 -2800 -2600 -2400
Position of vibrating wire (counts)
3
Frequency change (Hz)
10
Vibrating wire
102
101
100
10-1
10-2
10-3
9.0
9.5
10.0
10.5
Horizontal position (mm)
2013 PASI Meeting, Vic Scarpine
11.0
Note: Frequency
change is very sensitive
to ambient temperature,
mechanical vibration,
and magnetic field
Vibrating wire may
have much higher
dynamic range in the
halo region
14
Preliminary Estimates of
Instrument by Location
Current
Position/
Phase - BPM
Trans.
Profiles
Trans.
Emittance
Long.
Profiles
Halo
Beam
Loss+
Extinction
LEBT
2
----
----
1
----
----
----
----
MEBT
2
9
4
1
1*
1
TBD
1
HWR &
SSR1
----
12
1*
(between
CMs)
__
1*
(between
CMs)
__
TBD
__
HEBT
2
5
2*
1 + 1*
1
1
TBD
1
FE = focusing element
CM = cryomodule
2013 PASI Meeting, Vic Scarpine
* = laserwire
+ = charged/neutral
15
Technical Challenges
•
•
•
Many PXIE beam diagnostic instruments are based on previous designs
– Most are low technical risk
– Medium risk items
• MEBT chopper BPM measurements
• MEBT extinction measurement
• Wire scanner – laser wire combination unit
• Low-energy Beam Loss Monitoring
– Higher risk items
• Low-power laser wire
• Laser transverse emittance monitor
• Vibrating wire halo measurements and transverse and longitudinal
tails/halos in general
Largest risks involve either laser-based measurements or halo
measurements
Collaboration with other groups important for diagnostics success
– PASI Postdoc, Richard D’Arcy, to help with these problems
2013 PASI Meeting, Vic Scarpine
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