Beam position reconstruction
Pengjia Zhu
1
Analysis Overview
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BCM Calibration (finished)
BPM Calibration (finished)
Asymmetry correction for different acceptance(on going)
Hardware Overview
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Hardware overview
● Low beam current 50-100nA
● polarization of NH3 target sensitive with temperature and radicals
● Super harp installed to work in high current pulsed mode beam
● New BPM receiver with digital processing system
● Two raster systems
● Fast raster, 2mmx2mm rectangle
● Slow raster, 2cm diameter circle
● 2.5/5 T Transverse target magnet field
● Two chicane dipole magnet installed
● Limited space between second chicane magnet and target
● Antenna BPM chamber installed
Harp data analysis
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BPM: non-invasive device, relative readout, need to be calibrated before use
Harp: invasive device, read absolute beam position by using three wires, used for
calibrating BPM
Harp data analysis
Offline data:
● Index – sample index for harp, related to the number of steps the fork
moved
● Position – value of the wire position for each index
Position information implete during online data recording, use index
information to extend: pos=a*index+b
● Signal
Harp data analysis
Absolute beam position gotten from peaks of three wires:
(based on the survey information of three wires)
Harp data analysis
harp1
chicane
chicane
BPMA
harp2
BPMB
Absolute beam position at BPM location got from harp:
Based on survey information
Straight through setting needed
Harp data analysis
BPMA
harp2
BPMB
If no straight through calibration:
One BPM should be well calibrated from straight through setting
Use one calibrated BPM and one harp to calibrate another BPM
Antenna BPM Chamber
Signal
fo r
antenna :
each
2
2
r −ρ
ϕ=ϕ0 I 2 2
r +ρ −2r ρcos(θ−θ 0)
θ= π
4
3π
4
−
3π
4
−π
4
angle
for
4 antennas
I:
Beam current
r:
BPM vacuum chamber radius (17.3 mm)
ρ: radial position o f beam
θ0 : angle position o f beam
Assume:
Infinite chamber
Antenna small enough
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BPM calibration
: calibration constant
1. raw signal received in antenna VS recorded ADC data(linear region):
2. diff/sum value(temp value):
3. nonlinearity correction for diff/sum(temp value):
4. Calibrate with harp data
Position from harp, already transfered to BPM local coordinate(use survey data)
Constants
b: got from linear fit for current VS recorded ADC
data
● Some bpm calibrations did the calibration for
several currents
● Each harp scan position(one point) corresponding
to several runs with different
current(100nA,75nA,50nA)
● Assumption: those runs with different current
have same beam position
● Influence: key parameter to eliminate the
current effection, let calculated position immuse
to fluctuating current(50~100nA), especially for
the difference of b+ - b-
Pedestal – ADC value when no beam
Pedestal changes, use the most closed run's value. Pedestals calculated from
pedestal run or ADC value during beam trip
Pedestal change during experiment for left arm with 6 settings
BPM signal connected to DAQ system
Have redundancy in case a system would fail
Happex have better bit resolution and integrate longer time, more accurate
2Hz Software filter used for offline data analysis
Fixed trigger rate for Happex DAQ, could be treated as a sampling ADC
2Hz filter used for getting average beam position, to get better resolution
Position and angle at target (center beam position)
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Straight through – linear transport from BPMs to target
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With target field
Transport functions from BPMs to target
Functions fitted from BdL simulation from existed target field map
Position and angle at target (center beam position)
BPM A: 95.5cm upstream the target
BPM B: 69cm upstream the target
Only 26.5cm between them
0.2/0.27mm uncertainty at BPM A/B → 1.1mm at target
Position event by event at target
Average beam position info from BPM
position dispersed from fast raster, info from fast
raster's magnet current, recorded in ADC
position dispersed from slow raster, info from slow
raster's magnet current, recorded in ADC
Slow raster size: calibrated from carbon hole
Fast raster size: calibrated from BPM, them
transport to target
Optional slow raster information handling
– slow raster phase reconstruction
For slow raster:
● Known frequency
● Known function
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Can easily reconstruct the phase from data
Improve accuracy caused by ADC resolution
Can extract fast clock frequency from fit
Blue dot:data red curve: fitted
Uncertainty
Center position Uncertainty source :
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Pedestal ~ 0.7mm,0.7mrad
BPM resolution ~ 0.5mm,0.5mrad
Survey ~ 0.5mm
Target magnet field 0.3~0.9mrad for theta, depends on field setting
Calibration constant ~ 0.7mm,0.7mrad
● Harp/BPM Survey for calibration runs
● BPM resolution for calibration runs
Total uncertainty for center position for best situation:
1mm for pos, 1.1mrad for angle
thesis defense time in USTC:
March
May
<--------- my plan(2015)
November
lowest requirement:
● two papers
● BPM NIM paper, done for draft, publish soon
● ???
● preliminary physics result
● Earliest physics result --- asymmetry ?
Post graduate plan(short term):
Looking for a job: company/postdoc