video-based x-ray beam position monitoring at chess€¦ · nsls-ii xbpm mini workshop, 2009...
TRANSCRIPT
NSLS-II XBPM mini workshop, 2009
Video-based X-Ray Beam Position Monitoring at CHESS Peter Revesz, Cornell University, CHESS
Ithaca, NY 14850
Basic Types of XBPMs:
Intercepting barely intercepting non-interceptingMost fluorescent photo-electron types Gas luminescence screens wires
lateral photo-diodes
NSLS-II XBPM mini workshop, 2009
T=�Iox+�,B=�’Io(1-x)+�’
For symmetrical and linear detector:
x~D/S=(T-B)/(T+B)
Photo-Electron Beam Position Monitor for CHESS wiggler beam lines
guard-5kV
collector+ 5kV
guard-5kV
collector+ 5kV
TOP
BOTTOM
Disadvantage:Measures the fringes only:Hard bend contamination.
Benefits:Fast, robust, reliable
Possible problems:Linearity?
NSLS-II XBPM mini workshop, 2009
He gas luminescence
Diamond screen
The Classics form 2002 VBPM exhibition at G-line
NSLS-II XBPM mini workshop, 2009
The Principle of VBPMCentroid position Captured image Camera setup
Xcij � ()
iGii � () � ���
��
ij � ()
Gij � () � � Xc
ij � ()
iGii � () � ���
��
ij � ()
Gij � () � �Yc
ij � ()
jGii � () � ���
��
ij � ()
Gij � () � � Yc
ij � ()
jGii � () � ���
��
ij � ()
Gij � () � �
Xc and Yc in pixels, butIt is easy to cross-calibrate tomicrons by imaging a mm-grid.
No Z-jack is needed, the whole systemcan be mounted rigidly.
It is not just a “number” but visual information as well. Important also as a diagnostic tool.
NSLS-II XBPM mini workshop, 2009
Advantages and Disadvantages of VBPMs
PRO•Non-intercepting•Visual information•Position is basically what the user has•Provides beam profile•No Z-jack needed, easy calibration•Beam size information•Beam intensity information
CON•More complicated H/W•Requires special software •Requires computer•For analog cameras: noise creates artifact beam motion
•Non-vacuum•Possible radiation degradation•“Zingers”
NSLS-II XBPM mini workshop, 2009
05101520-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
Relative centroid position (m
icrons)
Gaussian position (microns)
12-bit 8-bit
How sensitive is the centroid measurement?
8-bit digitalization: 255 Grayscale steps
1/255
Pixels: 8�m
Sub-pixel motion
Computer simulation
Gaussian shift
NSLS-II XBPM mini workshop, 2009
Bench test of centroid position sensitivity
Optical bench
LED on Z-jack
NSLS-II XBPM mini workshop, 2009
Linearity and Offset
140150160170180190200-8
-7
-6
-5
-4
-3
-2
-1
0
1
Effect of asymmetry on centroid
Centroid position (m
icrons)
Intensity (a.u.)
Ycentroid Xcentroid Ysquared centroid Xsquared centroid
The use of squared centroid helps to reduce the artifact due to offset an asymmetry
���
�) , (
) , (2
2
y x Iy x I x
xsqc Squared centroid :-Helps to reduce the effect of offset for asymmetric profiles.
NSLS-II XBPM mini workshop, 2009
VBPM program and architectureBeam linesAnalog cameras, Sensoray 4 input USB 2.0 frame capture devices
Frame Capture:•Get pixel data in ROI•Adjustments:
median, rotation, flip
•Calculate:centroids,Intensity,FWHMs,edgesstandard deviations
Display:Image, centroids, trace, profiles
Camera/Image controlFor multiple cameras:
•Enable/Disable cameras•Set ROIs•Adjustments:
Brightness, gain, offset, averaging
•Calculate:centroids, Intensity,FWHMs, edges
Display:Image, centroids, trace, profiles
Calibrate:Pixel-to-micron Intensity-to-mA
Communicate:•Accept UDP connection
from server•Accept and respond to:
SENDALLLISTALL and SENDBYNAME
•Send data
Lab-wideLAN
USB
NSLS-II XBPM mini workshop, 2009
VBPM Centroid program user interface
Allows to control 12 cameras,
Allows operator to visuallyinspect all camera imagesto optimize settings,
Transmits positions,width, intensity to signal collector program,
Saves data,Saves/retrieves systemconfiguration
NSLS-II XBPM mini workshop, 2009
CHESS-East Position monitors
VBPMP.E
D-line diamondVBPMs in tunnelAnd cave
F1-F3-lineHe VBPMsin cave
E-line HeVBPM in tunnelAlso source size measurement
NSLS-II XBPM mini workshop, 2009
F-W_VBPMA-Ver_VBPMA-Hor_VBPM
00.0050.01
0.0150.02
0.0250.03
0.0350.04
0.0450.05
020000400006000080000100000120000
tiem (seconds)
Beam
position (mm
)
FW_VBPMFHB_VBPM
0
0.05
0.1
0.15
0.2
0.25
Beam
Current (A
)
Current(A)
NSLS-II XBPM mini workshop, 2009
Diamond VBPM image at G2 beam passed multilayers and focusing mirrors
Diamond Video BPM image at G1 shutter location (passed multilayers and focusing). Spill-over is seen.
CHESS-G-line Position monitors
NSLS-II XBPM mini workshop, 2009
G-line Beam position monitors
-0.5
0
0.5
1
1.5
2
20000300004000050000
time (seconds)
Postition (mm
)
G_PEG_VBPMG2_VBPM_Vert
G-line PE vs. VBPM
-0.2
-0.1
0
0.1
0.2
0.3
20000300004000050000
time (seconds)
Position (m
m)
G_PEG_VBPM
G-line position signals
NSLS-II XBPM mini workshop, 2009
Some VBPM pitfalls
•Offset effect on position•Noise and ground-loops•“Zingers”•Intensity saturation•Contamination, humidity
•Eliminate background light, adjust offset•Short video cables, filters and video amplifiers, ultimately use digital camera
•Image filtering i.e. median, shilding•Optimize optics, shutter time.
To minimize these effects:
NSLS-II XBPM mini workshop, 2009
Conclusion and Summary
Video BPMs give multitude of important operational information about X-ray beam conditions.
The future:Application of intelligent cameras, where the frame processing is inside the camera with built-in FGPA and DSP. This will reduce noise, the network data traffic volume and make possible faster frame capture.
P. Revesz and J.A. White An X-ray beam position monitor based on the photoluminescence of helium gas Nuclear Instruments & Methods in Physics Research, Section A 540, n 2-3, 470-9 (2005)
Jeffrey A. White, Peter Revesz, Ken FinkelsteinE-line: A new crystal collimator beam line for source size measurements at CHESSNuclear Instruments and Methods in Physics Research A 582(2007) 66–69
K.D. Finkelstein, Ivan Bazarov, Jeffrey White, Peter Revesz Crystal Collimator Measurement of CESR particle-beam Source Size CP705, Synchrotron Radiation Instrumentation: Eighth International Conference edited by T. Warwick et al. American Institute of Physics proceedings, 597-600 (2004)
references