Considerations on ODR beam-size monitoring for gamma = 1000 beams Page: 4 of 5
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ODR EXPERIMENTAL RESULTS
An opportunity to test the feasibility of the near-field
monitor at 900 MeV was identified in discussions with
staff at FLASH in Germany and Frascati in Italy. In this
case a complementary test was proposed to the ongoing
far-field ODR experiments of the Frascati team . The
converter consisted of an aluminized Si nitride wafer with
a slit chemically etched of 1-mm height. A test beam with
6 bunches and 1 nC per bunch operating at 5 Hz was
generated in the FLASH facility and transported to the
test station. Ultimately 10 images were summed to
improve statistics for the ODR signal obtained using an
800 x 80 nm band pass filter. The beam was positioned on
the top edge of the slit, and then the actuator was stepped
in 100-pm steps. An example of the image obtained with a
400-pm beam offset from the top edge is shown in Fig. 6.
The dark current from the photoinjector has been
subtracted from the total beam intensity. The dim ODR
image is seen near both top and bottom edges. The ROI
sampled only the top image and gave an ODR profile
width of about o(=360 gm as shown in Fig. 7, as
compared to the original OTR-measured beam size of 205
With the first experimental results in the near-field at
y=1800, we performed post-experiment modeling for
these specific parameters. The results of the numerical
evaluations are shown in Fig. 8. The top plot shows the
total intensity profile for different impact parameters
starting at 500 gm. The ODR x profile was calculated to
range from 286 gm to 400 gm for impact parameters from
500 to 1200 gm for total intensity, in reasonable
agreement with the experiment. The lower plot shows the
calculated beam-size sensitivity for the 200 gm + 20%
horizontal size. The ODR x-profile clearly tracks the
changes with its roughly 30-pm change in sigma per step
or 10-12% relative changes. In these cases, the dots on
the curves are the ODR results and the solid lines are the
Gaussian fits to those points. It is clear the Gaussian
assumption is appropriate.
340 X position (ch)
150 200 250 300 350
Figure 6: Initial near-field ODR image of the 900-MeV
electron beam at FLASH passing through 1-mm tall slit at
a location 400 gm below the top edge. This is a 10-image
sum with the dark current subtracted from the 16-bit
digitized CCD camera data.
180 200 220 240 260 280 300 320 340
X position (ch)
Figure 7: Horizontal protnie projection of the ODR top
image from Fig. 6. The observed rms width is about 360
gm compared to the OTR image's profile size of 205 pm.
The calibration factor is 36.4 gm per channel (ch).
0.6 = e~oc
-1000 0 1CDC 2000
-500 0 500 1000
LX ( m)
Legend: c symbol: simulated, line: Gaussian fitted.
Figure 8: Calculated near-field ODR horizontal profiles
for the FLASH case with the variation of impact
parameter (top) and the 20% variation of initial beam size
around 200 gm (lower).
In summary, we have extended our investigations on
the feasibility of near-field ODR monitoring of particle
beams as a noninterceptive method. Our modeling was
extended to the challenging y=1000 regime to address the
potential applications at Fermilab for electrons and
possibly protons. With the recent successful proof-of-
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Lumpkin, A.H.; /Fermilab; Yao, C.-Y.; /Argonne; Chiadroni, E.; Castellano, M. et al. Considerations on ODR beam-size monitoring for gamma = 1000 beams, article, April 1, 2008; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc900483/m1/4/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.