First Beam to FACET Page: 3 of 3
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Sector 20 were also implemented using EPICS. The
damping rings and most linac systems needed for FACET,
however, continue to use the earlier SCP-based
architecture developed for the SLC.
Starting in June, 2011, the vacuum system was pumped
down, the new beam transport system magnets were
energized, and the various diagnostic instruments were
tested and calibrated to the extent practical. When the
electron beam was turned on and accelerated, it was first
directed into the existing "scavenger" line, which was
used in the past to transport electrons to the positron
production target. This transport line can be used as a
momentum-defining spectrometer to assist in setting up
and steering the beam down the linac. When the beam had
been established with a charge of 2 x 1010 electrons/pulse
and energy of nearly 20 GeV, it was directed into the
FACET area and steered through the compressor chicane.
On June 23, the beam reached the dump.
Since then, various technical problems have been
identified and corrected, instruments have been tested and
calibrated with the beam, and beam-based alignment
studies have been carried out for all the quadrupole
magnets. Figure 7 illustrates a typical beam cross section
observed on the OTR profile monitor near the IP. Also
shown are horizontal and vertical projections of the
observed spot and Gaussian fits to the projections.OTRSLI20:3206
1300
1200
hog
,101300
arbitrary choice and can be adjusted relatively easily as
needed. The repetition rate has been limited to 10 Hz to
limit the production of residual radioactivity, but this rate
can be raised to 30 Hz at any time. The next challenge in
the commissioning program will be to further reduce the
longitudinal and transverse dimensions of the beam at the
interaction point.
Table 1: Summary of FACET Beam Parameters
Design Achieved
Energy 20-23 GeV 19.65 GeV
Particle type Electrons (and Electrons
later positrons)
Charge per 2 x 1010 (3 nC) 2 x 1010 (3 nC)
pulse e or e per pulse e per pulse
Repetition rate 30 Hz 10 Hz
Spot size 20 x 10 pm 60 x 40 pm
Bunch length 15 - 40 pm 40 pmSUMMARY
On June 23, 2011, an electron beam was successfully
-120G
transported through the new FACET system to a dump in
Sector 20 in the linac tunnel. This was achieved while the
last third of the linac, operating from the same control
1000 room, but with a separate injector system, was providing
an electron beam to the Linac Coherent Light Source
1000 2000 3000 -8OO -600 -400 (LCLS), demonstrating that concurrent operation of the
two facilities is practical. With the initial checkout of the
2000 - new transport line essentially complete, attention is now
turning toward compressing the electron bunches
1500 longitudinally and focusing them transversely to support a
variety of accelerator science experiments.soo
0
-800 -600
x (umn)Figure 5: Beam profile measured with
near the IP.an OTR screen
Table 1 summarizes beam parameters observed
recently. The beam energy achieved is a somewhatACKNOWLEDGMENTS
We wish to acknowledge and thank the engineering and
technical support personnel at the SLAC National
Accelerator Laboratory for their efforts in constructing
the facility described here and for preparing the
equipment for first operation. We would also like to
thank the staff of the Accelerator Operations and Safety
Division for their efforts in support of the commissioning
and first operation of this facility.s
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Erickson, R.; Clarke, C.; Colocho, W.; Decker, F. -J.; Hogan, M.; Kalsi, S. et al. First Beam to FACET, article, December 13, 2011; United States. (https://digital.library.unt.edu/ark:/67531/metadc840822/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.