binohep'ucl'ac'uk

1
A Prototype Energy Spectrometer for the ILC at
End Station A in SLAC
bino_at_hep.ucl.ac.uk al_at_hep.ucl.ac.uk
F. Gournaris, A. Lyapin, B. Maiheu, D. Miller,
M. Wing, UC London, UK M. Chistiakova, Yu.
Kolomensky, M. Sadre-Bazzaz, E. Petigura,
Berkeley and LBNL, USA M. Slater, M. Thomson, D.
Ward, University of Cambridge, UK H.-J.
Schreiber, M. Viti, DESY, Germany S. Kostromin,
N. Morozov, V. Duginov, JINR, Dubna, Russia M.
Hildreth, University of Notre-Dame, USA S.
Boogert, G. Boorman, Royal Holloway University of
London, UK C. Adolphsen, R. Arnold, C. Hast, D.
McCormick, Z. Szalata, M. Woods, SLAC, USA
The setup used in 2006 included 1 doublet and 2
triplets of Beam Position Monitors (BPM). These
were new cavities developed at SLAC for the ILC
linac as well as the old SLAC linac BPMs.
End Station A facility at SLAC
A testbeam experiment T-474 has been set up at
Stanford Linear Accelerator Center in the End
Station A beamline to demonstrate the performance
of the Spectrometer at a 28.5 GeV beam. The
studies focused on the stability of various
components with an aim of measuring the energy
with a precision of 10-4 over a few days.
Precision of the orbit reconstruction measured
over 1 hour
T-474 BPM setup as in 2006
Resolution of the BPMs and precision of the
position measurement were measured with the 8 BPM
setup in 2006, sub-micron resolution was measured
for most BPMs and 1µm drifts over 1 hour of
operation were observed.
Cavity BPMs designed for the ILC linac
Cavity BPM previously used in the SLACs main
linac
Resolution of individual BPMs in µm
The setup of 2007 included 4 dipole magnets
mapped and commissioned before the installation
and monitored in-situ. Additional probes provided
a measurement of the ambient magnetic field. BPMs
were used to predict the beam orbit in the middle
of the chicane which was compared to the actual
reading in BPM4. The residual was inversely
proportional to the beam energy.
Four dipole magnets were commissioned and
installed in the ESA beamline. In the process of
commissioning the field was found to be uniform
to the level of 10-4 in the region of 15 mm, the
stability of the integral of about 100 ppm,
integral field stability 60 ppm per 10C.
A high resolution Zygo interferometer system
monitors mechanical motion of BPMs at the center
of the chicane in the horizontal plane.
Future Plans
In early 2007 the T-474 collaboration was taking
data with the full Spectrometer chicane. SLAC
linac control system allowes to change the
setpoins of the energy feedback in a range of a
few hundred MeV. In order to check the
spectrometer the energy of the beam was scanned
in 50 MeV steps. This scan was clearly tracked by
the Spectrometer. In addition, Spectrometer data
was compared to the data from the "energy" BPMs
located at high dispersion points in the ESA
extraction line and a good correlation was
observed.

• Installation of a new BPM prototype in the
  center of the chicane
• Extension and further commissioning of the gain
  monitoring system
• Installation of metrology grid to improve the
  accuracy of the interferometer system
• Data taking in July 2007, planning to run in 2008