Updated:
16.01.2013
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The rebuilt µE4 beam line
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The rebuilt µE4 beam is a large acceptance beam line for muons
with low momentum (< 40 MeV/c). It was specially designed to
serve the needs of the low-energy muon (LEM) beam facility at PSI, i.e.
maximum µ+ intensity at 28 MeV/c and a
beam spot fitting to the size of the muon moderator target of the
LEM apparatus. In order to keep costs and time for reconstruction low
the new beam line had to follow the existing µE4 channel until
the end of the main shielding of the proton beam.
The large acceptance is achieved by using two normal conducting
solenoids (WSX61 and WSX62)
as the first focusing elements feeding the 40o degree bending magnet
ASR61. This magnet has
a pole face rotation of 33o degree at the entrance and exit in order
to provide momentum dispersion in the center of the second bending magnet
ASR62 where the momentum
bite can be varied by a horizontal slit system (FS62). ASR62 and
ASR63 have rectangular
pole shoes and bend by 34o degree each. The two vertical and horizontal
slit systems FS61 and FS63 can be used to reduce the intensity.
Focusing is done with four triplets of large aperture
QSM (QSM601 - QSM612)
quadrupole magnets. A new static
separator (SEP61)
with crossed electric and magnetic field (E x B) strongly reduces the
electron/positron contamination. The maximum fields will be 22.2 kV/cm (400 kV, 18 cm
gap between the electrode plates) and 50 mT.
Some older and partly out-dated documentation can be found
here.
Besides the reconstruction of the µE4 channel the experimental area has been
rebuilt to provide sufficient space for the LEM apparatus and other experiments.
The beamline has been commissioned during 2005. The LEM experiment started successfully
with an engineering run between october and december 2005 to test and put into operation
the completely new setup with new data acquisition hard- and software
and a new slow control system.
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Beam transport calculations
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We compared the beam properties of the new µE4 beam line
with the existing piE3 beam line
( achromatic mode)
where the LEM experiments are
presently performed. The program Turtle was used for the calculations
and the results (for 60mm target E )are summarized
here.
Two modes of operation are possible for the new beam: when using the full
acceptance the momentum resolution is limited to 5%. With a reduced
acceptance the momentum resolution can be improved to 1.5%. The corresponding
Transport beam envelopes are shown here.
An estimate of the vertical beam shift due to horizontal WSX misalignment
is shown here.
In order to correct a possible vertical beam shift
the first QSM triplett can be operated asymmetrically. This introduces an
efficient magnetic dipole component that allows vertical steering of the beam.
The measured beam transport properties and a comparison with the calculations
can be found in
T. Prokscha, E. Morenzoni, K. Deiters, F. Foroughi, D. George, R. Kobler, A. Suter, V. Vrankovic,
The new µE4 beam at PSI: a hybrid-type large accpetance channel for the generation of a high intensity
surface-muon beam, Nucl. Instr. Meth. A (2008), doi:10.1016/j.nima.2008.07.081.
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Beamline elements: calibration, power supplies, device.lis, settings
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Calibration of magnets and slits
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List of power supplies
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The file device.lis for
Urs Rohrer's Setpoint program for beamline control.
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Beamline settings for 28 MeV/s, separator off (e+/µ+ = 4):
- WSX on, max. intensity with best focussing on LEM
moderator target (3 x 3 cm2, 0.5m downstream of QSM612), momentum width 9.5%(FWHM).
µ+ intensities (for 40mm target E): 228 M/mAs (per mA of proton current) integral, and 98 M/mAs on moderator.
At 300 kV separator voltage the rates reduce to 210 M/mAs and 86 M/mAs, respectively.
For 60mm target E length, the rate on moderator is about 50% higher.
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WSX off, low intensity with good
momentum resolution of 1.5% (FWHM).
µ+ intensities (for 40mm target E): 0.46 M/mAs integral, and 0.42 M/mAs on moderator.
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