Abstracts Brochure - CERN

TUPCH171
TUPCH172
TUPCH173
27-Jun-06 16:00 - 18:00 TUPCH — Poster Session
Calculation, Measurement and Analysis of Vacuum Pressure Data and Related Bremsstrahlung
Levels on Straight Sections of the ESRF
One of the major personal safety issues
R. Kersevan, P. Berkvens (ESRF)
of modern synchrotron radiation (SR) light
sources is the minimization of the exposure
of beamline staff and users to high-energy bremsstrahlung (BS) radiation generated in the straight sections of the
storage ring and entering the optics hutches of the beamlines. This is particularly important when insertion device
(ID) narrow-gap chambers are installed, nowadays characterized by very low specific conductances. At the ESRF,
this has led to the implementation of systematic measurements of BS levels and vacuum conditioning curves, in
conjunction with the installation of non-evaporable getter (NEG)-coated ID chambers. A dedicated beamline is used
to do on-axis measurements of the BS intensity during the initial conditioning period of newly installed NEG-coated
ID chambers. This paper will show results of measurements and calculations performed throughout the years, and
comment on the suitability from the radiation safety point of view of the installation of NEG-coated chambers in large
numbers around the ring.
Status Report on the Performance of NEG-coated Chambers at the ESRF
At the ESRF, the use of NEG-coated nar-
R. Kersevan, M. Hahn, i. Parat (ESRF)
row gap chambers for insertion device (ID)
straight sections has become the standard
choice for in-air IDs. A total of 25 chambers have been installed at different times in the ring, with 19 being installed
as of Jan 2006, for a total length of 82 m. The vacuum performance has been excellent for all but one of them.
It has been found that the now standard "10mm" design, i.e. a 5 m-long, 57x8 mm2 ellipse, is compatible with the
multi-bunch operation at 200 mA. Runs at higher currents, performed in preparation of current upgrades, have gone
smoothly. During 2005, a 3.5 m-long prototype of a chamber suited for installation in the achromat part of the lattice
has been installed in the ring. It was characterized by a much smaller cross-section (30x20 mm2, HxV) as compared
to a standard chamber (74x33 mm2, HxV), and by the absence of three lumped pumps, replaced by the NEG-coating.
The data taken during a full run have been extremely encouraging, to the point of considering the adoption of a
similar design for a future upgrade of the storage ring lattice and vacuum system. A status report will be given,
alongside with a discussion of future plans.
Understanding of Ion Induced Desorption Using the ERDA Technique
In heavy ion synchrotrons like SIS18 at GSI
M. Bender, H. Kollmus (GSI) W.A. Assmann (LMU)
high energetic ions can impact on the beam
pipe and release gas molecules. This so
called "ion induced desorption" deteriorates the accelerator vacuum and as a consequence the beam life time and
luminosity. To minimize the pressure increase it is necessary to understand the physics of ion induced desorption.
The elastic recoil ion detection analysis (ERDA) can give a time resolved element specific depth profile of a probe
under ion bombardment. A UHV-ERDA setup has been installed at GSI to investigate correlations between desorption
and material properties as well as its dose dependant evolution. Recent experiments have shown the influence of
the surface state of a sample such as the oxide layer on steel as well as the importance of a high-purity bulk such as
in silicon and OFHC copper. We will present the results of gold coated copper in comparison to stainless steel as
applicable materials for accelerators.
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