| Paper | Title | Page |
|---|
| TUP51 | Electropolishing on Single and MultiI-Cell: COMSOL Modelling | 247 |
| | - M. Bruchon, B. Visentin, F. Eozenou
CEA-Saclay
| |
| | In the framework of cavity electropolishing
improvement, modelling allows evaluating some
parameters not easily accessible by experiments and
can also help us to guide them. At CEA Saclay,
COMSOL software is used to model electropolishing
of cavity in two dimensions. First, single-cell
electropolishing with different shapes (TESLA, ILC
Low Loss (LLILC), ILC Reentrant (REILC) and the
optional Half Re-entrant profile [1, 2]) is studied with
acid inflow like in our set up. Then some
improvements of both outflow and inflow of the acid
are considered. This work is extended to TESLA
nine-cell cavities in collaboration with KEK to
understand if electropolishing process is related to
some misunderstood RF performances [3, 4]. | |
| TUP69 | Optimization of Baking Parameters for Electropolished Niobium Superconducting Cavities | 304 |
| | - B. Visentin, Y. Gasser, M. Bruchon, F. Eozenou, J. P. Charrier
CEA-Saclay - D. Reschke, A. Brinkmann
DESY Hamburg
| |
| | High gradients, on bulk niobium cavities, can only be
reached after an imperative baking at low temperature
to suppress the high field Q-drop.
We demonstrate in this paper that the commonly used
standard process (under ultra high vacuum at 120 degree C for
48 hours) could be now simplified in terms of duration
(3 hours at 145 degree C) and requirement (argon atmosphere
instead of vacuum). Some efforts to more reduce
duration, down to only one hour, have been undertaken
to validate hypothesis and understand baking
phenomenon. The next improvement step with the
open-ended treatment of cavities in oxygen free
atmosphere is underway and it does not seem hard to
achieve. This new "fast baking" procedure will be very
useful in the XFEL and ILC projects where Nb cavities
mass production is required. | |
| TUP71 | Parameters Investigation for Niobium Electro-Polishing | 313 |
| | - F. Eozenou, M. Bruchon, J. Gantier
CEA-Saclay
| |
| | Electro-polishing (EP) experiments are carried out on
niobium samples at Saclay in order to highlight the
influence of parameters such as temperature and acids
concentrations (hydrofluoric and sulfuric). First results
given at the 12th SRF Workshop have been completed.
The importance of the HF/H2O ratio has been precisely
investigated and diluted mixtures have been tested during
long time experiments: removal rates, surface states,
lifetime of the bath and possible hydrogen contamination
will be reported.
In addition, some experiments have been carried out
with dissolved niobium in fresh mixtures, giving some
ideas about mechanisms involved in EP. Furthermore,
dissolved salts as well as different acids have been tried
as an alternative for hydrofluoric acid use. | |
| TUP80 | Single Cell Electro-Polishing at CEA Saclay: First Results | 343 |
| | - F. Eozenou, M. Bruchon, Y. Gasser, Y. Boudigou, B. Visentin, J. P. Charrier, S. Berry, C. Antoine
CEA-Saclay - D. Reschke
DESY Hamburg
| |
| | The goal of the Work Package 5.1 of the CARE SRF
program is to study electro-polishing (EP) of niobium and
thus isolate an ideal set of parameters for 1.3 GHz single
cell cavity treatment that should be applied to industry.
The more challenging aspect concerns acid composition's
optimisation, made of a mixture of hydrofluoric (HF) and
sulfuric (H2SO4) acids with possible additional water.
Preliminary experiments have been carried out on
samples to guide the program on single-cell cavities. In
that way, a set-up for horizontal EP has been installed in
our laboratory.
This set-up has been successfully qualified with the
standard recipe used at DESY since the first EP on
TESLA-shaped cavity has reached an excellent gradient
above 42 MV/m. The search for new parameters makes
then sense. Different configurations have been
investigated: higher temperature, lower voltage and new
acids' concentrations. Dummy cavities have been electropolished
with a new mixture:
1vol HF(40w%) - 2vol H2SO4(95w%) - 7vol H2O,
(1-2-7) with high water content.
Different cavities have also been electro-polished and
results including surface aspect, RF measurements and
impurities forming will be related. | |
| WEP70 | Nb coating of copper cavities by UHV cathodic arc | 675 |
| | - L. Catani, A. Cianchi, D. DiGiovenale, J. Lorkiewicz, S. Tazzari
INFN Roma - R. Nietubyc, M. J. Sadowski
The Andrzej Soltan Institute for Nuclear Studies - M. Bruchon, B. Visentin
CEA-Saclay - B. Ruggiero, R. Russo
Istituto di Cibernetica del CNR and INFN-Na
| |
| | Niobium thin film coated copper RF cavities are an
interesting alternative to niobium bulk cavities mainly
because copper is cheaper, has higher thermal
conductivity and better mechanical workability and
stability than niobium. Unfortunately the observed
degradation of the sputter-coated cavities quality factor
with increasing accelerating voltage prevents their use
in future accelerators specified to work at field values
higher than 15MV/m. To try and overcome this
limitation we have developed an alternative coating
technique based on a cathodic arc system working
under UHV conditions. Main advantages of this
technique compared to standard sputtering are the
ionized state of the evaporated material, absence of
gases to sustain the discharge, high energy of atoms
reaching the substrate surface and possibility to have
high deposition rates. Recent results on the
characterization of niobium film samples produced by
UHV cathodic arc are presented, showing that the
technique can produce high quality films under
different angle of deposition. The system to
demonstrate the deposition of a single cell cavity have
been commissioned and first tests will be presented and
discussed. | |