Download Summary_BPPC_16_05_12

Summary of the ELENA BPPC Meeting
held on 12th May 2016
Present: W. Bartmann, P. Belochitskii (chair), L. Bojtar, G. Bregliozzi, C. Carli,
J. Ferreira Somoza, M. Fraser, E. Harrouch, J. Jentzsch, A. Jones, L. Joergensen,
V. Gomes Namora, R. Ostojic, S. Pasinelli, G. Riddone, L. Sermeus
Overview Vacuum Acceptance Test Kicker ELENA (G. Bregliozzi)
Three vacuum tests with the magnet installed in the tank have been made so far,
one without NEG coated plates and two more after installation of the NEG coated plates
(with different bake-out and NEG activation cycles). Higher pressures than expected
have been observed in all tests; the lowest pressure measured so far of 3.6x10-10 mbar at
the end of the last test is about a factor 90 higher than the nominal pressure for the ring.
Accumulation tests (evolution of partial pressure after switching off the ion
pumps) indicate (i) presence of air (with Ar present indicating a virtual leak with a rate
1.5x10-7 mbar l/s as a leak is excluded after leak detection) and (ii) that the NEGs are
not correctly activated. The fact that the material used to construct the tank had not
been vacuum fired contributes to the higher than expected pressures. However, the
main reason is believed to be high outgassing from the ferrites and/or, possibly, an
internal leak.
Proposal for injection kicker tank and discussion on next steps: after replacing
the ion pump connected at the bottom of the tank by a large pumping speed (2000 l/s)
NEG pump and after another bake-out at 300oC, one expects to reach a pressure of about
5x10-11 mbar. Provided this pressure, about a factor 10 higher than nominal, is achieved
leading to a localized bump over a length of less than 1 m, with pressure close to
nominal for the rest of the ring, this would allow ELENA commissioning. Another test
with the proposed higher pumping speed before installation in the ring is discussed to
verify that the proposed cure is indeed effective and to gain from one additional bakeout. The decision should be taken within a few days and depends as well from other
priorities of vacuum tests.
Other possible measures to improve the pressure and/or the understanding of
the observations: even though three more very similar (spare) magnets exist, other
tests, e.g. to measure ferrite outgassing rates, are believed to be unrealistic with the
available resources.
Situation for other components: the limit pressures measured after bake-out and
NEG activation for various components tested on a test stand are listed on the last slide.
The acceptance tests are performed with 10 l/s N2 pumping speed. In all cases, the
lowest pressure measured was significantly higher than nominal (by up to a factor 50
for the scraper tank). As the pumping speed in the ring will be higher than during the
acceptance tests, the pressures to be expected after installation in the ring will be
significantly lower, but precise extrapolations are difficult; however, a good
understanding of the pressures to be expected is important to make sure that they are
low enough and limit the impact on the beam.
Impact of the Stray Field from the Experiments on Beam Steering of the Lines and
Update on the latest Version of the Lines (J. Jentzsch)
Impact of Stray Fields from Experiments and Beam Steering
Steering along the transfer lines in presence of magnetic fields due to the
solenoids operated by the experiments from the ELENA extraction to the ALPHA
experiment has been studied neglecting other weaker perturbations as the earth
magnetic field, misalignments and offsets of the position measurements. The stray fields
have been estimated using a simplified model (current loop) with parameters given by
the experiments. 21 steerers per plane and 18 profile monitors to determine the
horizontal and vertical beam position are available. The strength of the steerers has
been determined running MICADO. An acceptable correction assuming that the field
generated by all experiments (no shielding) is seen by the beam has been obtained using
14 correctors with maximum strength of 25 mrad1.
Another measurement of magnetic fields generated by the experiments is
proposed and endorsed to verify the validity of the model. In particular, measurements
with only one solenoid switched on at a time are of interest.
The effect of switching on and off individual solenoids has been studied as well
under the assumption that magnetic shielding will be put in place. The main conclusion
is that magnetic fields would have to be attenuated by a factor of at least 800 to make
switching of magnets of the experiments a negligible perturbation for operation.
Update on the Design and Geometry of the Transfer Lines
The latest approved (on 30th March 2016) version of the reference document is
EDMS 1388169 v2.02.
Work on an update (version 2.03) to resolve several issues already mentioned in
version 2.02 and additional ones is on-going. Changes w.r.t. version 2.02:
 AEGIS (in present location, which is project baseline): A change of the focal point
can be implemented with an appropriate setting of the quadrupoles; no change of
the hardware to be installed foreseen.
 ATRAP 1 and 2 lines: bending radius of vertical static deflectors had to be reduced
to gain space in the vertical lines. Optics has to be rematched. The layout of the
vertical lines will change. Small changes of the hardware (positions of ZQNAs and
profile monitors not affected) of the LNE lines nearby possible.
 GBAR: minor change possible due to a request to increase the length of the LNE50
line. The experiment requests that no additional quadrupoles should be installed
in this extension (space kept for later installation of a trap by GBAR). Thus,
certainly no change for most of the line until LNE50.BSGWA5060.
Possible changes of the layout due to options discussed, but not within baseline (ECR
under approval or to be written to clarify feasibility and cost):
 Beam stopper to be used as EISb protecting ALPHA.
 Re-installation of AEGIS in a new location adjacent to GBAR: in this case, the
LNE02 line would not be needed, but an additional line LNE51 (with a fast and
slow deflector to be added in the LNE50 line just after the magnetic pick-up
LNE.APULB.5030).
 Fast valves for the experiments.
Minutes by C. Carli
1
Investigations on maximum available strength after the meeting: with ±3kV converters for the
steerers, the maximum available strength is almost 30 mrad. Maximum voltage of converters
being checked now.