MSWG Meeting 29-August-2014
Present:
T Bohl, F Caspers, L Gatignon, K Hanke, H Damerau, S Gilardoni, B Salvant, K Cornelis, H Day, E
Shaposhnikova, B Goddard, R Jacobsson, E Metral, W Bartmann
Agenda:
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Approval of minutes
Main presentations:
o ZS impedance measurements – Hugo Day
o SHiP: introduction and motivation – Richard Jacobsson
o SHiP: extraction and machine implications – Brennan Goddard
AOB
ZS impedance measurements – Hugo Day
Hugo explained that the ZS (electrostatic extraction septa in the SPS) have a complex impedance
spectrum with strong resonances between 500 - 700 MHZ and 1 – 1.2 GHz. Lower frequencies
depend on the external circuit.
Simulations with a more complete model give a better agreement with the measurements; certain
modes are not yet identified which needs still to be understood.
Probe measurements find resonance lines seen by the wires; the Q- factors remain to be quantified.
The effect of an RF grill was studied. It suppresses significantly resonances below 500 MHz for a
single module. The effect in case of connected devices is not known.
Discussion:
E Shaposhnikova asked whether a comparison to the measurements from 2001 was done since it
seems that more resonances appear now - an exact comparison could not be done due to lack of the
data. The higher frequency lines come from residual mismatch due to reflections. They are not
removed in order not to destroy the amplitude profile, but shall be ignored. The 2001 measurement
must have had a better matching circuit and was therefore cleaner.
Cutoff frequ of vacu pipe 600 MHz
Terminations for multiple devices with operational electronics, karel.
Elenea, high peak at 1 ghz, only without rf screen, yes. with grill and pmping port. Later.
Resonace peak more from pumpoing module, maybe not only due to pumping, study with
simulations if coincidence
Peak at 1.38 ghz can come from rf insert, doesn’t ressembel operation
Below 600 MHZ rf grill beneficial, problem at higher frequencies.
It depends on frequency range which is more concern. What is q? not evaluated. Can excite
resonsance with probe, still to do , not trivial to evaluate.
Why grill transparent at higher frequ, not grill is transp, you start hitting other resonces, you are
looking at differenct structure, half wave guide modes, in the stricter, changes.
The grill is only installed [problem for alignment, dimension using HV and meachaniacla limitation.
Karel, seems to come big contr from pumpoing port. Peak at 1 GHz. Aslo BI equipment. Like for lhc,
retract with rf shield . we have alos around MS, so intotal 20 pumping ports.
Normalised with number of pumping modules, no, absolute. Bruno
Karel, zs impedance impo for itself, sparks. Which voltages on anodes, ion traps. Not only on beam
but on ZS on itself. Must be voltages induced higher than we try to set. Wheter is possible
communication between wire and different output. Depends on frequ range. Beam drivne HV
breakdown can be. Induced voltages on different parts are interesting. Bunch by bunch timescale.
Can we model the circuit. Change pumping port to other place.
Idea is to have pumping directly at zs. Need to know for upgrade where to go. Ground anode? Or not.
Length of cables.
Simone where is beam sitting, 200 MHZ inj 1 GHZ ext, 1.4 still interesting to study.
SHiP: introduction and motivation – Richard Jacobsson
Richard introduced (SHiP – Search for Hidden Particles) as general purpose experiment for hidden
Sector exploration. After LHC run 1 the interest for the Hidden Sector was much increased and the
proposal would allow for a significant physics reach beyound past and current experiments in the
cosmologically interesting region. Also, ντ physics can be uniquely investigated.
The facility and physics case is based on the current injector complex and the SPS with the aim of
2x10e20 particles on target in 5 nominal years inheriting the CNGS beam time share.
Commissioning shall take place in 2022, nominal operation should start in 2023 with a 5-10 years
time scale.
Discussion:
F Caspers asked about the active magnetic muon shield – the absorber after the magnet would cause
multiple scattering and bring the muons back into the center again. A purely magnetic field is
foreseen, starting with a dipole and downstream another C-shaped turned magnet. Its return field is
in the centre where there is no more muon flux.
S Gilardoni was asking on the prediction of number of events per year – as many Charms as possible,
it should be about 10 times more than ATLAS and CMS, taking into account the acceptance.
SHiP: SPS configuration and beam transfer - Brennan Goddard
The required 2x10e20 p.o.t. over five years mean 4e19 p/y for SHiP and another 1e19 for the present
NA physics. The total of 5e19 to be extracted in LSS2 is twice the record from previous years and it
will be difficult to improve on this.
The 1 s slow extraction in LSS2 looks feasible but may limit the performance due to losses, septum
performance and radiation damage.
TT20 beam transfer was studied already for LAGUNA and seems straightforward. A new splitter
design is necessary to keep compatibility with the NA physics. Its design is feasible.
Beam impact on the target requires to dilute the beam via an active sweep. The sweep might be
constrained by the experiment acceptance and muon shielding.
The planning of LS2 work is critical for the overall schedule, next steps are detailed technical studies
on critical items, with more accurate costing and scheduling.
Machine studies to be performed in 2015 to test extraction limits and losses.
Discussion:
E Shaposhnikova was asking whether the energies in the beam parameter table are 395 – 405 those energie levels are for interlocking reasons to not mix up different destinations, like HiRadMat
and LHC. The measured current in dipoles defines the beam destination.
S Gilardoni was asking where the 1% losses at extraction come from – just by geometry 0.5% are lost
on the wires. The half integer extraction which features a shorter spill was much more difficult. Due
to the faster particle amplitude rise the beam had to be brought closer to the septum.
The extracted beam might have an intensity overshoot in the beginning which is usually not used by
NA experiments and intensity spikes throughout the spill of 2-3 times the average value – this can be
vetoed in the experiment. K Cornelis was commenting that the spill quality depends on the particle
distribution, for a Gaussian beam a less spiky spill quality can be reached. R Jacobsson answered that
the detector can tolerate intensity spikes, it might be more of a concern for the target.
The impact of the spill shape needs to be checked. In addition to the 50, 100 and 150 Hz lines in the
frequency spectrum it has to be considered that the slowly extracted beam will still have the 200
MHz rf structure. Even if the beam is seen debunched in the machine it is not necessarily at
extraction.
K Cornelis was asking why the beam can’t be blown up instead of being diluted – with the sweep a
uniform painting can be reached and by this a higher density in the centre be avoided.
As other possibility a chromatic focal point which moves with momentum on the target can be
thought of. The sweep has to be done in the line and not in the ring due to aperture limitations.
S Gilardoni was asking if a ‘fast’ slow extraction could be envisaged – there are no kickers available.
Losses at extraction and ZS lifetime might be significantly improved with reduced energy, 10% energy
reduction being already important for the ZS. R Jacobsson answered that 400 GeV are ideal because
below the charm rates will be quickly reduced, but a 10% lower energy could be acceptable. This
would also reduce the flux in the PS and thus radiation.
Concerning the ramp rate, the limit of the new power converters has to be considered.
Concerning the question if any similar proposal were existing – no, the SPS is the most powerful
machine in this energy range and provides the highest possible sensitivity for this experiment.
In case of a newly built splitter magnet, a spare shall be foreseen.