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MKP Strategy Meeting: 31/03/2015
2nd MKP Strategy Meeting
31/03/2015
Indico Site: https://indico.cern.ch/event/381415/
Present: Antonios Adraktas, Mario Beck, Hugo Day, Francesco Maria Velotti, Benoit Salvant, Luc
Sermeus, Carlo Zannini, Mike Barnes
Apologies: Laurent Ducimetière, Jan Uythoven, Lorena Vega Cid, Wim Weterings
Francesco: The nominal position of the MKP-L is such that the central position of the circulating beam
is 70 mm from the HV busbar. Allowing for a 5 mm misalignment gives 65 mm clearance from the
circulating beam to the HV busbar.
 A 5 sigma envelope for a 100% MKP system kick (e.g. due to a timing error) on FTP circulating
beam is 67.8 mm (just touches ground busbar of MKP-L) – see slide 4.
o Thus, if the MKP-L is turned around and moved horizontally 32.9 mm closer to the beam,
this same fault condition would result in the miskicked circulating beam passing through
the MKP-L beryllium ground conductor – see slide 6.
 In the case of an erratic on MKPA (S type), a significant portion of the miskicked
circulating beam would still pass through the beryllium ground conductor – see
slide 7.
• TIDP aperture at MKP location => 32.1 mm
• TIDVG aperture at MKP location => 58.3 mm
 With the MKP-L turned around and moved horizontally 32.9 mm closer to the beam, a 100% MKP
system kick (e.g. due to a timing error) on 26 GeV LHC circulating beam would result in the
miskicked beam touching the ground busbar of MKP-L – see slide 9.
o In the case of an erratic on MKPA (S type), theoretically, no LHC beams should touch the
MKP aperture. The beam is lost between the sextant 1 and 2 - mainly on to the TPST-MST
in LSS2 – see slides 10 and 11.
Luc stated that a relatively high rate of erratic’s occur each year (60 in the 3 months since
1/01/2015, mainly due to the presence of several old tubes which have suffered from bad gas
pressure adjustment in the past. This can be improved by replacing tubes more often).
Jan/Laurent/Luc/Etienne to discuss the strategy that would be adopted in the case of an erratic (e.g.
turn-on all main switches).
Carlo
The MKP-S, as per the MKP-L, shows an important reduction in longitudinal impedance as the
horizontal beam position approaches the ground busbar. Thus, when the MKP-S is measured in the
lab we should see this behaviour.
Mario
Impedance simulations were presented showing the predicted influence of serigraphy upon
longitudinal impedance (slide 4 shows definitions of variables used):
 finger length – an increased length of serigraphy, spaced over the width of the ferrite, reduces the
frequency of the first impedance peak and narrows the resonance (slide 5);
 finger thickness – the width of the serigraphy, in the range 0.5 mm to 5 mm, spaced over the width
of the ferrite, has little effect upon either the frequency of the first impedance peak or the width
of the resonance (slide 6);
 number of fingers – increasing the number of the serigraphy fingers (each 2 mm wide), spaced
over the width of the ferrite, decreases the frequency of the first impedance peak and narrows
the resonance (slide 7);
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MKP Strategy Meeting: 31/03/2015

placement of fingers– modelling the serigraphy over only the central 100 mm of the ferrite, rather
than over the full width, has little influence (comparison of slides 7 and 8). However confining the
serigraphy to only the central 50 mm of the ferrite , decreases the frequency of the first impedance
peak and narrows the resonance (slide 8);
 very wide serigraphy fingers – slide 9 shows the predicted impedance for:
o a single finger of width 50 mm;
o two fingers each of 25 mm width;
o three fingers each of 25 mm width
Increasing the number of wide fingers decreases the frequency of the first impedance peak
and narrows the resonance. Note: wide serigraphy is not good for field rise-time.
Mario will carry out detailed power deposition calculations for each of the above simulations (slides 5
to 9).
Carlo/Mario will analytically estimate the effect of a uniform thickness of 40 nm Titanium
(420 nOhm.m) upon the beam coupling impedance. A thickness of 40 nm corresponds to a DC
resistance of 10.5 Ohms per square. For the MKP-L (~700 mm length) this give ~52 ohms, from end to
end. Mike stated that the 40 nm thickness is expected to be the maximum compatible with 100 ns
field rise-time.
Mike (on behalf of Lorena)
Slide 5 - The 2D Ansys simulations show a very fast drop of the maximum predicted temperature at
the beginning of cool down and a very fast rise at the start of power deposition: this is mainly in the
area where the power deposition is introduced, and is probably due to thermal resistance of ferrite.
To be discussed whether a rapid local change of temperature is potentially (mechanically) damaging
to ferrite (Luc/Laurent/Mike).
Benoit suggested obtaining a more representative power deposition distribution from the CST
simulations (presently, for the ANSYS simulations, the power deposition is modelled in a narrow strip
immediately above and below the beam position). Although an improved model of the spatial
distribution is not expected to influence the steady-state temperature, it might significantly reduce
the predicted fast temperature excursions (Mario to study the spatial distribution and communicate
the results to Lorena and Mike).
Slide 6 - A significant reduction in predicted ferrite temperature can be obtained by shifting the MKP
horizontally so that LIU type beam is closer to the ground busbar. Halving the power deposition
reduces the ferrite temperature from 195°C to 130°C.
Slide 7 - The results obtained with the 2D model are very pessimistic in comparison with the ones from
the 3D model (3D model is potentially more accurate). The 3D model also shows a much reduced local
temperature excursion when the power deposition is started or stopped – probably because the HV
cell plates have a significantly lower thermal resistance than the ferrite.
Slide 8 - By increasing the modelled emissivity of the tank, from 0.14 to 0.6, thermal radiation is
increased and the predicted ferrite temperature, for LIU type beam, is significantly reduced (195°C to
140°C).
Slide 9 - Modelling a 7 hour LHC fill cycle (typical), rather than 5 hours, reduces the predicted ferrite
temperature significantly from 195°C to 165°C (for LIU type beam).
Slide 10 - The predicted ground conductor temperature, after 6.5hrs of scrubbing, is 45°C for LIU type
beam (1450 W/m). However 45°C was measured after 6.5hrs (W50, 2014) with ~800W/m. This
difference may be due to either incorrect data for modelled emissivities, the 2D model being
pessimistic, or a combination of the two.
Lorena will measure the emissivity of an MKP tank (Luc has an empty tank) and update the ANSYS
model appropriately.
There are apparently several “spares” plates and a beryllium conductor: Lorena will measure the
emissivity of these and update the ANSYS model appropriately.
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MKP Strategy Meeting: 31/03/2015
Lorena will run both 2D and 3D simulations for a 10 hour scrubbing run, with 800 W/m, to compare
the predicted ferrite and ground busbar temperatures for the 2 simulations, and also with the 45°C
measured for the ground busbar after 6.5hrs (W50, 2014).
Antonios
Antonios presented field uniformity predictions for the present MKP-L. In addition he presented the
predicted field uniformity for a theoretical version where the ground busbar is extended horizontally
into the aperture. The idea behind extending the ground busbar into the aperture was to reduce the
inductance – if the capacitance were also decreased (by appropriately modifying capacitor plates), to
keep the same impedance, the kick rise time would be reduced.
Slide 6 – the field uniformity is within ±1% of the central field over the majority of the aperture.
Slides 7 to 9 – extending the ground busbar into the aperture does, as expected, reduce the inductance
but the field becomes significantly less uniform towards the ground busbar. Thus this is not a feasible
option for the MKP-L.
Luc to check whether the MKP-L can readily be rotated in the tunnel.
Luc mentioned that the means of aligning a rotated MKP-L would need to be examined.
Miscellaneous
Once Thomas Kramer is back at CERN, and has finished the tests on the MKP-S, this magnet will be
moved into the clean room for longitudinal impedance measurements as a function of horizontal
position in the aperture (Luc/Carlo/Mario/Hugo). These measurements, which will be carried out with
the tank cover in place, will be compared with predictions.
When the MKP-S is opened, the number and position of the transition pieces will be noted (Luc).
Overall conclusions
Simulations of serigraphy and the evaluation of power deposition are ongoing. However at present
beam optics and field uniformity considerations would permit the MKP-L to be turned around and
offset ~30 mm horizontally. The predicted ~halving of beam induced power deposition needs to be
confirmed by comparing measurements and predictions for an MKP-S.
Previous meetings:
11/03/2015: https://indico.cern.ch/event/378398/
https://indico.cern.ch/event/378398/