L4-BCC-025-20110407
7 April 2011
Linac4 Beam Coordination Committee - Meeting 25 held on 7 April 2011
Present:
Oliver Aberle; Giulia Bellodi; Christian Carli; Asen Christov; Jean-Pierre Corso;
Alessandro Dallocchio; Herta Richter; Jean-Baptiste Lallement; Oyvind Dahle Lauten;
Alessandra Lombardi; Cesare Maglioni; Bettina Mikulec; Suitbert Ramberger; Federico
Regis; Federico Roncarolo; Ivo Daniel Vicente Leitao; Vasilis Vlachoudis; Joachim
Vollaire; Maurizio Vretenar; Sylvain Weisz; Wim Weterings.
1. Minutes of the last meetings
The minutes of the BCC-24 have been approved.
2. Follow-up of action items
No update.
3. BIDs general schedule and costs (C. Maglioni)
The following table summarizes the deliverable status and costs.
Deliverable
Test bench dump Alu
(3&12 MeV)
Commissioning dump
(50&100 MeV)
Main Dump
(160 MeV)
Shielding
(160 MeV)
TL Stoppers
(160 MeV)
LBE/LBS dumps
(160 MeV)
LBS Slit
(160 MeV)
Shielding TL
(160 MeV)
Status
2 Units installed
Available June-11
1 U installed, 1Spare
Design on going
Available Feb-12
1 U installed, 1Spare
Preliminary design
Available Sept-13
Cost (M&M, Design, FSU)
1 U installed
35 kCH-F
2 U installed
Analysis of requirements started
Available Feb-13
2 U installed
Preliminary design on going
Available Sept-13
1 U installed
Feasability study started
Available Sept-13 (if decision
taken now)
1 Unit
37 kCH-F
137 kCH-F
195 kCH-F
221 kCH-F
143 kCH-F
174 kCH-F
60 kCH-F
Concerning the transfer-line beam stopper, the existing tank will be re-used.
Simulations for the material and cooling are ongoing.
3.1.
Discussion
C. Maglioni asks how many, and where do we need beam stoppers.
C. Carli answers that both old beam stoppers should be kept in the L2 transfer line for
the ions. One new beam stopper is required in the new part of the transfer-line.
L4-BCC-025-20110407
7 April 2011
4. LBE & LBS line dumps - 160 MeV : Conceptual design and preliminary
analyses (F. Regis)
For the design of the LBE and LBS lines dumps, the following beam parameters have
been selected as worst case design scenarios:
 LBS (accident): 8 mA, 400 µs, 1.1 Hz, mean power 567 W (2 shots before
interlock)
 LBE (commiss): 40 mA, 400 µs, 1.1 Hz, mean power 2834 W (12 h/day ~ 2
months)
.The LBS line position should be at least 200 mm from the SEM grid, in order to
reduce problems of measurement perturbation and irradiation of the measurement
system. At this aim, the absorbing core of the dump is such as to reduce the
backscattering to the SEM grid. The LBE dump main design constraints are due to the
average beam power of 2834 W which leads to more thermo-structural constraints
than for the LBS dump. As for the LBS dump particle backscattering has to be
reduced.
It was therefore decided to go for a common design, merging the aforementioned
constraints of the two dumps. RP studies were done on the LBS dump by J. Vollaire.
More calculations are anyway needed to estimate the concrete thickness to go below
2.5 µSv/h, as well as to define the activation of the cooling water.
The design is based on a cylindrical R4550 graphite absorbing core housed in a
Cu10100 OFE copper jacket. Fluka and Ansys simulations were done for the worst
operation case (LBE commissioning scenario). Different cooling circuit were studied.
According to an optimized thermal steady state analysis, eight 18 mm diameter pipes,
placed at 70 mm off centre, could limit the graphite core temperature to 450°C, the
copper temperature to 36°C and cooling pipe to 27°C. Structural analysis showed that
the stress level was within the failure limits for both graphite and copper.
The next steps will be:



Introduction of the thermal conductance model for the graphite-to-copper
interface
Detailed structural analysis (quasi-static, dynamic, fatigue,..)
Detailed RP study of the cooling water activation
An open discussion is open with RP about possible dump length reduction.
4.1.
Discussion
C. Carli confirmed that the bending magnet angle of the LBS line is now fixed to 35°,
which means that the dump will be placed in the wall and not in the ceiling.
B. Mikulec says, about the installation planning of the LBS line, that we should take
into account that a drilling machine has to go in.
Concerning LBS, LBE lines and PSBooster operation, C. Carli sent, after the BCC,
the minutes of the meeting on Discussion on Beam Stoppers in the Linac4 to PSB
transfer line and PSB access with Linac4 held on 11th January 2011. These minutes
are attached in Appendix 1.
5. Linac4 commissioning dump at 50 and 100 MeV (O. Lauten)
It was decide to use a common design for the 3-12 and 50-100 MeV dumps. The
design is based on a copper base (C10100 OFE or C15000 Cu-Zr) and a graphite plate
L4-BCC-025-20110407
7 April 2011
tilted by 5.5°. Fluka and Ansys simulation were done in the transient state assuming a
perfect contact between copper and graphite. The temperature of the graphite could
reach locally 500°C at 100 MeV. The cooling system was designed for absorbing
1600 W. In order to keep the cooling pipe temperature below 100°C and limit the
cooling water temperature increase to 5°C, the dump has to be cooled by 4 pipes with
a 9 mm diameter. The assembly between copper and graphite still need to be defined
(track system, clamp, adhesive bonding, brazing). The use of this dump can be also
studied at 3 and 12 MeV.
5.1.
Discussion
M. Vretenar asks if the water cooling is needed for all energies.
O. Lauten says the cooling is required for 12, 50 and 100 MeV.
A. Dallocchio asks if we can afford having cooling at 3 MeV.
C. Maglioni answers that this is still to be investigated.
6. New main dump - 160 MeV: Cooling concept analyses (I. Leitao)
The old design was very fragile being based on a stack of 150, 300 µm metallic foils.
For the new design two geometries were studied: Cylindrical core (water cooling) and
circular plates core (air cooling). The dump has been design for the following beam
parameters: 160 MeV, 400 µs pulse, 1.1 Hz, 40 mA corresponding to a mean power
of 2834 W. The 70% beam size at the dump entrance in the worst case is 8.9 (h) *2.2
(v) mm². Different materials were simulated. After one shot, for both designs, Al and
Cu are far above their critical temperature limits. After 2 pulses, a graphite core could
reach more than 700°C making it use impossible if not in vacuum.
The following table summarizes the advantage/disadvantages for both designs.
Cylindrical Core
Circular Plates Core
High efficient cooling → Greater distance between
the center of the core and cooling pipes → Less
activation of water
Low efficient cooling → Plates must be thin →
Fragile structural design
Possible to use graphite (in vacuum)
Impossible to use graphite (burn at 500°C)
Water supply already built
Need to build air supply
Water consumption: ~10 L/min ~5260 Tons/Year
Air is for free
Easier to design → Less project time
Harder to design → More project time
6.1.
Discussion
M. Vretenar says that the main advantage of the cylindrical core is the possible use of
graphite.
S. Weisz says that the design of the LBE/LBS dumps are really similar to the main
dump design, we could therefore have a common design.
C. Maglioni answers that the environment is really different, but we could investigate
the option to have the same design (especially since the LBS dump is not in the
ceiling anymore) provided that the shielding are different.
M. Vretenar asks if the cooling circuit of the main dump can be connected to the main
linac4 water circuit (RFQ water circuit is independent).
L4-BCC-025-20110407
7 April 2011
J. Vollaire says that we should consider the potential activation of the water in the
dump cooling circuit, and investigate what does it implies to spread this water in all
accelerating structures.
Open Action: Can the cooling circuit of the main dump can be connected to the main
linac4 water circuit (J. Vollaire, S. Moccia).
7. Potential beam pipe damages in Linac4 (C. Maglioni)
The beam loss effect was studied in different cases:
1) Failure of first H bending after PIMS:
 1.5mm thick SS pipe – beam with 66mrad angle
The beam pipe reaches the melting temperature after 2 pulses. 55% of the beam
power is deposited in the pipe.
 1.5mm thick SS pipe – head-on beam
Only 3 % of the beam power is lost in the pipe. The melting temperature is not
reached even after 40 pulses.
2) Failure of LTB.BHZ40 dipole in BS4
 450mm thick undulated chamber – beam with 66mrad angle.
Data are available, still need to be analyzed.
 10mm thick Al2O3 ceramic chamber – beam with 66mrad angle.
The melting temperature of the ceramic chamber is not reached after 20 pulses.
The head-on case is safer than the 66mrad one: in the latter case beam deposits more
power (55% of the beam) and with higher energy density peak (4560J/cm^3/pulse).
The ceramic chamber case is safer than the SS one: in the case of Al2O3, the total
deposited power is higher (thicker) but with lower energy density peak (2320
J/cm^3/pulse). The sole thermal analysis is not exhaustive to state on the integrity of
the beam pipe in all cases.
7.1.
Discussion
A. Lombardi says that this study should be an input for the interlocks and asks, in case
of a dipole failure, where the beam will be lost.
G. Bellodi answers that the beam is mainly lost in the dipole. After the meeting, she
sent a mail, attached in Appendix 2, summarizing the feedback/opinion from magnet
experts.
Open Action: M. Vretenar asks what could be typically the range for angles between
beam and beam pipes in case of mis-steering (A. Lombardi).
Open Action: A. Dallocchio says that the risk of having a hole in the vacuum
chamber due to beam loss close to a graphite component (dumps, slits) reaching more
than 500°C should be considered. In this case, depending how fast the air reaches this
element, graphite could burn (C. Maglioni, G. Vandoni).
8. AOB.
No AOB.
Jean-Baptiste Lallement
L4-BCC-025-20110407
7 April 2011
Next meeting: Thursday ?? May 2011, 14:00, 354-1-1.
APPENDIX 1
Discussion on Beam Stoppers in the Linac4 to PSB transfer line and PSB
access with Linac4 held on 11th January 2011
Present: C. Carli, M. Gruwe, K. Hanke, A. Lombardi, C. Maglioni, B. Mikulec,
R. Steerenberg, M. Vretenar, S. Weisz, M. Widorski
Present situation:


During Booster access, 50 MeV proton beams from Linac2 beam can be sent
to the LBE/LBS measurement lines located in the PS tunnel (inflector zone).
More details on the Booster access system can be found in the EDMS
document https://edms.cern.ch/document/901496/1 shown by R. Steerenberg.
A drawing of these lines is here.
During PSB access, two beam stoppers in the first part of the BI line between
the bending magnet LTB.BHZ40 and the wall separating the zones guarantee
that no beam can enter the PSB zone. Note that this is a non-standard solution;
The beam sent to the Booster follows a straight line in this region and, thus, no
veto sent to a bending magnet is possible. Two stoppers are installed for
redundancy and NOT because one stopper is not sufficient to stop the beam.
In the future with Linac4:



For "normal" operation (after PSB upgrade and re-commissioning), it is not
very important to to bring the beam into the LBE/LBS lines during PSB
access. However, it would be preferable to be able to use the lines for transfer
line commissioning during the PSB upgrade (hardware installation in the PSB
zone).
We agree to investigate whether temporarily removing a piece of the vacuum
chamber of the BI line and to install a concrete block before the wall
separating the zones (proposal by K. Hanke) would allow using the LBE/LBS
lines with Linac4 beam during PSB upgrade installations.
=> M. Widorski will investigate whether it is conceivable to bring the 160
MeV Linac4 beam into the LBE/LBS lines during hardware installation in the
PSB zone. After the meeting, a drawing (see here) of the separation between
the PS tunnel and the PSB zone including this separation wall has been
obtained by A.Kosmicki (the wall is 6m thick, but note the "caniveau" under
the ceiling).
L4-BCC-025-20110407
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7 April 2011
=> C. Maglioni will provide detailed information about the two beam stoppers
installed in the BI line.
Later during "normal" Booster operation after the upgrade, it will not be
possible any more to bring beam into the LBE/LBS lines during PSB access.
During PSB access, the beam will be sent to the Linac4 dump. The elements to
guarantee that no beam can reach the Booster are the first bending magnet
(veto sent to power converter) after Linac4 and beam stoppers in the this first
part of the line and, thus, during PSB access, no Linac4 beam will reach the
PS tunnel. Note that these element guarantee as well that no beam can reach
the PS tunnel (inflector zone) during access there (see:
https://edms.cern.ch/document/990203/1).
Thus, no beam stoppers are required any more in the BI line to guarantee
absence of Linac4 beam from the PSB zone during access there. M.Widorski
raises However, the situation is different for ions from Linac3, which . Even
though the present Pb beams are harmless, it is not obvious whether this will
still be valid for possible beams in the future (possibly higher intensities and
higher penetration depths for lighter ions). Thus, we envisage that two beam
stoppers in the BI line should stay there in the future with Linac4.
APPENDIX 2
-----Original Message----From: Giulia Bellodi
Sent: Wednesday, March 02, 2011 6:54 PM
To: Cesare Maglioni; Vasilis Vlachoudis
Cc: Alessandra Lombardi; Christian Carli; Bettina Mikulec; Maurizio
Vretenar
Subject: Linac4 beam-induced damage - update
Dear all,
Just to recap the issue: as a follow-up of FLUKA/ANSYS studies on
potential Linac4 beam-induced damage to vacuum pipes in the case of
power failure of one of the dipoles in the transfer line, a question
was raised about damage risks to the downstream or surrounding magnet,
given that in one of the cases studied 97% of the beam power was
deposited beyond the chamber directly into the magnet body.
I therefore contacted magnet experts to get their feedback/opinion, and
here's the summary of the main facts, as received:
1)The weak point of dipole magnets is the insulation coil (with a
melting temperature around 200-300 deg C). However, coils are
perpendicular to beam direction (which helps in case of impact).
2) Power supplies values are controlled by the BIC interlock system to
stay within a pre-defined fourchette of values. One would then need the
coincidence of a double failure (power supply failing or off-range &
BIC not reacting) to lose the beam, which is an unlikely occurrence.
3) In case of dipole damage/degradation, one complete spare unit is
available for each of the new magnets and the replacement would take
typically one day.
L4-BCC-025-20110407
7 April 2011
On the basis of this input and of the current baseline that the
watchdog should be able to react at best within 1 sec (cutting off the
next pulse at 1Hz rep rate), the decision taken by the core team this
morning is that the damage risks are low enough that the need for
further in depth studies of thermo-mechanical stress effects in the
magnets is presently not justified.
Simulation results on the case of beam impact on undulated/ceramic
chambers are on the other hand still needed as input to the watchdog
specifications.
Regards,
Giulia