L4-BCC-028-20110901
7 September 2011
Linac4 Beam Coordination Committee - Meeting 28 held on 1st September 2011
Present:
Giulia Bellodi; Franck Borgnolutti; Christian Carli; Alessandro Dallocchio; Klaus Hanke;
Lutz Matthias Hein; Mark Jones; Ioan Kozsar; Jean-Baptiste Lallement; Alessandra
Lombardi; Bettina Mikulec; Antony Newborough; David Nisbet; Uli Raich; Suitbert
Ramberger; Benoit Riffaud; Federico Roncarolo; Carlo Rossi; Lars Soby; Maurizio
Vretenar; Thomas Zickler.
1. Minutes of the last meetings
The minutes of BCC-27 are approved.
2. Follow-up of action items
No update.
3. Introduction (C. Carli).
The modification of the transfer-line layout, started in spring 2011, is due to several
reasons:
 Mismatch between ordered power converters and quadrupole parameters.
 Improved beam dynamics with first bending further downstream.
 Incompatibility between Y vacuum chamber and H-type magnets initially
foreseen (now, 3 shorter bends instead of 2).
The optics was changed matching a new design of the magnets. Integration and design
is on-going. All the needed equipments are defined. It is now important to confirm the
minimum beam pipe diameter.
4. Optics (A. Lombardi).
The horizontal 70° bending is now done with 3 bends instead of 2 in order to use
shorter H bends and avoid interference with the beam pipe. The 2.5 m vertical step
slope was reduced from 28° to ~15° in order to decrease the maximum integrated
gradient of the adjacent quadrupoles from 4 T to 1.8 T. The nominal beam quality,
flexibility and sensitivity are unchanged seen from PSB. Steering sensitivity,
commissioning strategy and dispersion control still need to be studied. In L4Z, the
“forward method reconstruction” improves the accuracy on the emittance evaluation
from profile measurements in presence of space charge (3 SEMGrids needed with
0.3-0.5 mm resolution).
4.1.
Discussion
F. Roncarolo remarks that one more SEMGrid is needed for the emittance
measurement in L4Z wrt what was before and says that a resolution of 0.5 mm can be
achieved.
A. Lombardi says that with a 0.3 mm resolution, the emittance could be estimated
with 5% accuracy.
5. Design office (B. Riffaud).
The layout and naming is now frozen. The transfer line was divided into 6 zones:
1. From last PIMS module up to first bending.
2. The 70° bending area (made of the 3 H bends).
L4-BCC-028-20110901
3.
4.
5.
6.
7 September 2011
From the last H bend up to the first vertical bend.
The vertical step.
Between the second bend of the vertical step up to BHZ20.
L4Z, from the first 70° H bend up to the L4 dump.
The design is detailed for every zone. The design of the supports is on-going and will
be finalized once the interface with equipments will be frozen. The magnet apertures
foreseen (100 mm) for steerers and L4T quadrupoles and the requirements for the
beam do not allow using a standard vacuum chamber. The additional cost for
construction of a special chamber with inner and outer diameter of 95 and 98 mm is a
bit less than 1 kCHF per meter. The decision to keep the foreseen 100 mm magnet
aperture and to construct special vacuum chambers is taken (outside magnets and
where easily possible, a standard chamber with inner diameter of 100 mm will be
used). The beam instrumentation interfaces have to be frozen as soon as possible.
5.1.
Discussion
B. Mikulec and F. Roncarolo say that a BCT in the L4Z, before the dump, is missing
in the layout.
C. Carli asks if we could use 1 T jack instead of 2.5 T.
B. Riffaud answers that the only advantage of changing the jack type could be a gain
in space.
6. Magnets (F. Borgnolutti, T. Zickler).
The interference between the beam pipe and the initial 35° bending led to change the
design of the transfer line and to use 3, lighter, smaller and less expensive 23.3° bends
instead of 2. The magnet parameters are presented and summarized in the following
table.
Integrated field
0.78 T.m
Bending angle
23.33°
Length
1.03 m
Mass
1504 kg
Width
800 mm
Max current
672 A
A new quadrupole design fitting the power converters parameters was presented in
July. The aperture is 50 mm radius as planned, and the integrated gradient had been
reduced from 4 T to 1.8 T. The main magnet parameters are the following:
Nom field: 1.8 T; Nom peak current: 119.6 A; Max RMS current: 9.2 A; Inductance:
2 6mH; Resistance @ 20°c : 0.279 Ω.
The design report is in preparation. The first magnet should be available at CERN
beginning of 2013.
The steerer magnet design is identical to the Linac4 steerer (100*100 mm) and 2
prototypes are made using different type of steel to study dynamic effects. They were
measured 2 weeks ago and the results will be presented by M. Buzio.
The bending magnet width of the design presented is slightly larger than the one of
the previous version to ensure that the Y-shaped vacuum chamber fits. The
L4-BCC-028-20110901
7 September 2011
implication is the slightly less margin is available for the “line of sight” in the vertical
step. M. Jones and J.-P. Corso will verify that there is still sufficient margin.
T. Zickler pointed out that the beam optics has to be frozen very soon, otherwise the
magnets for the transfer-line cannot be delivered anymore according to the project
schedule.
The engineering specifications of the 3 magnets will be issued and follow an approval
process.
6.1.
Discussion
D. Nisbet says that the inductance of the new bending magnets is 50% higher than
what he was expecting. The initial understanding was that 3x ‘short dipoles’ would be
electrically identical to 2x ‘long dipoles’. In the design presented, for the inductance
parameter 3x ‘short dipoles’ = ~3x ‘long dipoles’, thus a 50% increase in inductance
(61 mH instead of 44 mH). It should be OK and there is still some margin.
A. Lombardi says that we should keep some margin on the maximum field.
D. Nisbet answers that we could gain some margin working on the pulse length or
other parameters.
7. Power supplies (D. Nisbet).
The list and the status of the power converters needed for the transfer-line magnets is
presented. In order to fit the new quadrupole design parameters, the power converters
will be upgraded using new technology capacitors. At present, the modules still fit in
the available space in the racks. The cost increase of the modification is negligible
and it will be standardize to all Linac and TL magnets. The invitation to tender is
about to be lunched and the production should start in March 2012. The power
converters design remains unchanged for the steerer magnets, and the bending ones
should be compatible with the new magnet design.
7.1.
Discussion
D. Nisbet says that monitoring the bending current to 0.5% (necessary if we want a
hardware interlock on the bendings) is not foreseen and requires a specific
development estimated to 1 FTE.Year.
M. Vretenar asks what could be the effects of increasing the aperture of the bending.
T. Zickler made clear that increasing the gap will increases the required ampere-turns
respectively the current to be delivered by the power converter.
D. Nisbet says that the main limitation does not really come from the maximum
current but from the RMS current.
There is a discussion on increasing the number of turns of the coil in addition to a
possible gap increase. This increases the inductivity (some margin) and decreases the
required (peak and very likely rms as well) current.
A. Lombardi asks to get, as soon as the magnet design is finished, the field margin wrt
nominal field.
8. Diagnostics (F. Roncarolo).
The type and number of every diagnostics needed for the transfer-line are summarized
in the following table:
L4-BCC-028-20110901
7 September 2011
MONITOR TYPE
Quantity
L4T LINE
BCT
7
BLM
6
SEM GRIDS
3 (H+V)
BPM
12
BSM
1
L4Z LINE
WS or SEM GRID
1 (H+V)
BCT
1
The BCTs will be identical to the one installed in the LEBT. The acquisition
synchronicity with the distributor needs FPGA code update.
BPMs design is identical for all Linac4. The diameter is 100 mm and the length about
250 mm. A 50 ns pulse length beam position measurement is foreseen. Old BPM (17
in the L2 TL) could be replaced for standardizing the electronics.
The SEM Grids design is identical to Linac4. The pulse length should be limited to
100 µs to preserve to devices. A new electronics under development will be tested at
the 3 MeV test stand.
The BLM electronic is under design. Special screened cables will be used to avoid
EM noise. Cabling is on stand-by, waiting for the final beam optics and BLM
locations.
There are plans to develop a Laser stripping monitor. This requires separating the Hfrom the neutral (laser-stripped) H0 with a bending magnet equipped with a Y shaped
vacuum chamber. This can be done either using the chamber of the first horizontal
bending magnet (monitor to be installed in the L4Z line) or by installing a Y shaped
chamber in a bending further downstream (chamber could be installed already now to
add the monitor later) as well.
Software development is ongoing.
9. AOB.
No AOB.
Jean-Baptiste Lallement
Next meeting: 13 October 2011, room 6-R-12.