Experience with beam instrumentation at
Linac4
Prepared by Jean-Baptiste Lallement and Alessandra
Lombardi
Thank you BI colleagues for
• Instrumentation that overall worked very well
• An outstanding support during the whole commissioning
period (keep it up, we are not done)
• An open mind to our feedback
List of permanent instruments
Low energy (03MeV)
Medium (10160MeV)
160 MeV
SEM grids
1/1
4/4
6/6
Wirescanners
2
4
6
Beam transformers 3
3
5
BLMs
1
9
9
Pick-ups
0
15
10
BSMs
0
0
2
Avant-propos
The Linac4 beam instrumentation layout was
frozen 7 years ago.
We had permanent diagnostics and dedicated
test benches for the staged commissioning
Different diagnostic types and measurement
techniques development and commissioning
spread over the last 5 years…
Not much time in the last commissioning
stage to used and measure what we would
have liked…
The reliability run is the good occasion
Beam Current Transformers
• The first thing we look at (and not only
when something goes wrong)
• Essential for operation (watchdog)
• Necessary for setting up the beam up to 30
MeV
LEBT and MEBT magnets
DTL1 transmission curve
Generally reliable
Issues with amplifiers required access to
the tunnel (reliability…)
Calibration still an issue ?
BCTric app is not very user friendly
Synchro between beam and acquisition
Overall OK
Watchdog OK
Beam Loss Monitors
Never really used them – But they do clearly show losses – Is there an application ?
Could be complementary to other diags
(profile, BPMs) to help in setting up steerers
and quads.
We did see losses when playing with settings
in the high energy part (above 100 MeV)
The one between L4D – L4C is sensitive to the
RF in the CCDTLs. It look like its signal only
depends on the presence and level of the RF
in the CCDTLs
Not yet used enough to give feedback at this point
Bunch Shape Monitor(s)
Used the first one at 3 and 50 MeV on the temporary bench
• An expert tool, not for everyday operation
• Excellent tool to measure the longitudinal
emittance.
• Will be used in the Linac4 (after the last PIMS)
and in the transfer line (after the debuncher)
• Will be the only measurement between the linac
and PSB and it will take the function of the
present LBS.
• It will be of fundamental importance after the
connection
Not much time to test and use it at 100 and
160 MeV.
Need of a BI expert to make measurements.
Needs an application
Beam Position Monitors
Started to use at 50 MeV – multipurpose tool
• Only tool for on-line steering (trajectories)
and setting up the cavity phases and
amplitudes (ToF).
• Essential at each restart
Used during the different commissioning
stages above 50 MeV.
Need of a BI expert to set it up (ToF).
Application needed
Transverse profile measurements
at 45 keV(tunnel and Test stand )
Very difficult regime, with many physical processes in
action (space charge, neutralisation, uncontrolled
emittance increase, losses)
The SEM grids are completely inadequate under
every aspect :
•
•
•
•
Resolution
Size (we cannot measure under operating conditions)
Effect of the bias
Effect on the neutralisation and RFQ transmission
We need to find (another?) solution
SEM and wire scanners
• Used to verify beam size, set up buncher
phases and measure transverse emittance
from beam sizes
• Not essential for operation but essential for
setting up
Used extensively up to 100MeV, measured
values are generally in very good agreement
with expectations.
Time resolved measurements are very useful
(e.g. chopper set-up) and work well
Overall OK but issues with vacuum to be
addressed.
Not all of them available yet.
Application is very heavy and blocks the
computer quite often.
Emittance meter: slit and grid
• Direct emittance meter possible at the low energy
end 45keV, 3 MeV, 12 MeV
• At 3, 12 MeV (temporary bench) we had excellent
measurement.
• Control and interface is ok for short-term
measurement campaign but definitely not suitable
for source test stand.
Summary
Red : instrument not usable
Yellow : instrument ok, interface missing
Green : all good.
Low energy (03MeV)
Medium (10160MeV)
160 MeV
SEM grids
1/1
4/4
6/6
Wirescanners
2
4
6
Beam transformers 3
3
5
BLMs
1
9
9
Pick-ups
0- wish a couple of
pickups
15
10
BSMs
0
0
2
Concluding remarks
• The reliability run is a good occasion to bring the
instrumentation in an operational state (=usable by
operators)
• The instrumentation that was more useful is the one one
that is more user-friendly coupled with a validated machine
model.
• Post-processing of data is insufficient in general and it
added a lot of strain during commissioning both on BI and
on the commissioning team. Let’s avoid this -if possible- for
the connection to the PSB.
• Laser based instrumentation : so far it was like an
independent experiment and I wish that this paves the way
to new diagnostics for the linac accessible also to us and the
OP team.