cern be newsletter may 2012
TRANSCRIPT
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Beams Department
The Newsletter does not necessarily reflect the views of the Beams Department
The contributions solely reflect the views of their author(s)
Issue 4 NEWSLETTER May 2012
Ins ide This Issue
p. 1 Editorial R. Billen
p. 2 BE Newsletter Survey Outcome The Editorial Team
p. 3 HL-LHC motivations and challenges Riccardo de Maria, BE-ABP-LCU
p. 5 Vhicule de service ou priv ?BE-ASR-SU
p. 5 Tuning the LHC Marek Gasior, BE-BI-QP
p. 7 ACCOR
Marc Vanden Eynden, BE-CO-FE
p. 8 Safety Column BE Safety Unit
p. 9 Management Changes ASR-AS
Edi tor ia l
Dear Readers,
Heres issue number four of the BE Newsletter,
the first one of the exciting year 2012. I suspect
that you were all eagerly and impatiently awaitingthis copy and I take full responsibility for its
lateness. Indeed, prior to this publication, I
preferred to launch a survey in order to find out if
we are on the right track. For the success of the
BE Newsletter, it is important to find its place in
our scientific-technical world of communication,
where we are already submerged with
information. The content has to be sufficiently
interesting but complimentary to the existing
media.
The survey took place last February and I would
like to thank all of you for having taken the time tocontribute with your replies and suggestions. I
admit that I was happily surprised with the
outcome, which is positive and encouraging on all
aspects. You will find the details further in this
newsletter, which are based on the 144 received
replies a statistically significant and
representative sample .
If I would make a convolution of all responses, I
would come up with a statement as follows: The
average BE Newsletter Reader reads with interest
and curiosity about half of each newsletter; he is
not concerned about the language issue French or
English; he is quite comfortable with the balance
of the subjects and the level of complexity of the
content, and in addition, he would like to write an
article himself!. Based on this, I can only
conclude to pursue and go ahead with the
publication series. Three issues are planned for
2012, so dont be shy and contact your
correspondent to submit your contributions!
Ronny Billen
Editor, BE Newsletter
Next issue
The next issue will be published at the
end of August. Contributions for thatissue should be received by the middle
of August at the latest.
Suggestions for contributions are
always most welcome: simply contact
your Correspondent (see last page).
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BE Newslett er Survey Outc ome
This article summarizes the result of the 144
replies on our questionnaire that was launched last
February. From the first question, it shows that
each of the newsletters is read by the majority of
people, with only a minor decrease over thesubsequent issues.
The fact that the authors are given the liberty to
write their articles in English or in French is not at
all a blocking factor for the readers.
In addition, a fair amount of the articles is read, as
most colleagues are curious to know what is going
on in other groups (or even in their own ;-).
Overall, the topics of the articles are scientific,
administrative or even very general. The balance
is not always obvious, so thats why we asked.
The result is quite acceptable as shown in the
graph below.
The diversity of the 800+ members of the
department is vast, in terms of academic
background and professional experience, so the
question on complexity was legitimate. Again,
our worries seem to be unjustified.
The most encouraging result was that 56 people
(i.e 39%) replied that they would actually like to
contribute to the BE Newsletter! It also shows
from the constructive comments that the interest is
real. We have discussed your suggestions with
the correspondents and have retained the feasible
ones.
The Editorial Team
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HL-LHC mot ivat ions and
chal lenges
The High-Luminosity LHC project (HL-LHC led by
Lucio Rossi and Oliver Bruning [1]) is the lastincarnation of the plans to extend the LHC discovery
potential by about a five-fold increase of the rate of
collisions in the ATLAS and CMS detectors. The
rate of collisions, and therefore the rate of interesting
events that the high energy physicists can study, are
proportional to a quantity called luminosity, which
depends on the characteristics of the colliding beams
and represents the key performance-figure of a
collider.
The time scale of the upgrade project is set by two
main arguments, namely the time to double thestatistics and the lifetime of magnets close to the
interaction points (IPs), which are essential for the
efficiency of the collisions. The HL-LHC project is
based on the estimate that one of these two
conditions will occur not far after 2020. Hence, a
long shutdown, called LS3, is already foreseen in the
CERN planning as illustrated in Fig. 1.
Figure 1. Scenario for the evolution of the
luminosity, time needed to double the statisticalsignificance and proposed shutdowns.
How the luminosity of the LHC can be enhanced? In
simple terms this can be achieved by packing more
particles in the overlapping volume of the two
colliding proton beams (called luminous region).
The first strategy is to pack more particles in the
same volume, increasing the beam current and the
so-called brightness of the beam. Therefore, more
intense and brighter beams need to be produced by
the LHC injector chain (a companion CERN project
the LHC Injector Upgrade - LIU led by Roland
Garoby and Malika Meddahi [2] - aims at exactly
that) and have to be preserved during the injection,
acceleration and collision phase in the LHC ring.
However the whole is challenged. The particles of
the circulating beam generate strong electromagnetic
fields that interact again with the beam and strip
clouds of electrons from the walls of the vacuum
chamber, leading to instabilities that reduce the
number of colliding particles and increase the
amount of heat that needs to be extracted to maintain
the superconducting state of the magnets.
Nevertheless one has to anticipate the future
limitations, gain room above ultimate performance
and identify the most likely scenarios on which
concentrate efforts as exemplified in Fig. 2.
Figure 2. Parameter space of the HL-LHC in terms
of bunch intensity and emittance [3].
A complementary way to increase the luminosity is
to reduce the volume of the luminous region only,
while keeping the same beam current and brightness
by focusing the beam with magnetic lenses much
more than today. To achieve that one needs to
replace the magnets close to the IP by larger-
aperture magnets in analogy to what one would need
for building a more powerful magnifying glass. The
analogy with optical systems has been recently
pushed forward, transforming this lens in a two-
stage telescope, thanks to a novel technique
(Achromatic Telescopic Squeezing Scheme [4],
already tested last year Fig. 3), which allows very
compact luminous region by focusing kilometers
away from the IP.
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Figure 3. Optics functions measured in one LHC
ring showing the telescopic squeeze in the ATLAS
region.
The smaller the beam size is at the IP, the larger itbecomes at the first focusing magnets and the
stronger is the integrated magnetic field gradient
needed to bend the particles back to the center of the
beam pipe. Most of the R&D effort is to produce
new focusing magnets with a larger aperture that are
longer or stronger (by using new superconducting
materials like Nb3Sn) or both. Not only magnets
need to be replaced but all the area has to be
redesigned for the increased radiation levels intrinsic
to the collision process. The two circulating beams
need to be separated by a crossing angle to avoid
parasitic collisions and to avoid that the motion ofone beam is perturbed by the field of the other one.
Unfortunately, the crossing angle reduces the
overlap between bunches and therefore the
luminosity. While some tradeoffs could be
envisaged to find the optimal parameter set, a set of
additional devices (crab-cavities), never used in
hadron collider, are being designed and prototyped
to restore the full overlap between the beams[5].
Organized in pairs, the first one rotates the bunches
in the crossing plane at the IP and a second one
restores their initial motion in the rest of the
machine, as shown in Figure 4.
Figure 4. Effect of the crab cavities on the beam.
While the experiments like to observe many
collision events, they do not want all of them
occurring at once, otherwise it would be very
difficult to reconstruct what really happened. If this
is acceptable at the present level of luminosity, it
becomes a real concern for the upgraded luminosity
levels, a factor five higher or more than nominal. In
addition the luminosity rapidly decays from the
initial peak due to the intrinsic burn off of particles
participating to the collisions, as illustrated by the
red lines Fig. 5. The upgrade relies then on a
mechanism to dynamically compensate the particle
burning and maintain the luminosity at a lower
initial value: this is called luminosity leveling, and it
maximizes the overall number of useful collisions
[6].
Figure 5. Luminosity evolution with various leveling
scenarios.
The list of challenges has not been exhaustive, in
fact, many systems - including collimation, machine
protection, cryogenics, beam diagnostics, vacuum,
powering, civil infrastructures organized in fifteen
work packages - are being involved in the final
design. Not to mention the detectors themselves, that
will undergo major upgrades as well.
In conclusion the HL-LHC project aims at making
the last years of the lifetime of the LHC as exciting
as these first years, by exploiting new technologies
and the expertise built on the current machine toincrease the rate of interesting events for the physics
community. The new set of parameters will
potentially allow a peak luminosity of twenty times
or so higher than the nominal luminosity of the
LHC. The final aim is to allow the LHC to reach
3000 fb-1
of integrated luminosity in the 20-25 year
lifetime. The project will span over the next 10 years
with a strong effort by the BE, EN and TE
departments, in collaboration with twenty institutes
in the ERA (European Research Area), USA and
Japan expanding the best tradition of the global
CERN endeavors.
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References:
[1] L. Rossi LHC Upgrade Options and Plans, in Proceedings of
IPAC2011, San Sebastian, Spain;http://cern.ch/HiLumiLHC.
[2] R. Garoby, Plans for the upgrade of the LHC injectors, in
Proceedings of IPAC2011, San Sebastian, Spain;
http://cern.ch/liu-project.
[3] O. Bruning, HL-LHC Parameter Space and Scenarios,Proceedings of Chamonix 2012 workshop on LHC Performance.
[4] S. Fartoukh, Breaching the Phase I optics limitations for the
HL-LHC, Proceedings of Chamonix 2011 workshop on LHC
Performance.
[5] R. Calaga, Crab Cavity Workshop, Proceedings of
Chamonix 2012 workshop on LHC Performance.
[6] F. Zimmerman, New ideas, presented at HL-LHC/LIU
Joint Workshop. 30 March 2012.
Riccardo De Maria, ABP-SU
Vhicule de service ou pr iv ?
(Circulaire administrat ive N20)
Qui na jamais dcid, faute de voiture CERN
disponible, de prendre son propre vhicule pour un
dplacement inter-site ? Aprs tout, tout le monde le
fait Mais connaissez-vous les rgles en vigueur ?
La politique de lorganisation est de favoriser
lutilisation des vhicules CERN lors des
dplacements professionnels. Lorsque cela nest pas
possible et lorsque lutilisation des navettes CERN
nest pas une solution adquate, vous avez la
possibilit de prendre votre vhicule personnel.
Si vous souhaitez en savoir plus, la Circulaire
administrative N20 (Utilisation dun vhicule priv
lors de dplacements pour les besoins du service) est
le document de rfrence. Elle est disponibleici.Le
CERN Admin e-guideet sa FAQ sont galement des
sources dinformations utiles.
Avis aux motards : Par vhicule personnel, laCirculaire administrative N20 entend une voiture,
un vlo ou un vlo lectrique. Elle interdit par
contre lusage dune moto ou dun scooter pour tout
dplacement professionnel. Vous pouvez venir et
repartir du CERN moto, mais cest tout !
BE-ASR-SU
At each of the biannual Beam Instrumentation
Workshops (BIW) since 1992, the Faraday Cup is
awarded for an outstanding contribution to the
development of an innovative beam diagnostic
instrument of proven workability. This award
recognizes and encourages innovative achievements
in the field of instrumentation of particle accelerator
beams. The winner is selected by the BIW Program
Committee from candidates proposed by
laboratories from all over the world. The award is
sponsored by Bergoz Instrumentation and consists of
a diploma and a monetary prize. This year the
Faraday Cup went for the third time in its 20 year
history to a CERN scientist. After Edward Rossa in
1994 and Andreas Jansson 2002, in 2012 the honour
was awarded to Marek Gasior of BE/BI for "High
sensitivity tune measurement by direct diode
detection":
Tuning the LHC
In every accelerator the particles are kept inside the
vacuum pipe by the field of quadrupolar magnets,
forcing the particles to follow sinusoidal motion, so
called betatron oscillations, around the ideal
trajectory, known as the orbit. The number of
periods of these oscillations per turn is called
betatron tune. If the tune is an integer number then it
means that the particles follow the same trajectory
every turn and the amplitude of the betatronoscillations increases resonantly until the particles
are lost by hitting the vacuum pipe or other limiting
aperture. The same thing can happen if the trajectory
repeats every 2 turns (1/2 integer resonance), every
3 turns (1/3 integer resonance), and so on. These
resonances generally get weaker the higher the
order, but such a crowd of resonances leaves only a
small choice for the tune if we want a large
accelerator to circulate the beam for long time with
small losses. For example, the LHC is designed to
collide protons with a betatron tune of 59.31; that is
every turn the particles do 59 full betatron
oscillation periods (integer tune) plus a further 0.31
of a period (fractional tune).
If you want to test your imagination further with
more sinusoids, try to imagine that what has just
been said about the LHC only concerns the
horizontal plane and that the particles also oscillate
in the vertical direction with a tune of 64.32. To
have even more sinusoids, now consider the fact that
in a single LHC nominal bunch there are about 100
billion protons (10
11
), each following its ownsinusoid in both horizontal and vertical planes.
Since all protons do not have exactly the same
http://cern.ch/HiLumiLHChttp://cern.ch/HiLumiLHChttp://cern.ch/HiLumiLHChttp://cern.ch/liu-projecthttps://hr-docs.web.cern.ch/hr-docs/admincirc/en/AC%2020_Rev2_01.2011.pdfhttps://hr-docs.web.cern.ch/hr-docs/admincirc/en/AC%2020_Rev2_01.2011.pdfhttps://hr-docs.web.cern.ch/hr-docs/admincirc/en/AC%2020_Rev2_01.2011.pdfhttps://admin-eguide.web.cern.ch/admin-eguide/voitures/proc_vehicules_prives_fr.asphttps://admin-eguide.web.cern.ch/admin-eguide/voitures/proc_vehicules_prives_fr.asphttps://admin-eguide.web.cern.ch/admin-eguide/voitures/proc_vehicules_prives_fr.asphttps://hr-docs.web.cern.ch/hr-docs/admincirc/en/AC%2020_Rev2_01.2011.pdfhttp://cern.ch/liu-projecthttp://cern.ch/HiLumiLHC -
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energy, in consequence their trajectory sinusoids are
also slightly different, as more energetic particles are
less deflected by the quadrupoles. The superposition
of all 1011
horizontal and vertical sinusoids
determines the LHC beam size for one bunch. And
now imagine on top of this that there are 1380
bunches colliding in the LHC...
As the accelerator tunes are so important, they have
to be measured with high accuracy and maintained
on their reference values. At the time of writing the
LHC design report this task was considered very
difficult, as the standard method to measure the tune
required significant external excitation to
synchronise the motion of individual particles.
Otherwise their betatron oscillations appear chaotic
to a beam position monitor (BPM), yielding no net
signal. The excitation means that the particles followlarger amplitude sinusoids and in consequence, the
beam size gets bigger (what is known as emittance
growth), lowering the collision rate and increasing
the timeto-discovery. For this reason the LHC
beams can be excited only up to the micrometre
level.
The challenge of measuring the LHC tunes was
entrusted to the BE-BI-QP section, where a new
technique was developed, allowing the observation
of very small beam oscillations. The trick used to
achieve an unprecedented sensitivity is to pass theshort, high amplitude pulses obtained from a beam
position monitor to simple diode detectors; similar to
those used in old radio receivers. The detectors
convert the tiny modulation of the BPM pulses
related to beam oscillations into a convenient signal
in the audio frequency range. This can then be nicely
processed to deliver the tune content. The
dominating part of the BPM signal related to the
beam intensity, which typically limits the
performance reach in other tune measurement
techniques, becomes a DC voltage after the
detectors. This is easily blocked using a simplecapacitor at the detector outputs. The use of diode
detectors brings many new advantages to the tune
measurement system, which has resulted in an
elegant and relatively simple design sensitive to
beam oscillations at the nanometre level. It was a big
surprise that with the achieved sensitivity it is
possible to see the tiny oscillation of LHC beams
present even without excitation. Today the LHC
Base-Band Tune measurement system based on
diode detectors, known as the BBQ system, is
mostly used with natural beam oscillations or with
very little additional excitation. This provides the
input data for the tune feed-back system, which
automatically corrects the strength of the
quadrupoles to keep the tunes on their reference
values.
LHC BBQ installation and its most important parts:
the diode detector and analogue front-end
LHC tunes measured in the control room
As a side effect of the LHC BBQ development,
today the LEIR, PSB, PS and SPS accelerators all
have similar tune measurement systems based on
diode detectors. BBQ systems built at CERN are
also in use at 5 other laboratories worldwide.
Another discovery during the BBQ development
was that the natural beam oscillations contain more
information than just the tunes and they are nice to
listen to! A few samples of beam sound from the
early BBQ development days as well as more
information on the system can be found at
www.cern.ch/gasior/pro/bbq/index.html.
Marek Gasior, BE-BI-QP
http://www.cern.ch/gasior/pro/bbq/index.htmlhttp://www.cern.ch/gasior/pro/bbq/index.htmlhttp://www.cern.ch/gasior/pro/bbq/index.html -
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ACCOR
The Accelerator Controls Renovation Project
(ACCOR) was initiated in 2009 at the level of the
A&T sector in order to re-engineer the control
system of the CERN PS Accelerator complex. Theobjective was two-fold: make the key technical
choices required in order to face the obsolescence of
the real-time front-end systems (about 450
operational systems based on PowerPC processors
running the LynxOS operating system) and
rationalize our organization in terms of control
system responsibilities.
Concerning technical choices, a full evaluation of
the operational constraints and of the state-of-the-art
embedded technologies was conducted in close
partnership with the equipment groups, leading to
the signature of major contracts with European
hardware manufacturers for a total of about 4
MCHF. This competitive exercise decreased the
cost of a typical front-end system by more than
60%! The new technological choices based on
VMEBus64x and PICMG1.3 standards running the
Linux operating system on Intel multi-core
processors will allow us to capitalize on the long-
term CERN VMEBus experience while suppressing
old vendor-specific dependencies (LynxOS
operating system) and performance limitations. Theusage of the FESA real-time software framework is
being generalized for all front-end systems, offering
to all CERN embedded software programmers the
benefits of high-level and well supported
functionalities compatible with the high-level
application software layers.
From a management perspective, it was clear in
2009 that CERN could not continue with two
Different control system organizational models for
the PS complex and for the LHC. Thanks to the
close collaboration of all parties at the level of theControls Coordination Committee (CO3), the LHC
model is now being generalized for all Accelerators.
If all is clear, one could then question what are the
remaining challenges for the ACCOR project? The
first challenging aspect concerns the understanding
of the operational complexity and dependencies of
the legacy systems for which the CERN knowledge
is either gone or remain in the head of very few
people. Each system, for each Accelerator, required
an in-depth analysis of its current architecture and
the definition of precise re-engineering plans with allparties involved. BE-CO Machine Controls
Coordinators play here an essential role and ensure a
close collaboration with projects like LIU.
Last but not least, the forthcoming CERN long-
shutdown in 2013 (LS1) represents a unique
opportunity for the ACCOR project to attain his
objective. As many critical operational systems will
be re-engineered during LS1, the challenges will be
risk contingency, proper planning with the
equipment groups, qualification of the new systems
and finally, careful re-commissioning with
operations. Risks do exist but the excellent level of
motivation and collaboration of all parties will help
us to control it, bringing the PS Accelerator
Complex control system at the same level of
performance as the LHC and ready to cope with the
numerous challenges in front of us.
Marc Vanden Eynden, BE-CO-FE
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Safet y Colum n
Road Safety
Yes, we know that you know. You haveseen the ads, read the postersNevertheless it is worth showing itagain; just to check that, of course, youalways apply these rules.
Driving too fast for the conditions is baddriving: Driving too close to the car in front,passing on the right and failing to signal are widely
accepted as examples of bad driving. However,
some drivers fail to accept that driving too fast is
also poor driving, despite the fact that this is a
contributory factor in hundreds of deaths and
thousands of injuries every year.
Consider the consequences of causing an accidentdue to driving at excessive speed:If you cause anaccident you will have to live with the emotional
consequences of deaths or injuries caused to others.
Dont assume its safe to break the speed limit onrural roads because there is less traffic or anopen road ahead: Be aware that there may be
unexpected hazards, such as blind bends, vehicles
coming out of junctions and animals on the road.
Don't make or answer calls when you'redriving: All phone calls distract drivers' attentionfrom the road.
Do not drive when tired.You can find more tips at
http://think.direct.gov.uk/index.html
Merci tous davoirparticip la Journe
Mondiale de la Sant etde la Scurit au
Travail !
Thanks to all the
participants to theWorld Day for Safetyand Health at Work!
BE Safety Unit
http://think.direct.gov.uk/index.htmlhttp://think.direct.gov.uk/index.html -
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Management Changes
The request to be informed about the changes in
the departmental management, responsibilities
and roles came clearly out of the survey. In order
to satisfy this request, there will be a recurrent
chapter in the BE Newsletter. These are the
managerial modifications since this year:
New BE Deputy Group Leaders:
Marc Tavlet ASR
Maurizio Vretenar RF
New BE Section Leaders:
Marc Tavlet ASR-SU (Safety Unit)
Jean-Jacques Gras BI-PM (Profile
Measurements)
Vito Baggiolini CO-DO (DevOps)
Carlo Rossi RF-IS (Injector Synchrotrons)
Frank Gerigk RF-LRF (Linacs RF)
Ed Ciapala RF-SRF (SC RF Cavity
Technology)
The RF Group led by Erk Jensen was fullyrestructured. We wish these people all the best in
their new responsibilities.
Newsletter Contacts
Correspondents:
ABP G. Arduini & H. Mainaud Durand
ASR C.E. Sala
BI E. B. Holzer
CO M. Draper
OP E. Lienard
RF W. Hfle
Copy Editor L. Van Cauter-Tanner
Design Editor E. Gavriil
Editor-In-Chief R. Billen