CERN BE Newsletter May 2012

7/31/2019 CERN BE Newsletter May 2012

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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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2 Beams Department News le t t er Issue 4

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


3/9


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


8/9


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

CERN BE Newsletter May 2012

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Transcript of CERN BE Newsletter May 2012