Accelerator Reliability Workshop – Cape Town 2011 L. Hardy – ESRF Operation Group1 A BRIEF...

Accelerator Reliability Workshop – Cape Town 2011 L. Hardy – ESRF Operation Group 1

A BRIEF HISTORY OF

ACCELERATOR RELIABILITY


WHAT IS RELIABILITY ?

Military standard definition of reliability:

« The probability that an item will perform a required function without failure under stated conditions for a stated period of time »

Note:

• A functional definition of failure is needed. For example, a failure means different things to the user and to the person repairing the failure,

• The system's operating conditions must be specified (e.g. external temperature).

• A period of time is needed.


RELIABILITY: A MODERN CONCEPT, YOU SAID ?

« As concerns the gold ring set with an Emerald, we guarantee that for 20 years the emerald will not fall out of

the gold ring. If the emerald should fall out of the gold ring before the end of 20 years, we shall pay unto Bel-Nadin-

Shumu an indemnity of 10 mana of silver. »

Record found on a clay tablet in Egypt - 429. BC …

Source :


« The probability that an item will perform a required function without failure under stated conditions for a stated period of time. »

When was the probability concept ‘born’ ?

Then followed an exchange of letters between Pascal and Fermat in which the fundamental principles of probability theory were formulated for the first time.

1654: The Chevalier de Méré, a French nobleman, called Pascal's attention to an apparent contradiction concerning a popular dice game.

• The game consisted in throwing a pair of dice 24 times,

• The problem was to decide whether or not to bet money on the occurrence of at least one "double six" during the 24 throws. A well-established gambling rule led de Méré to believe that betting on a double six in 24 throws would be profitable, but his own calculations indicated just the opposite …

The Dutch scientist Christian Huygens learned of this correspondence and shortly thereafter (in 1657) published the first book on probability; entitled De Ratiociniis in Ludo Aleae, which was a treatise on problems associated with gambling


FIRST STEPS OF RELIABILITY THEORY

• Not formally used before World War I

• During and after World War I, reliability was just a measure of the number of accidents the planes had per hour of flight time.

• 1926: Walter Shewhart, Harold F. Dodge, and Harry G. Romig laid down the theoretical basis for using statistical methods in quality control of industrial products, founding the trial and error approach to reliability study

• Again, no formal use before World War II

• 1920-1930: telephones and electron vacuum tubes grew in demand need to make them more economically and improve their reliability. These two new technologies spurred early reliability studies.


FIRST RELIABILITY MODELS REALLY START WITH WORLD WAR II

The V-1 rocket: reliability of 1 success out of 11 attempts reliability of 9.1%

The mathematician Robert Lusser analysed the missile system and quickly derived the product probability of series components making the first step into the development of the Reliability Theory

Robert Lusser

for a series system:

Rs = R1 * R2 * * Rn

where Ri is the probability of survival for 1 element

A system with a large number of components like the V-1 will reach a low reliability level even with very reliable components


FIRST RELIABILITY MODELS REALLY START WITH WORLD WAR II

For a series system: Rs = R1 * R2 * * Rn where Ri is the probability of survival for 1 element

Lusser’s studies resulted in Werner Von Braun’s redesign leading to the V-2 rocket. The V-2 rocket used the principles of redundancy to enhance the rocket’s reliability.

As a result, the reliability of V2 rockets increased from 30 % from the first launch (8 september 1944) to 70 % (end of the war).

SUMMARY I:

• We are in 1944

• Reliability theory and first reliability principles emerge with rockets technology

What is the status of the Particle Accelerators at that time ?


A BRIEF HISTORY OF ACCELERATOR NON-RELIABILITY

1924: Ising: the first Linac model

1928: Wideröe: a model based on RF voltage

March 1936: the first external cyclotron beam: 5.8 MeV deuterons

This is the race for accelerator physics principles…


1941: 184-inch cyclotron (>100 MeV) for U235 / U238 separation (Berkeley)

1947: proton Linac built under supervision of Alvarez

1959: CERN 24 GeV PS is the highest energy accelerator in the world

PS inauguration (1960)

The race to higher intensities, higher energies…



SUMMARY II:

• 1950’s : Particle accelerator technology is already well advanced

• Emergence of basic principles of reliability

• Until 50-60’s , reliability is not at all a concern for accelerator technology


THINGS WILL CHANGE IN THE 70’S


A BRIEF HISTORY OF ACCELERATOR RELIABILITY…

1968: First dedicated X-ray source (bench test): Tantalus (Wisconsin - USA)

1972: meson factories. E.g.: Los Alamos (LAMPF): 800-MeV beam

( + PSI, TRIUMF)

LAMP aerial view

Rosen: « we need more particles per unit time rather than more energy per particle ! »

1970: First beam line (Nina) with Users on an X-ray source: SRS Daresbury (UK)

One mention of ‘reliability’ in 17 pages (Particle Accelerators

© Gordon and Breach, 1973, Vol. 4, pp. 211-227)


USERS NEED RELIABILITY AND AVAILABILITY !!

MEDICAL APPLICATIONS

1956

A BRIEF HISTORY OF ACCELERATOR RELIABILITY…


ACCELERATOR RELIABILITY NOWADAYS

With some examples, let’s get an idea of what we can reach today:

Institute Scheduled User time

[hours]

Delivered time

[hours]

Storage Ring availability

[%]

Fault/year MTBF

[Hours]

Mean Time to recover

[hours]

KEK storage Ring 2008

4344 4302 99.0 % 40 109 1.0

Advanced Photon Source (APS) 2010 5000.1 4924.8 98.5 % 48 104 1.57

ESRF

(X-ray Light source) 2010

5606 5538 98.8 % 83 67.5 0.8

Australian

Light Source 2010 4859 4784 98.5 % 82 59.25 0.9

Swiss Light Source 2009 5007 4941.9 98.7 % 69 72.6 1


ACCELERATOR RELIABILITY NOWADAYS

From the previous graph, we can conclude that nowadays, with lot of efforts to obtain high reliability, typical particle accelerators (running 208 days – 5000 hours / year) have :

98 % < Availability < 99%

0.8 hour < Mean Time to Recover < 1.6 hours

40 < Faults / year < 100

60 hours (2.5 days) < MTBF < 109 hours (4.5 days)

i.e., on average, a typical X-ray source stops 1 hour every 3 days

Is it sufficient for the requirements of future accelerators?

DEFINITELY : NO


Example: Accelerator Driven System (ADS) requirements

Reminder: What is an ADS ?

This is a sub-critical reactor driven by a proton accelerator.

The accelerator bombards a target with high-energy protons which produces a very intense neutron source through the spallation process.

Basic accelerator requirements: protons, ~ 1 GeV, ~ 10 mA

Cyclotron ? Linac ?

1 proton on the spallation target will release about 20 neutrons


What is it used for ?

• Destroy heavy isotopes contained in the used fuel from a conventional nuclear reactor, while at the same time producing electricity.

Why ? Because the long-lived transuranic elements in nuclear waste can be fissioned, releasing energy in the process and leaving behind the fission products which are shorter-lived. This would shorten considerably the time for disposal of radioactive waste.

• Enhanced safety of ADS: once the accelerator is turned off, the system shuts down.

• If the margin to critical is sufficiently large, reactivity-induced transients can never result in a super-critical accident with potentially severe consequences

Why is this a promising technology ?




Why an ADS must be extremely reliable ?

Thermal shocks (i.e., on / off cycles, i.e., unexpected trips) must be avoided on critical parts (beam window, reactor vessel, inner barrel and turbine system)

The beam trip requirements follow from thermomechanical considerations of the spallation target and subcritical assembly and, for power production applications, reliable electrical power delivery to the grid

A Nuclear Power Plant has a hard limit on the number of thermal cycles during its lifetime, mainly due to thermal fatigue in the vessel and main instrumentation



Until now, the reliability goal of the accelerators was ‘we do the best we can’.

With ADS, the reliability is for the first time a CONSTRAINT (technical and economical).

September 2010, following Monte Carlo simulations, there was a consensus about ADS reliability requirements

Reminder: the best statistics (KEK) are 40 faults / year but … 1 hour to recover, not 5 minutes !

Accelerator and Target Technology for Accelerator Driven Transmutation and Energy Production H. Aït Abderrahimh, J. Galambosd, Y. Gohara, S. Hendersonc*, G. Lawrencee, T. McManamyd, A. C. Muellerg,

S. Nagaitsevc, J. Nolena, E. Pitchere*, R. Rimmerf, R. Sheffielde, M. Todosowb


SUMMARY III:

• Nowadays accelerator reliability figures : 1-hour failure every 3 days (70/80 faults/year)

• First ADS prototypes could tolerate 50 failures / year, only stopping for a few minutes!

• Industrial ADS can NOT tolerate more than 2/3 failures (> 5 mins) / year !

When preparing this talk, I read many papers about ADS and realised that :

• Many references for ADS papers come from … Accelerator Reliability Workshops !

• ADS community performs fascinating work to explore all ways to improve accelerator reliability.

• ADS community is, like us …, dreaming of a centralised database about reliability of accelerator equipment / components (topic for Friday !)



A CHAIN IS AS STRONG AS ITS WEAKEST LINK

- Design optimization (margin, materials, modelling, )

- Preventive Maintenance

- Experience from other Institutes

- Realistic Operation Schedule

- Redundance

- Avoid human mistakes with automation when necessary

- Avoid unnecessary interlocks (passive sensors are sometimes sufficient)

FAILURE

- Fault Diagnostics !

- Rigorous Spare part Policy

- Experts on standby 24 hours/day ready to intervene

- Operator training

- Fast interchangeability of components (<- design …)

- Repair procedures

Before the failure After the failure: minimise time to repair

The optimization of ALL the above points (and many more) is thoroughly considered by the ADS community (as well as by others …).


ACCELERATOR RELIABILITY NOWADAYS : one example at the ESRF

0

50

100

150

200

250F

ri 0

4 F

eb 0

8:00

Sat

05

Feb

08:

00

Su

n 0

6 F

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8:00

Mo

n 0

7 F

eb 0

8:00

Tu

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Feb

08:

00

Wed

09

Feb

08:

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Fri

11

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08:

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Sat

12

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8:00

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8:00

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Feb

08:

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16

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08:

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u 1

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8:00

Fri

18

Feb

08:

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Sat

19

Feb

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8:00

Mo

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8:00

Tu

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Feb

08:

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Wed

23

Feb

08:

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25

Feb

08:

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Sat

26

Feb

08:

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8:00

Mo

n 2

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8:00

Tu

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Mar

08:

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02

Mar

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3 M

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8:00

Fri

04

Mar

08:

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795.5 hours (33.1 days) of delivery without a single failure

7/8+1 7/8+1 7/8+1 16 BunchUniform

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16 Bunch

107 refills !


CONCLUSIONS

• Accelerator reliability is no longer a wish but has become a constraint (ADS)

• A requirement of 2-3 trips > 5 mins per year is a goal for the next generation

• Reliability is now considered at all stages of the accelerator’s life (from design to maintenance in routine operation)

• Exchanges and workshops are essential to explore all possibilities and take the best from everyone: ARWs have an active role to play !


• Centralized information about accelerator reliability is missing and should be discussed at this ARW (Friday)!

• Centralized database (what should it contain ?) :https://sites.google.com/site/particleacceleratorreliability/Home

• Accelerator reliability papers

• Statistics and records of present accelerators

• etc

HOMEWORK FOR FRIDAY !

http://reliability.forumotion.com/

https://sites.google.com/site/particleacceleratorreliability/Home

http://reliability.forumotion.com/


I have some questions …

• In your lab (or company), was the rate of faults / year simulated and taken into account for the design ?

• (For the Industrialists here: are you subject to penalties if you exceed a certain number of failures / year ?)

• Homework for Friday :

• Any ideas on how to build a centralized failure database for accelerator sub-equipment /

components ?• How would it be organised ?• To which level of equipment should

it extend ?• Where should it be hosted ?•

Date post:	17-Dec-2015
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Accelerator Reliability Workshop – Cape Town 2011 L. Hardy – ESRF Operation Group1 A BRIEF...

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