Beam diagnostics, monitoring and control in accelerators

Viatcheslav Grishin

RLTP -2018

Задачи диагностики пучка

Aim: assist in commissioning, tuning and operating the accelerator and to improveperformance

1. Ввод в эксплуатацию нового или модернизированного ускорителя: – проводка пучка по каналам транспортировки; – измерение и согласование эмиттанса пучка и акцептанса ускорителя; – контроль пучка в процессе настроики инжекции и захвата

2. Оперативное управление ускорителя в процессе регулярнои работы, измерение и коррекция следующих параметров: • равновесная орбита пучка;• бетатронные и синхротронная частоты;• хроматизм;• поперечные и продольныи размеры пучка;• связь бетатронных колебании;• средняя энергия и энергетическии разброс частиц пучка; • светимость (в коллаидерах).

3. Задачи ускорительнои физики необходимые для оптимизации ускорителя : – измерение и коррекция структурных функции; – изучение нелинеинои динамики пучка; – исследование коллективных эффектов и подавление неустоичивостеи; – анализ внешних возмущении движения пучка.

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Мониторинг потерь пучка

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• A serious problem for high currentaccelerators is high density of the beam, which is able to destroy the equipment and to make a quench of super conductivemgnets.

• Loss of even a small fraction of the intensive beam would results in high radiation and destruction of the equipment.

The Beam Loss Monitor (BLM) system must be sensitive to different level of losses in different accelerator locations. BLM system protectionshould limit the losses to a level, whichensures hands-on-maintenance or intervention. On the other side, the BLM system should be sensitive enough to enablethe fine tuning and the machine studies withthe help of BLM signals. Beam loss monitoringis the cornerstone element in the accelerator protection and beam setup.

EMU – Ion sourceESS, Lund, Sweden

Beam Instrumentation

• Large range of technologies• Fields involved include:

Accelerator physics – particle physics – RF technology –optics – mechanics – electronics – software engineering – ... • Harsh environment:

Radiation (SEE, radiation ageing, activation)Many sources of measurement noise and background

Place readout close to detector, but radiationRF heating by the beamAccessibility and maintenanceSometimes: cryogenic temperaturesMostly: must operate in vacuum and be UHV compatible

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Требования к системе мониторов потерь пучка

• Sensitivity• Dynamic range• Time response• Type of radiation• Shield-ability (from unwanted radiation)• Response to excesive radiation ( saturation effects)• Physical size of BLM• Test-ability• Calibration techniniques• System end to end online test• Cost

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Instrumentation varies

Linac and transport lines : single passSynchrotron : multi passHadron Accelerators:

collider, storage ringspallation neutron sourcetherapy accelerator

Electron Accelerators:synchrotron light sourcefree electron laser linac

• Protons/Ions: non-relativistic for Ekin < 1 GeV/u • Total Beam Energy (beam particles x particle energy) low ↔ high• Non-intercepting ↔ Intercepting ↔ Destructive (often depending

on beam energy)

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Resources and References

• the CERN accelerator school ”Beam Instrumentation 2018” in Helsinki (Finland), especiallyRhodri Jones: Diagnostics Examples from High Energy CollidersManfred Wendt: BPM SystemsGero Kube: Beam Diagnostic Requirements Overview

• Eva Barbara Holzer: Beam Instrumentation andBeam Diagnostics at WE-Heraeus-Seminar onAccelerator Physics for Intense Ion Beams , 2012

• Peter Forck: Lecture on Beam Instrumentation and Diagnostics at JUAS

• Thomas Shea , Ryoichi Miyamoto: several presentations at ESS (Lund, Sweden)

• В.В. Смалюк : Диагностика пучков заряженных частиц в ускорителях, Новосибирск 2009

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Examples of BI at LHC : BPM, BLM

BPMpickup

BPMpickup

BPMpickup

BPMpickup

BPMpickup

BPMpickup

BPMpickup

BPMpickup

beambunch

beam orbit(trajectory)

pickupsignal

Read-outelectronics

BPMdata

required foreach BPM pickup

Part 1 BPM pickups

& 2

Courtesy M.Wendt

Beam Diagnostics Systems in ESS Linac

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Spokes Medium β High βDTLMEBTRFQLEBTSource HEBT & Contingency Target

2.4 m 4.6 m 3.8 m 39 m 56 m 77 m 179 m

75 keV 3.6 MeV 90 MeV 216 MeV 571 MeV 2000 MeV

352.21 MHz

704.42 MHz

Instrumentation in LEBT

Tom Shea - NCFE meeting, Catania

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EMU

NPM

FC

• FC– Measure the total beam current

• Doppler– Measure the ion species fraction

• EMU– Measure the transverse phase

space

• NPM– Measure beam profile and

position– Will be used as an optical BPM

to measure the beam trajectory

• BCM (downstream of this chamber)– Measure the transported current

Doppler (port hidden on bottom side)

Instrumentation in LEBT

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Solenoid 1 (Steerer 1)

Chopper CollimatorSolenoid 2(Steerer 2)

Iris

- FC- EMU (H)- EMU (V)- NPM (H)- NPM (V)- Dpl

- NPM (H)- NPM (V)- BCM

Permanent tank Commissioning tank

Beam stop

- EMU (V)- NPM (H)- NPM (V)- FC

BCM

Source extraction

Courtesy R.Miyamoto

Measured parameters

• Beam intensity• Beam energy• Ideally: 6D phase space of the beam

– Transverse position (mean x, y) – Transverse profile– Bunch length– Mean momentum and momentum spread– Emittance and space reconstruction (transverse and longitudinal) – Beam halo measurements

• Tune, chromaticity, coupling, beta function, dispersion • Beam Losses• Polarisation • Luminosity

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Classification of some BD devices

13H. Koziol, CAS

•Different devices(techniques) to measurethe same quantity•Same device to measuredifferent quantities•Effect on beam dependson circumstances:

N none- slight, negligible + perturbingD destructive

Different Labs (different

machines) have different

names

Current Measurements

Faraday cups: Measurement of the beam’s electricalcharges • Low energies only• Particles are stopped in the device• Destructive• Sensitive to low currents• Absolute accuracy: ≈ 1% (some

monitors reach 0.1%)

14courtesy of PANTECHNIK

Courtesy P. Forck

Цилиндр Фарадея (Faraday cup)

• Цилиндр Фарадея (Faraday cup) — один из стареишихдатчиков интенсивности пучка, основным достоинством которого является высокая точность измерения заряда. В простеишем виде цилиндр Фарадея представляет собои массивныи, электрически изолированныи электрод, стоящии на пути пучка заряженных частиц. Когда пучок частиц поглощается материалом электрода, цилиндр Фарадея оказывается электрически заряженным. К электроду с помощью подводящего провода подключается сопротивление, замыкающее цепь на землю. Таким образом, цилиндр Фарадея является частью замкнутои электрическои цепи, состоящеи из двух частеи —вакуумнои, в которои носителями заряда являются частицы пучка, и твердотельнои, где носителями заряда являются электроны проводимости.

• При отсутствии потерь заряда электрическии ток в проводнике эквивалентен току пучка в вакууме.

• Главным критерием является допустимая утечка заряда за счет проницаемости цилиндра Фарадея для частиц пучка.

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Current Measurements

Beam Current Transformer (BCT)

Non-interceptiveIndependent on beam energy

Beam acts as single turn primary winding of transformer measuring AC component of beam current

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N Turn winding

U = L · dI/dt

Courtesy E.B.Holzer

Beam Current BCT

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Beam current IBeam=eNq /t=eNqc/w

Magnetic field of the beam is very low (Example: 1 μA, r = 10cm 2 pT; compared to earth magnetic field of ≈50 μT)

Aim of the Torus: Capture magnetic field lines with cores of high relative permeabilitySignal strength nearly independent of beam position.

BergozCourtesy P.Forck

Электромагнитные датчики (Трансформаторы тока пучка)

• Магнитоиндукционныи датчик для измерения интенсивности имеет вид обмотки с распределенными по азимуту витками, охватывающими пучок. Для измерения интенсивности испольуют датчик в режиме трансформатора тока, когда сигнал пропорционален току пучка.

• Прототипом всех магнитоиндукционных датчиков тока является пояс Роговского (AC Current Transformer, ACCT), представляющии собои трансформатор, вторичная обмотка которого намотана на кольцевои сердечник из ферромагнетика, а первичнои «обмоткои» является траектория тока пучка, пролетающего сквозь кольцо. Сигнал в измерительнои цепи генерируется переменным магнитным потоком, создаваемым током пучка, и представляет собои переменное напряжение, частота которого равна частоте следования импульсов тока пучка.

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Transformer Housing

Courtesy S. Varnasseri and H.Hassanzadegan

Beam Position Monitors

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BLM Pickups

Quadrupoles

beam

Courtesy M. Wendt

•Among the most numerous instruments

Measurements:* Transverse beam position (typically next to focusing elements) * Beam trajectory or closed orbit injectionoscillations* Tune and lattice function in synchrotrons

Working principle:

•Image current in vacuum chamber walls: equal size and

opposite sign of the AC beam component

•Monitor the image wall current with a plate inserted in the

beam pipe

•Adapt BPM electronics integration timesingle-bunch ↔ multi-bunch

turn-by-turn (single pass) ↔ multi-turn average

BPM Systems

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are based on Beam Position Monitors (BPM), which are beam detectors located along the accelerator

– BPM: Beam Position Monitor• Beam pickup with signal processing (read-out) electronics

– Often colleagues just refer to the beam pickup as BPM

– BPMs are typically located near each quadrupole magnet• Use 4 or more BPMs per betatron oscillation period

• deliver beam orbit (trajectory) information– Non-invasive monitoring based on the EM-field of the passing beam– Synchronized BPMs deliver beam timing information

• Beam orbit measurement– turn-by-turn, batch-by-batch, bunch-by-bunch, or averaged over many turns

• Beam phase or time-of-flight (TOF) information in linacs

• are a powerful beam diagnostics tool– Machine commissioning, characterization of the beam optics,

measurement of beam parameters, trouble-shooting,…

M. Wendt

Main use of BPM systems:Measure & correct orbit or trajectory

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Orbit excursion too large ⇒ need to correct

Courtesy R.Jones, Finland, 2nd – 15th June, 2018

Electrostatic BPM

-- - - -+

+ + ++- +

++- -

+ -++

-- +

-- ++- + -

-- - - - -+ +

++- +

+ +- -+

-+ +- -

+ -+ -- -

- - - -++ +

+- ++

+- -+ -+

+

-- +

-- ++-+-

V

- - - - - - -

-+

+ ++ +

--+ -

+ - +- + -

- - -+ ++

- ++ -+ - -+ -+

- -- - -

++ + -

++ -- +-

-

-

-

-

-

-

courtesy O.R. Jones R

Beam Position Monitor Principle

d

• The BPM principle is based on symmetry– The beam displacement d is detected by a pair of symmetrical

arrange electrodes

– What happens if the beam / bunch intensity changes?!• The 𝚫-signal still contains beam intensity information!• Need to “normalize” the 𝚫-signal

courtesy O.R. Jones

=–

𝜟 ∝ 𝐩𝐨𝐬 × 𝐢𝐧𝐭

Transverse Profile and EmmitanceMeasurements

25

Emittance Measurements:Linear machine• Transfer profile and angulr

distributionCircular machine:• In dispersion free region

Beam Profile measurements:• Secondary emission grids and screens• Wire scanners• Synchritron light monitors• Ionization and luminescence monitors

Secondary Emission (SEM) Grids, Harps

26

•When the beam passes through, secondaryelectrons are emitted from a wire, proportional to beam intensity•The current flowing back onto the wires is measured using one amplifier/ADC chain for each wire •Very high sensitivity, semi-transparent •Good absolute measurement•Spatial resolution limited by wire spacing to <≈ 0.25mm• Dynamic range: ≈ 106

Grid: wires in both transversal planes Harp: wires in one transversal plane SEM: strips

Courtesy E.B.Holzer

Сеточныи датчик (secondary emission grid)

• Вторично-эмиссионныи датчик (secondary emission grid, secondaryemission monitor, SEM) представляет собои сетку из металлических полосок или проволочек,помещенную на пути пучка. Так как вторичная электронная эмиссия — это поверхностныи процесс, то в датчике можно использовать очень тонкую фольгу или проволочки (1−10 мкм) без потери чувствительности. В конструкции вторично- эмиссионного датчика предусматриваются высоковольтные электроды, создающие электрическое поле для отвода вторичных электронов.

27

Courtesy P.Forck and G.Kube

Luminescent Screens

• destructive method

• part of deposited energy results in excitedelectronic states → used also for beam position (instead of BPMs)

• light emission (CCD)

• high energy deposition (→ Bethe Bloch) especiallycritical for heavy ion machines

• degradation of screen material

28

C.Bal et al., Proc. of DIPAC 2005 Lyon, France, 57

Люминофорныи экран

• Для визуального наблюдения пучка частиц используется люминофорныи экран (luminescent screen, phosphor screen), помещаемыи на пути пучка.

• Люминофорныи экран представляет собои пластину с нанесенным на нее слоем люминофора — вещества, излучающего фотоны видимого света при попадании на него частиц пучка. Взаимодеиствуя с веществом люминофора, частицы пучка теряют часть своеи энергии на ионизацию, в свою очередь часть ионизационных потерь преобразуется в оптическое излучение.

• Процесс излучения происходит в три этапа: 1) поглощение атомами вещества энергии частиц пучка; 2) передача части поглощеннои энергии центрам

люминесценции с их возбуждением в излучающее состояние; 3) возврат центров люминесценции в основное

состояние с эмиссиеи фотонов. • Экран вводится в вакуумную камеру с помощью дистанционно

управляемого привода, изображение пучка на экране регистрируется камерои.

29Courtesy: CH. Wiebers (DESY)

Profile Monitor:Luminescent Coatings and Gases

Inserting luminescent materials into the beam is invasive, but there are options for protection applications

30

Apply thin coating to cooled surfaces of targets and windows

Use residual gas (N, H, or near targets, He)

beam

metal

coolant

luminescent coating

metalcamera

gas

Courtesy P.Forck

Scintillation Screens

• Typically for setting-up with low intensities, thickscreens (mm) emittance blow-up

• Sensitivities of different materials vary by orders ofmagnitudes

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Courtesy P. Forck, JUAS

Bunch Shape Monitor (BSM)

primary beam hits thin wire , potential -10 keVconversion of primary hadron beam into low energy secondary electrons

RF deflector converts time into space coordinatesOperation close to RF zero-crossing

Intensity profile with spatial resolving detector

32

Courtesy Perry

A.Feschenko, S. Gavrilov

Wire Scanners

• A thin wire (down to 10 μm) is moved across the beam• Has to move fast to avoid excessive heating of the wire • Rotational scanner up to 10 m/s with special

pneumatic mechanism (linear scanners slower) • Detection

– Secondary particle shower detected outside the vacuum chamber e.g. using a scintillator/photo-multiplier assembly

– Secondary emission current detected as for SEM grids– Correlating wire position with detected signal gives the

beam profile– Wire vibrations limit position resolution Secondary particle shower intensity in dependence of primarybeam energy

33

for beam energy below 150

MeV use instead secondary

emission (SEM) current of

isolated mounted wire

Courtesy G. Kube, DESY/MDI

Wire Scanners (ESS type)

34Courtesy B.Cheymol and J L Blasco

Ionization Profile Monitor

Residual Gas IonisationDynamic range: up to 103

≈ 10 times more sensitive than LuminescenceImage broadening due to space charge More complicated to build

High voltageGuiding magnetic fieldCompensation magnets for the beam

35

• Residual gas ionization induced by beam

• High electric field to drive ions toward a sensitive detector

beam profile transversal projection

2 profilers (X and Y projections)

C.Thomas

Beam Loss Measurements for Protection and Diagnostics

Common types of monitors • Long ionisation chamber (charge detection)

Up to several km of gas filled hollow coaxial cablesLongitudinal position information by arrival time measuremente.g. SLAC – 8m position resolution (30ns) over 3.5km cable lengthDynamic range of up to 104

• Cherenkov fibersTime resolution 1 nsMinimal space requirementInsensitive to gamma background, E and B fieldsRadiation hard (depending on type)Combination fiber / readout can adapt to a wide dose rangeDynamic range 104

36

Beam Loss Measurements for Protection and Diagnostics

Common types of monitors• Short ionisation chamber (charge detection)

Typically gas filled with many metallic electrodes and kV bias Speed limited by ion collection time - tens of microsecondsDynamic range of up to 108

• PIN photodiode (count detection) Detect charged particleInsensitive to photons from synchrotron radiation

due to coincidence counting in two back-to-back mounted PIN diodes

Count rate proportional to beam loss Speed limited by integration timeDynamic range of up to 109

• Scintillators plus photo-multipliers• Diamond

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Diamond Detectors

• Fast and sensitive

• Small and radiation hard

• Used in LHC to distinguish bunch by bunch losses

• Dynamic range of monitor: 109

• Temporal resolution: few ns

• Investigations now ongoing to see if they can work in cryogenic conditions

38

Courtesy E.B.Holzer

Ionization Chambers

• Ionization chambers are the main type of loss monitors used in hadron machines.

• Gas-filled chambers containing an electrode pair with biasing high voltage.

• Operated in ‘ionization’ mode, the detector is insensitive to HV fluctuations.

• “Small” chambers are installed along specific components and provide adequate spatial resolution.

, Slide 39

Beam loss monitors, produced by CERN-IHEP collaboration

• Ionization chambers (IC) , which are installed at local aperture minimum and loss locations.

• Secondary Emission Monitor (SEM) – detector at very high dose rates locations.

• Little Ionization Chamber (LIC) – detector, designed to reduce the sensitivity to saturate for higher losses.

• Flat Ionization Chamber (FIC) -detector designed to geometry considerations.

40

LIC

FIC

Families of BLM , producedPrortvino

BLM Ionization Chambers and SEM at CERN

BLM LHC system had ~3929 monitors with 3518 Ionization Chambers (IC), 108 LIC and 191 SEM

BLM PSB system had 32 installed IC and 32FIC.

LINAC 2 had 5 ICLINAC 4 installed 24 IC~100 ICs are in PS

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LHC Radiation Day, B. Dehning

29.11.2005

• Ion-chambers can be build from radiation hard materials (ceramic, metal),

with no aging. Take care about the feedthroughs. No problems up to more than 108 rad

• Large numbers >4000 for CERN => cheap

• LHC: It is necessary to periodically verify the connection to the corresponding channels of the electronic system and the signal quality of all detectors by radioactive source.

Ionization Chamber

IONIZATION CHAMBERS

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• Design criteria: Signal speed and robustness

• Parallel electrodes (Al) separated by ~0.5 cm

• Voltage 1.5 kV

– Standard LHC

– ESS, GSI, LUPAC

– Length 50 cm; Sensitive volume 1.5 l

– 61 electrodes

– N2 gas filling at 1.1 bar

• Composition of the chamber is the only component in the BLM system which is not remotely monitored online: Properties of the chamber gas are sufficiently close to air at ambient pressure (i. e. inside a detector which has developed a leak) in order not to compromise the precision of the BLM system, but sufficiently different to detect a leak during the annual test of all the chambers with a radioactive source.

– Electron / ion collection time 300ns / 80s

– Monitor dynamic range (> 108):

limited by leakage current through insulator ceramics (lower) and saturation due to space charge (upper limit).

IHEP VACUUM STAND

44

2005 2018

0

20

40

60

80

100

120

140

160

180

200

220

240

0 3 4 6 8 10 11 12 13 15 17 19 21 23 25 27

Время, час

Тем

пер

ату

ра,

С

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

P,m

bar

Stand heat treatment cycle of the ionization chambers

Stand heat treatment cycle of Secondary

Emission Monitors .

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40 45

Time [hour]

Te

мp

erа

тu

re [

°C]

1,E-10

1,E-09

1,E-08

1,E-07

1,E-06

1,E-05

1,E-04

Стенд

Мониторы

Давление[мбар]

IHEP designed and built the Ultra

High Vacuum production stand, which

is equipped by quadrupole mass

spectrometer, detecting the

composition of the gases inside the

system. The pumping system consists

of two arms – manifolds with 18

connection ports with individual

valves for each ionization detector of

different types and dimensions, SEM

or proportional chambers.

Courtesy A.Larionov

QUALITY TEST AT DETECTORS PRODUCTION

45

The various tests were performed at IHEP before,

during and after the production to verify the quality

of chambers. All welds are He leak tested, including

the head.

Tests of IC

46

Dose rate to current conversion for ionization chambers: energy deposited by ionizing particles in the chamber gas is converted to a signal current.

1 Gy/s = 5.4E-5 A (for IC) 1 Gy/s = 3.86E-6 A (for LIC)

Courtesy E. Nebot del BustoThe monitors are testing at different

environment:

Xrays measurement in Spiral2 by

J.Marroncle (CEA) and ESS team in

Uppsala (Sweden),

in magnetic field at 1.5 Tesla in H2

channel at CERN.

HRM

H2

DETECTORS VERIFICATION

47

Each detector is calibrated by using a strong gamma source in the CERN Gamma Irradiation Facility

(GIF and next generation GIF++).

For each detector the tests consists of leakage current and radioactive source induced signal measurements.

830 IC -2017830 IC -2017

4250 IC -2008

Verification of IC in LHC tunnel

48

•LHC: It is necessary to periodically verify the connection to the corresponding channels of the electronic system and the signal quality of all detectors by radioactive source.

Courtesy D. Gudkov

Secondary Emission Monitor

49

<10-7 bar< 1% ionization to avoid nonlinearities

In accelerator areas with very high dose rates SEM chambers are employed to increase the dynamic range. The SEM is characterized by

a high linearity and accuracy, low sensitivity, fast response and a high radiation tolerance. The signal and bias electrodes are made of Ti to

make use of Secondary Emission Yield stability. The emission of the electrons from surface layer of metals by the passage of charged

particles is only measurable in a high vacuum , which leads to an ultra high vacuum preparation of he components and to an additional

active pumping realized by a getter pump (NEG). The sensitivity is about a factor of 3-7 x 104 smaller than in the ionization chamber.

A nice signal of a SEM and IC at IP3 in 2011

Little IonizationChamber

50

• The LIC detectors have been designed to reduce the sensitivity to saturate for higher losses with respect to LHC IC and to be a good extension to the IC. While IC performance works well for protection, the limited dynamic range of read-out electronics are satured for high losses and LIC is the most feasible detector. The LIC active zone consists of 3 parallel Aluminium electrodes, nitrogen filled with ceramics insulator SEM type.

Pressure

N2, [mbar]

U, [kV] Current

,

[pA]

100

1,5

< 1

100 2,0 2,3 spark

200 2,0 3,0 < 1

200 2,5 spark

300 2,5 3,0 < 1

300 3,0 spark

400 3,0 < 1

500 3,0 < 1

Choice of LIC working pressurewith two and one shieldings

Finally – 1.1 bar and 280 LICs refilled

Flat Ionization Chamber

51

The FIC detectors designed to geometry considerations and foreseen to be located and currently installed in LHC

booster. The prism FIC active zone consists of 3 parallel Aluminium electrodes, nitrogen filled with special designed

ceramics insulator SEM type.

Design and production of the

first flat ionization chamber (FIC).

CERN,IHEP (Protvino)

A. Larionov, B. Dehning, V. Grishin, V. Seleznev, A. Kopyrin

Design and production

of the first flat ionization chamber.

Bernd’s proposal:

- the flat ionization chamber with dimension in beam

direction about 50mm for Booster;

- the standard rectangular st. steel tube with 50x80mm

dimensions and 2mm wall thickness.

It was executed check-up of the tube wall strength as

flat chamber is pumping during production time.

Check-up of the tube wall strength

• For st.steel 304L: yield strength – σy=170MPa,

coefficient of strength stock ny = 1,5.

• Permissible stress for yield strength:

σy.p= σy/ny=113MPa

• The wall thickness is as S=224b/√ σy.p + C = 2,1mm, where b=80mm –wall length, C=0,4 –thickness tolerance.

• Finally rectangular tube with 2mm wall is suitable.

Flat IC assembly

• Outer dimensions: 50x80x310mm.

• Working volume ~100 sm³.

Summary

• Диагностика пучка – одна из наиболее активно развивающихся дисциплин , находящаяся на перекрестке разных областеи: ускорителеи, физики, электроники, программирования и …

• Обычно основных приборов достаточно для рутиннои работы ускорителя

• Но для постоянно возникающих проблемах необходимы новые приборы и методы

• Никогда не бывает мало диагностики пучка

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