Beam diagnostics, monitoring and control in accelerators Viatcheslav Grishin RLTP -2018
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
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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
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•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
31
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
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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.
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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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