time of flight ( tof ) : basics
DESCRIPTION
Time of Flight ( ToF ) : basics. Start counter. Stop counter. TOF – General consideration - early developments combining particle identifiers with TOF A ) TOF for Beam Detectors or mass identification - TOF Constituents - based on the use of SEE effect: - PowerPoint PPT PresentationTRANSCRIPT
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Time of Flight (ToF): basicsStart counter Stop counter
• TOF – General consideration - early developments combining particle identifiers with TOF
• A) TOF for Beam Detectors or mass identification - TOF Constituents - based on the use of SEE effect: - Thin Foils (SE generation) - SE transport
- SE detection ( mainly MCP – some basic set-up )
• B) Fast electronics - Fast preamplifiers and discriminators LE; CFD; ARC-CFD - Time walk and jitter –basic consideration
• C) Timing MCA-DAQ
2. Lecture
3. Lecture
1. Lecture
• D) Combining TOF with BPM technique
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Timing MCA
a) Classical approach TPHC (TAC) – ADC
b) TDC - direct Time-Digitizer (TDC) - Time - Expansion (Time-to-Charge) - direct Digital Interpolation TDC
c) DAQ for Timing
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Principle of TPHC (TAC)
ADC (13-14 bit) (Dead Time 1-4 µs)
Performance
Time resolution ----- FWHM ~ 5ps
Differential DNL ----- <+/- 2%
Integral INL --------- < 0.1%
Ranges ---- 50; 100; 200 ns Multiplier x 1; 10; 100, 1k or 10k
Delay ----- 0.5 µs to 10.5 µsWidth ----- 1µs to 3 µs
Strobe circuitry: INT or EXT mode
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Selection of ADC - DAQ for TAC solution
Tconv. = T clock x N
• Linear slope - CC Gen.
• VREF comparator
• clock• synchronized counter
To set the DGF-4C in integrator mode · set Integrator (ch.#) =1) · chose an integration time ~ 2-3µs · set gap time of energy filter = 0
To set the Analog Input attenuators: JPx01 - OFF for 1:7.5 attenuator JPx02 – ON for 50 ohm termination
TAC + Standard ADC +CC
TAC + DGF (Rev.F) + CC
SAR-ADC Tconv. ~ 1µs
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Principle of Direct Time Digitizer
tm(stop) –tm(start) = N. T0(oscillator)
even with a clock with F0 ~1-5 GHz the timing resolution is
to poor, namely 1ns or 200 ps in comparison with the 5 ps of previous the TAC – ADC combination up-graded versions of TDC: - time expansion; - interpolated; - time vernier
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(t” – t’) vs. (tm(stop) –tm(start)) expansion factor
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Time expanding (multihit) TDC
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Principle of Interpolating in Direct Time Digitizers
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An interpolating Time-to-Digital converter implemented on an FPGA structure
Start
Stop
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tD = MTr / ND
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- tentative 1ps time resolution
• Start_ Slow Digitally Controlled Oscillator -- Slow DCO ~ Ts (period) • coarse counter
• Stop Fast DCO ~ Tf (period)
• T input = T Sp - TSt =
= Tcoarse + Tfine = NsTs +Nf (Ts-Tf)
~ 65 ns CMOS technology ~ 1ps resolution
Y. Park et al, A Cyclic Vernier TDC Converter synthesized from a 65 nm CMOS technology, ISCA2010
A cyclic vernier TDC
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Part 3 AMS – Combining TOF technique with Beam Profile Monitors (BPM)
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• Beam Profile Monitor (BPM) - Why they are needed ?to reconstruct the kinematics of the ions after they are decelerated to energies of ~ 5 MeV/u (in the context of the HISPEC/DESPEC, also of importance to the RISING/PRESPEC)
• slowing down relativistic beams energy straggling and particle space divergence
• Beam Detectors are requested to: - to determine the Beam Profile , - to determine the Particle Trajectories Tracking - combining TOF with BPM ∆M/M ~ 1/300
and all these at highest transparency and larger active surface!
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1) E.J. Sternglass, Phys. Rev. 90 (1953),p.380 and 2) H.P. Garnir et al, SEE from thin foils… NIM 202 (1982), p.182-192
Total SEE yield as a function of the target’s tilt angleTotal SEE yield as a function of the target
temperature for Ar+ ions at different energies
( the beam current is interpreted as a temperature effect, i.e. the rise of temperature increased vibrations of the atoms mean free path of electrons is shortened yield decreases)
The total yield of Secondary Electrons emitted when ions pass through a thin carbon foil function of beam current and tilt angle of the target
- Sternglass theory and latter the Modified-Sternglass theory, namely a two steps mechanism: - formation of internal secondary electrons in material as a result of excitation and ionization processes - SEE (secondary electron emission) - escape from the target
θ┴
Target
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θ┴
Target
Beam axis
H.P. Garnir et al, SEE from thin foils…, NIM 202 (1982) p.182-192 and E.J. Sternglass, Phys. Rev. 90 (1953),p.380 and E.J. Sternglass, Phys. Rev. 108 (1957),p.1
Total SEE yield as a function of the target’s tilt angle
According to Sternglass, in a tilted target there is an increase of length of the ion track within the “escape zone” which enhance the production of electrons near the surface without modifying the escape probability !!
The total yield of Secondary Electrons emitted when ions pass through a thin carbon foil as a function of tilt angle of the target
at least in the energy range 0.2 – 2 MeV
Parameter A shows that at low velocity,60% of the SEE yieldis independent of theangle of incidence andfor helium beam, thispercentage decreases with the ion energy
Cl+
He+
Ion velocity (mm/ns)
A
γc
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Commercial foils (films):
A) Goodfellow• Polycarbonate (PC) (brand names: Lexan; Macrofol; Macrolon)
Density ρ ~ 1.2 g cm-3
( minimum) Thickness 2 µm + Al ( ρ ~ 2.7 g cm-3) ( Au: ρ ~ 19.3 g cm-3 )
• Polyethylene terephthalate (Polyester, PET, PETP) (brand names: Amite; Dacron; Hostaphan; Mylar; Melaynar; Terylene etc.) Density ρ ~ 1.4 (1.3) g cm-3 (minimum) Thickness 2 µm + Al ( ρ ~ 2.7 g cm-3) ( Au: ρ ~ 19.3 g cm-3 )
• Polyimide (brand names: Kapton, Kinel; Upilex; Upimol; Kaprex) Density ρ ~ 1.42 (1.3) g cm-3 (minimum) Thickness 25 µm + Al (why only larger as 25µm ??)
B) Jeonyoung Electrochemicals (Gyeonggi-do, South Korea) is specialized in ultra-thin metal foil surface finishing by Ni, Ag, Cu - single-sided or double-sided 0. 1~2um-thick Ni-plated copper
C) Dali Electronics ? ( India) (www.domadia.com) - 1 µm SS 302, SS 304,…SS 318L etc. Ultra thin Stainless Steel Foils
D) …
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Secondary electrons path ion path
W. Starezecki at al./ LNL-Padova NIM 193 (1982) 499-505
Cu-Be 20µm diam. @ 1mm 98% transparence
1cm
see Michael PfeifferSIMION simulations
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(a)
(b)
Experimental set-up to determine the time spread of an electrostatic mirror. The electrons emitted from both side of the C foil are accelerated by a harp and directed to the MCPs by bending through: - a mirror (a), or - directly (b)
Time of flight spectrum of: ~6 MeV α particle; both start & stop from MCP detectors
- 213 MeV 58Ni elastically scattered at 4 ° from a 20 μg/cm(*2) 12C foil-target
C-foil
10-20 µg/cm2
+ ~3.5 µg/cm2
• LiF evaporated onto the C-foil to enhance theSE emission
~157 ps
~280 ps
W. Starezecki at al./ LNL-Padova NIM 193 (1982) 499-505
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Heavy Ion Magnetic Spectrometer @ PRISMA (LNL-Padova )
• Large MCP - 80x100 mm (as @IKP-FAIR)• C-foil ~20µg/cm*2• Grids at 4mm and only 300eV (see Shapira et al.) (20µm gold-plated Tungsten@ 1mm)• SE drift path ~ 10 cm• External Magnetic field ~120 Gauss (important for position resolution!)
beam test 40Ca
~ 400 ps
~ 350 ps
Lab. test alpha-particles
G. Montagnoli et al. NIM A 547 (2005) 455-463
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• Carbon foil ~ 20 µg/cm2 –self supporting ! • good mass resolution ( 1/300)• ions direction with an uncertainty smaller than 0.5° and off-line tracking yields and velocity determination • ext. magnetic field (‘cyclotron’ frequency)
Notes for the file: - only one HV-PS IKP experience … - three grids ( 20µm Tungsten + Au @ 1mm) - magnetic field – reaction chamber size or external coil ?
G. Montagnoli et al. NIM A 547 (2005) 455-463
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O.H. Oldland, et al, A fats position sensitive MCP for charged particles, NIM A 378 (1996), p.149
• Gold plated tungsten ~150 µm diameter and NO Cu round frame and NO rectangular • grounding Cu plates ( shielding, reduce reflections due to mismatched of characteristic impedance• two differential amplifier at each end of a delay line with collection in only one of the wire of the parallel pair• due to differential amplifier, the signal is compensated for capacitive coupling, i.e. only collected charge signal
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M.B. Williams, S.E. Sobottka- High Resolution Two Dimensional readout of MCP withLarge Area Delay Lines, IEEE Trans. NS, 36, Feb.1989, p.227
- The characteristic impedance of both delay lines is Z0 ~ 130 Ω the preamplifier impedance ~ 130 Ω - The differential preamplifier with Zi ~ 300 Ω and balance-to-balanced transformers with turns ratio 2.75:1:75
- outer collecting winding ~ 700 V-inner collecting winding ~705 V- no-collecting windings ~ 650 V- central electrode ~ 500 V
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D. Shapira et al. / Factors affecting the performance of SED, thin foil…BPM, NIM A 449 (2000) 396-407
3-4 mm
3-4 mm
3-4 mm
45 mm
45 mm
Foils:C ~ 30µg/cm2
Mylar ~ 290 µg/cm2
Foil at 30° (relative to the beam direction )
( 2x to balance theelectrostatic forces)
(position sensitive read-out)
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Effect of multiple scattering
Angular spread in particle trajectories after traversing 4 µm thick Mylar
• 2µm Mylar (580 µg/cm2)
• tilted at 30°
SRIM
formula:
The number of secondary electrons:
two tendencies: - proportional with Zp
2/ Ep
(atomic number and particle energy)
- Code SRIM to estimate multiple scattering contribution of thicker
foils 16O ions exiting the foil binned as a function of polar angle
D. Shapira et al. / Factors affecting the performance of SED, thin foil…BPM, NIM A 449 (2000) 396-407
K.E. Pferdekämpfer, H.G. Clerc, Energy spectra of SE eject by ions from foils, Z. Physik A 280 (1977), p.155
R.A. Baragiola, Heavy particle induced SE from solids, NIM B 78 (1993) p.223
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Ion Beam Diagnostics with Particle Detectors
Paolo Finocchiaro, Low Intensity Ion Beam Diagnostics with Particle Detectors, INFN-LNS
The use of a thin CsI(Tl) scintillator
combined with gamma detectorsto identify theradioisotopes as afingerprint of theemitting nucleus
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O.H. Oldland, et al, A fast position sensitive MCP for charged particles, NIM A 378 (1996), p.149
~50-100 µg/cm2
The foil structure: ~0.5 µm Mylar + 20 µg/cm2 Al + 500Å CsI (SE x5)
GANIL- fast sensitive MCP based charge particle tracking
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O.H. Oldland, et al, A fats position sensitive MCP for charged particles, NIM A 378 (1996), p.149
The measured detector resolution ‘ρ’ plotted together with the theoretical curve – both function of the magnetic field for different target voltages: 3; 5 and 7 kV resp.
3kV 5 kV 7 kV
F = qE + qv x B
v = v┴ + v ║
Circular trajectory in a plane
perpendicular to the E and B - fields with the ‘cyclotron’ frequency :
ω = (qB)/(γm)
Radius of the orbital motion:
R = (mv)/(qB)
External magnetic field - helical trajectory with a so called ”cyclotron” frequency
[tesla] [tesla] [tesla]
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K.Kosev et al, A high-resolution TOF-Tracking capabilities…, NIM A 594 (2008) p.178
• intrinsic timing resolution 240 ps (FWHM)• position resolution 1.8 +/-0.3mm (FWHM)• foil thickness 163 µg/cm2• intend to be used at SIS-GSI, Darmstadt• relative large MCP detectors ( with active area > 12 cm2 )
TOF-BPM at ELBE electron accelerator
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- from foil to mirror front side (field free drift) region- inside electrostatic mirror (~ homogeneous field ??)- electrostatic mirror out and MCP in (-out ?)
d ~ 270 mmFoil 1-to-Foil 2
Apparent (intrinsic) MCP detectors resolution ~ 170 ps
K. Kosev et al, FZ Dresden-Rosendorf NIM A 594 (2008) 178-183
Simulation – SIMEON 3D( http://www.simion.com )
40Cl ~ 40 MeV
Alpha-particle ~ 5.8MeV
Detection efficiencyforwardemitted SE
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Calculated position resolution as a function of the grid wires pitch.----------- for particle deflected in the middle of the electrostatic mirror__________ for particle deflected at the edge of the electrostatic mirror
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- Angular resolution after reflection - ~ 1.5 - 2.5.10 ² sr - TOF time resolution - ~300 ps- Transparency/module - ~70 %
-
G. Pascovici, Institute of Nuclear Physics, Univ. of Cologne
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Michael Pfeiffer
SIMION3D simulation for TOF, BPM for the HISPEC-DESPEC @ FAIR
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Sketch of the “Hexanode” X;Y;Z – 2D
O. Jagutzki et al, Multiple Hit Readout of a MCp with a three layer DL anode, IEEE Trans. NS, Vol. 49,(2002), p. 2477
The hexanode readout
• Expanding the application of delay-line anodes for experiments with serious multihit demands• Maximize the multihit minimize the electronic dead-time• With three layer arrangement one can build also a delay- line anode with central-hole, e.g. to allow the beam pass through
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• Single Delay Line (SDL) configuration which consist of a planar zig-zag electrode etched into a copper layer on a substrate, that runs the entire length of the anode pattern. • It is interleaved with two sets of wedge shaped electrodes that are half a period out of phase the determination of the X and Y event centroid coordinates are totally independent for the SDL anode configuration.
• The charge is divided between the delayline and the wedges in a ratio that may be chosen to suit the X and Y resolutionrequirements.• Material: SiO2; Duroid ε ~10 & HF; 5mm thick; Cu~18µ
O.Siegmund et al, High resolution Delay Line readouts for MCPs, NIM A310 (1991)p311
Xc = (T +Td) .v/2 v - signal propagation
T - the difference in signal arrival times
Yc = fQ1/(Q1+Q2)
Q1;Q2 the charge signal
detected at the two wedge electrodes
R0~ 43 Ω; v/2 ~ 0.53 mm/ns Td ~ 60 ns size: 53 x 53 mm
Qi - CSP
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A. Prochazka, C. Nociforo et al.
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• Timing Preamplifier - Ultra Fast current tr (intrinsic) ~ 600ps• Position Preamplifiers Differential read-out (X2 (active) - X1 (passive))
Pulser InT- Output
Timing
DDL differential read-out
X1
X2
T1
(X1-X2)
tr < 600ps (intrinsic)
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DAQ
G. Pascovici, Institute of Nuclear Physics, Univ. of Cologne
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