Time of Flight (ToF): basics
Start counter
1. Lecture
•
Stop counter
TOF – General consideration
- early developments combining particle identifiers with TOF
• A) TOF for Beam Detectors or mass identification
2. Lecture
- 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
3. Lecture
- Fast preamplifiers and discriminators LE; CFD; ARC-CFD
- Time walk and jitter –basic consideration
• C) Timing MCA-DAQ
• D) Combining TOF with BPM technique
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
Principle of TPHC (TAC)
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 µs
Width ----- 1µs to 3 µs
Strobe circuitry: INT or EXT mode
ADC (13-14 bit)
(Dead Time 1-4 µs)
Selection of ADC - DAQ for TAC solution
TAC + Standard ADC +CC
•
•
•
•
TAC + DGF (Rev.F) + CC
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
Tconv. = T clock x N
SAR-ADC Tconv. ~ 1µs
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
(t” – t’) vs. (tm(stop) –tm(start))  expansion factor
Time expanding (multihit) TDC
Principle of Interpolating in Direct Time Digitizers
An interpolating Time-to-Digital converter implemented on an FPGA structure
Start
Stop
tD = MTr / ND
A cyclic vernier TDC
- 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
Part 3
AMS – Combining TOF technique
with Beam Profile Monitors (BPM)
•
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!
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
( 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)
Total SEE yield as a function of the target
temperature for Ar+ ions at different energies
Total SEE yield as a function of the target’s tilt angle
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 angle
γc
The total yield of Secondary Electrons emitted
when ions pass through a thin carbon foil 
as a function of tilt angle of the target
Beam axis
θ
┴
Target
at least in the energy range 0.2 – 2 MeV
A
Cl+
He+
Ion velocity
(mm/ns)
Parameter A shows
that at low velocity,
60% of the SEE yield
is independent of the
angle of incidence and
for helium beam, this
percentage decreases
with the ion energy
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 !!
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
Commercial foils (films):
A) Goodfellow
•
Polycarbonate (PC) (brand names: Lexan; Macrofol; Macrolon)
Density ρ ~ 1.2 g cm-3
-3
( minimum) Thickness 2 µm + Al ( ρ ~ 2.7 g cm ) ( 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) …
Secondary
electrons path
ion path
1cm
Cu-Be 20µm diam. @ 1mm
 98% transparence
see Michael Pfeiffer
SIMION simulations
W. Starezecki at al./ LNL-Padova
NIM 193 (1982) 499-505
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)
~280 ps
(a)
C-foil
10-20 µg/cm2
+ ~3.5 µg/cm2
• LiF evaporated
onto the C-foil to
enhance the
SE emission
(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
W. Starezecki at al./ LNL-Padova
NIM 193 (1982) 499-505
~157 ps
Heavy Ion Magnetic Spectrometer @ PRISMA (LNL-Padova )
Lab. test
alphaparticles
~ 350 ps
beam test
40Ca
• 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!)
~ 400 ps
G. Montagnoli et al. NIM A 547 (2005) 455-463
• 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
• 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
O.H. Oldland, et al, A fats position sensitive MCP for charged particles, NIM A 378 (1996), p.149
- outer collecting winding ~ 700 V
-inner collecting winding
~705 V
- no-collecting windings
~ 650 V
- central electrode
~ 500 V
- 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
M.B. Williams, S.E. Sobottka- High Resolution Two Dimensional readout of MCP with
Large Area Delay Lines, IEEE Trans. NS, 36, Feb.1989, p.227
(position sensitive
read-out)
( 2x to balance the
electrostatic forces)
Foils:
C ~ 30µg/cm2
Mylar ~ 290 µg/cm2
3-4 mm
3-4 mm
3-4 mm
Foil at 30°
(relative to the
beam direction )
D. Shapira et al. / Factors affecting the performance of SED, thin foil…BPM, NIM A 449 (2000) 396-407
Effect of multiple scattering
The number of secondary electrons:
• 2µm Mylar
(580 µg/cm2)
• tilted at 30°
SRIM
formula:
 two tendencies:
- proportional with Zp2/ 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
Angular spread in particle trajectories after traversing
4 µm thick Mylar
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
Ion Beam Diagnostics with Particle Detectors
The use of a thin
CsI(Tl) scintillator
combined with
gamma detectors
to identify the
radioisotopes as a
fingerprint of the
emitting nucleus
Paolo Finocchiaro, Low Intensity Ion Beam Diagnostics with Particle Detectors, INFN-LNS
GANIL- fast sensitive MCP based charge particle tracking
The foil structure:
~0.5 µm Mylar
+ 20 µg/cm2 Al
+ 500Å CsI (SE x5)
~50-100 µg/cm2
O.H. Oldland, et al, A fast position sensitive MCP for charged particles, NIM A 378 (1996), p.149
External magnetic field - helical trajectory with a
so called ”cyclotron” frequency
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)
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
[tesla]
5 kV
7 kV
[tesla]
[tesla]
O.H. Oldland, et al, A fats position sensitive MCP for charged particles, NIM A 378 (1996), p.149
TOF-BPM at ELBE electron accelerator
•
•
•
•
•
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 )
K.Kosev et al, A high-resolution TOF-Tracking capabilities…, NIM A 594 (2008) p.178
Apparent (intrinsic) MCP detectors
resolution ~ 170 ps
d ~ 270 mm
Foil 1-to-Foil 2
Simulation – SIMEON 3D
( http://www.simion.com )
Detection
efficiency
forward
emitted SE
40Cl ~ 40 MeV
- from foil to mirror front side (field free drift) region
- inside electrostatic mirror (~ homogeneous field ??)
- electrostatic mirror out and MCP in (-out ?)
Alpha-particle ~ 5.8MeV
K. Kosev et al, FZ Dresden-Rosendorf
NIM A 594 (2008) 178-183
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
- 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
Michael Pfeiffer
SIMION3D simulation
for TOF, BPM for the
HISPEC-DESPEC @ FAIR
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 delayline anode with central-hole,
e.g. to allow the beam pass
through
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
R0~ 43 Ω;
v/2 ~ 0.53 mm/ns
Td ~ 60 ns
size: 53 x 53 mm
• 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 delay
line and the wedges in a ratio that may
be chosen to suit the X and Y resolution
requirements.
• Material: SiO2; Duroid
ε ~10 & HF; 5mm thick; Cu~18µ
Xc = (T +Td) .v/2
v - signal propagation
T - the difference in
signal arrival times
Qi - CSP
Yc = fQ1/(Q1+Q2)
Q1;Q2 the charge signal
detected at the two wedge
electrodes
O.Siegmund et al, High resolution Delay Line readouts for MCPs, NIM A310 (1991)p311
A. Prochazka, C. Nociforo et al.
T- Output
Timing
Pulser In
tr < 600ps
(intrinsic)
T1
X1
(X1-X2)
X2
DDL differential read-out
• Timing Preamplifier
- Ultra Fast current
tr (intrinsic) ~ 600ps
• Position Preamplifiers
Differential read-out
(X2 (active) - X1 (passive))
DAQ
G. Pascovici, Institute of Nuclear Physics, Univ. of Cologne