Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015 Beam Test of LGADs Hartmut F.W. Sadrozinski with Astrid Aster, Vitaliy Fadeyev, Patrick

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Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Beam Test of LGADsHartmut F.W. Sadrozinski

with Astrid Aster, Vitaliy Fadeyev, Patrick Freeman, Zachary Galloway,

Herve Grabas, Edmond Lee, Zhijun Liang, Abe Seiden, Andriy Zatserklyaniy SCIPP, Univ. of California Santa Cruz, USA

Marta Baselga, Pablo Fernández-Martínez, David Flores , Virginia Greco, Salvador Hidalgo, Giulio Pellegrini, David Quirion,

IMB-CNM, Barcelona, Spain

Nicolo Cartiglia, Francesca Cenna, Marco FerreroINFN Torino, Torino, Italy

Beam Test set-upAmplitude spectraTime resolutionThin sensorsLow-energy protons

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Low-Gain Avalanche Detector (LGAD)

Low-Gain Avalanche Detector (LGAD)

Marta Baselga, Trento WorkshopFeb. 2013

High-Field: Gain

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November nights in the H6 Beam Line….

2 300FZ LGAD (run 6474 G = 10-15) with Civitek Broad Band (BB) amp & CSA amp 50um epi LGAD (run 6827 G = 2-3) with Civitek BB. And Trigger: fast SiPMData taken with digital scope at 10 ps sample speed.

300 FZ BB

300 FZ CSA

50um epi

SiPM Trigger

Trigger: (OR of 300um FZ sensors). AND.SiPM

( SiPM resolution ~50 ps?).

Thanks to the AFP beam test group (Joern Lange and Michael Rijssenbeek)

for help and use of the trigger

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300um FZ: 1 MIP = 55mV

50um epi: 4 MIPs = 13mV

A(300um, G=15) = 17* A(50um, G=3)

The 300um FZ data are well explained as a sum

of 3 Landau distributions: 1, 2 and 3 MIPS

Multiple Landau fit to Amplitude Spectrum


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5

Multiple Landau fit to 1000V, 800V, 600V Bias

Spectra were taken at 3 bias voltages.

The fits to 1, 2 and 3 MIPS peaks can be

used to determine the beam composition and

the linearity and voltage dependence of the

gain, (clearly seen by the straight red line).


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BUT:Define the ratio of MPV at bias V relative to 600V bias.

The observed bias dependence of the MPV ratio is larger than the one of the total charge measured with back-side -TCT!

Is this predicted by simulations?

The max amplitude (MPV) of 1-3 MIPS scales with the bias.

The ratio of the max amplitude (MPV) of 2 and 3 MIPs relative to 1 MIP is constant vs. bias.

Bias Dependence of the Amplitude of MIPs

Hartmut F.-W. Sadrozinski, Beam Test of LGADs, 10th Trento, Feb. 2015

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Properties of the Landau distributions

The ratio sigma/MPV is constant

as a function of multiplication,

indicating that the excess noise

factor is not playing a role yet

Pulse Height Dispersion

DA/A = 0.7079d-0.266

According to our fits, the

Landau have a smaller width

than what is proposed by the

parametrization of Meroli et al.


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Time Resolution and Slew Rate

The time resolution depends on rise time τr , and τr depends on the collection time (i.e. the detector thickness). 3 terms: time walk due to amplitude variation, time jitter due to noise, binning.

Introducing the slew-rate S/ τr = dV/dt

(binning error is negligible at 10 ps sample rate)we find that for constant noise N, to minimize the time resolution, we need to maximize the slew-rate dV/dt of the signal.

Need both large and fast signals.

2bin2r

2RMS

thr

2 )12

TDC( +)

S/N

1( +)]

S

V([ = t

2bin22RMS

th2 )12

TDC( +)

dV/dt

N( +)]

dV/dt

V([ =t


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(300um FZ, BB) (50um epi, BB)

The expected dependence of the time resolution on the amplitude is observed both for FZ and epi sensors.

The time resolution varies from about 200 ps at low amplitude to about 100 ps at high amplitude.

Fixed low threshold and low CFD analysis are comparable,

The time jitter is a large fraction of the time resolution.

Amplitude Dependence of Time Resolution


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Surprise:Essentially σnj is independent of the amplitude, for FZ and epi, which means that the time-walk corrections are not working (yet!). For FZ beyond an amplitude of ~45 mV, there will be more than one MIP in an event.For epi: all events are multi-MIP.

Time Walk Contribution to the Time Resolution


As a measure of the time walk, define a jitter-less time resolution σ2

nj as the time resolution with the jitter subtracted

σ2nj = σ2

t - σ2j

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1000V Ch 2, 300um,

G = 15, C = 11 pF 500V Ch 1, 50um,

G = 3, C = 34 pF

Slew-Rate for MIPs: dV/dt(300um,10pF) = 4*dV/dt(50um, 34pF)

dV/dt distribution

Time-walk resolution is ~ independent of slew-rate: NO 1/(dV/dt)

Slew-Rate dependence of the Time Resolution


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Hartmut F.-W. Sadrozinski, Beam Test of LGADs, 10th Trento, Feb. 2015

Large Amplitude events: > 1 MIP

Amplitude distribution varies with slew-rate dV/dt.50% of large dV/dt events are Multi-MIP events!

About 50% of the large amplitude events show irregular rising edge due to overlap of several MIPs.

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As expected from the pulse pictures, the constant fraction discriminator (CFD) analysis with large fractions does not work for large amplitudes (multiple MIPs): the timing error rises with amplitude instead of falling!

Time resolution vs. Amplitude (300umFZ, BB)


Better when limiting the pulse amplitude to 1 MIP?

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In the CERN Beam Test, the Capacitance was 10 pF Weightfield WF2 simulation shows that changing to 2 pF (smaller sensors) improves slew rate by factor 2

Time resolution depends on slew-rate dV/dt (≈Signal/rise time)


Effect of Detector Capacitance (300um FZ)

N. Cartiglia, F. Cenna et al. “Weightfield”, 2014 IEEE NSS-MIC

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The beam test had large LGAD diodes with 34 pF capacitance.

We now have LGAD diodes with C = 6 pF which will improve the slew rate by factor 3.7

Future sensors with C = 2pF will improve theslew-rate by a factor 5.2

Risetime34pF 7.1E-102 pF 3.9E-10

Effect of Detector Capacitance (50um epi)Lower capacitance will improve dV/dt


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E [MeV] rel. dE/dx Time res. [ps]10 20.7 4.120 12.1 6.950 5.9 14.2

100 3.6 23.3200 2.2 38.2

Large dE/dx increases the slew-rate dV/dt

Predictions from WF2 simulations:For MIPs in 50 um sensorstime resolution: 30 ps with gain = 10 time resolution: 84 ps without gain

Predicted time resolution for protons in Ultra-fast Silicon Detectors without gain:

With USFD with gain = 10, the time resolution isimproved by another factor3 !

Low-energy protons afford very good time resolution, allowing the measurement of the proton energy by time-of-flight TOF.

Time Resolution for low-energy Protons


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Direction and energy of (low-energy!) secondaries are measured in telescopes of Ultra-Fast Silicon Detectors (UFSD) and projected back to identify the beam location.

D = 30 cm

UFSD: 50 um thin, pixels 300um x 300 um, Time resolution of 30 ps, i.e. “100ps & Gain = 10” allows energy measurement by TOFEnergy resolution on secondaries:100 MeV pions: 16% 100 MeV protons : 4%

UFSD will operate at 10 MHz rate and provide real-time beam diagnostics.

Protons

Head phantomHadron beam

Longitudinal distribution of energy deposition (Bragg peak) and number of secondaries

Interaction Vertex Imaging IVI with UFSD


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Protons of 200 MeV have a range of ~ 30 cm in plastic scintillator. The straggling limits the WEPL resolution.

Replace calorimeter/range counter by TOF:Light-weight, combine tracking with WEPL determination

Future: 4-D UFSD as WEPL Detector in pCT?


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• Beam Tests = “Lessons learned”.

• Multi-MIPs events need to be eliminated so that the slew-rate

dependence of the time resolution can be studied.

• Time resolution of about 200 ps has been found for single MIP, in agreement with simulations for the capacitances present.

• Improvements can be expected with lower capacitances (smaller detectors), especially for the 50 um epi sensors.

• Predictions for the time resolution of therapeutic low-energy protons in thin sensors show very good energy resolution using Time-of-Flight

TOF over a 30 cm distance.

Conclusions: Beam Test

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o Ultra-fast silicon detectors (UFSD) afford very good time resolution for low-energy proton (or ions) since they have very high slew-rare.

o The large slew rate due to the high specific energy loss of low-energy protons is enhanced by a factor 3 when a UFSD with gain = 10 is used. Timing resolution of < 10 ps for protons with E < 150 MeV are predicted.

o The fact that UFSDs have their best timing capability when the sensor is thin (< 50 um) goes hand-in-hand with the fact that tracking of low-energy protons need thin sensors to reduce MCS (Multiple coulomb scattering).

Use of UFSD in ToF for low-energy Protons


Documents

Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015 Beam Test of LGADs Hartmut F.W. Sadrozinski with Astrid Aster, Vitaliy Fadeyev, Patrick