PMT simulation within Offline - Université de Pariscreusot/Presentations/AlexMal... ·...
Transcript of PMT simulation within Offline - Université de Pariscreusot/Presentations/AlexMal... ·...
PMT simulation within
Creusot Alexandre, Veberič DarkoMalargue April 2009
Introduction
TWO MAIN OBJECTIVES
Solve the discrepancy between experiment and simulation in the photoelectron number.
Update the current Offline model
Investigation of several PMT simulation models
Thin film treatment of the photocathode
Comparison with Photonis calibration experiment
Fast and simple model
Define a new effective quantum efficiency
Test of the validity of the model
Stateofart
=> Presented in November 2008
Further improvements: the multiplier structure=> PE number of 69
=> Photocathode simply refractive or absorbent
=> Photonis calibration taken into account
+46%+95%+31%increase70956348
Maximum of the Water absorption length: 100mLiner reflectivity: 94%
For VEM
Thin film model of PMT
Characteristics
Mirror reflectivity = 97%
Multiplier reflectivity = 30%
Neck reflectivity = 0%
Glass index = 1.47
PHOTOCATHODE: COMPLEX INDEX OF
REFRACTION
Photocathode absorption A(, )
Fresnel equations for a thin film(d is the thickness of the photocathode)
n=−i
n=η− iκ
Photocathode absorption A(, )
d = 20 nm = 442 nm
Conversion factor
Reference: for a perpendicular beam and for = 375 nm26% of the photons are detected (Photonis experiment)
Definition: probability for an absorbed photon to free an electron
Assumption: This probability does not depend on wavelength [there is an experimental evidence it does not depend on angle]
The conversion factor cf is obtained from the dedicated simulation of the Photonis experiment and is equal to 0.4
Quantum efficiencyDefinition: the quantum efficiency q is the probability for a
photon to free an electron at the crossing of the photocathode
Obtained with the Offline GEANT4 simulation modules
q λ=A λc f
Incoming photons
: Angle between the arrival direction and the normal to the photocathode surface
Distribution of the wavelength of the photons arriving on the photocathode
Wavelength Angle
Glass cutoff Outgoing photons reflected at the dome
water interface
Reflection at the dome entrance
(waterdome interface)
PMT dome
waterPMT dome
water
Effective quantum efficiencyDefinition: the effective quantum efficiency qeff is the probability for
an incoming photon to free an electron.
where is the probability for the αphotons transmitted in the PMT to
reach again the photocathode.correction factor
qeff will be used in the original, simple and fast model of PMT (current model used in Offline)
qeff λ=q λ1α λ
qoffline
Results
Results
3.033.053.02Q/A58 ns58 ns59 ns
868848NPE
Offline rescaledThin filmOfflinemodel
=> and Q/A are the same
=> NPE improved significantly and comes close to the experimental value (94)
Comparison with Granada measurement
See Sergio Navas presentation for more information
Angular dependence
Conclusion
+46%70
+83%88
+79%+95%+31%increase
86956348
rescaled
Photonis calibration taken into account
The problem of the PE number is solved
fine tuning by adjustment of the tank variables
The thin film model can safely be approximated with the current (simpler and faster) Offline model if q
eff is used.
no need of the slow Geant4 tank module (with tracking of all photons)
Outlook
The thin film model will be implemented in the Offline framework and the quantum efficiency of the current model
will be updated to the effective one
Additional measurements: internal part of the PMT (multiplier reflectivity, mirror absorption…)
USERS SHOULD RUN THE SIMULATION WITH THE CURRENT OFFLINE MODEL AND THE
EFFECTIVE QUANTUM EFFICIENCY!
Comparison with Granada measurement
Wavelength