1. Radiation Monitor: Concepts, Simulation for an Advanced Read Out
R.Cardarelli end A.Di Ciaccio
INFN-Roma Tor Vergata
Super-B Collaboration meeting 31/05/2012
Isola d’Elba La Biodola

2. Outline Location of the beam monitor in the Super-B detector
Geant4 simulation to define the parameters of the monitor detector and F.E. electronic
Test of a mono c. v.s. poli c. diamond detector with SiGe amplifier
Conclusions and future plane

3. Radiation Monitor near SVT.
Diamond detectors
Primary goal: protect the SVT from high beam losses
Next features: time of flight measurements to distinguish collisions events
from background

4. Geant4 beam monitor simulation

5. Tentative detector shape
R1 = 18.2 mm
R = 18 mm
L = 7 mm
S = 1 mm
R = 12 mm
S = 1 mm

6. Geant4 results: rate per mm**2 for radiative Babbha
Expected rate on Beam-monitor rings 1, 2
Bins da 1mm2
Highest rate about 0.25 MHz / mm2 (on Backward)
Possible explanation : SuperB beam asymmetry
Forw
Back

7. Geant4 results : Edep Rate vs Edep Possible threshold at 150 KeV
Violet band
Particelle al minimo di ionizzazione

8. Geant4: time of flight
70 ps

9. Geant4 summary results L = 1 x 1036 cm-2 s-1
Rate (MHz)
Edep/sec
(GeV/s)
nHits/Event
Edep/Hit
(GeV)
Rate/mm2
(MHz/mm2)
% Hits
(>150KeV) Z
(mm)
Tube Ext (Back)
19.9
1780
0.09
9.0x10-5
0.035
22%
-80
Tube Ext 2 (Back)
46.4
2080
0.20
4.5x10-5
0.082
10%
-126
Tube Ext (Forw)
12.8
1115
0.06
8.7x10-5
0.023
21% 80
Tube Ext 2 (Forw)
30.0
1305
0.13
4.3x10-5
0.053
126

10. Diamond Detector (area 16mm**2)
Rate/mm2
(MHz/mm2)
Tube Ext (Back)
0.035
Tube Ext 2 (Back)
0.082
Tube Ext (Forw)
0.023
Tube Ext 2 (Forw)
0.053
CVD Parameters:
traccolta: 20ns (on 1mm thickness)
tintegr: 30ns
Ethr > 150KeV
max expected rate in selected regions for beam monitor 82 KHz /mm2
With a detector area of 16mm2 this corresponds to 1312 KHz
Only 10% above 150KeV (only 130 KHz counted by the detector).
130 KHz corresponds to 0.3% electronics dead-time

11. Ionization currents on CVD diamonds
Total Edep
Edep/sec
(GeV/s)
Tube Ext (Back)
1780
Tube Ext 2 (Back)
2080
Tube Ext (Forw)
1115
Tube Ext 2 (Forw)
1305
Edep per mm2 al secondo
N e-h pair / mm2 X s
Area ring
Current I per mm2
Energy necessary to produce a e-h pair in diamond
For a sensor of 16mm2 an ionization corrente of nA

12. geometry of the detector Diamond detector 4mm x 4mm
8 diamond detector for ring
Beam monitor caracteristics L = 1 x 1036 cm-2 s-1
detector sized
8 X16 mm2
leakage current
8 nA
Ionization current
0.67 nA
hits rate
130KHz
Detector Transit time
20 ns
Electronic Integration time
30 ns
Electric resistance
1011 Ωcm
Energy threshold
150KeV
Diamond detector 4mm x 4mm

13. Tentative electronic diagram
Disipation
power 8µW HV
500 Volt
100 kOhm
10m coax. Cable Ǿ = 0.7 mm
Pico
Amp
Diamond
detector
amp
Coincidence
caunter
CPU
amp

14. BJT Si v.s. SiGe BJT Si BJT performances β=τc/τt ft=1/τt N= K*τt
τc= base life time
τt = base transient time
τt (Si) >> τt (SiGe)
diffusion
Fermi energy B E C
acceleration
BJT SiGe
Fermi energy B E C

15. Strategy for a new front-end(SiGe)
A (mV)
In signal A
T(ns)
F= 1 / T
T(ns)
100
A (mV)
Out signal
100 10
T(ns) 10
100
1000 ft
F (MHz)

16. Amplifier, AC, (BJT SiGe, BFP740)
Voltage supply Volt
Sensitivity mV/fC
noise e- RMS
Input impedance Ohm
B.W MHz
Power consumption mW/ch
Low cost – 3 eur./ch
Radiation hardness Mrad, 1015 n cm-2

17. Diamond detector under tests
Mono crystal diamond
thickness ,5 mm
Area x 4 mm2
HV Volt
Dissipation power μW

18. Current vs HV (sCVD- diamond detector)

19. Americium Sr-90
Am-241
Sr-90
noise

20. Coincidence with cosmics.
10ns
Diamond
detector PM

21. Coincidence with cosmics
2mV
5ns

22. Signal minimum ionization particle
20ns/div.
20ns/div.

23. Drift of the signal shape (s-CVD diamond)

24. Diamond detector under tests
poly crystal diamond
thickness ,5 mm
Area x 4 mm2
HV Volt
Dissipation power μW

25. Poly-CVD Diamond alfa-Am source ( log scale)

26. Idea on a new detector layout
Transient time 5 ns Area 16 mm2
0.25 mm

27. Conclusions
A Geant4 MC simulation of the SVT beam monitor was performed to determine
Geometry
Expected background rate
Beam monitor FE electronics specification
Next steps: further test of CVD diamonds (mono and poly-cristalline) with beams

28. Alfa Americium – 241
Alfa Americium-241
Noise

29. Amplifier, AC, (BJT SiGe, BFP650)
Voltage supply Volt
Sensitivity mV/fC
noise e- RMS
Input impedance Ohm
B.W MHz
Power consumption mW/ch
Low cost – 3 eur./ch
Radiation hardness Mrad, 1015 n cm-2

30. Alfa Americium – 241
Alfa Americium-241
noise

31. Amplificatore RC due stadi, AC, (BJT Si)
Tensione di lavoro Volt
Sensibilita’ mV/fC
Rumore e RMS
Impedenza di ingresso Ohm
B.W MHz

32. Simulazione
Ove possibile, si sono utilizzate coppie vicine di volumi simili per ottenere un sampling più fine della rate attesa nella regione
Tronco di cono inclinato per massimizzare il cammino della particella all’interno del volume

33. Signal minimum ionization particle
40ns/div.

34. Two stage ac amplifier, AC, (BJT Si BFQ67)
Voltage supply Volt
Sensitivity mV/fC
noise e- RMS
Input impedance Ohm
B.W MHz
Power consumption mW/ch
Low cost – 3 eur./ch

35. Noise distribution

36. Parametrizzazione dei rivelatori
Calcolo della corrente di leakage su un sensore al diamante di 1mm x 1mm con una tensione applicata di 500V
Resistenza offerta dal sensore
Corrente di leakage che attraversa il sensore a fascio spento
Per un sensore di 16mm2 si ottiene una corrente leakage di:
0.5x16 = 8 nA ovvero 80 x A
La corrente indotta dai fasci è 10 volte minore di quella di leakage quindi si richiede un elettronica in grado di rivelare piccole variazioni della corrente
(almeno 1/10 della minima corrente da misurare)