tube#44: hv scan · 2015-06-30 · ∆vmcp1-to-mcp2 the electrons releasing from the first mcp have...
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Independent Bias Design (IBD)
HVpc
HV1T
HV1B
HV2T
HV2B
Ground
∆V1
∆V2
∆V3
∆V4
3.15 mm
2 mm
2 mm
Signals
3
4.2 nsRise time: 610 ps
Electron backscattering
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2
00
2 em ltUe
=
Photoelectron travel time:
Delay and range of backscattered photoelectrons:
1 02 sint t β≈ 1 2 sind l β≈
Maximum backscattered time:
( )1 0max2t t≈
L (cathode-to-MCP) should be small
( )1 max2d l≈
Tube#32
1.2 ns
[*] Samo Korpar, EDIT 2011
[*]
Tube#44
inelastic backscattering elastic
backscattering
L=3.15 mmL=2 mm
∆Vpc-to-mcp1
▪ The backscattering is related to the distance (3.15 mm) between the photocathode and the MCP. The large distance separates the time resolutions of the direct photoelectrons and backscattered photoelectrons
▪ The second peak is due to the inelastic electron backscattering ▪ The long flat tail is due to the elastic electron backscattering ▪ The second peak gets closer to the main with the increase of the bias HV
between the photocathode and the MCP
5
∆V=100 V ∆V=300 V ∆V=500 V
σ1 = 46 ps σ1 = 34 ps
σ1 = 30 ps
∆t=400ps
2.2 ns 1.4 ns 0.9 ns
∆t=180ps ∆t=120ps
∆Vpc-to-mcp1
!▪ To suppress the backscattering peak,
one need to reduce this distance and increase the bias voltage
▪ Proper HV: 300 V < ∆Vpc-to-mcp1 < 400V
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[V]pc-to-mcp
V6
100 200 300 400 500
t [ps
]6
0
200
400
600
800
1000
1200
Delay of backscattering
[V]pc-to-mcp
V6100 200 300 400 500
[ps]
1m
30
35
40
45
50
55
60
65
Time resolution
[V]pc-to-mcp
V6
0 100 200 300 400 500
Gai
n
10
12
14
16
18
610×
Gain
∆Vmcp
▪ The rise time improves with the gain and finally becomes stable
▪ The gain increases to a maximum (3*e7) and then decreases.
▪ The ratio of backscattered electrons features a 100 V wide plateau at 60%.
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[V]mcp
V6
800 850 900 950 1000
Gai
n
610
710
810 Gain of a pair of MCPs
[V]mcp
V6
820 840 860 880 900 920 940 960 980 1000
[ps]
rise
T
610
620
630
640
650
660
670
Rise time
Rat
io [%
]
30
40
50
60
70
80
∆V_mcp [V]800 850 900 950 1000 1050
Backscatted electrons
low gain
high gain but noisy
Ratio of the second peak
∆Vmcp
▪ HV on the MCP is one main source of the rise time
▪ HV on the MCP dominates the time resolution
▪ Proper HV: 860 V < ∆Vmcp < 960V
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[V]mcp
V6800 850 900 950 1000
[ps]
1m
28
30
32
34
36
38
40
42
44Time resolution
∆V=820 V ∆V=880 V ∆V=980 V
σ1 = 35 ps σ1 = 33 ps σ1 = 35 ps
∆Vmcp1-to-mcp2
▪ The electrons releasing from the first MCP have wide energy and angular spread.
▪ This voltage should be moderate to ensure enough electron energy for the second MCP, and enough transverse spacial spread to distribute the electrons to multiple pores of the second MCP.
▪ Proper HV: 200 V < ∆Vmcp < 400V, depending on the HV on the MCPs
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[V]mcp1-to-mcp2
V6
0 100 200 300 400 500
Gai
n
6
8
10
12
14
16
18
206
10×
Gain
[V]mcp1-to-mcp2
V6
100 200 300 400 500
[ps]
rt
500
550
600
650
700
750
800
850
900
Rise time
[V]mcp1-to-mcp2
V60 100 200 300 400 500
[ps]
1m
20
25
30
35
40
45
50
55
60
Time resolution
∆Vmcp=900 V
∆Vmcp2-to-anode
▪ This voltage is one of the main sources of the rise time.
▪ This voltage has little effect on the time resolution.
▪ Proper HV: results are unreasonable at low voltages. Tests need to be repeated
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Ris
e tim
e [p
s]
600
650
700
750
800
∆V_mcp-to-anode [V]-100 0 100 200 300 400 500 600
rise time
Gai
n
5E+06
1E+07
1.5E+07
2E+07
∆V_mcp-to-anode [V]-100 0 100 200 300 400 500 600
gain
σ [p
s]
30
31.6
33.2
34.8
36.4
38
∆V_mcp-to-anode [V]-100 0 100 200 300 400 500 600
time resolution???
Conclusion
▪ Due to the Large gap between the photocathode and the MCP, the inelastic electron backscattering forms a second peak in the timing distribution. The time resolution given in this report is from the first peak that represents the direct incident electrons.
▪ The HV on each stack component is scanned. ▪ Proper HV:
• 300 V < ∆Vpc-to-mcp1 < 400V; • 860 V < ∆Vmcp < 960V; • 200 V < ∆Vmcp < 400V • ∆Vmcp2-to-anode has to be retested.
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Next▪ Detail study on the electron backscattering ▪ Detail study on the ion feedback
Tube45
▪ In the first day, there was a 20 ns noise pulse which can be seen in the self-trigger mode without light
▪ In the second day, this noise pulse disappeared.
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first day second day