hv boards and mumetal integration - pessina gianlugipessina.mib.infn.it/biblio/lhcb/rich meeting...
TRANSCRIPT
1
HV BOARDS and MUMETAL Integration
Claudio Arnaboldi
Tito Bellunato
Emanuele Panzeri
Gianluigi Pessina (*)
INFN Milano Bicocca
2
HV BOARDS and Magnetic field SHIELDING
-20 kV
-19.7 kV
-16.4 kV
The acceleration and focusing of the photoelectrons need 3 high voltages
The magnetic field must be shielded. A mumetal is foreseen around each HPD with a small gap, less than 1 mm: good insulation must be provided.
mumetal
mumetal
3
HV BOARDS: half column organization
-20 kV
-19.7 kV
-16.4 kV
A
B
C
A
B
C
A
B
C
A
B
C
5GΩ
Monitoring simplified diagram
The single -20 kV line enters each semi-column. It is split by a voltage divider in the final 3 HV voltages.
The 3 voltages feed the rest of the semi-column.
Two kind of boards are used: one with the splitter, the other with the voltage monitoring. Both of them bias a pair of HPDs.
A monitoring system is provided. Only one monitoring system is needed per semi-column. Therefore, the boards are not fully populated.
4
Column view: summer test 2005
HPDsHalf-column
Board with splitter
Board with splitter
Board with/without splitter
Board with/without splitter
Picture from Didier Piedigrossi
5
HV boards and LV boards
Picture from Didier Piedigrossi
LV boards
6
HV connections to the HPDs
Picture from Didier Piedigrossi
HV cables from HPDs
7
HV Boards layout: the PCB
The PCB measures 165 mm x 90 mm x 2 mm.The PCB has four layers.The HV tracks are buried under 0,8 mm of FR4 fiber glass to obtain very large insulation (FR4 has a dielectric strength of 80 KV/mm)
FR4
CopperPCB cross-section
2 m
m
0.8
mm
Many precautions has been taken to suppress any form of electrostatic breakdown.
The first step was a 4 layer PCB with buried tracks. Cuts has been implemented to be filled with rubber to shield the electric field parallel to the board itself.
8
HV Boards layout: silicon rubber protection
A silicon rubber having 20 kV/mm of break-down voltage covers the boards on each side.
9
HV Boards layout: silicon rubber protection and GND
New version
10
HV boards characterization
GND BS
= current monitor
= voltage monitor
To test the boards after production a sort of “analog boundary scan” is provided.
The line GND BS collects only the leakage current (nA range), while in the Main GND the whole biasing current from the splitter and the monitoring resistors is measured (tens of µA).
After the test the GND BS is connected to the main GND to provide low a impedance path.
Every board is checked in such a way for days under HV bias before passing the test.
Main GND
11
Test and monitoring of the HV boards in Milano
PC with MATLAB
Programmable power supply
HV Power SupplyISEG
HV HV boardsboards
Multichannel multimeter
Protection network
= analog values
= Digital data
Watch dog
ISEG
GPIB
GPIB
UPS
12
Results from irradiation
This board was covered with the so called DC 3-4241.
The leakage current is very small, at the limit of the instrumentation set-up.
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5Board covered by DC 3-4241 (after neutron irradiation)
Days
Lea
kage
cur
rent
(nA
)
-22
-21.5
-21
-20.5
-20
-19.5
-19
Hig
h V
olta
ge (K
V)
Average Ambient conditions: 20±2 °C and 50±8 % relative humidity.
Neutron irradiation gave no effects on the working condition of this board.
13
Monitoring
2.5 V
1.2 MΩ
1.4 MΩ Pt1000Pt1000
Keithely 2700 6½ digit
multimeter
Elmb
10 GΩ
1.8 MΩ
HV board
We tested the monitoring system with the ELMB boards:
14
ElmbElmb resultsresults
0,036
0,0365
0,037
0,0375
0,038
0,0385
0,039
0,0395
0,04
1
260
519
778
1037
1296
1555
1814
2073
2332
2591
2850
3109
Board 1Board 2
day0 1 2 3
mV
00,10,20,30,40,50,60,70,80,9
1
1
241
481
721
961
1201
1441
1681
1921
2161
2401
2641
2881
3121
Board 1Board 2
day0 1 2 3
mV
ZOOM
The system works fine.
15
Mumetal Integration
mumetal
mumetal The gap between the mumetal and the HPD is very small, less than 1 mm. The mumetal is to be connected to GND for safety reasons.
It needs an electric shielding material with very good insulating properties between the HPD and the mumetal to avoid discharges.
16
Which insulator?
Kapton 8x25.4 µm: excellent dielectric properties,good mechanical characteristicsexcellent radiation tolerancehygroscopic
extremely long (6 months!) delivery time
Polyester 3x125 µm: very good dielectric properties (only 10% less than Kapton)excellent mechanical characteristicsgood radiation tolerance
(tested up to 50 times the total estimated dose in LHCb)delivery time 4-5 weeksnon hygroscopicslightly flammablethicker
We tested two different insulator types:
17
Experimental results
The testing concerned the electrostatic discharge properties when the insulator is put in the final set-up.
The magnetic shielding investigation is in progress.
18
Mumetal Integration: Kapton
0 0.5 1 1.5 2 2.5 3 3.5 4-5
-4
-3
-2
-1
0
1
2
Leak
age
curre
nt fr
om c
apto
n (n
A)
Leakage current from capton
Days0 1 2 3 4
-25
-21
-17
-13
-9
-5
-10
HV
(kV
)
The measured leakage was consistent with the specs.
19
Mumetal Integration: Polyester
A dummy HPD has been biased with the 3 HV provided from an HV boards biased with a ISEG supply voltage.
The measurement is a sort of mini-system test.
20
Measurement conditions
(Slightly) dummy HPD: complete and functional withhigh leakage current from the silicon sensor
Polyester film 3x125 micron wrapped around
Mumetal shield 760 micron thick, dimensions in specs
HV board prototype and ISEG power supply at nominal value 20 kV
Monitoring HV, current from the HPD pins (grounded)and from the mumetal (grounded)
21
Leakage from polyester
0 2 4 6 8-5
-4
-3
-2
-1
0
1
2
3
4
5C
urre
nt fr
om m
umet
al (n
A)
Leakage current from mumetal (20-Jul-2005 11:33:58)
Days0 2 4 6 8
-20
-15
-10
-5
0
HV
(kV
)
Shut Downduringweek-end
The leakage from the system is adequately small.
22
Conclusion: Polyester vs Kapton
• Dielectric strength: ~10% less for same thickness
• Non hygroscopic• Cheaper (~factor 20)• Promptly available (4 weeks vs 6
months)• Easier to handle• Slightly less radiation resistant, but
still factor 50 safe (data from NASA)
23
Future actions
Continue test in dry environment
Stop cycling and leave maximum HV for one month
Independently test breakdown properties(current profiles, sparks) without HPD
24
Spare slides
25
Actual monitoring circuit
A
B
C
A
B
C
5GΩ
VREF>0
Monitoring
Since the ELMB it is able to read only positive voltage levels we propose the following scheme where an offset is added > 0 V
RA
RA
RA
RB
RB
RB
The voltage measured is:( )
HAB
B
REFHAB
B
VRR
R
VVRR
RVmeas
+≈
−+
=
VH
VH