Transcript (ppt)

GLAST LAT Project
HV-short risk evaluation from bubbles cut - 12 Nov, 2004
Preventive Cuts (Pcut) Procedure
• originally thought to prevent
delaminations in TVAC
• only performed on 8 tower0
trays on W-side (8layers)
• 26.5 cm/tile
• 4.24 m/layer
• ~34 m total length of tower0
preventive cut
L. Latronico
from ANNEX 02 to NCR/FM/INFN/RM2/003
1
GLAST LAT Project
HV-short risk evaluation from bubbles cut - 12 Nov, 2004
Bubble Cuts (Bcut) Procedure
Small (<2mm) cut far
from bias lines (>1mm)
using an edged scalpel
Insulation test (OL) with
an ohm-meter between
tray and shield plane
Used for tower0 trays
and # TowerA trays
Estimate of total bubble-cut for tower0 = 17layers x 2bubbles x 2mm <~ 7cm
L. Latronico
2
GLAST LAT Project
HV-short risk evaluation from bubbles cut - 12 Nov, 2004
Tower0 trays summary chart
Tower
Position
Tray
S/N
Tray
type
W
Pcut
Bcut (side)
18
001
TOP
Sand-Blasted (SB)
N
FAIL TVAC
Y17
No Si
17
048
MID
SB
N
Y(T/B)
X16-X17
No Si
16
047
MID
SB
N
FAIL TVAC
Y15-Y16
No Si
15
004
MID
Hand-Blasted (HS)
Y
Y(T/B)
X14-X15
No Si
14
017
MID
HS
Y
Y
Y13-Y14
No Si
13
012
MID
HS
Y
Y(T)
Y(B)
X12-X13
HV-short on bottom
12
011
MID
HS
Y
Y(T/B)
Y(B)
Y11-Y12
HV short on bottom
11
008
MID
HS
Y
Y(T/B)
Y(B)
X10-X11
HV short on bottom
10
006
MID
HS
Y
Y(T)
Y(B)
Y9-Y10
HV short on bottom
9
046
MID
SB
N
Y(T)
N
X8-X9
OK
8
007
MID
HS
Y
Y(B)
N
Y7-Y8
OK
7
010
MID
HS
Y
Y(B)
N
X6-X7
OK
6
009
HEAVY
HS
Y
Y(T/B)
N
Y5-Y6
75 disc. ch.
5
008
HEAVY
HS
Y
Y(T/B)
N
X4-X5
183 disc. ch.
4
035
HEAVY
SB
N
Y(B)
N
Y3-Y4
249 disc. ch.
3
011
HEAVY
SB
N
Y(T)
N
X2-X3
1319 disc. ch.
2
023
LIGHT
N
Y(T/B)
N
Y1-Y2
OK
1
015
LIGHT
N
Y(B)
N
X0-X1
21 disc. ch.
0
002
BOTTOM
N
Y(T)
N
Y0
L. Latronico
HV Short (side)
layers
Comments
OK
3
GLAST LAT Project
HV-short risk evaluation from bubbles cut - 12 Nov, 2004
Conclusions – risk assessment
• 0 short on shield lines
• 4 HV short on trays Pcut and Hand-Sanded W
• 23 layers OK on HV line (6 Pcut, 15 Bcut)
• 27 layers OK on shield line (8 Pcut, 17 Bcut)
 all shorts due to W whiskers generated from tiles hand-sanding which entered
long, deep Pcuts – such whiskers were actually observed
on towerA:
 NO Pcuts
 W tiles are etched and primed, therefore very flat, clean and whiskers-free
 Bcuts are superficial (see procedure)
Let’s calculate anyway a conservative HV-short probability:
a HV short would cause 1 ladder loss (on tower0 trays with HV-short we
disconnected HV resistors on MCM boards for all 4 ladders to avoid current flow)
Prob(1ladder-loss/Bcut) = 4 / 34 m x 2mm = 0.23 10-3 ,
i.e. 1ladder-loss every 4250 Bcut or
1 ladder with HV-short every 2150 ladders (assuming 1 Bcut every 2 ladders)
L. Latronico
4
GLAST LAT Project
HV-short risk evaluation from bubbles cut - 12 Nov, 2004
Conclusions – schedule constraints
List of available trays
type
TrayI
D
Bcut - bottom
Bcut - top
B
003
NA
10
B
004
NA
6,10,11
H
012
6,10,11
6,7,15
ready
H
010
7,10,11
6,7,10,11
ready
H
020
6,7,11,12
H
006
10,11
6,7,9,10,11
ready
H
005
10,11
11
ready
H
037
7
H
018
L
013
L
MCM pocket
ready
ready
small
11,15
small
7
7,11,12,16
small
013
7
7,11,12,16
small
L
004
10
6,10
small
M
042
II test article
TrayID
Bcut bottom
Bcut - top
MCM
pocket
M
078
10
1.14
small
M
082
11
11,12,10,14,15
ready
M
051
6
7,10
small
M
077
assembled
M
063
ready
M
050
assembled
M
053
M
066
M
079
M
064
7,8,12
M
081
7,10,14,15
M
080
2,7,15
11,10
ready
M
076
11
10
small
M
062
10
6,7,9,10,1
small
M
002
11
T
002
6,10
type
7
6,10
7,11
assembled
ready
assembled
7,12
ready
ready
ready
NA
NCR
3 trays without Bcut and MCM pocket deep enough to hold MCM
 GA flow will be slowed until new trays are available without Bcut
L. Latronico
5