Transcript Comments HERA Quench Statistics (K. Wittenburg) Bernd Dehning 12 Dec 2007 1

Comments HERA Quench Statistics (K. Wittenburg)
Bernd Dehning
12 Dec 2007
Bernd Dehning
1
Quench levels and transient
beam losses at HERA
Beam losses in operation (transient, continuous). What
beam losses lead to magnet quenches (for top energy
AND for injection). How to set BLM to avoid quenches?
By Kay Wittenburg, Div. MDI,
Deutsches Elektronen Synchrotron DESY, Hamburg, Germany
12 Dec 2007
Quench
2
HERA - Beam Current and Aborts
12
12

aborts (relative)
curent/10 [mA]
10
events / week
10

events/current/10
8


4
2
2
0
0
Average about 5 beam
aborts per week
6
4
Beam abort scale with
beam current
8
6
Initial phase – more beam
Maximal current
(luminosity) lowest number
of beam aborts (relative)
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
year
12 Dec 2007
Bernd Dehning
3
Statistic of BLM events 1993 - 1995
21
100
1993
1994
1995
90
18
80
15
1/3 BLMs
no BLMs
all
50
9
40
Errors
Quenches
5 ms events
BLM-Alarms
I beam current
30
6
20
3
10
47
44
41
38
35
32
29
26
23
20
0
45
42
39
36
33
30
27
24
21
39
36
33
30
27
24
21
18
15
0
12
0
9
events/week
60
12
beam current [mA]
70
week
12 Dec 2007
4
Statistic BLM events 1995 - 1997
21
100
1995
1996
90
1997
18
80
15
50
9
40
Errors
Quenches
5 ms events
BLM-Alarms
I beam current
30
6
20
3
10
42
39
36
33
30
27
24
21
18
15
12
9
6
46
43
40
37
34
31
28
25
22
49
46
43
40
37
34
31
28
25
0
22
0
19
events/week
60
12
beam current [mA]
70
week
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Statistic BLMp events 1998 - 2000
start after 5 month shutdown
20
1998
2000
1999
100
18
16
80
60
Since Week 39 (1998)
RF Interlock active
Less BLM alarms,
less 5 ms events,
less quenches
10
8
Errors
Quenches
5 ms events
BLM-Alarms
I
beam current
40
6
4
20
2
33
35
31
27
23
19
15
11
7
3
52
48
44
40
36
32
28
24
20
16
12
8
4
48
44
40
36
0
32
0
28
events / week
12
beam current [mA]
14
week
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Statistic BLMp events 2001 - 2003
start after 5 month shutdown (Lumi upgrade)
20
2001
2002
2003
2004
100
18
16
80
14
Errors
5 ms events
60
10
BLM-Alarms
I
Ibeam current
8
40
6
4
20
2
53
45
49
37
41
29
33
21
25
9
13
17
5
50
42
46
34
38
26
30
18
22
6
10
14
2
46
50
38
42
30
34
22
26
14
18
47
51
0
39
43
0
31
35
events / week
beam current [mA]
Quenches
12
w eek
12 Dec 2007
All
by 5 ms PS failure events
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Quench experiences (comparison with calculations) cont.
Num ber of Quenches
dispersion bump
13
12
11
10
Frequency
9
8
secondary's coll.
32 different locations
75 quenches (1994-2005)
most at 300 GeV/c in 1996, since 1997 4 BLMs at 198m locations
7
6
5
4
3
2
1
W
L
W 162
L
W 166
L
W 192
L
W 251
L
W 274
L
SR 344
4
SR 1 6
2
SR 5 1
2
SL 2 7
1
SL 16
1
SL 98
3
SL 45
6
O 97
R
O 768
R
O 628
R
O 299
R
O 199
R
O 173
L
O 198
L2
O 98
L
N 486
R
3
N 46
R
N 198
R
1
N 16
L1
N 16
L1
N 74
L1
N 98
L2
N 51
L
W 439
R
W 34
R 6
W 32 2
R
25
2
0
Location of m agnet
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Quench experiences (comparison with calculations) cont.
Two types of thresholds :
1.
1/10 of critical loss rate produce an alarm (rates varies with energy)
12 Dec 2007
2.
9
More than 4 BLMs above 1. dump the beam (for all energies above injection)
Quench experiences (comparison with calculations) cont.
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HERA experience with Beam loss induced Quenches 1994 - 2004
Slow losses
unknown
Diverse
Very fast losses
(< 5ms)
5%
Kollimator6%
Injection
2%
Operating
27%
3%
BLMs <4
8%
S = 200 Quenches
ALZ
Magnet PS
12%
13%
RF
8%
5 ms events
16%
12 Dec 2007
More about failures:
K. Wittenburg (DESY): Beam loss & machine protection
33rd ICFA ADVANCED BEAM DYNAMICS WORKSHOP on
HIGH INTENSITY & HIGH BRIGHTNESS HADRON BEAMS
Bensheim, Germany
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Note: A quench in HERA is not a disaster! It takes typ. 1-2 h to recover from cryogenic
HERA Summary I

About 11 quenches / year

About 100 aborts / year



64 % of quenches with a loss duration < 5 ms (200
turns), LHC 4 turns reaction times
20 % of quenches due to malfunctioning of BLM/MPS
(alarm system) and less than 4 monitors, at LHC the
operation has to be stopped until reasons are found
and repaired, every monitor triggers
Most of the quenches occurred not at injection
energy, longer recovery time
12 Dec 2007
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HERA to LHC Considerations

Much higher reliability is needed at LHC compared to
HERA (24 dangerous failures in system)



Adjustment of thresholds only once (beginning)
during 11 years of operation
Threshold are wrong by a factor 5 to 10 (never
readjusted)
LHC has two beams and much more components ->

Assuming the same reliability of components -> LHC will
have several times more aborts as HERA, operational
efficiently is strongly affected
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LHC Considerations, Ranking of Priorities

Safety must have the highest priority for the MPS system

Any procedure of changing threshold will reduce reliability < = > a
critical waiting of advantages has to be made (HERA one change in
11 years)

The operational efficiency has to be set to second highest
priority

The masking of BLM channels with the safe beam flag will not
result in a higher LHC availability and it is safety critical, a
judgment is needed if needed at all (HERA not available)

The occurrence of few percent of quenches has to be compared
with the safety implications changing thresholds
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Threshold Settings, Operation Time and Costs

Scenarios



Scenario 1


After 3 quenches change threshold value (by trial and error)
=> lost time: 3 recovery times (minimum 3x5h=15 hours)
Scenario 2


Threshold too high => quench of the magnets
(ideally: no beam loss induced quenches)
Threshold too low => beam abort
After 3 aborts change threshold value (by trial and error)
=> lost time: 3 false aborts (3x2h=6 hours)
9 different main magnets family and assuming average lost time of 10 hours
=> about 100 hours lost

200 days of operation, 4800 hours, operational efficiency 50 %, 60% at top energy
=> 1400 hours => 7% of beam time or:
=> ~10 kCHF/hour of LHC operation 1 106 CHF
12 Dec 2007
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