Beam Losses and Machine Protection (real life) By Kay Wittenburg,
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Transcript of Beam Losses and Machine Protection (real life) By Kay Wittenburg,
Beam Losses and Machine Protection (real life)
By Kay Wittenburg,Deutsches Elektronen Synchrotron DESY, Hamburg, Germany
Experiences from HERA (accidental losses)
Beam Dump: why?
Loss-Mechanisms1) After an equipment failure (e.g. Power supply(ies) trip) the beam starts to
oscillate (position or size) with an exponential growing amplitude. First losses occur after a time (length) which depends on the failure typ– then the beam “explodes” within a very short time.
2) Mislead beam. Might be very fast (< 1 turn). Reasons: Kicker, Operation, …
t0
X or Y
FailureFirst losses
TotalBeamloss
Aper-tur
long shortt, l
Beam loss induced Quenches 1994 - 2004
Injection
27%
Magnet PS
13%
5 ms events
16%
RF
8%
ALZ
12%
BLMs <4
8%
Operating
3%
K ollimator
2%
Diverse
6%
unknown
5%
Injection
Magnet PS
5 ms events
RF
ALZ
BLMs <4
Operating
Kollimator
Diverse
unknown
Note: A quench in HERA is not a disaster! It takes typ. 1-2 h to recover from cryogenic
= 189 Quenches
More statistics
HERA experience with
Statistic of BLM events 1993 - 1995
0
3
6
9
12
15
18
21
9
12
15
18
21
24
27
30
33
36
39
21
24
27
30
33
36
39
42
45 0
20
23
26
29
32
35
38
41
44
47
week
ev
en
ts/w
ee
k
0
10
20
30
40
50
60
70
80
90
100
be
am
cu
rre
nt
[mA
]
Errors
Quenches
5 ms events
BLM-Alarms
beam current
no BLMs 1/3 BLMs all
1993 1994 1995
I
Statistic BLM events 1995 - 1997
0
3
6
9
12
15
18
21
19 22 25 28 31 34 37 40 43 46 49 22 25 28 31 34 37 40 43 46 6 9 12 15 18 21 24 27 30 33 36 39 42
week
even
ts/w
eek
0
10
20
30
40
50
60
70
80
90
100
bea
m c
urr
ent
[mA
]
Errors
Quenches
5 ms events
BLM-Alarms
beam current
1995 1996 1997
I
No quench
Dump due to losses
HERA BLM Alarm System
5 ms event, PS failure, HF failure
92 BLM Alarms
Old HERA Beam-Loss-Alarm-Topology
ALIs
ALIs
ALIs
ALIs
Alarm loop-Zentrale
Alarmloop
DUMP
BLMs + BPMs +Alarm-modules “Alarm-Loop-
Interface”
Internal Power-Supply-Alarm
Galv. Trenn.
HF failure input
Clean Dump due to HF alarm
Statistic BLMp events 1998 - 2000
0
2
4
6
8
10
12
14
16
18
20
28 32 36 40 44 48 4 8 12 16 20 24 28 32 36 40 44 48 52 3 7 11 15 19 23 27 31 35 33
week
even
ts /
wee
k
0
20
40
60
80
100
bea
m c
urr
ent
[mA
] Errors
Quenches
5 ms events
BLM-Alarms
beam current
1998 1999
I
2000
Since Week 39 (1998) RF Interlock activeLess BLM alarms,less 5 ms events, less quenches
start after 5 month shutdown
Statistic BLMp events 2001 - 2003
0
2
4
6
8
10
12
14
16
18
20
31 36 41 46 51 15 20 25 30 35 40 45 50 3 8 13 18 23 28 33 38 43 48 53 5 10 15 20 25 30 35 40 45 50
week
even
ts /
wee
k
0
20
40
60
80
100
bea
m c
urr
ent
[mA
]
Errors
Quenches
5 ms events
BLM-Alarms
beam currentI
2003 2004
I
2001 2002
start after 5 month shutdown (Lumi upgrade)
All by 5 ms PS failure events
What is a critical PS?
Alarm timing during failure of a critical magnet power supply
t0
X oder Y
Power supply failure
Aper-tur
BLM-Alarm
ACCT-Alarm
Improved and faster internal Power-Supply-Alarm
Magnet-current-Alarm
Total-loss
Too late
No faster BLM Alarmsdue to spiky background!
ALIs
ALIs
ALIs
ALIs
Alarm loop-Zentrale
Alarmloop
DUMP
BLMs + BPMs +Alarm-modules “Alarm-Loop-
Interface”
Beam-Loss-Alarm-Topology
Internal Power-Supply-Alarm
Galv. Trenn.
faster
Active
New
ACCT-Alarm
DCCT-Alarm
Faster clock rate
Magnet current-Alarm
More Failure inputs:PS, HF, …
Improvements Beam-Dump:before: 570 safter: 10 s
Alarm at 0
Turn by turn current of bunch #1
DCCT beam current
BPM SL345had wrongreadings. =>local Bump atone Quad. => < 4 BLM- alarms
Story (1):Statement: In HERA each cold Quad has a BPM.Instruction: Install a BLM close to each BPM to cover all cold Quads.DONEEvents: Quenches of one Magnet in the middle of the arc during ramp.Observation: No Orbit distortion, no beam losses.?????
After a few days, some tries, some quenches:Observation 2: The correction coils in this area showed higher valuesCalculations: The correction coils drive a local closed bump.WHY THE BPM and BLM DIDN’T SHOW ANYTHING????Observation 3: There is no BPM (because there is a cold-box. No BPM foreseen)Observation 4: Therefore there is no BLM (see above)Analysis: The automatic Orbit correction makes the local bump by accident.
Consequence: Now we installed a BLM!=> flexible system
Alarm Zentrale failure:Threshold went from 5 to 30
Story (2):Due to a wrong cabling, the alarms of 20 BLMs were subtracted and not added
Story (3): Fieldbus-commands for other modules on the bus were interpreted by the ALZ
Injection:10 bunches injected into first Dipoles
Collimators went too far into the beam.=>Losses in the magnets behind. (no quench but happened in earlier years.Very high Collimator BLM thresholds)
protons
Operating (1):Wrong rampfile was chosenby operator.
Operating (2):Fast switch-onof magnets.Alarm loop (A1) was still disabled
Diverse: Hitting a cable during drilling(no quench)
Experiments PS-manipulation coasting beamOperating diverse diverses Operating
dump?
Remarks:What was first? Transient recorders most helpful. Here: p-beam was lost 8 ms before e-beam.
Quench Quench
Dump of 19% coasting beam isnot a problem in HERA.
Some loss induced quenches were not documented in the Logbook?!?!?
The Endnow open for discussion
Dear colleagues,In Session V we are planning a discussion on failure scenarios leading to accidental beam loss. We would kindly ask you for your help, since the number of possible failures scenarios is (nearly) infinite.There are some obvious type of failures: power converter fault, magnet quench, unsynchronised beam dump, .....More subtle failures were also reported. One example: due to a wrong delay set in the beam dump kicker electronics, a number in a register became negative, and the dump kicker did not fire.We would greatly appreciate your help for a discussion on all kind of failures and accidental beam losses:a) What are the most common failures leading to accidental beam loss that you know of?b) What kind of (atypical) failures did you experience?c) What diagnostics allowed to identify such failures?d) Other comments are welcome...In the session we would hope to compile a list of failures - as an input to machine protection systems for various accelerators. It would be very nice if you would stimulate the discussion by presenting one or two slides on your experience. Thanks a lot, and see you soon, Rüdiger Schmidt and Kay Wittenburg
Events from BNL (RHIC) and SNS (R. Keller)
Slides from B. Macek
LHC requirements (R. Schmidt)
Dear Conveners,
I will prepare a slide or two on our experience and will be guided by your 4 questions. It is an important topic for operation of high intensity accelerators that I am pleased to see is being addressed.
Regards,
Bob Macek
I probably won't have an occasion to participate in your session, but here are my two cents worth of input on loss-relevant failure scenarios caused by the injection system (front end) of the SNS accelerator chain.1) Our biggest worry was and is failure of one of the two chopper systems not providing chopper pulses (due to failure of the timing system or the chopper electronics). This would result in spraying beam on the Ring extraction septum. Possible protection: interlock based on wave pattern recognition, monitoring the actual chopper excitation currents.2) Interference between the global control system (EPICS) and the dedicated timing system could lead to extending the ion source discharge and Linac pulse length or macroscopic duty factor. This is primarily a dump load concern, but I could imagine it resulting in higher beam loss as well if the rf system cannot cope with the additional average load. A cure for this effect might be very hard to find because the root cause is incompatibility between two systems.Best regards,
Rod Keller
Solution 2: Proton and Positron ring in Lumi-Optic - BPM thresholds reduced to around 3 mm. Clean dump - no detectable current loss before dump triggered.Congratulations! Logbook comment to the test: “In dem Quencharchiv steht die Schwelle in der Alarmloopzentrale auf 30 und es werden 30 anstehende Alarme angezeigt. Wenn das Setzen von 40 Monitoren noetig war, dann deutet dies darauf hin, dass in den Alarmkassetten nicht alle BPMs Scharf geschaltet sind (leider sind dies Jumper im Tunnel unter Beton). Naja, wenn 3/4scharf sind, geht das ja noch.“
< 4 BLMsStill 4 loss induced quenches in 2004: