unreliable data, see first slide warning!!! data taken on these shifts had attenuation factors set...
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UNRELIABLE DATA, SEE FIRST SLIDE
WARNING!!!
• Data taken on these shifts had attenuation factors set incorrectly and problems with faraday cup bunch charge measurements
UNRELIABLE DATA, SEE FIRST SLIDE
#3091
• Effect of attenuation and timing on the BPM readings– Final “AP” conclusions might depend on attenuation/timing!– Or, more provocatively, can you prove any “AP” result you want
by changing the attenuation and timing? – How do we know what the ‘correct’ attenuation/timing is– Ignore for now? will require time consuming investigation
• Transient in first part of train in ER mode measured on AR1-BPM-1
• Linac set to give bunch minimum energy spread.• BPM response to varying bunch charge, consistency with
AR1-1 screen observations
UNRELIABLE DATA, SEE FIRST SLIDE
#3091 Horizontal Transient AR1-BPM-02Standard 60 Pc, with ok-ER, after tuning attenuation and setting timings to the ‘correct’ values. There is initial steep transient then a shallower one. Overall about 2 mm.
After improving ER. Transient has reduced to ~ 1.2 mm overall. Side note: note the average x position has changed too.
2 mm
1.2 mm
UNRELIABLE DATA, SEE FIRST SLIDE
#3091 Effect of Bunch ChargeGood ER, see previous slide, LA = 1.0
LA = 0.5. Note the average x position has changed by 1 mm
UNRELIABLE DATA, SEE FIRST SLIDE
Conclusions
• Observed transient in x position, y position and ‘charge’, x transient much larger than y
• Observed an effect of bunch charge on BPM reading
UNRELIABLE DATA, SEE FIRST SLIDE
X-transient
• What is the cause of the x-transient?– 1. Intrinsic bunch energy variation over train– 2. Intrinsic bunch x position variation over train– 3. Intrinsic bunch charge variation over train
variation in BPM response to charge– Various combinations of 1,2,3
UNRELIABLE DATA, SEE FIRST SLIDE
X-transient Discussion• On #3091 before we improved the ER we made the following observation. • Dispersion on AR1-BPM-02 is 0.33 m (checked in MAD and ELEGANT by James and me)• So a ~ 2mm transient = 0.6 % momentum transient (using beam momentum = 26.5 MeV)• The dispersion on AR1-1 is 0.88 m (MAD value)• So the x-variation over train (if due only to 0.6 % energy variation) at AR1-1 should be ~ 5.5
mm• But the observed size on AR1-1 at 10 uS was ~ 2 mm full width (no picture unfortunately)
inconsistent!• One reason for the inconsistency could be that the x-variation is not really 2 mm at AR1-BPM-
02. The apparent x-variation could be due to the varying bunch charge over the train and BPM non-constant response to different bunch charges – AW theory, and supported by the observation that the average beam position on AR1-BPM-02 does
change with LA– But could changing the LA really change the beam position, from dynamical effects of charge
variation?• Is the AR1-1/BPM-02 comparison too simplistic/invalid? Would 0.6 % bunch energy variation
really give 2 mm full width on AR1-1? Several problems – We only use 10 us on AR1-1 whereas the 2 mm variation on the BPM is over the WHOLE TRAIN. – e.g. if energy variation isn’t linear over train? – e.g. if the first ~ microseconds of the train have lower bunch charge?
• A. Kalinin made point that you would expect to see a similar size transient in x AND y if the BPM charge-response is to blame. This is not observed.
UNRELIABLE DATA, SEE FIRST SLIDE
Shifts #3121,3122,3123, Fri-Sat 14-15th September
• AR1-BPM-01 used for first time.• Other AR1 BPMs used while varying dispersion
using AR1-Q1.• Also ST2-BPM-3 used. • Various bunch charges used from 30 pC to 150
pC, in the confusion of scope settings.• Pop-in Dump in and out • 16 MHz bunch rep, 100 uS
UNRELIABLE DATA, SEE FIRST SLIDE
#3121 Fri 14th Sep Shift 3 PW
• All data at 30 pC bunch charge. • Different AR1 quad strengths used
• Largest dispersion is at ST2-BPM-3 mid chicane ~ 0.5 m
• On this shift had AR1-BPM-01, AR1-BPM-03, AR1-BPM-04, AR1-BPM-05 available
• Difficult to get large dispersion (in ER conditions) on any AR1 BPMs, can get -0.3 m on BPM3-4 with Q1/4 = 2.38 A
• Collected much data with pop-in dump in and out
Q1/4 = 2.2 AQ1/4 = 2.05 A
Q1/4 = 2.38 A
10 15 20 25 30 0.50.00.51.0
10 15 20 25 30 0.50.00.51.0
10 15 20 25 30 0.50.00.51.0
Q1/4 = 2.05
Q1/4 = 2.2
Q1/4 = 2.38
Q2/3 = 1.0 A
AR1BPM3-4 ST2BPM3
See slide of extra notes for dispersion calculations
UNRELIABLE DATA, SEE FIRST SLIDE
#3121 energy variation/transient over the train• On a previous shift (#3091) had seen transient of ~ 1mm in first 10 uS on AR1-
BPM-02 where we think the dispersion is fixed at + 0.33 m • Any transient seen on this shift? Of ALL the data taken, most obvious transient
seen on ST2-BPM-03 with AR1Q1/4 = 2.2 and dispersion at this location predicted as + 0.5 m
0 500 1000 150012.0
12.5
13.0
13.5
H orizonta l B PM
0 500 1000 15000.0
0.5
1.0
1.5
2.0
V e rtic a lB PM
0 500 1000 15000.0
0.1
0.2
0.3
0.4Cha rge
Compare with AR1-BPM-02 observation on #3091 (dispersion = + 0.33)
BUT DIDN’T SEE MUCH EVIDENCE OF THIS TRANSIENT, ON THE OTHER BPMS
UNRELIABLE DATA, SEE FIRST SLIDE• Do see a small transient on AR1-BPM-01 at which
we expect dispersion to be zero, and upstream of the quads we’re using
• 4 separate observations
• This transient was not seen on any other BPM except ST2-BPM-03 shown on previous slide
#3121 energy variation/transient over the train
0 500 1000 1500
2.0
2.1
2.2
2.3
H orizonta l B PM
0 500 1000 1500
1.8
1.9
2.0
2.1
2.2H orizonta l B PM
0 500 1000 1500
2.0
2.1
2.2
2.3H orizonta l B PM
0 500 1000 1500
2.0
2.1
2.2
2.3
H orizonta l B PM
UNRELIABLE DATA, SEE FIRST SLIDE• Generate ‘large’ dispersion of -0.3 m on AR1-BPM 3,4 using Q1/4 = 2.38 A
• What is this? Linear energy variation over train? Why? Are we sure ER is maintained here?
• If the previous observations show an energy transient at start of train, it is not seen here.
#3121 energy variation/transient over the train
0 500 1000 1500 1.4 1.2 1.0 0.8 0.6 0.4 0.20.0
H orizonta l B PM
0 500 1000 1500
2.8 2.6
2.4
2.2
2.0 1.8
H orizonta l B PMBPM3 BPM4
UNRELIABLE DATA, SEE FIRST SLIDE
#3121 Effect of Pop-In dump• AR1-BPM-04 with large dispersion = - 0.3 m• Bunch position change over the train actually seems smaller with the
dump IN• Overall shift of train position to more negative values. • If dispersion is negative, this implies an overall DECREASE in energy of the
train when the dump is in. NEED MORE EXPLANATION HERE.• Effect of dump doesn’t seem to introduce a ‘droop’• Somewhat inconclusive
0 500 1000 1500
2.8 2.6
2.4
2.2
2.0 1.8
H orizonta l B PM
0 500 1000 1500
3.2
3.0
2.8
2.6
2.4H orizonta l B PMdump indump out
UNRELIABLE DATA, SEE FIRST SLIDE
#3121 Extra notes
• AR1 set to Q1/4 = 2.2 A, • Q2/3 = 1.0 A • These are equivalent to • K(Q1/4),(Q2/3) = 9.20,-4.22 • For K.E. = 26.0 MeV. • I have my own spreadsheet to convert current
-> K, and cross-checked it with the magnet table.
UNRELIABLE DATA, SEE FIRST SLIDE
#3122
• On this shift we had ~ 150 pC• Again see transient on AR1-BPM-01. It’s “up and down” here.
• Massive transient on ST2-BPM-03
0 500 1000 1500
0.1
0.0
0.1
0.2
0.3
Horizontal BPM
0 500 1000 1500
0.1
0.0
0.1
0.2
0.3
0.4H orizonta l B PM
dump indump out
0 500 1000 1500 7 6 5 4 3 2 10
H orizonta l B PM
UNRELIABLE DATA, SEE FIRST SLIDE
#3123
• Charge problem solved and back to normal 60 pC.• Dump out vs dump in investigations• Some varying of AR1-QUADS but don’t know how useful this
is with these two BPMs
0 500 1000 1500 0.20.0
0.2
0.4
0.6
0.8
Horizontal BPM
0 500 1000 1500 5
4
3
2 1
0
H orizonta l B PM
dump indump out
ST2-BPM-03
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