unreliable data, see first slide warning!!! data taken on these shifts had attenuation factors set...

UNRELIABLE DATA, SEE FIRST SLIDE

WARNING!!!

• Data taken on these shifts had attenuation factors set incorrectly and problems with faraday cup bunch charge measurements


#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


#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


#3091 Beam Dump In Good ER, see previous slide

Beam dump in


#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


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


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


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.


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


#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


#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


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


#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


#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.


#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


dump indump out

0 500 1000 1500 7 6 5 4 3 2 10

H orizonta l B PM


#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

unreliable data, see first slide warning!!! data taken on these shifts had attenuation factors set...

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