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- 02 Standard 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 Beam Dump In Good ER, see previous slide Beam dump in

UNRELIABLE DATA, SEE FIRST SLIDE #3091 Effect of Bunch Charge Good 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 th 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 14 th 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 A Q1/4 = 2.05 A Q1/4 = 2.38 A Q1/4 = 2.05 Q1/4 = 2.2 Q1/4 = 2.38 Q2/3 = 1.0 A AR1BPM3-4ST2BPM3 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 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 m Compare with AR1-BPM-02 observation on #3091 (dispersion = ) 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

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 BPM3BPM4

UNRELIABLE DATA, SEE FIRST SLIDE #3121 Effect of Pop-In dump AR1-BPM-04 with large dispersion = 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 dump 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 dump indump out

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 dump indump out ST2-BPM-03