Outcome of MD on TCP cut:
can we tighten the primary?
D. Mirarchi, R. Bruce, M. Fiascaris,
A. Mereghetti, B. Salvachua, S. Redaelli
Special thanks to: D. Amorim, N. Biancacci, X. Buffat,
L. R. Carver, R. Rossi, M. Soderen, G. Trad
Introduction
•
Studies performed during MD4 and MD5 blocks
 MD4: TCPs closed from 5.7 s at injection to 4.5 s at flat top during the ramp
 MD5: TCPs closed from 5.7 s at injection to 5.0 s at flat top during the ramp
During 2016 physics fills TCPs closed from 5.7 s at injection to 5.5 s at flat top during the ramp
•
Main analysis shown in the next:
 Lifetime analysis along the cycle
 Beam transmission along the cycle
 Comparative studies carried out w.r.t. last 5 physics fill (5442, 5443, 5446, 5448, 5451)
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D. Mirarchi, CWG #210
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MD4 - overview
1)
Injected 1 nominal + 4 pilot per beam
2)
Dedicated collimator functions used during the ramp to bring TCPs at 4.5 s at flat top
3)
TCPs alignment checked at flat top (centres found within ±40 mm)
4)
Standard cycle played until End of TOTEM bump
5)
All TCSGs closed from 7.5s to 5.5s in steps of 1s
Significant instability in B1 observed
Beams dumped
due to erratic on
an MKB kicker:
15h recovery,
MD over
Prep. Ramp
Ramp
Flat Top
Squeeze
Adjust
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MD5 - overview
1)
Injected 3x48 bunches + 1x12 bunches per beam
2)
Dedicated collimator functions used during the ramp to bring TCPs at 5.0 s at flat top
3)
Standard cycle played until all IPs colliding (1&5 head-on, 2&8 similar leveling w.r.t. standard): full LRBB
4)
All TCSGs closed from 7.5 s to 6.5 s
5)
Octupoles decreased to 0 A and beams separated up to 4 s (total separation) in steps of 0.5 s
6)
Beams brought back to collision
7)
ADT switched OFF and separation scan repeated
Beams dumped by instability on 12b train
at 3.5 s separation
Prep. Ramp
Ramp
FT
Squeeze
Adjust
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Lifetime calculation
Two possible methods to measure beam lifetime:
Losses on collimators
FBCT
Based on decomposition matrix for transformation Gy/s ➔ p/s
Direct measurement of p in the machine
Sensitive to “fast” change of lifetime (s)
Very noisy signal and sensitive to
“slow” change of lifetime (tens of s)
Valid only at 6.5 TeV and specific IR7 settings
(matrix evaluated using loss maps during commissioning)
Valid at any energy/ collimators settings
FBCT used for lifetime comparisons during ramp:
Example of smoothing with ±20s window
1) Smoothing of signal done through running average
2) Lifetime calculated using smoothed signal
 Same time window used for both 1) and 2)
07/11/2016very sensitive to this time window:
D. Mirarchi,
CWG
#210 ±30s tested, results obtained with ±20s
5 shown
 Calculation
±10s,
±20s,
Lifetime
MD5
MD4
Prep. Ramp Ramp
Flat Top
Squeeze
Prep. Ramp
Ramp
FT
Squeeze
 Minimum lifetime measured in the 5 reference fill ~37.9 h (Fill 5448)
 Minimum of lifetime takes place during ramp also in all reference fills
(except when collisions are established)
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Transmission during ramp
FBCT signal normalised at beginning of Ramp BP
Beam 2
Beam 1
•
Transmission during physics fill ≥ 99.7%
•
Very similar transmission observed with TCPs at 5.0s
•
Measured transmissions with TCPs at 4.5s: ~97.2% and ~ 98.8% for Beam 1 and Beam 2
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D. Mirarchi, CWG #210
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Transmission during squeeze
FBCT signal normalised at beginning of Squeeze BP
Beam 2
Beam 1
•
Transmission during physics fill ≥ 99.8%
•
Very similar transmission observed with TCPs at 5.0s
•
Measured transmissions with TCPs at 4.5s: ~98.8% and ~ 99.1% for Beam 1 and Beam 2
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Transmission along cycle
FBCT signal normalised at beginning of Ramp BP
Beam 2
Beam 1
•
Transmission during physics fill from Prep. Ramp to Collision ≥ 99.2%
•
Very similar transmission observed with TCPs at 5.0s
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Are really the tighter TCPs scraping more beam?
or it was blown up from the beginning?
Example of Beam 2 transmission along the cycle (normalization at beginning of Ramp BP)
Fill in MD4 never went to collisions
•
Some instabilities during MD4 observed already at injection energy (see Nicolo’s talk)
•
Checked measured beam emittance by BSRT: nothing particular observed during MD4 (2/1.6mm in H/V)
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Conclusion
MD4 - TCPs at 4.5s and TCSGs at 5.5s:
 Reduced minimum lifetime of about a factor 10 during ramp (really due to TCPs?)
 Significant reduction of beam transmission (really due to TCPs?)
 Large instability observed in Beam 1 when TCSGs set at 5.5s
MD5 - TCPs at 5.0s and TCSGs at 6.5s
 Very similar lifetime and transmission with respect to standard 2016 physics fill
with TCPs and TCSGs at 5.5s and 7.5s, respectively
 Beams were stable along the cycle (usual “random” B1V instability observed during adjust)
 Beams were stable also with 0 octupoles and 4s BB separation
 Beams became unstable only with both 0 octupoles and ADT OFF at 3.5s BB separation
(impossible to get during operations)
Based on present results: safe to go to 5.0/6.5s (TCPs/TCSGs) for 2017 operations
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