MD1447: b*-Reach: Collimation
Hierarchy Limit and Impedance
D. Amorim, N. Biancacci, E. Bonanno, L. R. Carver, D. Ferrazza, T. Lefevre, T. Levens, A. Mereghetti,
E. Quaranta, S. Redaelli, B. Salvant, G. Valentino, D. Valuch, M. Wendt
22nd Aug 2016
A.Mereghetti
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MD Merit
To study the possibility to further reduce the operational limits of the IR7 collimator
hierarchy, taking into account constraints from operational tolerances and impedance;
 Follow up of a previous activity, i.e. MD314 (2015 MD2), the main outcomes of which
were:
•
Feasibility of 2s-retraction between IR7 TCPs and TCSGs  operationally deployed
in 2016!
•
IR7 hierarchy broken on B1V only when 1s-retraction is deployed  hint of
TCSG.D4L7.B1 as responsible for hierarchy breakage, but no time to verify this
hypothesis and to find the actual origin of breakage;
•
Deploying measured beam sizes (instead of nominal ones) in setting collimator
gaps solves the breakage – but it does not help in spotting its origin!
PRSTAB 15-051002
22nd Aug 2016
A.Mereghetti
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MD Merit (II)
Aim of MD1447 (2016):
•
To identify the origin of the hierarchy breakage already seen on B1V, when
1s-retractions are deployed;
•
Alignment:
•
•
•
•
To verify stability (as done in 2015);
To keep trying faster alignments;
To continue the benchmark of the LHC impedance model against
measurements;
To quantify the contribution from a single TCSG collimator:
•
•
•
important missing point from last year MD;
relevant for HiLumi (reduction of impedance contribution from collimators) + in
view of installation of a prototype of low-impedance collimator (during
forthcoming EYETS);
The actual impedance challenge, with many teams involved! Thanks to
everyone!
22nd Aug 2016
A.Mereghetti
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MD Overview
B2 RF trip
Characterisation of 1sretractions after alignment with
nominal/measured beam sizes
1 nominal + 17 pilots
Orbit drift
Characterisation of 2sand 1s-retractions before
alignment
Alignment: 1h:10m (2015:
~45min)  harder scraping
conditions;
Introducing tilt angle at selected
TCSGs
22nd Aug 2016
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Collimation Hierarchy Limit
•
•
•
•
Qualification (betatron) LMs before alignment;
Alignment;
Qualification (betatron) LMs before alignment; Closed orbit drift;
Source of hierarchy breakage;
22nd Aug 2016
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Before Alignment
Qualification with betatron LMs of the 2s / 1s retractions;
MD1447
2016 OP
TS1
Comm.
1s
2s
B1H
2.83E-4
2.75E-4
2.2E-4
2.4E-4
B1V
1.95E-4
1.45E-4
1.3E-4
1.3E-4
B2H
2.04E-4
2.84E-4
2.8E-4
2.7E-4
B2V
1.03E-4
2.21E-4
1.7E-4
2.0E-4
MD314 (2015)
2016: TCLAs@11s
Courtesy of D.Mirarchi
•
•
•
Cleaning inefficiencies at 2s-retraction a bit worse
(~10%) than what seen in qualification for operation;
B1V: hierarchy breakage;
B2: cleaning inefficiency clearly decreases when
moving from 2s- to 1s-retractions;
22nd Aug 2016
MD314 (2015)
A.Mereghetti
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Hierarchy Breakage
[email protected]
[email protected]
Hierarchy breakage found on B1V when deploying 1s-retractions (as in 2015)
TCLAs@14s
(2015)
TCLAs@11s
(2016)
TCLAs@10s
(2015)
TCLAs@11s
(2016)
TSG.D4L7.B1
22nd Aug 2016
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Alignment - Centres
Time required: 1h:10m (i.e. ~20m more than 2015 record) – harder scraping conditions (i.e. cross-talk
between beams, B1 tails scraped down to <3s);
Esp: false spikes (possibly due to vibrations of the other jaw)  visible on 100Hz BLM data (not in 1Hz);
Reproducibility within 100mm
22nd Aug 2016
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Alignment – Beam Size Ratio
Time required: 1h:10m (i.e. ~20m more than 2015 record) – harder scraping conditions (i.e. cross-talk
between beams, B1 tails scraped down to <3s);
Esp: false spikes (possibly due to vibrations of the other jaw)  visible on 100Hz BLM data (not in 1Hz);
22nd Aug 2016
A.Mereghetti
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Closed Orbit Drift
Shortly after alignment (i.e. ~01:30 AM), the orbit in IR7 started drifting:
• Qualification LMs (until ~02:30 AM) after alignment did not show any hint of
hierarchy breakage (not shown in these slides);
• It took another 1.5h (until ~04:00 AM) to spot the problem down to CO – at the
beginning we thought of a mess in settings while changing from measured to
nominal beam sizes…
• Especially in B1V, the CO changed at the TCPs (~60mm), “restoring” the usual
CO drift wrt end of
hierarchy;
R&S (absolute)
CO correction
Residuals resulted in a less pronounced (still clearly visible) hierarchy breakage – see later
22nd Aug 2016
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Source of Hierarchy Breakage
•
•
•
Tilt angles lead to (fake) large measured beam sizes 
using measured beam sizes to set collimator gaps allow to
by-pass hierarchy breakage (as seen in 2015);
Identification of collimator(s) at the origin of breakage
(suspect: TCSG.D4L7.B1, from 2015) and possible cures most promising: angle to compensate a possible tank
misalignment;
Lack of time (CO): we inserted the 3 largest tilts and
removed them one by one until breakage is seen again;
PRSTAB 15-051002
A4L7.B1: -350mrad;
D4L7.B1: 500mrad;
A5L7.B1: -300mrad;
After CO correction
(residuals)
22nd Aug 2016
A.Mereghetti
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Source of Hierarchy Breakage (II)
•
•
•
Tilt angles lead to (fake) large measured beam sizes 
using measured beam sizes to set collimator gaps allow to
by-pass hierarchy breakage (as seen in 2015);
Identification of collimator(s) at the origin of breakage
(suspect: TCSG.D4L7.B1, from 2015) and possible cures most promising: angle to compensate a possible tank
misalignment;
Lack of time (CO): we inserted the 3 largest tilts and
removed them one by one until breakage is seen again;
PRSTAB 15-051002
A4L7.B1: 500mrad;
D4L7.B1: -350mrad;
A5L7.B1: -300mrad;
After CO correction
(residuals)
22nd Aug 2016
A.Mereghetti
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Source of Hierarchy Breakage (III)
•
•
•
Tilt angles lead to (fake) large measured beam sizes 
using measured beam sizes to set collimator gaps allow to
by-pass hierarchy breakage (as seen in 2015);
Identification of collimator(s) at the origin of breakage
(suspect: TCSG.D4L7.B1, from 2015) and possible cures most promising: angle to compensate a possible tank
misalignment;
Lack of time (CO): we inserted the 3 largest tilts and
removed them one by one until breakage is seen again;
PRSTAB 15-051002
A4L7.B1: 500mrad;
D4L7.B1: -350mrad;
A5L7.B1: -300mrad;
After CO correction
(residuals)
22nd Aug 2016
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Impedance Measurements
A.k.a. the impedance challenge
In the following, just introduction (see next talk)
22nd Aug 2016
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Impedance Measurements
To measure the tune shift at FT induced by changing TCSG gaps:
•
All TCSGs at once: DQ ~ 10-4 (expected);
•
Only one TCSG (D4L7.B1/D4R7.B2, i.e. TCSG on the vertical
plane, with smallest beam size among all TCSGs): DQ ~ 10-5
expected);
Challenging measurement, since DQ ~ 10-4 already takes quite a lot of postprocessing (esp. noise filtering) to be clearly seen;
 Tried out different methods:
• BBQ signals with reduced chroma / octupoles, and chirping with ADT;
• ObsBox signals in case of coherent bunch oscillations induced with MKQA;
• Schottky;
 Many teams involved: BE-ABP, BE-BI, BE-RF…
…thanks a lot to everyone!
22nd Aug 2016
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Impedance Measurements (II)
(N.Biancacci)
B1 Q’ 20 -> 5
B2 Ioct 470 -> 400
TCSG*7
20 <-> 6.5
sigma
Damper gain
0.05 -> 0.01
Chirp on
D4*
D4*
20 <-> 6.5 20 <-> 6.5
sigma
sigma
MKQA kicks
B/D4*
20 <-> 6.5
sigma
D4*
at 8 sigma
22nd Aug 2016
No damper:
Instability
D4*
10 <->6.5
sigma
D4*
20 <->10
sigma
A.Mereghetti
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Impedance Measurements (III)
Very good results with kicking the beam by means of MKQA (see next talk);
 Gotten the desired sensitivity / resolution;
 Clean in terms of losses!
Gain: 20%,
50%,
100%
22nd Aug 2016
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•
•
Conclusions
Hierarchy limit:
• Re-alignment:
• very stable  centres change within 100mm;
• Performed in 1h:10m (i.e. ~20 more than 2015 record);
• Hierarchy breakage found on B1V when 1s TCP-TCSG retractions are deployed (as
seen in 2015 )  tilt angle of tank translates in (fake) large beam sizes  if used to
set collimator gaps, these allow to by-pass the hierarchy breakage (as seen in 2015 );
• TCSG.D4L7.B1 at the origin of hierarchy breakage:
• Candidate collimator found in 2015;
• Smallest beam size  operational margins become relevant;
• One of the collimators with largest tilt angle;
Impedance measurements (see next talk):
• Performed challenging measurement of tune shift induced by single collimator at FT;
• Tried out three different methods of measurements: resolution ~10-5 seems at reach!
 Outcome will put a word on the feasibility of TCSGs at retractions smaller than
those presently deployed, from the point of view of impedance;
 Relevant also for HL-LHC, as outcomes are important ingredient to change
baseline settings;
• MD ended with instability threshold measurement, with ADT switched off, showing the
need for it when TCSGs are set at 6.5s;
22nd Aug 2016
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Spare Slides
22nd Aug 2016
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CO drift wrt end of R&S (absolute)
Closed Orbit Drift (II)
22nd Aug 2016
A.Mereghetti
CO correction
21