MD3263LR beam-beam compensation using DC wires

Guido STERBINI 2

S. Fartoukh, Y. Papaphilippou, A. Poyet, A. Rossi, G. Sterbini

on behalf of the MD3263 team

PREPARATIONS MEETINGS: https://indico.cern.ch/event/706919/ and https://indico.cern.ch/event/721944/

MD REQUEST : https://asm.cern.ch/md/requests/LHC/3263

LSWG: 17th May: https://indico.cern.ch/event/720630/

DRAFT PROCEDURE: https://cernbox.cern.ch/index.php/s/VVZE5DsdPYnx9c0

LMC: 23rd May, https://indico.cern.ch/event/731283/

DRAFT NOTES MD2202 (Wire MDs 2017): https://www.overleaf.com/read/cnghnvxcmxvg

05/25/2018

LMC approved the proposal

3Guido STERBINI5/17/2018

J. Uythoven

• Exact time slot to be defined in the window 12-17 June.

• Our preference to schedule it as early as possible.

4

Hardware overview of wire prototypes

Guido STERBINI5/17/2018

• MD GOAL: Align and power the 4 wires (all

together) to establish a IR1 and IR5

compensation. Compensation is targeted for

b*=30 cm and 150 mrad, Q=(.31, .32), Q’=(15,15).

5

MD Rationale

Guido STERBINI5/17/2018

2017 MD#4, A. Poyet

Strategies similar to 2017 MD.

• Having as many PACMAN

flavours as possible (B2<3e11 p,

SETUP BEAM)

• Start with a burn-off dominated

regime.

• Go to the 150 mrad: reducing more

the crossing is less favorable

taking into account the MD

constraints (>5 sCOLL+3 mm)

• B2 emittance BU and tails

population to look for the the

BBLR signature.

• Compensation ON-OFF cycles

and tail repopulation when

conpensation ON

6

Filling scheme, 25ns_158b_3b_2_0_0_48bpi_MD3263_MD#1

Guido STERBINI5/17/2018

B1, strong beam B2, weak beam

SUPER-PACMAN

PACMAN

REGULAR

PILOT

SETUP FLAG, <3e11 p

Collision only in IR1/IR5

7

Why a PILOT on the B2?

Guido STERBINI5/17/2018

2017 MD#1: good q-measurement with bunch not colliding HO 2017 MD#4: poor q-measurement (2 bunches colliding HO)

K . Fuchsberger

Gated BBQ on PILOT at top

energy (octupoles/ADT

OFF+COARSE settings)

• The non-collide PILOT in B2 will serve

to measure the tune in the machine and

to test the Q-feedforward (when

powering the wires).

• There is a high probability that the

PILOT get unstable.

• We had a parasitic test (FILL 6619) with

a PILOT+gated BBQ at 6.5 TeV:

promising.

8

Problem with the alignment of the wire in IR1 right

Guido STERBINI5/17/2018

TAN D2

WIRE COLLIMATOR

offset 0.8-1.2 mm• Once in collision at 150 mrad

center at 5.5 sCOLL

(TCL.4L5.B2) and 5th axis-

align the 4 wires.

• Known alignment issue on

the TCLVW.A5L1.B2: crucial

to measure in detail the

needed H-offset of the 5th

axis.

N. Fuster

9

Octupoles strategy

Guido STERBINI5/17/2018

2017 MD#4

B1/2 separated +BU

• As last year we need to set the ramp to have octupoles at 550 A at FT.

• Once in collision the IOCTB2=0 A.

• During the BU on B2 in H/V plane we need to separate the two beams and put

the IOCTB2=300 A.

• Constraint of present prototype, optics and setup: we dimension the experiment

to correct only two RDTs with the 2 wires at the same jaw position in scoll.

1. We start with IR1 (3 ON/OFF cycles, then OFF).

2. After IR5 (3 ON/OFF cycles, leave ON).

3. After IR1 + IR5 (3 ON/OFF cycles).

IR1, A. Poyet

Wire powering strategy

IR5, A. Poyet

Using the Q-knob for the feedforward

Db/b~5% on the

BSRT with 2 wires

(IR5 L+R) with 350 A

at 6 scoll+3 mm

• Present strategies to have a local dipole/quadrupole feedforwards (all wire will

have a independent feedforward). Strategy applied in MD#4 last year.

• Still to be implemented [G.-H. Hemelsoet and M. Solfaroli]

• Still under investigation the interlock policy (we dumped once last year…)

2017 MD#1

Main observables

• Fast BCT

• BSRT (no coronagraph)

• WS on B2 systematically at top energy

• BBB lumi from ATLAS/CMSdBLM

• Temperature and outgassing on the wire jaws

IF time allows

• When compensation is ON, close qc/2 from 150 to 130 mrad.

• To do that we have to use the MD orchestration tool

[M. Hoestettler]

• Compensation: 3 ON/OFF cycles, then OFF.

• Dump.

DRAFT PROCEDURE:

https://cernbox.cern.ch/index.php/s/VVZE5DsdPYnx9c0

14

BACKUP SLIDES

The beam-wire distance “problem”

15

Courtesy of R. Bruce

3m

m

Optimal beam-wire distance= 5.7 mm

• The optimal beam-wire, dw, is

extremely challenging with the present

prototype: collimator at 3-4 scoll.

• In 2017 we tested the 5.5 scoll

distance in IR5 (safe beam):results

showed that we can have

compensation effect (at least for

ROUND optics) by addressing only two

RDTs.

• In 2018 to explore the 5 scoll.

The present roadmap

MD1• Compensation of IR5 and IR1 at 5.5 scoll at 30 cm and 150 urad.

MD2• Compensation of IR5 and IR1 at 5 scoll at 25 cm and 145 urad.

MD3• Repeat MD1/2 using the wire of the opposite jaw. 1 FILL.

EoF MD

• We would need to change the B2 tune to make it more sensitive to BBLR (or play other tricks) and power all 8 wires.

MD4

• OPTION 1 (preferred): repeat with a small train in B2 (>12 bunches) and possibly with tighter collimator settings than the EoF.

• OPTION 2: test the compensation by using different Xing angles in IP1/5 (170/120 urad) (loss of LR compensation of B2, B6,…).

SA

FE

B2

NO

T S

AF

EB

2

17

MD3, EoF and MD4 : opposite wire

Partial compensation of “even” RDTs

“Internal” wires “External” wires “Internal”+ “External”

RDTs full compensation NOT possible

One could consider to put the

two wires in series.

In this way (only for the “even”

multipoles) one double the

available Iw and could see an

effect also at nominal position ⇒end of fill MDs.

A. Poyet