LHC Crystal MD22/09/2015 – LSWG #7

R. Rossi for the LHC Collimation team and the UA9 Collaboration

R. Rossi - LHC Crystal MD 2

Table of contents

• Motivation• Introduction• List of measurements• Preliminary results• Conclusion

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Motivation

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Beam

Absorber

Crystal ???

Promises of crystal collimation at the LHC:• Improve collimation cleaning achieved with fewer

collimators;• Reduce electro-magnetic perturbations of collimators

to the beams (impedance);• Improve significantly the cleaning for ion beams.

<θ>MCS ~ 3.4 μrad (7 TeV)

Amorphous (0.6 m of C)

Crystal (Channeling)(4 mm Si)

<θ> ~ 40-50 μrad (7 TeV)

IP7 zoom

Goal : Observe the CH behaviour for the first time in LHC.

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Introduction13 hours were assigned to test both installed crystals (H & V) at injection energy (450 GeV).

Several fill of one or two nominal bunches on beam were used.The transversal dumper (ADT) was used to increase beam loss rates and have a clear signal on the BLMs. 22/09/15

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List of measurementsPrinciple: Crystal aligned and set as primary collimator, all colls at nominal settings. • Fast angular scan to find channeling orientation• Detailed angular scan for crystal characterization • Linear scans with absorber to characterize the channeled beam• Loss maps with reduced TCSGs for cleaning efficiency.

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Beam

Absorber

Crystal Angular Scan

Absorber Scan

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Preliminary results H crystal 2h were needed to successfully observe the channeling orientation looking at the losses immediately downstream the crystal.

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Angular scan for horizontal crystal.This scan was performed with all TCP.IR7 and TCSGs upstream the crystal retracted of 1 mm and 18 mm w.r.t. their nominal settings, respectively.AM

AM

VR

CH

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Loss Map Horizontal plane

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Raw dataThe picture shows losses on the whole machine during an angular scan, with the reduced settings of collimators.

Daniele Mirarchi

Preliminary – pending detailed calibration

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Loss Map comparison

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Preliminary – pending detailed calibration

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ConclusionVery successful MD, all the measurements program was completed:

– Channeling observed for the first time at the LHC for both crystals– Goniometers: important validation of new hardware (first test of technology

to be used by EN-STI in other application, e.g. TDI) • Data for offline analysis

– Channeled halo measured to evaluate multi-turn channeling efficiency and bending angle.

– Loss maps performed with crystals in Channeling orientation and with standard collimation system to compare the performance.

Next goal Crystal-collimation test at 6.5 TeV Collimation of ions beam

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Backup

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Preliminary results V crystal

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Same measurement done on vertical plane with QM crystal.

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List of measurements• Fast angular scan on whole goniometers range

– Identification of channeling orientation• detailed angular scan around angles determined with the measurement above

– indication of optimal channeling orientation, scans repeated in different fills to test the system stability– measurement of nuclear interaction rate at the crystal, characterization of local losses for different working regimes – measurement of reduction of nuclear interaction rate (AM/CH) and measurement of crystal bending angle (extension of VR region)

• Crystal placed in optimal channeling orientation and linear scans with selected TCSG is performed – study the extracted beam profile, deflection angle, and multiturn channeling efficiency – validation of expected crystal orientation

• Loss map with reduced set of collimators in IR7 (all collimators upstream the crystal retracted of … sigma) – validation of working principle with reduced number of collimators – comparative studies w.r.t. present collimation system

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Beam

Absorber

Crystal

Angular Scan

Absorber Scan

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Preliminary results H crystal

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With the same reduced collimator layout and crystal fixed in CH, absorber scan has been performed.The absorber is retracted and inserted again. Rising of losses downstream the absorber show the extracted beam and circulating beam interception.