Introduction to the SPS crystal extraction experiment L

Introduction to the SPS crystal extraction experiment L. S. Esposito, EN-STI 1 July 2020, BI Technical Board

Particle interactions in a bent crystals Two coherent effects are used for crystal-assisted beam deflection in particle accelerators: Channeling → larger deflection with reduced efficiency • Volume Reflection → smaller deflection with larger efficiency 2. Channeling P= ≤ 85 % Horizontal Deflection - • Beam divergence ~ 10 μrad Powerful device! 4 mm long device bending 400 Ge. V/c protons by 50 μrad. Equivalent to a magnetic field ≈ 115 T!!! 5. Volume Capture 3. dechanneling 1. amorphous W. Scandale et al, PRL 98, 154801 (2007) W. Scandale et al. , Nucl. Inst. and Methods B 268 (2010) 2655 -2659 1 July 2020 6. amorphous 4. Volume Reflection P = 98 % Beam-Crystal Angle - L. S. Esposito | Introduction to the SPS crystal extraction experiment 2

Coherent interactions in bent crystals Channeling : Transverse energy < potential well Single pass measurements with 400 Ge. V protons. Strip crystal (110) with a bending of 144 μrad. (1) & (6) amorphous (2) channeling (3) dechanneling (4) volume reflection (5) Volume capture 110 Horizontal Deflection - Critical angle 111 Planar channeling (CH) Dechanneling (DC) Volume Reflection (VR) Particles can be trapped in a channel, also if a curvature is given to the crystal lattice. The particles direction will be modified by θb = l/R 1 July 2020 Beam-Crystal Angle - L. S. Esposito | Introduction to the SPS crystal extraction experiment 3

UA 9 layout in SPS LSS 5 BLM QD 52310 QF 52210 RP 3 Absorber W 100 cm BLM Absorber W 60 cm BLM Cp. FM BLM RP 1 BLM Collimator Graphite 1 m BLM IHEP GONIO 2 BLM Absorber RP 3 RP 0 Primary Beam RP 0 BLM 2 Timepixes 1 Timepix 3 Collimator Graphite 1 m Crystal 3 4 Beam Pipe IHEP GONIO 1 ~ 85 m QD 52110 2 Timepixes Crystal 1 2 ~ 43 m QF 52010 ~6 m RP 1 ~ 44 m 1 Timepixes Detectors available: • LHC BLMs • Timepix(3) • Cp. FM • [Scintillator] 1 July 2020 L. S. Esposito | Introduction to the SPS crystal extraction experiment 4

Fixed-Target scenario for ALICE beam crystal Target Medpix Absorber Configuration: crystal – target – detector – absorber Method • the circulating beam is transversally excited to pump particles from the core to the halo • the halo is deflected by the crystal • into the extraction channel • Or into a massive absorber to observe the spill (poor man solution) Observables q beam splitting efficiency q background produced by the crystal (and the target) with protons and Pb-ions Test based on the same operational scenario of RD 22 (1990 -’ 97) (beam splitting induced by a shaker and a bent crystal) q split flux intensity and harmonic content q the collimation adequacy 1 July 2020 L. S. Esposito | Introduction to the SPS crystal extraction experiment 5

Beam measurements Cp. FM LHC BLMs Timepix F. Addesa et al. /Nucl. Instrum. Methods Phys. Res. , A 946 (2019) 162513 W. Scandale et al. / ar. Xiv: 1909. 02756 W. Scandale et al. / Physics Letters B 748 (2015) 451– 454 BLMs are used to investigate beam losses at given locations, i. e. after a crystal – as in this case – to search for the channeling signature or in other machine location (such as the DS) 1 July 2020 Monitoring and characterization of channeled beam with in-vacuum Cherenkov detector. Need further improvements to be considered operational. Timepix image of the doublechanneled beam spot. Especially useful for the alignment in case the BLM signal is too small L. S. Esposito | Introduction to the SPS crystal extraction experiment 6

Synergy with the non-resonant extraction beam crystal Medpix Absorber Configuration: crystal – detector – absorber Observables q Time and frequency spectrum of the split beam as a function of the exciter frequency spectrum q Split beam flux and induced loss as a function of the q Crystal bending angle q Core beam depletion speed q Exciter frequency range (white versus pink noise) q Exciter spectral density q Lifetime of the crystal 1 July 2020 L. S. Esposito | Introduction to the SPS crystal extraction experiment 7

Findings in beam splitting Halo density in channeling mode The ADT level changes the diffusion speed of the beam core to the halo region I = 2. 9× 1010 ADT =25% Timepix Projected halo density along the horizontal axis (self-normalized to the total No of impinging particles) 1 July 2020 L. S. Esposito | Introduction to the SPS crystal extraction experiment 8

Conclusions The UA 9 experiments (SPS, North Area) has reached an extremely high level of competence in particle beam manipulation by means of bent crystals, beyond the initial scope of the crystal collimation for LHC Technologies for the crystal production, qualification and alignment have been well developed and validated over the years A key point for a fast and reliable operation of crystal-collimation and crystal extraction is the instrumentation! 1 July 2020 L. S. Esposito | Introduction to the SPS crystal extraction experiment 9

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