Critical beam losses during Commissioning & Initial Operation

Critical beam losses during Commissioning & Initial Operation Guillaume Robert-Demolaize (CERN and Univ. Joseph Fourier, Grenoble) with R. Assmann, S. Redaelli, C. Bracco & T. Weiler; thanks to B. Dehning, B, Holzer & L. Ponce

OUTLINE • Introduction • Loss distribution from betatron cleaning • Minimum workable BLM system for collimation studies • Conclusion – Future studies Critical Beam Losses during Commissioning and Initial Operation

Introduction • Purpose of the LHC Collimation system: provide cleaning efficiency and protection, using collimators and absorbers => ~ 40 elements per ring are being implemented in the machine (Phase 1 of the system) • About 3700 Beam Loss Monitors (BLMs) can be counted around the two rings of the machine => do we need all BLM information to understand the cleaning performance and losses from the “leaking halo” ? Critical Beam Losses during Commissioning and Initial Operation

Base principles of the LHC collimation system • Collimators intercept beam halos (first, secondary, …) with some leakage which gets lost around the ring: the cleaning inefficiency of the system is then defined as: • The leakage lost over a given length of the machine (10 cm in our studies) is then counted as local cleaning inefficiency (unit = m-1). • Goal of this presentation is to show that it is sufficient to useonly a limited number of BLMs for commissioning the collimation system. Critical Beam Losses during Commissioning and Initial Operation

Critical BLMs for collimation • There are two types of critical BLMs for the collimation system: -- BLMs at the collimators: needed from early on for the set-up of the collimators (experiments in SPS performed successfully in Fall 2004 for the first time),-- BLMs at loss locations of “leakage halo”: the halo exiting IR3/IR7 is lost in characteristic locations and not spread everywhere around the ring (implying all BLMs should be used)=> critical loss locations characterize the efficiency of our system: can we identify those critical locations (= BLMs) ?? Critical Beam Losses during Commissioning and Initial Operation

How to address this question • Performing full simulations with ALL movable LHC Collimation System equipments: 41 collimators/absorbers per ring for Phase 1. • Only betatron cleaning is considered in the following for on-momentum beam halo • Check leakage halo losses in cold elements of the machine • Notes: * results presented for Beam 1 only (Beam 2 tracking in preparation) * heavy computing effort in resources and time (CPU limited) * local energy deposition: FLUKA takes our data as input * losses at collimators: induced showers can propagate downstream Critical Beam Losses during Commissioning and Initial Operation

CPU usage ← granted by share with experiments ← limit of Collimation allocated CPUs 2 students - 2 fellows Tracking on 64+ CPUs Critical Beam Losses during Commissioning and Initial Operation

Parameters for obtaining loss maps • Data done for the two types of tracked halo (horizontal and vertical) and the two optics defined as reference cases: -- injection optics: 450 GeV, b* = 17 m at all IPs, -- collision optics: 7 TeV, b* = 0.55 m at IP1 & IP5 (else 10 m). Intermediate b* values can be studied if necessary (in case of big losses in experimental insertions). • Assumed quench limit values: h =10-3 m-1 (injection) h =2 x 10-5 m-1 (collision) • Results presented in the following slides focus on the horizontal halo only. Critical Beam Losses during Commissioning and Initial Operation

Collimators settings – Injection (1/2) Critical Beam Losses during Commissioning and Initial Operation

Collimators settings – Injection (2/2) Critical Beam Losses during Commissioning and Initial Operation

Collimators settings – Top energy (1/2) Critical Beam Losses during Commissioning and Initial Operation

Collimators settings – Top energy (2/2) Critical Beam Losses during Commissioning and Initial Operation

Error scenarios In the following we consider free orbit oscillations, always at the worst phase (found in simulation scan), following 2 scenarios: • Static case: -- collimators are always re-centered around the perturbed orbit -- the error amplitude can reach the estimated aperture tolerances of 4 mm (injection optics) / 3 mm (collision optics) • Dynamic case: -- collimators are still centered on the nominal closed orbit -- peak amplitude of error is ~ 1.5 s Critical Beam Losses during Commissioning and Initial Operation

Loss map – 450 GeVIdeal case ▬► halo ↕x 5 => Ideal case: below the quench limit (factor 5); not true during start-up though Critical Beam Losses during Commissioning and Initial Operation

Sample perturbed orbit ▬► halo ↑ │ │ │ ± 4 mm │ │ ↓ Critical Beam Losses during Commissioning and Initial Operation

Loss map – 450 GeV Perturbed orbit – worst phase, 4 mm amplitude ▬► halo ↕x 2.5 => Loss of a factor 2 in efficiency at worst locations !!! Critical Beam Losses during Commissioning and Initial Operation

Going downstream from IR7 ▼ = critical BLM high dispersion ↓ high dispersion + high b ↓↓↓↓ ▼ ▼ ▼ ▼ ▼ ▼ Ideal case ▼ ▼ ▼ ▼ ▼ ▼ ▼ 4 mm orbit ▼ ▼ => Same loss locations !!! Modulation of the peaks: a way to measure orbit ??? Critical Beam Losses during Commissioning and Initial Operation

Effect of optic (dispersion) ↑ peak loss location => Losses due to first high dispersion location !!! Characteristic loss locations can be understood from halo properties and optics. Critical Beam Losses during Commissioning and Initial Operation

Why off-momentum losses for on-momentum primary halo ? • Collimators in IR7 intercept off-axis particles => induced proton-collimator material interaction follows several processes. • Single-diffracting scattering: generates off-momentum halo=> always lost at one of the first high dispersion points: critical locations for limiting losses are therefore well defined (as seen in the IR7 +Arc 7-8 case) • Sets fundamental limitation of the LHC betatron cleaning insertion: single-diffracting scattering can never be avoided !!! Critical Beam Losses during Commissioning and Initial Operation

IR8 + Arc 8-1 ▼ ▼ Ideal case ▼ ▼ 4 mm orbit Critical Beam Losses during Commissioning and Initial Operation

Effect of optic (beta) ← peak loss location => Losses due to high betatron location !!! Critical Beam Losses during Commissioning and Initial Operation

IR1 Ideal case 4 mm orbit Critical Beam Losses during Commissioning and Initial Operation

IR2 TDI.4L2 TCLIA.4R2 Losses here are due to scattering from TDI Ideal case 4 mm orbit Critical Beam Losses during Commissioning and Initial Operation

IR3 Remember: only betatron cleaning Ideal case ▼ ▼ 4 mm orbit Critical Beam Losses during Commissioning and Initial Operation

IR6 Losses at the TCDQ equipment: → problem of local showers downstream of it under study ▼ Ideal case 4 mm orbit ▼ => We made one turn after IR7: 13 critical BLMs identified at injection (in addition to the ones foreseen at the locations of collimators). Critical Beam Losses during Commissioning and Initial Operation

Going further in error amplitude │ │ ← specified orbit │ │ │ │ │ │ │ │ │ │ │ │ │ │ + 80 % + 130 % Critical Beam Losses during Commissioning and Initial Operation

7 Tev Study halo ▬► IR2, IR5 & IR8: nominal crossing schemes IR1: where orbit perturbation is applied Static orbit: ± 4 mm in the arcs, ± 3 mm in the insertions (many thanks to W. Herr !!!) . Critical Beam Losses during Commissioning and Initial Operation

Going downstream from IR7 ↓high dispersion ▼ ▼ ▼ Ideal case ▼ high dispersion + high b ↓↓↓↓ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ With orbit error => From below quench limit to about twice above; additional BLMs show up, but most of them are at the same locations than injection case. Critical Beam Losses during Commissioning and Initial Operation

IR8 + Arc 8-1 ←TCTs: generate a new quartiary halo => critical BLMs to be located here as well Ideal case ▼ ▼ ▼ With orbit error ▼ ▼ ▼ Critical Beam Losses during Commissioning and Initial Operation

IR1 ← TCTs Ideal case With orbit error Critical Beam Losses during Commissioning and Initial Operation

IR2 ← TCTs Ideal case With orbit error Critical Beam Losses during Commissioning and Initial Operation

IR3 Remember: only betatron study so far Ideal case With orbit error Critical Beam Losses during Commissioning and Initial Operation

IR4 Ideal case With orbit error Critical Beam Losses during Commissioning and Initial Operation

IR5 Ideal case ← TCTs With orbit error Critical Beam Losses during Commissioning and Initial Operation

IR6 Losses at the TCDQ equipment: → problem of local showers downstream of it under study Ideal case With orbit error => After one complete turn: 18 critical locations (in addition to collimator ones and at the triplets) Critical Beam Losses during Commissioning and Initial Operation

Dynamic scenario - Process • Dynamic studies: collimators are not re-centered around the perturbed orbit. • Purpose of this scenario: check the sensitivity of the system to fast orbit changes => how does the system behave if a secondary collimator gets closer to become a primary (back to a single-stage system) ? What is the effect on the cleaning efficiency ? • In the following, only the collision optics case is presented (results for injection optics still being analyzed). Critical Beam Losses during Commissioning and Initial Operation

Effect on the cleaning system - Lattice TCP.C6L7 TCSG.B4L7 TCSG.6R7 ↓zero orbit change ↑critical secondary Critical Beam Losses during Commissioning and Initial Operation

Loss Map for a 0.95 s offset (only IR7 elements) same critical locations !!! ↓ => Loss of a factor 4 in local cleaning efficiency in IR7 !!! Critical Beam Losses during Commissioning and Initial Operation

Requirements for commissioning • For commissioning of the LHC and its collimation system, one needs to be sure to operate in safe conditions => with the results presented here, we can already point out critical locations !! • The determined positions and peak values of losses can then be used to define a minimum workable LHC BLM system for collimation studies. Critical Beam Losses during Commissioning and Initial Operation

Summary table for injection black: nominal & perturbed case red: only in nominal case + collimator locations + critical locations for IR3 => 13 critical locations in total Critical Beam Losses during Commissioning and Initial Operation

Summary table for collision black: nominal & perturbed case red: only in nominal case blue: only in perturbed case + collimator locations + triplets + critical locations for IR3 => 18 critical locations in total, 6 of which being identical as in the injection case !! Critical Beam Losses during Commissioning and Initial Operation

Critical loss locations Critical Beam Losses during Commissioning and Initial Operation

Longitudinal distribution of beam losses – detailed studies for BLM positioning Dipole: all along the magnet Quadrupole: up to the middle of the magnet Critical Beam Losses during Commissioning and Initial Operation

Remarks • Early scenario checked (as seen in R. Assmann’s previous talk) as well: identical loss locations • Cases studies here refer to closed orbit perturbation spread all along the lattice: do not take into account possible local bumps in orbit!!!=> expect certainly some few additional high loss locations. • injection optics: many regions, not that critical collision optics: few regions, more critical Critical Beam Losses during Commissioning and Initial Operation

Conclusion • The tools we developed allow us to study where the most critical regions of the machine are expected: -- for both mode of operation of the LHC (injection & collision), with still other optics possible, -- for any given scenario of beam losses, to check how flexible the system can be depending on the mode of operations. • In close collaboration with the BLM team, detection and monitoring of these critical regions shall be achieved to allow efficient commissioning of the LHC Collimation System. Critical Beam Losses during Commissioning and Initial Operation

Critical beam losses during Commissioning & Initial Operation