Beam halo and beam losses in IR1 and IR5 R. Assmann, AB MIBWG June 15th, 2007 RWA, 31/5/2007

The LHC Challenge Talk at EPAC 2002 in Paris: “Requirements and Design Criteria for the LHC Collimation System”. High stored energy and stored energy density! Small collimation gaps! RWA, 31/5/2007

8.5 W/m Preventing Quenches Shock beam impact: 2 MJ/mm2 in 200 ns (0.5 kg TNT) Maximum beam loss at 7 TeV: 1% of beam over 10 s 500 kW Quench limit of SC LHC magnet: 8.5 W/m RWA, 31/5/2007

System Design “Phase 1” Momentum Cleaning Betatron Cleaning “Final” system: Layount is 100% frozen! RWA, 31/5/2007  Outcome of accelerator physics + energy deposition optimization

SC triplet and experiment Multi-Stage Cleaning Without beam cleaning (collimators): Quasi immediate quench of super-conducting magnets (for higher intensities) and stop of physics. Required cleaning efficiency: always better than 99.9%. Beam propagation Core Unavoidable losses Primary halo (p) Secondary halo p p Shower p Tertiary halo Impact parameter ≤ 1 mm p e p collimator Primary Secondary collimator Shower SC triplet and experiment e Absorber TCT RWA, 31/5/2007

The LHC “TCSG” Collimator 360 MJ proton beam 1.2 m 3 mm beam passage with RF contacts for guiding image currents Designed for maximum robustness: Advanced CC jaws with water cooling! Other types: Mostly with different jaw materials. Some very different with 2 beams!  For design see TS seminar A. Bertarelli. RWA, 31/5/2007

Functional Description Two-stage cleaning (robust CFC primary and secondary collimators). Catching the cleaning-induced showers (Cu/W collimators). Protecting the warm magnets against heat and radiation (passive absorbers). Local cleaning and protection at triplets (Cu/W collimators). Catching the p-p induced showers (Cu collimators). Intercepting mis-injected beam (TCDI, TDI, TCLI). Intercepting dumped beam (TCDQ, TCS.TCDQ). Scraping and halo diagnostics (primary collimators and thin scrapers). RWA, 31/5/2007

Top Level Collimator Controls S. Redaelli et al Successful test of LHC collimator control architecture with SPS beam (low, middle, top level) RWA, 31/5/2007

 Multi-turn loss predictions Cleaning Efficiency Simulations: 5 million halo protons 200 turns realistic interactions in all collimator-like objects LHC aperture model (p losses) and FLUKA G. Robert-Demolaize & S. Redaelli  Multi-turn loss predictions RWA, 31/5/2007

Ramp: Efficiency with Collimators Scaled for Constant Beam Tolerances Efficiency / m dN/dt = 0.1%/s, N = 3e14 p, ideal Cleaning efficiency Quench limit requirement Beam energy [TeV] C. Bracco et al RWA, 31/5/2007

Efficiency Assumption always: Lost protons/ions are hitting the primary collimator (multi-turn diffusion process with 5 nm per turn). Ideally: Protons/ions just disappear (“black hole” collimator):  100 % efficiency (1 - #protons escaping / total)  0 inefficiency (# protons escaping / total)  zero heat load from halo protons on SC magnets In reality: A few protons/ions can escape:  efficiency < 100% (we talk about > 99.95%)  inefficiency > 0 (we talk about < 5 × 10-4) Quenches: Heat load per m. Critical parameter are losses per m of SC magnet, or efficiency per m! No problem if losses are distributed over 27 km…  efficiency (we talk about > 99.994% per m)  inefficiency (we talk about < 2 × 10-5 per m) RWA, 31/5/2007

7 TeV Proton Loss Distribution p losses ~ inefficiency G. Robert-Demolaize et al RWA, 31/5/2007

Beam Losses in IR1 and IR5 Betatron halo losses: Momentum halo losses: No direct losses in IR1 and IR5 triplets or experiments when collimators are correctly set up. Fully protected by tertiary collimators (H and V on each incoming beam). Load of tertiary beam halo at tertiary collimators about 0.05% of total losses: For example: @ TCP @ TCT Peak loss (0.2h, 4e11 p/s)  < 2e8 p/s (spike) Parasitic losses (20h, 4e9 p/s)  < 2e6 p/s (normal) Completely uncritical for triplet quench with tertiary collimators in place. Efficiency will be lower during commissioning and early running. Losses should never be higher than listed above in normal operation. Experiments will see the showers from the tungsten collimators. Momentum halo losses: No detailed loss maps yet. Momentum losses much lower than betatronic. RWA, 31/5/2007

Preparing Commissioning at 7 TeV 0.8 mm at a typical collimator 0.2 mm at a typical collimator Phase 1  Commissioning is being prepared: Controls, tools, scenarios, … RWA, 31/5/2007

IP1/IP5 MARS15 Extended Model Machine, interface and related detector elements in  550 m from IP1 and IP5: 3-D geometry, materials, magnetic fields, tunnel and rock outside (up to 12 m laterally). Tungsten tertiary collimators TCTV and TCTH at 145.34 and 147.02 m from IP, respectively, aligned wrt BEAM2 coming to IP5 and BEAM1 coming to IP1. First source: tails from betatron cleaning in IP7 – files of proton hits in TCTs for BEAM1 and BEAM2 from Tom Weiler. Second source: beam-gas interactions of BEAM2 at 0 to 550-m from IP5 using gas pressure map from CERN colleagues. MARS15 calculations: power density and dynamic heat loads in inner triplet quads, absorbed and residual doses in the entire region, and particle fluxes at CMS and ATLAS. Most calculations completed for IP5; started for IP1. CERN/LARP Collimation, Aug. 23, 2006 IP1/IP5 TCT Collimators - N.V. Mokhov

IP1/IP5 TCT Collimators - N.V. Mokhov TCTV and TCTH Models Aspect ratio V:H = 1:12 CERN/LARP Collimation, Aug. 23, 2006 IP1/IP5 TCT Collimators - N.V. Mokhov

Betatron Cleaning: Hadron Fluxes in IR5 Total in TCT – TAN region Charged hadrons at 0 to 150 m CERN/LARP Collimation, Aug. 23, 2006 IP1/IP5 TCT Collimators - N.V. Mokhov

Betatron Cleaning: Radiation Loads in IR5 Peak power density in Q3 SC coils: 6.e-5 mW/g Peak absorbed dose: a few kGy/yr Peak residual dose: 7 mSv/hr CERN/LARP Collimation, Aug. 23, 2006 IP1/IP5 TCT Collimators - N.V. Mokhov

Betatron Cleaning: Radiation Loads in TCT-TAN Region Peak absorbed dose: 12 MGy/yr in jaws, 20 kGy/yr outside jaws Peak residual dose: 8 mSv/hr on jaws, 0.1 mSv/hr around TCTs CERN/LARP Collimation, Aug. 23, 2006 IP1/IP5 TCT Collimators - N.V. Mokhov

Beam1 and Beam 2 Asymmetry Beam1, 7 TeV Betatron cleaning Ideal performance TCDQ Quench limit (nominal I, t=0.2h) Local inefficiency [1/m] Beam2, 7 TeV Betatron cleaning Ideal performance TCDQ Quench limit (nominal I, t=0.2h) Local inefficiency: #p lost in bin over total #p lost over length of aperture bin! RWA, 31/5/2007

Asymmetry IR1/IR5 Beam 1 betatron halo losses on TCT left sides of IP: IR1: 5e-4 of total halo loss IR5: 5e-6 of total halo loss Beam 2 betatron halo losses on TCT right sides of IP: IR1: 2e-5 of total halo loss IR5: 3e-4 of total halo loss Halo losses in experimental insertions are asymmetric. Detailed losses depend on collimator settings, phase advance and halo phase space properties. Above settings assume IR2 and IR8 collimators present and at same setting as IR1/IR5 teriary collimators. We might open them and losses in IR1/IR5 will increase (small gaps not needed in IR2/8 & trapped mode issues with higher b*, small gaps in IR2/8).  In worst case increase losses by a factor ~2. RWA, 31/5/2007

Summary Tertiary collimators are in place and shield IR1/IR5 well against halo losses. Triplet quenches from beam halo now uncritical. Showering studies done. Betatron halo losses at tertiary collimators should be as follows (nominal intensity, nominal cleaning efficiency, nominal optics, IR2/8 retracted): Below ~4e6 p/s in stable physics conditions (20h beam lifetime) Below ~4e8 p/s for “long spikes” (0.2h beam lifetime for up to 10s) Never higher than this but likely quite a bit lower in early years. Accidential losses at 7 TeV can put 1 nominal bunch into the edge of the horizontal TCT (will not happen with correct collimator set-up, will damage TCT: scratch of surface, unlikely is a water leak). Momentum halo loss maps to be produced, but losses will be lower. Team in place to support studies: C. Bracco, T. Weiler, S. Redaelli, R. Assmann RWA, 31/5/2007

Acronyms TC… = Target Collimator TCL… = Target Collimator Long TCP = Primary collimator TCSG = Secondary collimator Graphite TCSM = Secondary collimator Metal TCHS = Halo Scraper TCL… = Target Collimator Long TCLI = Injection protection (types A and B) TCLP = Physics debris TCLA = Absorber TCD… = Target Collimator Dump TCDQ = Q4 TCDS = Septum TCDI = Injection transfer lines TD… = Target Dump TDI = Injection RWA, 31/5/2007