CLIC: next generation ? B. Dalena, CERN 5 th June 2009

Outline The Physics Case –Complementary to LHC physics –New territory to discover Linear Colliders –General introduction –Main challenges CLIC- the Compact LInear Collider –The two beam accelerator scheme –The CLIC technological issues Conclusion

The Physics case

Path to higher energy History: Energy constantly increasing with time Hadron Collider at the energy frontier Lepton Collider for precision physics LHC coming online soon Consensus to build Lin. Collider with E cm > 500 GeV to complement LHC physics (European strategy for particle physics by CERN Council)

Hadron versus lepton collisions Colliding particles can be elementary particles (leptons) or composite objects (hadrons) –LEP: e + e - –LHC: pp Hadron collider: –Hadrons easier to accelerate to high energies –Only a fraction of total energy goes in the E CM Lepton Collider: –well-defined E CM –well-defined polarization (potentially)  are better at precision measurements +

Example of LHC vs lepton colliders: Higgs LHC might discover one, or more, Higgs particles, with a certain mass However, discovery and mass are not enough Are we 100% sure it is really a SM/MSSM Higgs Boson? –What is its spin? –Exact coupling to fermions and gauge bosons? –What are its self-couplings? So, are these properties exactly compatible with the SM/MSSM Higgs? Confidence requires a need for precision

Higgs: Spin Measurement The SM Higgs must have spin 0The SM Higgs must have spin 0 In a lepton collider we will know E cmIn a lepton collider we will know E cm A lepton collider can measure the spin of any Higgs it can produceA lepton collider can measure the spin of any Higgs it can produce e + e –  HZ (mH=120 GeV, 20 fb–1) Slide: B. Barish

TeV e+e- physics Higgs physics –Tevatron/LHC should discover Higgs (or something else) –LC explore its properties in detail Supersymmetry –LC will complement the LHC particle spectrum and their properties Extra spatial dimensions New strong interactions... => a lot of new territory to discover beyond the standard model Energy can be crucial for discovery! “Physics at the CLIC Multi-TeV Linear Collider” CERN “ILC Reference Design Report – Vol.2 – Physics at the ILC”

LiNEAR COLLIDERs

Limits of circular colliders We want E cm as high as possible for new particle accelerators Circular colliders  particles bent  two limitations occurs: I) Synchrotron radiation energy loss P  E 4  limited LEP to E cm =209 GeV (RF energy replenishment) P  m 0 -4  changing to p in LHC  P no longer the limiting factor II) Magnetic rigidity Technological limit of bending magnet field strength (fixed ρ  cost)  Limits LHC to E cm =14 TeV (  B )  Superconducting magnets needed

Linear versus Circular Colliders Storage Rings Acceleration+collision every turn “re-use” RF “re-use” particles  efficient  Synchrotron Radiation  Cost Luminosity  Event rate Linear Collider One-pass acceleration+collision RF used only once Particles dumped at each collision  need high gradient  need small beam sizes ~40 MHz ~10 Hz m2m2 nm 2 n b = bunches/train N = particles per bunch f rep = repetition frequency  x,y = sizes of the beam at IP H D = beam-beam enhancement factor ~10 34 cm -2 s -1

1 st challenge: E CM Accelerating cavities used once  the length of the linac is then given by: 1.E CM 2.Accelerating gradient [V/m]  1 st main challenge of future linacs: maximize gradient to keep collider short enough ! (Gradient limited by field break down) E.g. for E e =0.5 TeV and an average gradient of g=100 MV/m we get: length = E[eV] / g[V/m] = 5 km Needs two linacs (e+ and e-) and 2 long final focus sections ~ 5 km  total length for this example 15 km Main linac

Accelerating structures: NC traveling wave Normal Conducting standing wave structures would have high Ohmic losses => traveling wave structuresNormal Conducting standing wave structures would have high Ohmic losses => traveling wave structures RF ‘flows’ with group velocity v G alongRF ‘flows’ with group velocity v G along the structure into a load at the structure exit pulsed RF Power source d RF load CLIC Main linac

Accelerating cavities: SC standing wave Superconducting standing-wave cavitites: negligible Ohmic lossesSuperconducting standing-wave cavitites: negligible Ohmic losses ILC (from P. Tenenbaum, Main linac

2 nd challenge: interaction point beam sizes (picture from A. Seryi, (values for CLIC, 11/2008 Vertical size is smallest In order to maximize the luminosity we need very small beam sizes at the interaction point. ) IP

 Emittance Key concept in linear colliders: Generation and preservation of very small emittance! Generation of small emittances: electrons "easy" by synchrotron radiation damping -> damping rings Preservation of small emittances: precision alignment and steering, limitation of collective effects (synchrotron radiation, wake fields) Beam qualityLattice RMS beam size RTMLMain linac Beam Delivery Damping Rings Source

 generation  damping rings final emittanceequilibrium emittance damping time Reduce the phase space volume of the beams so that the design beam emittances are obtained. Emittance evolution: initial emittance damping driven by incoherent synchrotron radiation + RF gain theoretical limit: quantum character of the radiation Damping Rings

 preservation Implications –Intra-Beam Scattering, e - cloud… –Wakefield control –Very good alignment –Stabilization: ground motion studies, … –Precise instrumentation –Beam based corrections and feed-backs Transport the beam from the damping rings to the IP without significant blow-up in the different subsystems: RTML Ring To Main Linac (RTML) Main Linac BDS Beam Delivery System (BDS) RTMLMain linac Beam Delivery

How to focus the beam to a small spot? (1/2) How to focus the beam to a small spot? (1/2) If you ever played with a lens trying to burn a picture on a wood under bright sun, then you know that one needs a strong and big lens It is very similar for electron or positron beams But one have to use magnets (quadrupoles) (The emittance  is constant, so, to make the IP beam size (  ) 1/2 small, you need large beam divergence at the IP (  /  ) 1/2 i.e. short-focusing lens.) (from A. Seryi, Beam Delivery

Sequence of elements in ~100m long Final Focus Test Beam beam Focal point Dipoles. They bend trajectory, but also disperse the beam so that x depends on energy offset  Sextupoles. Their kick will contain energy dependent focusing x’ => S (x+  ) 2 => 2S x  +.. y’ => – S 2(x+  )y => -2S y  +..  that can be used to arrange chromatic correction (from A. Seryi, How to focus the beam to a small spot? (2/2) Beam Delivery

CLIC- The Compact Linear Collider

The CLIC Two-Beam Accelerator main beam 1 A, 156 ns 9 GeV TeV DRIVE BEAM PROBE BEAM

Why a Two-Beam scheme ? Luminosity scales as wall-plug-to-beam efficiency. Need to obtain at the same time high-gradient acceleration and efficient energy transfer. The use of high-frequency RF maximizes the electric field in the RF cavities for a given stored energy. However, standard RF sources scales unfavorably to high frequencies, both in for maximum delivered power and efficiency. A way to overcome such a drawback is to use standard low-frequency RF sources to accelerate the drive beam and use it to produce RF power at high frequency. The drive beam is therefore used for intermediate energy storage.  Luminosity

CLIC schematic 3 TeV Drive beam

CLIC RF power source Drive beam

Drive beam generation Klystrons conventionally generate a long beam pulse Fully loaded acceleration: efficiently accelerate long beam pulse Bunch interleaving: delay part of the pulse and interleave the bunches in a Delay Loop and Combiner Ring(s) => the long pulse (low frequency and low current) is transformed into shorter pulses of high current and high bunch repetition frequency 24 pulses – 101 A – 2.5 cm between bunches 240 ns 5.8  s 140  s train length - 24  24 sub-pulses 4.2 A GeV – 60 cm between bunches 240 ns initial Drive beam structure - final CR2 Delay loop drive beam accelerator 2.38 GeV, 1.0 GHz 326 klystrons 33 MW, 139  s 1 km CR1

Lemmings Drive Beam (from A. Andersson,

Power extraction structure PETS Must extract efficiently >100 MW power from high current drive beam Device where bunches of the drive beam interact with the impedance of structures and generate RF power Beam eye view The power produced by the bunched (  0 ) beam in a constant impedance structure: Design input parametersPETS design P – RF power, determined by the accelerating structure needs and the module layout. I – Drive beam current L – Active length of the PETS F b – single bunch form factor (≈ 1) Courtesy E. Adli

CLIC R&D issues: where? fully loaded acceleration recombination x 2 bunch length control recombination x 4 bunch compression two-beam acceleration structures 12 GHz structures 30 GHz deceleration stability S tructures S tructure materials Drive Beam generation DB decelerator CLIC sub-unit CTF3 is a small scale version of the CLIC drive beam complex: Provide the RF power to test the CLIC accelerating structures and components Full beam-loading accelerator operation Electron beam pulse compression and frequency multiplication Safe and stable beam deceleration and power extraction High power two beam acceleration scheme

CLIC R&D issues: where? fully loaded acceleration recombination x 2 bunch length control recombination x 4 bunch compression two-beam acceleration structures 12 GHz structures 30 GHz deceleration stability S tructures S tructure materials Drive Beam generation DB decelerator CLIC sub-unit CTF3 is a small scale version of the CLIC drive beam complex: Provide the RF power to test the CLIC accelerating structures and components Full beam-loading accelerator operation Electron beam pulse compression and frequency multiplication Safe and stable beam deceleration and power extraction High power two beam acceleration scheme

CLIC schematic 3 TeV Main beam

CLIC Main Beam complex Main beam

 preservation: alignment + stabilization Wakefield effects on the beam dynamics have already been used in the structure design stage Alignment procedure based on: –Accurate pre-alignment of beam line components (O(10µm)) accelerating structures 14  m (transverse tolerance at 1  ) PETS structures30  m quadrupoles 17  m –Beam-based alignment using BPMs with good resolution (100nm) –Alignment of accelerating structures to the beam using wake- monitors (5µm accuracy) –Tuning knobs using luminosity/beam size measurement with resolution of 2% Quadrupole stabilization (O(1nm) above 1Hz) Feedback using BPMs resolving 10% of beam size (i.e. 50nm resolution)

Synchrotron radiation in the CLIC BDS and IP solenoid The emission of Incoherent Syncrhotron Radiation (ISR) limits the luminosity in a TeV linear collider. The emission of ISR due to the CLIC BDS  Luminosity loss of about 24% (due to sector bend and final quadrupole magnets). When the magnetic field of the IP solenoid is added the loss further increases between [2,14]%, depending on the IP solenoid magnetic field strength and length

Beam-Beam in CLIC (from D. Schulte,

Comparison ILC - CLIC TeVILC-0.5CLIC-0.5CLIC-3remarks No. of particles/bunch CLIC can’t go higher because of short range wakefields No. of bunches/pulse Bunch separationns Short spacing essential for CLIC to get comparable RF to beam efficiency Bunch train length ms One CLIC pulse fits easily in small damping ring but intra train feedback difficult Charge per pulsenC Positron source much easier for CLIC Linac repetition rate Hz550 Pulse to pulse feedback more efficient for CLIC (less linac movement between pulses)   x,   y nm 10000, , , 20 CLIC has more stringent requirements for DR equilibrium  and  preservation Proposed site length km

CLIC detectors Different time structure of the beam ILC/CLIC has to be taken into account Changes for multi-TeV collisions (first vertex layer moved out, calorimeter deeper (9 ),…) ILC/CLIC collaboration, profiting from ILC developments Start-up with studies with SiD-like, ILD concept detectors

CONCLUSION World-wide Consensus for a Lepton Linear Collider as the next HEP facility to complement LHC at the energy frontier Energy range < 1 TeV accessible by ILC - CLIC up to 3 TeV CLIC technology based on: –normal conducting RF structures at high frequency –two-beam scheme Only possible scheme to extend collider beam energy into Multi-TeV energy range Very promising results, challenging R&D is still required CLIC-related key issues addressed in CTF3 by 2010

The CTF3 – CLIC world wide collaboration 39EPAC 2008 CLIC / CTF3 G.Geschonke, CERN Helsinki Institute of Physics (Finland) IAP (Russia) IAP NASU (Ukraine) Instituto de Fisica Corpuscular (Spain) INFN / LNF (Italy) J.Adams Institute, (UK) JINR (Russia) Oslo University (Norway) PSI (Switzerland), Polytech. University of Catalonia (Spain) RRCAT-Indore (India) Royal Holloway, Univ. London, (UK) SLAC (USA) Uppsala University (Sweden) Ankara University (Turkey) BINP (Russia) CERN CIEMAT (Spain) Cockcroft Institute (UK) Gazi Universities (Turkey) IRFU/Saclay (France) JLAB (USA) Karlsruhe University (Germany) KEK (Japan) LAL/Orsay (France) LAPP/ESIA (France) NCP (Pakistan) North-West. Univ. Illinois (USA) 28 institutes involving 18 funding agencies from 16 countries

SPARES

Tentative long-term CLIC scenario shortest, Success Oriented, Technically Limited Schedule Technology evaluation and Physics assessment based on LHC results for a possible decision on Linear Collider with staged construction starting with the lowest energy required by Physics First Beam? Technical Design Report (TDR) Conceptual Design Report (CDR) Project approval ?

Reminder: transverse beam size Luminosity: RMS beam size: Beam qualityLattice

 (s): ILC - example of traditional Final Focus (from A. Seryi, Traditional FF Final Doublet X-Sextupoles Y-Sextupoles

 emittance growth budget (from D. Schulte,

 emittance preservation Example from CLIC Main Linac: Cavities misaligned -  y = 100 μm rms -  y’ = 100 μrad rms - no quadrupole misalignments Final cavity position distribution -  y = 85 μm rms Alignment method 1. one-to-one correction 2. structure alignment 3. repeat from 1. three times (from A. Latina,

The CLIC scheme - What does the RF Power Source do ? Electron beam manipulation Long RF Pulses P 0, n 0, t Klystrons low frequency high efficiency Power stored in electron beam Short RF Pulses P A = P 0  N 1 t A = t 0 / N 2 n A = n 0  N Accelerating Structures high frequency high gradient Power extracted from beam in resonant structures The CLIC RF power source can be described as a “black box”, combining very long RF pulses, and transforming them in many short pulses, with higher power and with higher frequency

Bunch structure SC allows long pulse, NC needs short pulse with smaller bunch charge ILC ILC

Beam-Beam in CLIC Electric field from one bunch boosted by 2  2 as seen by particles in the other bunch Small beams, high Lorentz factors => Strong electromagnetic fields => Beam focusing Increase of luminosity Beamstrahlung Beamstrahlung

Higgs: self-couplings SM predicts g HHH  Potentially measured with polarized lepton collision via e + e -  HHZ (Graph: M.M.Mühlleitner) The Higgs potential:

CTF 3: CLIC Test Facility demonstrate Drive Beam generation (fully loaded acceleration, bunch frequency multiplication 8x) Test CLIC accelerating structures Test power production structures (PETS) demonstrate Drive Beam generation (fully loaded acceleration, bunch frequency multiplication 8x) Test CLIC accelerating structures Test power production structures (PETS) CLEX 30 GHz “PETS Line” Linac Delay Loop – 42m Combiner Ring – 84m Injector Bunch length chicane 30 GHz test area TL1 TL2 RF deflector Laser 4A – 1.2µs 150 MeV 32A – 140ns 150 MeV

The three main parameters RingsLinear colliders Particle type(s) ions, p/p, e +/- Collision energy accelerating cavities reused accelerating cavities used once Luminosity bunches collide many times several detectors simultaneously each bunch collides only once only one detector in use at a given time

What is a linear collider? Main part: two long linear accelerators (linacs), with as high accelerating gradient as possible The two beams are "shot" into the collision point, with a moderate repetition rate f rep ~10 Hz, to compare with LHC f rep =40 MHz How to compensate the resulting luminosity loss?? Challenges: –E CM –Interaction point beam sizes e+e- source damping ring main linac beam delivery Luminosity

Parameters comparison SLCTESLAILCJ/NLCCLIC TechnologyNCSC NC Gradient [MV/m] CMS Energy E [GeV] RF frequency f [GHz] Luminosity L [10 33 cm -2 s -1 ] Beam power P beam [MW] Grid power P AC [MW] Bunch length  z * [mm]~ Vert. emittance  y [10 -8 m] Vert. beta function  y * [mm]~ Vert. beam size  y * [nm] Parameters (except SLC) at 500 GeV

CLIC nominal parameters Center-of-mass energy3 TeV Peak Luminosity6·10 34 cm -2 s -1 Peak luminosity (in 1% of energy)2·10 34 cm -2 s -1 Repetition rate50 Hz Loaded accelerating gradient100 MV/m Main linac RF frequency12 GHz Overall two-linac length42.2 km Bunch charge3.7·10 9 Beam pulse length156 ns Average current in pulse1 A Hor./vert. normalized emittance660 / 20 nm rad Hor./vert. IP beam size before pinch45 / ~1 nm Total site length48.4 km Total power consumption390 MW