PARTICLE BEAMS, TOOLS FOR MODERN SCIENCE AND MEDICINE Hans-H. Braun, CERN

Transcription

1 5 th Particle Physics Workshop National Centre for Physics Quaid-i-Azam University Campus, Islamabad PARTICLE BEAMS, TOOLS OR MOERN SCIENCE AN MEICINE Hans-H. Braun, CERN 3 rd Lecture Introduction to Linear e + /e - Colliders and CLIC the Next Generation of Tools for Particle Physics o Linear Colliders - Motivation and Concept o Technical Challenges for Linear Colliders oclic

2 Collider History Since the 60s, most new revelations in particle physics have come from colliders Livingstone plot (adapted from W. Panofsky) Energy (exponentially!) increasing with time a factor 10 increase every 8 years! Hadron Colliders at the energy frontier Lepton Colliders for precision physics, catching up in energy ~10y later LHC coming online from 2007 Consensus to build a lepton linear collider with E cm > 500 GeV to complement LHC physics

3 Hadrons vs Leptons, typical event pattern for the Higgs particle Hadron collision Lepton collision p p e+ e- Simulation of HIGGS production e + e Z H Z e + e, H b b

4 Hadron Colliders Protons are composite objects Lepton Colliders Leptons are elementary particles p p e+ e- Only fraction ( 1/6) of total proton energy available for collision of constituents Can only use p t conservation Huge QC background Well defined initial state Momentum conservation eases decay product analysis With beam polarization full knowledge of initial state

5 Linear vs circular e + /e - collider e - e + e - e +

6 What is a Linear Collider R power Source R power Source Interaction Point with etector e + source e + Linac e - Linac e - source No big bending magnets But a lot of R acceleration High Accelerating Gradient to minimize size and cost Exceptional beam quality needed (colliding nm-size beams)

7 Why a Linear Collider Circular colliders re-use acceleration and beams accelerating cavities N N S S e+ e- collision point Charged particles emit synchrotron radiation in a magnetic field Much less important for heavy particles, like protons

8 Cost of Lepton Colliders Synchrotron radiation ΔE ~ (E 4 /m 4 R) m,e R Therefore Cost (circular) ~ a R + b ΔE ~ a R + b (E 4 /m 4 R) Optimization R ~ E 2 Cost ~ c E 2 Cost (linear) ~ a L, where L ~ E cost Circular Collider Linear Collider At high energy, linear collider is more cost effective Energy

9 A linear collider uses the accelerating cavities only once: Lots of them! Need a high accelerating gradient to reach the wanted energy in a reasonable length (total cost, cultural limit) damping ring e+ e- source beam delivery main linac R in R out E

10 SLC: The 1 st Linear Collider Built to study the Z 0 and demonstrate linear collider feasibility Energy = 92 GeV Luminosity = 3e30 E=20 MV/m Had all the features of a 2 nd gen. LC except both e + and e - shared the same linac

11 Challenges for Linear Collider Center of mass Energy E CMS =Length Accelerating field Rate of physics event N Event = cross section Luminosity

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13 Traveling wave structure, the building block of normal conducting electron linacs pulsed R Power source d Electric field R wall currents R load see Walter s talk

14 Klystrons, the R power amplifier for linear accelerators Klystron Modulator Energy storage in capacitors charged up to kv (between pulses) U kv I A f GHz P ave < 1.5 MW P peak < 150 MW efficiency 40-70% High voltage switching and voltage transformer rise time > 300 ns for power efficiency operation pulse length t PULSE > 1 μs favorable

15 R wall currents heat up cavity wall during pulse Acceleration ield E ACC ~ P R Temperature rise for given allowable ΔT ΔT E ACC ~ P ~ 4 t R 1 t PULSE PULSE To get accelerating fields of 100 MV/m pulse length is limited to 100ns or high accelerating fields there is a mismatch between klystron requirement t PULSE >1μs and R structure requirement t PULSE < 100ns

16 How to get High Luminosity?

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18 PX beam angular spread reduction of beam emittance with damping ring X focusing of beam to small size with final focus system PX beamwidth X PX X Emittance = beam width x beam angular spread Conserved quantity for linear focusing elements (i.e. quadrupoles)

19 amping Rings, reduction of emittance with radiation damping R cavity dipole γ N S R cavity δp replaced by R such that Δp z = δp. since y = dy/ds = p y /p z, we have a reduction in amplitude: δy = δp y But photon emission is a quantized, statistical fluctuation of photon number sets lower limit for emittance δp δp

20 Emittance preservation during acceleration in main linac Main problem: Transverse Wakes ields T ( s) = e λ(s - s ) W ( s ) ds 0 Δt b Bunch current generates transverse deflecting modes when bunches are not on cavity axis. Later bunches are kicked transversely Countermeasures etuning of dipole frequencies from cell to cell amping of dipole modes with HOM couplers Strong focusing Tight alignment and orbit control eedbacks Increase of bunch spacing Limit bunch charge

21 inal focus system to minimize beam size at IP Essential part of final focus is final telescope. It demagnify the incoming beam ellipse to a smaller size. A minimal number of quadrupole magnets, to construct a telescope with arbitrary demagnification factors, is four. However, energy spread of beam Leads to chromatic errors, which limit minimum beamsize at IP Telescope optics to demagnify beam by factor m = f 1 /f 2 = f1/l* final doublet () f 1 f 2 f 2 f 1 f 2 (=L * ) IP

22 inal focus with local chromatic correction quadrupoles sextupoles Chromaticity is cancelled locally by two sextupoles interleaved with final quadrupole doublet, a bend upstream generates dispersion across final quadrupoles Geometric aberrations of the sextupoles are cancelled by two more sextupoles placed in phase with them and upstream of the bend Just bend the trajectory ocus in one plane, defocus in another: x = x + G x y = y G y Second order effect: x = x + S (x 2 -y 2 ) y = y S 2xy

23 Solutions to pulse mismatch Use superconducting R cavities at cryogenic temperatures R pulse compression CLIC two beam scheme NLC project discontinued

24 The International Linear Collider (ILC) It is a project designed to smash together electrons and positrons at the center of mass energy of 0.5 TeV initially and 1 TeV later. The ILC Global esign Effort team, established in 2005, has been making its accelerator design. Recently, it worked out the baseline configuration for the 30-km-long 500 GeV collider. (from umihiko Takasaki / KEK) But theoretical limit: E ACC 50 MV/m because magnetic surface fields exceed B CRIT of superconductivity E CMS 1 TeV

25 CLIC aim: develop technology for e - /e + collider with E CMS = 1-5 TeV Physics motivation: "Physics at the CLIC Multi-TeV Linear Collider : report of the CLIC Physics Working Group," CERN report Present mandate: emonstrate all key feasibility issues by 2010

26 BASIC EATURES O CLIC High acceleration gradient (150 (>100 MV/m) Compact collider - overall length < 35 km Normal conducting accelerating structures High acceleration frequency (30 GHz) Two-Beam Acceleration Scheme Capable to reach high frequency Cost-effective & efficient Simple tunnel, no active elements Central injector complex Modular design, can be built in stages

27 CLIC TWO-BEAM SCHEME QUA rive beam A, 70 ns from 2.4 GeV to 240 MeV with -9MV/m QUA POWER EXTRACTION AN TRANSER STRUCTURE (=PETS) ACCELERATING STRUCTURES Main beam 1.5 A, 58 ns from 9 GeV to 1.5 TeV with 150MV/m BPM 30 GHz MW CLIC TUNNEL CROSS-SECTION CLIC MOULE (6000 modules at 3 TeV) m diameter

28 CT II, a two beam accelerator to demonstrate CLIC linac technology Goals of CT II design and construct a fully engineered representative CLIC style test section develop and test drive beam generation and transport demonstrate two beam acceleration scheme at 30 GHz with a string of R structures test active alignment system in an accelerator environment high charge drive beam 48 bunches q=1-14 nc b P=45-32 MeV =0.6 mm σ z CT II milestones design completed 1995 start of construction 1996 operation with 2 CLIC modules 1998 operation with 4 CLIC modules 1999 conversion into high power test stand 2000 ismantled GHz power extraction structure 3 GHz R gun GHz TWS GHz TWS Idler cavity low charge probe beam bunch compressor spectrometer laser 3 GHz R gun 3 GHz TWS train generator 1 bunch q=0.6 b nc 45 MeV =0.9 mm σ z 30 GHz accelerating structure configuration of 1999 TWS=travelling wave structure 22.3 m

29 30 GHz two beam accelerator 30 GHz power extraction structure for CT II drive beam (before brazing) drive beam probe beam 55 mm 30 GHz accelerating structure of CT II main beam 287 mm

30 CLIC 3 TeV CR1 84 m delay 21 m 352 klystrons 40 MW, 94 ms drive beam accelerator 2.37 GeV, 937 MHz combiner rings CR2 334 m decelerator, 21 sectors of 669 m BS 2.6 km BS 2.6 km BC2 e - main linac, 30 GHz, 150 MV/m, 14 km IP1 & IP2 e + main linac BC km train combination B 16 cm 8cm booster linac, 9 GeV, 3.75 GHz e - injector 2.4 GeV e - R 360m BC1 e + R 360m e + injector, 2.4 GeV

31 Phased construction of CLIC Linac 1 I.P. Linac 2 1 TeV Injector Complex 5.2 km 1.5 km 1.5 km 5.2 km 13.4 km Linac 1 I.P. Linac 2 3 TeV Injector Complex 14.2 km 2.6 km 2.6 km 14.2 km 33.6 km

32 Luminosity dependence on bunch charge & bunch length CLIC Parameter who drives who map* best knowledge constraints surface fields temperature rise power x pulselength ½ *main roads only main beam acc. structure optimise for best Luminosity/P AC module layout P R / structure PETS iterate bunch charge pulse length bunch length rep. rate drive beam current and energy iterate emittances beam transport R to end of linac beam transport BS damping ring main beam injector specifications drive beam generation P AC decelerator beam transport legend components key numbers Interaction point input assumptions Luminosity

33 CLIC parameters Center of mass energy GeV 3000 Main Linac R requency GHz 30 Unloaded / loaded gradient MV/m 172 / 150 Linac repetition rate Hz 150 No. of particles / bunch No. of bunches / pulse Bunch separation ns γ εx nm 660 γ εy nm 10 σx * nm 60 σy * nm 0.7 Bunch train length ns 58.4 Total length km 33.6 AC to beam efficiency % 12.5 Total site AC power MW 418 Luminosity cm -2 s Luminosity (in 1% of energy) cm -2 s Beamstrahlung mom. spread % 16 GeV per klystron GeV 8.5 Recent structure test result feasibility? will probably go down

34 The CLIC 30 GHz R Power Source rive Beam Generation Complex Main Beam Generation Complex

35 WHAT OES THE R POWER SOURCE O? The CLIC R power source can be described as a black box, combining very long R pulses, and transforming them in many short pulses, with higher power and with higher frequency 352 Klystrons low frequency high efficiency Power stored in electron beam Power extracted from beam in resonant structures Accelerating Structures high frequency high gradient Long R Pulses Electron beam manipulation for Pulse compression + requency multiplication Short R Pulses

36 R POWER SOURCE BUILING BLOCKS ull beam-loading acceleration in TW sections R in No R to load High beam current short structure - low Ohmic losses Most of R power to the beam Beam combination/separation by transverse R deflectors P 0, ν 0 Transverse R eflector, ν 0 2 P 0, 2 ν 0 P 0, ν 0 eflecting ield

37 Very efficient acceleration of drive beam, i.e. a ratio of beam power to input R power of >93%. This is achieved with the so called fully beam loaded operation. ull beam-loading acceleration in R accelerator sections R in No R to load V BEAM P BEAM High beam current short structure - low Ohmic losses Most of R power to the beam working point I BEAM Similar to the load of a power supply, which has to have a resistance matched to the internal resistance of the power supply for best efficiency.

38 elay Loop Principle double repetition frequency and current parts of bunch train delayed in loop R deflector combines the bunches

39 Higher combination factors reachable in a ring

40 CLIC R power source layout rive Beam Accelerator efficient acceleration in fully loaded linac elay Loop x 2 gap creation, pulse compression & frequency multiplication R Transverse eflectors Combiner Ring x 4 Combiner Ring x 4 pulse compression & frequency multiplication pulse compression & frequency multiplication rive Beam ecelerator Section (2 x 21 in total) Power Extraction rive beam time structure - initial rive beam time structure - final 70 ns 70 ns 4.5 μs 100 μs train length - 32 x 21 x 2 sub-pulses A 2.5 GeV - 64 cm between bunches 2 x 21 pulses 180 A - 2 cm between bunches

41 Motivation and Goals of CT3 collaboration Build a small-scale version of the CLIC R power source, in order to demonstrate: full beam loading accelerator operation electron beam pulse compression and frequency multiplication using R deflectors Provide the 30 GHz R power to test the CLIC accelerating structures and components at and beyond the nominal gradient and pulse length (150 MV/m for 70 ns). Walter s talk Tool to demonstrate until 2010 CLIC feasibility issues identified by ILC-TRC in 2003

42 CT3 layout 3.5 A b of 2.33 nc 150 MeV 1.4 μs - rive Beam Injector rive Beam Accelerator X 2 elay loop 42 m 30 GHz High Gradient Test stand 10 x I B, 10 x ν B X 5 Combiner Ring 84 m CLEX rive beam stability bench marking eceleratortest Beam Line Two-Beam Test stand & Linac subunit CLIC sub-unit 200 MeV Probe Beam Injector 35 A MeV 140 ns rive beam generation scheme

43 1 CT3 Status Nominal beam parameters achieved on ! Tunable R56 Chicane INJECTOR (SLAC & LAL & CERN) irst module Cleaning Chicane 8 m UMP 2.0m UMP Linac 6 m UMP Two-beam 16.5 m TBTS 16 m Test Area m ITB Transport path 1.4m CLEX LIL-ACS 150 MV/m 30 GHz UMP TBL 22.4 m 1.85m 22 m UMP 3.0m 3.0m 2 m LIL-ACS LIL-ACS CALIES Probe beam injector Main beam parameters Nominal I 3.5 A 5 A Achieved T P 1.5 ms 1.5 ms E 150 MeV 100 MeV To be completed by end 2006 ε n 100 π mm mrad 150 π mm mrad * σ t 5 ps 4 ps * R-to-beam efficiency ~ 94% * * for 3.5 A, 1.5 μs beam

44 commissioned with beam CT3 build by a collaboration like a particle physics experiment Thermionic Injector SLAC/USA IN2P3/rance Linac NWU/USA CERN L LN/Italy CR 2006 LN/Italy BINP/Russia CIEMAT/Spain IN2P3/rance Photo injector / laser 2008 CCLRC/UK IN2P3/rance 30 GHz production (PETS line) and test stand IAP/Russia Ankara Univ./Turkey ubna TL2 RRCAT/India CLEX (building in 2006) CEA&IN2P3/rance TSL/Sweden CIEMAT+Uni. Valencia+Uni. Barcelona/Spain NCP/Pakistan

45 1 CT3 complex rive Beam Injector rive Beam Accelerator 16 structures -3 GHz -7 MV/m 3.5 A μs 150 MeV X 2 elay Loop TL1 30 GHz and Photo injector test area 8 m UMP 2.0m UMP 6 m UMP Two-beam 16.5 m TBTS 16 m Test Area LIL-ACS 150 MV/m 30 GHz 2 m LIL-ACS LIL-ACS 22 m CALIES Probe beam injector 16 m TL2 ITB Transport path m 1.4m UMP TBL 22.4 m 1.85m CLEX UMP 3.0m 3.0m 35 A ns 150 MeV X 5 Combiner Ring CLEX 8 m 2.0m UMP UMP 1 UMP 6 m ITB m 16 m TBTS 2.5m walk around zone 1.4m UMP TBL 22.4 m 1.85m LIL-ACS 22 m LIL-ACS UMP 3.0m LIL-ACS TL 3.0m CALIES probe beam injector 2 m 42.5 m

46 CONCLUSIONS An electron/positron collider in LHC energy range has to be a linear collider Presently two schemes under consideration, ILC and CLIC CLIC is presently the only scheme to extend the Linear Collider energy into the Multi-TeV range CLIC technology is less mature than ILC technology, both still requires challenging R& before construction can start Very promising results were already obtained in CT II and in the first stages of CT3 Remaining key issues identified by ILC-TRC CLIC-related key issues addressed in CT3 aiming for a feasibility proof by 2010

47 Linear Collider, some Links & Literature R.B. Palmer, Prospects for High Energy e + e - Linear Colliders, Annu. Rev. Nucl. Part. Sci. vol. 40, p. 529, 1990 G. Loew (editor), ILC-TRC committee reports 1995, Includes descriptions of the various projects Accelerator school on Linear Collider CERN academic training lectures on CLIC CLIC home page ILC home page