Beyond LHC The Path towards Future Linear Colliders

Beyond LHC The Path towards Future Linear Colliders Roger Ruber Dept. of Physics and Astronomy Div. of Nuclear and Particle Physics 30 -Oct-2008 Dept. of Physics and Astronomy Uppsala University, Sweden Beyond LHC The Path Towards Future Linear Colliders

Outline This lecture • technologies for a future linear collider • highlights of related research Sections 1. circular versus linear colliders 2. accelerating gradient 3. RF power production 4. R&D projects for a future linear collider 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 2

1: Particle Collider History p p Outline 1. Colliders 2. Cavities 3. RF power 4. Projects hadron collider at the frontier of physics – huge QCD background – not all nucleon energy available in collision e+ [top quark] [W±, Z boson] [Nν=3] e[gluon] lepton collider for precision physics – well defined CM energy – polarization possible LHC starting up – energy constantly increasing – consensus for next machine Ecm ≥ 0. 5 Te. V for e+e- [charm quark, τ lepton] “Livingstone” plot (adapted from W. Panofsky) 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 3

Circular versus Linear Collider accelerating cavities N N S S Outline 1. Colliders 2. Cavities 3. RF power 4. Projects source Circular Collider many magnets, few cavities → need strong field for smaller ring high energy → high synchrotron radiation losses ( E 4/R) high bunch repetition rate → high luminosity main linac Linear Collider few magnets, many cavities → need efficient RF power production higher gradient → shorter linac single pass → need small cross-section for high luminosity: (exceptional beam quality, alignment and stabilization) 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 4

cost Cost of Circular & Linear Accelerators Outline Circular Collider 1. Colliders Linear Collider 2. Cavities 3. RF power 4. Projects ~200 Ge. V e. Circular Collider • ΔE ~ (E 4/m 4 R) • cost ~ a. R + b ΔE • optimization: R~E 2 → cost ~ c. E 2 30 -Oct-2008 energy Linear Collider • E~L • cost ~ a. L Roger Ruber - Beyond LHC: the path towards future linear colliders 5

2. Accelerating Gradient Outline 1. Colliders 2. Cavities 3. RF power 4. Projects 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 6

Accelerating Gap and Gradient Outline 1. Colliders Gap voltage required for acceleration • cannot be DC, because beam tube on ground potential 2. Cavities 3. RF power • use RF field (Maxwell equations) 4. Projects • breakdown limit (vacuum, Cu surface, Troom) gap voltage → high Ec requires high f 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 7

Drift Tube Linear Accelerator Structure Outline 1. Colliders 2. Cavities 3. RF power 4. Projects 30 -Oct-2008 Low velocity particles • for velocity < 0. 4 c (50 ke. V e-; 100 Me. V p) • standing wave • drift tube size and spacing adapted to – RF frequency – particle speed Roger Ruber - Beyond LHC: the path towards future linear colliders 8

Example of Drift Tube Linacs Outline 1. Colliders 2. Cavities 3. RF power 4. Projects 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 9

Disk-loaded Accelerating Structure Outline 1. Colliders 2. Cavities 3. RF power In free space, electro-magnetic wave travels faster than particles → couple wave to resonating structures → particle velocity equal to phase velocity Example shows standing wave structure (vgroup=0) with • π phase advance per cell 4. Projects RF load RF power source Particle bunch Electric field d 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 10

Superconducting RF Cavities (SCRF) Eacc limited by Bcritical Outline 1. Colliders 2. Cavities 3. RF power • ~59 MV/m (record single cell cavity) • ~32 MV/m (multi-cell cavity) 4. Projects © Cornell University 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 11

Advantages Superconducting RF Outline 1. Colliders 2. Cavities 3. RF power 4. Projects Very low losses due to tiny surface resistance → standing wave cavities with low peak power requirements • High efficiency • Long pulse trains possible • Favourable for feed-backs within the pulse train • Low frequency → large dimensions (larger tolerances) large aperture and small wakefields Þ Important implications for the design of the collider 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 12

Normal Conducting Accelerator Structures Outline Eacc limited by breakdown RF-field • > 60 MV/m 1. Colliders 2. Cavities 3. RF power 4. Projects Higher gradients than SCRF cavities, but requires • very high frequency: >10 GHz • very short pulse lengths: < 1μs • high ohmic losses → travelling wave (unlike standing wave in SCRF or low gradient NCRF) • fill time tfill = 1/v. G dz order <100 ns (~ms for SCRF) 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 13

High Frequency Structures Outline 1. Colliders 2. Cavities 3. RF power CLIC type T 18_vg 2. 4_disk designed at CERN build by KEK tested at SLAC 4. Projects Eacc = 106 MV/m • 11. 424 GHz • 230 ns pulse length • 10 -6 breakdown rate (BDR) 30 -Oct-2008 Frequency 11. 424 Cells 18+input+output Filling Time 36 ns Length 29 cm Iris Dia. a/λ 15. 5~10. 1 % Group Velocity: vg/c 2. 61 -1. 02 % S 11/ S 21 0. 035/0. 8 Phase Advace Per Cell 2π/3 Power Needed <Ea>=100 MV/m 55. 5 Roger Ruber - Beyond LHC: the path towards future linear colliders GHz MW 14

Field Gradient Limitations Outline 1. Colliders 2. Cavities 3. RF power 4. Projects 30 -Oct-2008 Field Emission – due to high electric field around the iris Quench (SCRF) – caused by surface heating from dark current, or – magnetic field penetration around “Equator” Contamination – during assembly Roger Ruber - Beyond LHC: the path towards future linear colliders 15

3. RF Power Source Outline 1. Colliders 2. Cavities 3. RF power 4. Projects 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 16

Klystron Microwave Amplifier Outline 1. Colliders 2. Cavities 3. RF power 4. Projects Modulator Energy storage in capacitors charged up to 20 -50 k. V (between pulses) high voltage switching and voltage transformer rise time > 300 ns Klystron U 150 -500 k. V I 100 -500 A f 0. 2 -20 GHz Pave < 1. 5 MW Ppeak < 150 MW efficiency 40 -70% for efficient power operation, pulse length tpulse>1μs favourable 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 17

Two-beam Power Distribution Outline 1. Colliders Two-beam Scheme • high power drive beam like the modulated klystron beam 2. Cavities 3. RF power 4. Projects • power extraction in a deceleration structure (PETS) • sub-harmonic frequency of main beam • compress energy density: “transformer” function • only passive elements 30 -Oct-2008 drive beam Roger Ruber - Beyond LHC: the path towards future linear colliders main beam 18

Drive Beam Generation Drive Beam Accelerator efficient acceleration in fully loaded linac Delay Loop x 2 gap creation, pulse compression & frequency multiplication Outline 1. Colliders RF Transverse Deflectors 2. Cavities Combiner Ring x 3 pulse compression & frequency multiplication 3. RF power 4. Projects Combiner Ring x 4 pulse compression & frequency multiplication Drive Beam Decelerator Sector Power Extraction Drive beam time structure - initial 240 ns 140 µs train length - 24 x 24 sub-pulses - 4. 2 A Ruber bunches - Beyond 2. 4 Ge. V -Roger 60 cm between 30 -Oct-2008 Drive beam time structure - final 240 ns 5. 8 µs LHC: the path towards future linear colliders 24 pulses – 100 A – 2. 5 cm between bunches 19

Drive Beam Generation Scheme Outline 1. Colliders 2. Cavities 3. RF power 4. Projects Courtesy A. Andersson 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 20

4: Projects for a Future Linear Collider Outline 1. Colliders 2. Cavities 3. RF power 4. Projects 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 21

The ILC and CLIC LHC should indicate which energy level is needed Outline 1. Colliders 2. Cavities 3. RF power 4. Projects ILC International Linear Collider • superconducting technology • RF frequency 1. 3 GHz • acceleration gradient ~31 MV/m • centre of mass energy 500 Ge. V • upgrade to 1 Te. V CLIC Compact Linear Collider • normal conducting technology • 12 GHz • ~100 MV/m • multi-Te. V, nominal 3 Te. V Teva. Tron LHC 2 Te. V 7 Te. V 6. 3 km 27 km ILC 1 Te. V 35 km 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear. Courtesy colliders Sandbox Studio / interactions. org 22

ILC: The International Linear Collider Outline 1. Colliders SC linacs: 2 x 11 km, 2 x 250 Ge. V Central injector circular damping rings IR with 14 mrad crossing angle 2. Cavities 3. RF power 4. Projects Parameter Value C. M. Energy 500 Ge. V Peak luminosity 2 x 1034 cm-2 s-1 Beam Rep. rate 5 Hz Pulse time duration 1 ms Average beam current 9 m. A 　(in pulse) Average field gradient 31. 5 MV/m # 9 -cell cavity 14, 560 # cryomodule 1, 680 # RF units 560 250 Ge. V 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 250 Ge. V 23

Progress in SCRF Outline 1. Colliders Record 59 MV/m achieved with single cell cavity at 2 K • improved surface treatment • shape optimization 2. Cavities 3. RF power 4. Projects TTF = TESLA, LL: low-loss, RE: re-entrant • 9 cell cavities in operation at DESY (FLASH/XFEL): – R&D Status ~30 MV/m – ILC requires <31. 5> MV/m 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 24

CLIC: Compact Linear Collider Outline 1. Colliders 2. Cavities 3. RF power 4. Projects Main Linac C. M. Energy 3 Te. V Peak luminosity 2 x 1034 cm-2 s-1 Beam Rep. rate 50 Hz Pulse time duration 156 ns Average field gradient 100 MV/m # accelerating cavities 2 x 71, 548 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders Φ 4. 5 m tunnel 25

CTF 3: CLIC Test Facility Outline 1. Colliders 2. Cavities 3. RF power • demonstration drive beam generation (fully loaded acceleration, frequency multiplication) • evaluate beam stability & losses in deceleration • develop power production & accelerating structures (damping, PETS on/off, beam dynamics effects) 4. Projects 3. 5 A – 150 Me. V 1. 5 GHz – 1. 4µs TBTS 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 28 A – 150 Me. V 12 GHz – 140 ns 26

Demonstration Fully Loaded Operation Efficient power transfer 1. Colliders 2. Cavities 3. RF power 4. Projects “Standard” situation: • small beam loading • power at exit lost in load “Efficient” situation: VACC ≈ 1/2 Vunloaded • high beam loading • no power flows into load 95. 3% RF power to beam Pout Outline field builds up linearly (and stepwise, for point-like bunches) 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 27

Demonstration Beam Re-combination Outline • delay loop (DL) gap creation (for CR extraction) and doubling frequency + intensity after DL 140 ns in DL 1. Colliders 2. Cavities 3. RF power 4. Projects • combiner ring bunch interleaving (delay loop bypass, instabilities) before DL 3 rd Oct. 2008 1 st turn 2 nd turn 3 rd turn 4 th turn 3 A Beam Current Combiner Ring 12 A 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 28

Demonstration Two-beam Acceleration Two-beam Test Stand Outline 1. Colliders Experimental area 2. Cavities 3. RF power 4. Projects CT F 3 Spectrometers and beam dumps CA LIF ES pro be- driv e-b eam bea m Construction supported by the Swedish Research Council and the Knut and Alice Wallenberg Foundation 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 29

Two-beam Test Stand experimental area Outline 1. Colliders 2. Cavities 3. RF power 4. Projects drive beam probe beam 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 30

Two-beam Test Stand Prospects Outline 1. Colliders 2. Cavities 3. RF power 4. Projects 30 -Oct-2008 Versatile facility • two-beam operation – high power drive-beam [~30 A vs. ~100 A at CLIC] – high quality probe-beam [~1. 0 A like CLIC] • excellent beam diagnostics, long lever arms • easy access & flexibility for future upgrades Unique test possibilities • power production in prototype CLIC PETS • two-beam acceleration and full CLIC module • experiments to study – beam kick due to RF breakdown or dipole modes – beam dynamics effects – beam-based alignment Roger Ruber - Beyond LHC: the path towards future linear colliders First beam, 3 Sep 2008 31

RF Waveform Distortion on Breakdown Outline 1. Colliders 2. Cavities 3. RF power 4. Projects from S. Fukuda/KEK • Pulses with breakdowns not useful for acceleration (beam kick and instabilities) • Low breakdown rate required (< 10 -6) for useful operation 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 32

Beam Kick Measurements Breakdown kick 6. 1 m Outline 1. Colliders 2. Cavities 3. RF power 4. Projects Dipole BPM 4: x 4 BPM 3: x 3 BPM 2: x 2 BPM 1: x 1 BPM 5: x 5 Incoming beam Two chicanes remove breakdown currents Estimated error • beam position: 10 μm, angle: 7 μrad • kick position: 31 μm, angle: 11 μrad • relative energy change from kick: 32 x 10 -6 (see M. Johnson, CLIC Note 710, CERN-OPEN-2007 -022) 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 33

RF Breakdown: a Reliability Issue Outline 1. Colliders Conditioning required • to reach nominal gradient but • damage by excessive field 2. Cavities 3. RF power 4. Projects Physics phenomena not yet completely understood! © CERN 1 mm 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 34

Ion Currents from RF Breakdown Outline 1. Colliders 2. Cavities 3. RF power 4. Projects studied in CTF 3 mid-linac test stand • arrival time profile at Faraday cup consistent with “hot Coulomb” explosion, allows calculation – amount of particles (>1010) – temperature (> 105 K) RF in Upstream Faraday Cup • need detailed analysis to improve understanding – sometimes multiple peaks ηN 0 = 5. 9 x 109 Accelerating Structure RF out Downstream Faraday Cup fit parameters: - ηN 0 = 7. 9 x 109 - ts = 4. 6 μs - α = 0. 47 ts = 7. 1 μs α = 0. 41 • need method to study in presence of beam 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 35

Acknowledgements For the contribution of material and advice, without which I would not have been able to make this presentation. My grateful thanks to • Alex Andersson, Erik Adli, Erk Jensen, Hans Braun, Daniel Schulte, Frank Tecker, Walter Wünsch, Akira Yamamoto and Volker Ziemann Some illustrations and photos courtesy • CERN, KEK and Symmetry Magazine 30 -Oct-2008 Roger Ruber - Beyond LHC: the path towards future linear colliders 36