Machine

1. Faus-Golfe C. Alabau-Pons IFIC - Valencia Machine

2. What is included ? • Why a Linear Collider ? • Some physics reasons, cost scaling… • Some history and current state of LC R&D • What is a Linear Collider ? • Luminosity issue • scaling laws for LC • Linear Colliders sub-systems • main accelerators (linacs) • sources • Damping Rings (DR) • Bunch Compression (BC) • Beam Delivery System (BDS): • collimation and final focus (FFS) • The International Linear Collider (ILC) • Parameters • Challenges A.Faus-Golfe / C. Alabau-Pons

3. Why a Linear Collider ? some physics reasons… Particle Accelerators are big microscopes: they have revealed many secrets of matter and brought the Sub-atomic World to our eyes A.Faus-Golfe / C. Alabau-Pons

4. Why a Linear Collider ? some physics reasons… THE ENERGY FRONTIER time early! 500 GeV ILC (moving off the line) Going further in the energy scale is needed to study the Higgs boson, and to find answers to questions that the Standard Model cannot solve: • why particle masses are so different • how can “dark matter” and “dark energy” be understood? • are all forces unified? • … A.Faus-Golfe / C. Alabau-Pons

5. Why a Linear Collider ? some physics reasons… The ILC, together with the LHC, would play a key role in exploring the world beyond the Standard Model A.Faus-Golfe / C. Alabau-Pons

6. Why a Linear Collider ? some physics reasons… The ILC would be a precision machine to complement the studies of the LHC due to the collision of point-like particles A.Faus-Golfe / C. Alabau-Pons

7. Why a Linear Collider, and not just build a bigger storage ring ? 500 GeV ILC LEP at CERN, CHEcm = 180 GeVPRF = 30 MW A.Faus-Golfe / C. Alabau-Pons

8. Why a Linear Collider, and not just build a bigger storage ring ? “A Possible Apparatus for Electron-Clashing Experiments” M. Tigner, Nuovo Cimento 37 (1965) 1228 “While the storage ring concept for providing clashing-beam experiments is very elegant in concept it seems worth-while at the present juncture to investigate other methods which, while less elegant and superficially more complex may prove more tractable.” The storage ring concept is limited in its energy reach. The reason is due to synchrotron radiation effects and the cost scaling of such facilities A.Faus-Golfe / C. Alabau-Pons

9. Why a Linear Collider, and not just build a bigger storage ring ? Synchrotron radiation from an e- in a magnetic field: average power radiated Energy loss per turn of a machine with an average radius r : Energy loss per turn has to be be replaced by the RF system, which is the major cost factor for a collider. A.Faus-Golfe / C. Alabau-Pons

10. Why a Linear Collider ? some cost reasons… RF system tunnel, vacuum systems,magnets.. Optimum when A.Faus-Golfe / C. Alabau-Pons

11. Why a Linear Collider ? an example of cost… A.Faus-Golfe / C. Alabau-Pons

12. Why a Linear Collider ? an example of cost… A.Faus-Golfe / C. Alabau-Pons

13. bang! Why a Linear Collider ? because no bends, but lots of RF! e+ e- 5-10 km Unfortunately, in abandoning storage rings new problems arise: • we cannot store the beams, LC is one-pass device where the beams must be accelerated (effectively from the rest) to the required energy on each pulse of the machine • we cannot take advantage of the stored beam to slowly ramp the energy up, we have to provide several km of RF (25-100 MV/m ~ 10 km) to achieve the energy in a single-pass Note that cost …this is really less cost effective? A.Faus-Golfe / C. Alabau-Pons

14. Why a Linear Collider ? an example of cost… A.Faus-Golfe / C. Alabau-Pons

15. Why a Linear Collider ?history and current state of R&D Over 19 years of LC R&D (majority fosused on a cost effective technology for the linac) but we have a very long way to go quoted as “proof ofprinciple” A.Faus-Golfe / C. Alabau-Pons

16. Why a Linear Collider ?history and current state of R&D LC R&D test facilities A.Faus-Golfe / C. Alabau-Pons

17. What is a Linear Collider ? the luminosity issue For anycolliding beams the cross section nb = bunches / trainN = particles per bunchfrep = repetition frequencyA = effective overlap area at IP For Gausian beams: s*xy=r.m.s. transverse beam size at the IP HD= beam-beam enhancement factor (typical value of ~2) A.Faus-Golfe / C. Alabau-Pons

18. What is a Linear Collider ?the luminosity issue: center of mass energy and beam power Introducing average beam power in theLformula yields This high beam power hasto be supplied continuously in order to accelerate each bunch train from the rest. This is constrained by: • available electrical power • high beam power within the machine (machine protection and dump issues) Some numbers: N= 1010 nb= 100 Ecm= 500 GeV frep= 100 Hz A.Faus-Golfe / C. Alabau-Pons

19. What is a Linear Collider ?the luminosity issue: center of mass energy and beam power AC (wall-plug) power Beam power RF power 28-40% 20-60% 6-24% >100 MW 8 MW linac technology choice (ILC 13.7%) Introducing AC power and its efficiency in the luminosity formula yields: A.Faus-Golfe / C. Alabau-Pons

20. What is a Linear Collider ?the luminosity issue: intense beams at the IP A consequence of one-pass nature of LC is lower collision rate than in storage rings, in terms of L the consequence is: LEP frep = 44 kHz (4 bunches) LC frep = 100 Hz (power limited) L loss a factor ~400 Having a large number of bunches (>100) per bunch train gain most of this loss back (high power bill), but still need at least two orders of magnitude more luminosity at 500 GeV. LC must push very hard on beam cross section at IP: s*x x s*y 106 reduction LEP 130 x 6 mm2 LC 200-500 x 3-5 nm2 L~1034 cm-2 s-1 but this have immediate consequences…. A.Faus-Golfe / C. Alabau-Pons

21. What is a Linear Collider ?the luminosity issue: intense beams at the IP The consequences are: • Very strong focusing (demagnification) at the IP, very strong quadrupoles close to IP. Chromatic and geometric aberrations must be cancelled very accurately to avoid dilution of beam sizes. • Extreme high charge densities leads to significant beam-beam effects as: • strong self-focusing (pinch) • instability which leads to tighter collision tolerances • high level of beamstrahlung radiation which dilutes the luminosity spectrum (luminosity per centre mass energy bin) • production of copious e+e- pairs created by the strong field of the bunches which are sources of background for the detector. • Tight tolerances on the vibration of the accelerator components, especially the final quadrupoles. A.Faus-Golfe / C. Alabau-Pons

22. What is a Linear Collider ?the luminosity issue: intense beams at the IP The consequences are: • Very strong focusing (demagnification) at the IP, very strong quadrupoles close to IP. Chromatic and geometric aberrations must be cancelled very accurately to avoid dilution of beam sizes. • Extreme high charge densities leads to significant beam-beam effects as: • strong self-focusing (pinch) • instability which leads to tighter collision tolerances • high level of beamstrahlung radiation which dilutes the luminosity spectrum (luminosity per centre mass energy bin) • production of copious e+e- pairs created by the strong field of the bunches which are sources of background for the detector • Tight tolerances on the vibration of the accelerator components, especially the final quadrupoles. A.Faus-Golfe / C. Alabau-Pons

23. Ey (MV/cm) y/sy What is a Linear Collider ?the luminosity issue: intense beams at the IP Beam-beam effects: Particles in the opposing bunch see the field created by the other bunch and are deflected by it (HD ). Typical electrical field (GeV/cm) of a flat beam (s*x>>s*y) in LC. deflection angle for equivalent to athin focusing lenswith focal length A.Faus-Golfe / C. Alabau-Pons

24. What is a Linear Collider ?the luminosity issue: intense beams at the IP The beam-beam effects are quantified by the disruption parameter: bunch length effective focal length of beam in storage rings in LC beta IP Enhancement factor : in LC “hour glass” effect A.Faus-Golfe / C. Alabau-Pons

25. What is a Linear Collider ?the luminosity issue: intense beams at the IP Hour-glass effect (sets a limit on the achievable beam size bunch for a given bunch length) Density plots of the bunch at IP in z-y plane: butterfly distortion (reduction of L) It is desirable to have: depth of focus A.Faus-Golfe / C. Alabau-Pons

26. What is a Linear Collider ?the luminosity issue: intense beams at the IP Beamstrahlung effects: As the particles are deflected by the beam-beam effect they radiate hard photons (beamstrahlung) and loose energy (synchrotron radiation not classical). The amount of beamstrahlung is a critical parameter for LC (background and luminosity spectrum dilution). The relative energy loss during collision due to beamstrahlung is : A.Faus-Golfe / C. Alabau-Pons

27. What is a Linear Collider ?the luminosity issue: intense beams at the IP To maximise L need to makesxsysmall but keep(sx+sy)large to reducedB Trick: use “flat beams” with sx>>sy “ribbon-like” beams 5 Setsxto fixdB, and makesyas small as possible A.Faus-Golfe / C. Alabau-Pons A. Seryi

28. What is a Linear Collider ?the luminosity issue: intense beams at the IP when we collide beams with dBS is only a function of we set sx to fix dBS(most LC designs dBS~3-10%) Introducing dBS in L: A.Faus-Golfe / C. Alabau-Pons

29. What is a Linear Collider ?the luminosity issue: intense beams at the IP Introducing in L the important parameter of vertical emittance and using the hour-glass constraint, we arrive at our final L scaling law: Taking a sensible choice limit of: A.Faus-Golfe / C. Alabau-Pons

30. What is a Linear Collider ?the luminosity issue: intense beams at the IP Final L scaling law: with For high L operation (given Ecm and dBS) we need: • high power PAC • high wall-plug to beam power transfer efficiency h • small normalized vertical emittance ey • short bunch lengthsz(and corresponding small by) A.Faus-Golfe / C. Alabau-Pons

31. What is a Linear Collider ?Linear Colliders sub-systems Generic LC (at least one half of it) Each sub-system pushes the state-of-the art in accelerator design A.Faus-Golfe / C. Alabau-Pons

32. What is a Linear Collider ?Linear Colliders sub-systems Generic LC (at least one half of it) provides the required e+ and e- bunches with the required time structure Each sub-system pushes the state-of-the art in accelerator design A.Faus-Golfe / C. Alabau-Pons

33. What is a Linear Collider ?Linear Colliders sub-systems accelerates the bunches to the damping ring energy Generic LC (at least one half of it) Each sub-system pushes the state-of-the art in accelerator design A.Faus-Golfe / C. Alabau-Pons

34. What is a Linear Collider ?Linear Colliders sub-systems Generic LC (at least one half of it) “damp” or reduce the phase volume of the bunches Each sub-system pushes the state-of-the art in accelerator design A.Faus-Golfe / C. Alabau-Pons

35. What is a Linear Collider ?Linear Colliders sub-systems Generic LC (at least one half of it) compresses the bunches longitudinally to the required IP length Each sub-system pushes the state-of-the art in accelerator design A.Faus-Golfe / C. Alabau-Pons

36. What is a Linear Collider ?Linear Colliders sub-systems Generic LC (at least one half of it) accelerates the bunches from damping ring energy to IP energy Each sub-system pushes the state-of-the art in accelerator design A.Faus-Golfe / C. Alabau-Pons

37. What is a Linear Collider ?Linear Colliders sub-systems Generic LC (at least one half of it) Beam Delivery System (BDS), which transports the high-energy bunches to the IP where they collide supplies the strong focusing to produce the nm-size beam at the IP Each sub-system pushes the state-of-the art in accelerator design remove the beam halo A.Faus-Golfe / C. Alabau-Pons

38. What is a Linear Collider ?Linear Colliders sub-systems Generic LC (at least one half of it) transport the “used” bunches to the dump and post-IP beam diagnostics Each sub-system pushes the state-of-the art in accelerator design A.Faus-Golfe / C. Alabau-Pons

39. What is a Linear Collider ?Linear Colliders sub-systems:main linac e- and e+ bunches are accelerated (gain energy) by RF fields inside so-called structures. Structures can be: • waveguide-like • resonant cavities the structures/cavities are so designed that the fundamental modes consists of a longitudinal electrical field (Ez) There are two basic ways of using an accelerator structure: • travelling-wave mode (TW) • standing-wave mode (SW) A.Faus-Golfe / C. Alabau-Pons

40. Ez z What is a Linear Collider ?Linear Colliders sub-systems:main linac c TW mode peak electric field RF phase longitudinal position bunch see constant field if: group velocity phase velocity Lowest order accelerating mode in a circular waveguide (TM01) has vp>c.To make of this mode as an accelerating structure, we need slow the wave down. In practice is achieved by inserting irises periodically A.Faus-Golfe / C. Alabau-Pons

41. Ez z What is a Linear Collider ? Linear Colliders sub-systems:main linac peak electric field SW mode c c RF phase acceleration is no longer constant but varies along the cavity. Total voltage per cavity of lengthl/2 is: the effective gradient is: A.Faus-Golfe / C. Alabau-Pons

42. What is a Linear Collider ? Linear Colliders sub-systems:main linac Cavity parameters stored energy per unit length Q-factor shunt impedance unit length power loss in structure walls per unit length shunt impedance defines the fill time power you need to feed and maintain a specified field depends on the geometry of the cavity/structure, and not on material or surfaces properties A.Faus-Golfe / C. Alabau-Pons

43. What is a Linear Collider ? Linear Colliders sub-systems:main linac Cavity parameters…some scaling with operating frequencies Q factor shunt impedance unit length normal conducting normal conducting superconducting superconducting LC on conventional RF are high frequencies (JLC/NLC 11.2 GHz, CLIC 30 GHz). For superconducting lower frequencies are more efficient (TESLA 1.3 GHz optimum). normal conducting superconducting not depends on material A.Faus-Golfe / C. Alabau-Pons

44. What is a Linear Collider ? Linear Colliders sub-systems:main linac Cavity parameters filling time time required for the cavity to reach required voltage TW structure SW cavity attenuation coefficient output RF power input RF power A.Faus-Golfe / C. Alabau-Pons

45. What is a Linear Collider ? Linear Colliders sub-systems:main linac When the beam is injected in the structures, the e+e- bunches will be accelerated and gain energy from the field. This energy must be replaced by power sources (klystrons), or a drop in the structure voltage will occur. We refer to this effect as beam loading. This could be expressed as: power loss per unit meter peak beam current power lost to the cavity walls power removed by beam (beam loading) dominant for conventional RF dominant for superconducting RF A.Faus-Golfe / C. Alabau-Pons

46. What is a Linear Collider ? Linear Colliders sub-systems:main linac When a bunch travels trough a structure with a transverse offset with respect to the structure axis, the bunch induces transverse modes (transverse wakefields) which then act back on the beam. single bunch head deflect the tail multi bunch earlier bunches deflect later ones If not compensated will lead to beam break-up, which destroys the transverse beam quality (emittance). The magnitude is function of the structure design (~a/l) scales as ~f-3. Single and multi-bunch compensation modes are mandatory. A.Faus-Golfe / C. Alabau-Pons

47. What is a Linear Collider ? Linear Colliders sub-systems:main linac Random cavity or structure alignment errors gives an additional emittance growth. r.m.s. alignment tolerance higher frequencies higher wakefields • higher gradients (Ez) • strong focusing (small b) • smaller bunch charge (N) offset of tolerances tranverse wakefield A.Faus-Golfe / C. Alabau-Pons

48. What is a Linear Collider ?Linear Colliders sub-systems:sources High beam powers where generally required to achieve the ambitious luminosity goals. From considerations of linac acceleration efficiency and wake field control: • accelerate large number of bunches in a single bunch train to achieve a high RF to beam power transfer efficiency • reduce the charge per bunch to mitigate the effect of the strong transverse wakefields The sources must provide the long bunch train. In addition, polarisation is mandatory for the e- source. A.Faus-Golfe / C. Alabau-Pons

49. What is a Linear Collider ?Linear Colliders sub-systems:sources e- sources are: laser-driven photo-injectors DC gun emittance is dominated by space-charge effects (v ~0.2c) factor 10 in x-plane factor 500 in y-plane en~10-5 mrad GaAs cathode used together with a laser light of 840 nm wavelength produces over 90% polarization but, require very high vacuum (<10-11mbar). This requirement rules out the high brightness RF guns that produces orders of magnitudes better emittance because typical vacuum is rather bad (10-7 mbar). A.Faus-Golfe / C. Alabau-Pons

50. to DR injector linac What is a Linear Collider ?Linear Colliders sub-systems:pre-accelerator Guns are DC, the polarized source is first bunched using a sub-harmonic (SHB) bunching section (RF), before finally being accelerated up to ~GeV before injection into the damping rings. Typical bunch length from gun is ~ns, too long for e- linac with f ~1-3 GHz, need tens of ps. A.Faus-Golfe / C. Alabau-Pons