The operation of LHC accelerator complex Beam Measurement and Diagnostics Thanks to Stefano Redaelli CERN Beams Department Operations Group

The Large Hadron Collider (LHC) The project was first proposed in 1982 at a Snowmass Study, organised by the APS. At a cost of $2.9B to $3.2B, it was supposed to re-establish US supremacy in the field of high-energy particle physics following the discovery in Europe of the W and Z. The next step was carried out. By 1986 a detailed design study, by a Central Design Group set up under Maury Tigner at Lawrence Berkeley Laboratory, was complete and in 1987 President Reagan set in motion the search for a site. In 1988 Waxahatchie, Texas was announced as the successful candidate and construction commenced. This decision was, perhaps, influenced by then Vice-President George Bush (senior) of Texas, Jim Wright of Fort Worth, then Speaker of the House of Representatives, and a powerful Senator, Lloyd Bentsen, also from Texas. Meanwhile the cost, taking into account the more realistic estimates of the Central Design Group, and including the proposed experimental facilities, had risen from the initial estimate of 2.9 B$ to 3.2 B$ and then to 5.3 B$ in 1986. The DOE took over the management of the project from the CDG and determined that the traditions of technical and cost control that had been built up in large laboratories, like Fermilab, were to be abandoned in favour of methods judged more appropriate for a project of this size. Contracts were placed and subsystems procured in a manner that had hitherto been used for large defense projects. This led to further escalation, first to 5.9 B$ and then, as review teams included into account “site-specific” costs, to 7.2 B$ and then 8.2 B$ (DOE, 1991). The final straw came when an Independent Cost Estimating Team of the DOE (1993) added 2.5 B$ for “peripheral expenses which would not have been incurred if the SSC had not been there”. The SSC was given a year’s reprieve but by 1994 when the US Congress saw fit to cut their losses and terminate the project the estimate was 11.8 B$. The reasons for cancellation were not entirely budgetary. There was a rival project – the Space Station – that many in the House of Representatives preferred.

Superconducting magnets

Bending B field F force B p F Two-in-one magnet design LHC: B = 8.33 T ⇒ E = 7 TeV

Focusing N S By Fx Fy Transverse focusing is achieved with quadrupole magnets, which act on the beam like an optical lens. Linear increase of the magnetic field along the axes (no effect on particles on axis). Focusing in one plane, de-focusing in the other! Circular machine – all accelerators need focussing – nowadays with quadrupole magnets, which act on the beam like an optical lens. Linear increase of the magnetic field along the axes (no effect on particles on axis). Focusing in one plane, de-focusing in the other! On the left we see a room temperature quadrupole On the right is a sc version Coils define the field shape x y

CERN Control Centre - Layout

What do experiments want? High energy High luminosity N = bunch population nb = number of bunches frev = revolution frequency σx,y = colliding beam sizes F = geometric factor B = bending field ρ = bending radius p = momentum e = charge Determined by the maximum field of bending dipoles, B Depends on machine parameters: charge per bunch (N), num. of bunches (nb) and transverse beam sizes (σ) “Thus, to achieve high luminosity, all one has to do is make (lots of) high population bunches of low emittance to collide at high frequency at locations where the beam optics provides as low values of the amplitude functions as possible.” PDG 2005, chapter 25

Original LHC design parameters Nominal LHC parameters Beam injection energy (TeV) 0.45 Beam energy (TeV) 7.0 Number of particles per bunch 1.15 x 1011 Number of bunches per beam 2808 Max stored beam energy (MJ) 362 Norm transverse emittance (μm rad) 3.75 Colliding beam size (μm) 16 Bunch length at 7 TeV (cm) 7.55 - ...

The LHC accelerator complex Beam 1 TI2 Beam 2 TI8 LHC proton path Year Top energy Length [GeV] [ m ] Linac 1979 0.05 30 PSB 1972 1.4 157 PS 1959 26.0 628 SPS 1976 450.0 6’911 LHC 2008 7000.0 26’657 The LHC needs most of the CERN accelerators...

Pulseds of PS SPS and LHC First 7 TeV collisions on March 30th Pulseds of PS SPS and LHC

LHC beam position monitors (BPMs) 4 buttons pick-up the e.m. signal induced by the beam. One can infer the transverse position in both planes.

Multi-turn acquisitions of beam position

Closed-orbit measurements > 500 measurements per beam per plane! More than 1 per quad! 1 Hz data + turn-by-turn are possible

Dispersion measurements Measure the orbit offset for different beam energies.

Tune measurements – transverse oscillations - Kick the beam with a fast kicker - Measure beam position at every turn - Make an FFT X’ Kick X

Beam size measurements - Flying wire moved across the circulating beam - Measure secondary particles - Calibrate wire position to get size in mm Scan IN Scan OUT

4000 of these guys in the machine!! Beam loss monitoring Ionization chambers detect secondary electromagnetic showers generated by particle loss. 4000 of these guys in the machine!!