The LHC: the energy, cooling, and operation Susmita Jyotishmati
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 10^11 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
Basic Concepts Charged particles are accelerated, guided and confined by electromagnetic field. Bending- Dipole Magnets-1232 dipole magnets of approx. 15 m length which are used to bend the beams Focussing- Quadrupole Magnets-392 quadrupole magnets, each 5 7 m long, to focus the beams. Acceleration- RF cavities
Lorentz Force- Magnetic Rigidity-
What do experiments want? High Energy- Determined by the maximum field of the bending dipoles. High Luminosity-
Emittance The beam emittance of a particle accelerator is the extent occupied by the particles of the beam in the space and momentum phase space as it travels.
Alternating gradient lattice
Equation of motion
Dispersion
Chromaticity
Closed orbit
Inside one cell
Definition of the collider parts Sector-An LHC sector is defined as the part of the machine between two insertion points.there are four even sectors, labelled S12, S34, S56, S78, and four odd sectors S23,S45, S67, S81. The naming is always clockwise. Octant-An octant starts from the middle of an arc and ends in the middle of the following arc. Octants are numbered following the number of the point which they include. Arc-The arc is the part of the ring occupied by 23 identical FODO cells. Cell-A cell is in turn subdivided into two half-cells each composed of three dipoles and one quadrupole (Q12 to Q34). The half-cells are numbered following the number of the lattice quadrupole they contain: there are 34 half-cells per half-octant. Dispersion suppressor- The dispersion suppressor is made of four special half-cells with two dipoles and one quadrupole (Q8 to Q11) which are situated on either side of an arc but do not belong to the arc. Insertion-An insertion is the part of the ring between two arcs. It consists of one dispersion suppressor, one long straight section and a second dispersion suppressor. Long straight section-the exact layout of the long straight section depends on the specific use of the insertion: physics, injection, beam dumping, beam cleaning. Matching section- The long straight section always starts and ends with a matching section (Q4 to Q7). Q6 and Q7 however, are missing in Point 6. In addition, the long straight section around the experimental insertions at Points 1, 2,5 and 8 include the inner triplet (Q1 to Q3) on either side of the interaction points. In the other long straight sections, Q1 to Q3 are missing and the numbering starts with Q4 so that the mid-arc quadrupole is always numbered 34.
LHC Layout
Bottle of hydrogen
Linac 2
Linac2-some pictures
Injector cycling
PS Booster
Filling the PS with LHC beams
PS bunch splitting
PS complex operation for filling LHCmultiple splitting
How do we get 2808 bunches?
How do we inject?
How do we extract?
Injection into LHC
Beam dump (IP6)
Interaction region
Energy Energy residing in the beam-10.4 GJ Energy residing in the magnet-362 MJ
Cooling Operating temperature is below 2 K to maximise the field strength of the superconducting magnets with NbTi windings. The superconducting magnet windings in the arcs, the dispersion suppressors, and the inner triplets will be immersed in a pressurised bath of superfluid helium at about 0.13 MPa (1.3 bar) and a maximum temperature of 1.9 K. In the long straight sections, with the exception of the inner triplets and the superconducting dipoles D1, the field strength and heat extraction requirements are such that operation at 1.9 K is not necessary. The superconducting windings of these magnets will be immersed in a bath of saturated helium at 4.5 K. The cryogenic system must be able to cope with the load variations and a large dynamic range induced by the operation of the accelerator as well as being able to cool-down and fill the huge cold mass of the LHC, within a maximum delay of 15 days while avoiding thermal differences in the cryo-magnet structure higher than 75 K.
Requirements from the cryogenic system The cryogenic system must be also able to cope with resistive transitions of the superconducting magnets, which will occasionally occur in the machine, while minimising loss of cryogen and system perturbations. must handle the resulting heat release and its consequences, which include fast pressure rises and flow surges. must limit the propagation to neighbouring magnets and recover in a time that does not seriously detract from the operational availability of the LHC. A resistive transition extending over one lattice cell should not result in a down time of more than a few hours. It must also be possible to rapidly warm up and cool down limited lengths of the lattice for magnet exchange and repair. Finally, it must be able to handle, without impairing the safety of personnel or equipment,the largest credible incident of the resistive transition of a full sector.
Cryogenics General layout of cryogenic system
Transverse cross-section of LHC tunnel
General architecture of the cryogenic system
Thermodynamic cryogenic flow scheme and instrumentation of an LHC lattice cell
Temperature levels
References. Stefano Redaelli-The operation of the LHC accelerator complex- LHC Physics Centre at CERN - Student lecture April 7th and 9th, 2010 CERN, Geneva, Switzerland. LHC Machine-Lyndon Evans1 and Philip Bryant (editors) European Organization for Nuclear Research CERN CH-1211, Genève 23, Switzerland The Large Hadron Collider project-equipment NAMING CONVENTIONS-Project Document No. LHC-PM-QA-204.00 rev 1.0