Lorenzo Resegotti

The Large Hadron Collider (LHC) in the LEP tunnel

After the remarkable start-up of LEP, the installation of a Large Hadron Collider, LHC, in the LEP tunnel will open a new era for the High Energy Physics. This report summarizes the main LHC parameters and subsytems and describes the more recent studies and developments.

The eight superconducting quadrupoles for the ISR high-luminosity insertion

Eight superconducting quadrupoles for a high-luminosity insertion in the ISR have been produced by industrial firms according to CERN design and manufacturing specifications, and assembled and tested at CERN. The horizontal cylindrical cryostats, which contain windings and steel yoke in a boiling helium bath, have a 173 mm warm bore. For 31 GeV beam energy, the maximum operating gradient on the quadrupole axis is 43 T m−1 and the maximum field in the windings is 5.5 T. Sextupole windings provide a linear variation of the gradient of up to 4% over the bore width and dodecapole windings trim the field pattern as a function of excitation. This paper reports about production history, acceptance tests, and performance. The results of magnetic measurements are also summarized. The insertion will be installed into the ISR as from August 1980.

A Superconducting High-Luminosity Insertion in the Intersecting Storage Rings (ISR)

A focusing insertion will be constructed at an intersection of the ISR, to achieve a reduction of the effective beam height by about a factor 6 in the interaction diamond and a corresponding increase of the luminosity. It will contain eight superconducting quadrupole magnets, capable of producing gradients of 43 Tm-1 in a warm bore of 173 mm diameter: four of them have a magnetic length of 1.15 m and four of 0.65 m. The magnets are also equipped with sextupole windings, to match the gradients to particle momenta over the beam width, and with dodecapole correction windings. After construction and successful operation of a prototype magnet in the laboratory, competitive tenders were obtained from industry on the basis of technical specifications and manufacturing drawings. The magnets proper and the cryostats are being manufactured under two separate contracts. The insertion will be installed within 1980 at intersection I8, for use in physics experiments with a large magnetic spectrometer.

Influence of mortar-induced stresses on the magnetic characteristics of the LEP dipole cores

The steel-concrete cores of the Large Electron Positron colliding-beam accelerator dipole magnets are built of regularly spaced soft-magnetic-steel laminations, the spaces being filled with cement mortar. The effect of compressive stresses on the permeability and the coercivity of soft magnetic steel has been measured and the consequences for magnetic characteristics of the cores have been evaluated. By controlled straining of the aged cores in a hydraulic device, the tension in the mortar is brought locally to exceed the rupture limit. Thus, the compressive stresses in the steel laminations are partially relieved and the loss of bending strength in the dipoles is reduced. The excitation characteristics of the cores are measured by means of a fixed set of excitation windings and measuring coils into which the cores are moved after stress relieving. These measurements include determination of the equivalent surface areas of flux loops, which are embedded in the lower poles and will permit measurement of the field integral on the center line during LEP operation. >

Operational Experience with the Superconducting High-Luminosity Insertion in the CERN Intersecting Storage Rings (ISR)

The eight superconducting quadrupoles and their cryogenic equipment for this insertion were installed in the ISR at the end of 1980. The insertion has been used to assess the problems of running a superconducting insertion in a storage ring as well as to provide high luminosity for physics. The luminosity is increased at intersection 8 by a factor of 7. By means of dedicated collimators and orbit corrections, safe working conditions could be established for the superconducting magnets during injection, accumulation, stable beam periods and when dumping the beams. Quenches were mainly caused by large accidental beam losses. Operating parameters for all standard beam energies, including acceleration to 31.4 GeV/c, have been established. At 26.6 GeV/c, with currents of 30.6 A in ring 1 and 30.3 A in ring 2, a luminosity of 1.4 1032 cm-2s-1 was obtained in the insertion. This is the highest luminosity reached so far in storage rings and it was obtained during a physics run. Satisfactory beam conditions could also be provided for antiproton physics at 26.6 GeV/c in ISR with both low-ß insertions on, in I1 and I8, respectively.

Implications of the Low Field Levels in the LEP Magnets

For the C-shaped laminated magnet cores, which have been adopted in the recent versions of LEP, advantage has been taken of the required low field levels to reduce the filling factor to less than one third. This both improves the performance and considerably reduces the price of the magnets. Starting from magnetic measurements on different steels, and by using a semi-quantitative model, it is shown that a satisfactory field uniformity can be maintained at an injection field of 0.017 T with a medium grade, low carbon steel, owing to the mutual compensation between the reduction in permeability with field level and the effect of coercivity. A novel method is being developed for fabricating these magnets using a cement mortar to fill the interlamination spaces and bind the laminations together. A 60 cm long, ¿-scale model has produced excellent mechanical and magnetic results.

On the Way to the Series Production of Steel-Concrete Cores for the LEP Dipole Magnets

CERN has now launched the series production of the steel-concrete cores for the LEP dipole magnets after a three-year development programme during which 14 prototypes were built in collaboration with industry. This paper describes the mechanical, geometrical and magnetic characteristics of these cores and the fabrication techniques which have been developed. Particular emphasis is put on the following points: - the controlled mixing of steel in order to reduce the field variations between cores. - the influence of the thickness and of the pitch of the laminations on the field quality, - the composition and working conditions of the mortar in relation to the tolerances on core geometry.

Studies of 400 GeV superconducting proton storage rings

A study has been made of the feasibility of building Large Storage Rings (LSR) at CERN using superconducting dipoles and quadrupoles with the 400 GeV proton synchrotron, SPS, serving as injector. Proton-proton collisions at centre-of-mass energies of up to 800 GeV can be obtained in six interaction regions. Two of these provide luminosities exceeding 1033 cm−2 s−1 and would be dedicated to large-transverse-momentum physics. The other four p-p intersections offer much experimental flexibility at somewhat lower luminosity. Provision is made to add an electron storage ring of 20–25 GeV to obtain e-p collisions at up to 200 GeV centre-of-mass energy with a luminosity of 1032 cm−2 s−1 in each of two special e-p interaction regions. Antiproton-proton collisions could be obtained by a minor rearrangement of some elements in two of the interaction regions.

CERN 400 GeV Proton Storage Rings with Superconducting Magnets

A design is presented for 400 GeV proton-proton storage rings to be added to the CERN SPS. An electron (20-25 GeV) ring is also foreseen and possibilities for antiproton-proton collisions. Eight interaction regions are planned (six for p-p and two for e-p) with high luminosity and good flexibility for physics experiments.