What next after LEP?

Work for the LEP electron–positron collider continues to drive ahead, however LEP is far from being the last word in CERN's long term plans. A clue was already in the LEP Design Study " …by the adoption of a beam height of only 80 cm, there is enough room left (in the tunnel) for the installation of a second machine at a later stage…".

A workshop, organized by ECFA and CERN in March 1984, examined the feasibility of a hadron collider in the LEP tunnel (Lausanne LHC workshop). There the idea emerged for a ring of superconducting magnets, installed above the LEP ring, to collide protons together (or protons with antiprotons) at as high an energy as possible. Since this meeting, considerably more work has been done to firm up ideas.

Using 10 Tesla dipole bending magnets, collision energies of 17 TeV (8500 GeV per beam) could be achieved with a respectable collision rate (luminosity 1033 cm–2 s–1). A 'two-in-one' aperture solution for the superconducting magnets is recommended for economy and compactness.

It is the relative ease of colliding proton beams (as compared to the difficulties of first making and then handling antiprotons) which promise high collision rates and make the proton–proton option the preferred solution. Despite the need to provide a large number of bunches (a figure of 3564 has been quoted), the two proton rings in the LEP tunnel could be filled using CERN's existing 450 GeV SPS machine and its proton supply in only a few minutes. Of course new injection lines would have to be built.

• July/August 1986 pp5–4 (abridged).


Elsewhere

In Europe the news of the initial approval for the US Superconducting Supercollider was received enthusiastically as it showed that the future of high-energy physics is regarded as being of paramount importance at the highest levels. While the US plans gather momentum, the possibility of a hadron ring in the LEP tunnel at CERN is still attractive. Although restricted in energy by the 'modest' dimensions of the LEP tunnel compared to the SSC (27 km circumference against 84), the LHC scheme scores points for the magnificent beam injection systems already in place at CERN, a complete tunnel, and several collision options.

• March 1987 p2 (abridged).


Superconducting magnet success

Technical preparations for a possible proton–proton collider (LHC) in the LEP tunnel have made substantial progress with the successful testing of the first LHC superconducting high-field 1 m long model magnet. The single aperture niobium-titanium wound dipole was designed by R Perin and his LHC magnet study team, and manufactured by Ansaldo Componenti, Genova.

Operating at 2 K, it reached and passed its 8 Tesla nominal field without any quench, the first three quenches occurring at central fields of 8.55, 8.9 and 9 Tesla respectively. It then attained 9.1 Tesla without quenching and operated at this level for some time.

This is the first time a high field 'accelerator quality' superconducting dipole model has been designed and built as a joint venture between a scientific laboratory and industry. CERN provided most of the know-how and the superconductor, while manufacture was taken over by Ansaldo.

• June 1988 p13 (abridged).


Magnets: beyond niobium-titantium

The superconducting proton ring being built for the HERA electron–proton collider at DESY has already demonstrated that niobium-titanium technology is mature, even on an industrial scale. The HERA-type design (coils around the beam-pipe, mechanical support collars and cold iron return) has gone on to become widely adopted, but reaches its natural limit for dipole construction using niobium-titanium near 10 Tesla.

This is now well understood and has been demonstrated with several test magnets developed in a collaboration between CERN and Italian supplier Ansaldo. A similar geometry was used with niobium-tin in a collaboration between CERN and Elin (Austria) which reached a record field for this kind of magnet of 9.45 Tesla in September 1989.

CERN's proposed LHC collider in the LEP tunnel envisages 10 T fields with a double aperture carrying the two beam pipes for the proton beams inside a single cryostat. Four contracts have been placed with European firms for the development of one-metre, double-aperture niobium-titanium magnets with a view to placing further orders for full-scale, 10 m prototype units. Using superfluid helium at 1.8 K instead of conventional 4.2 K cryogenics provides the necessary additional potential.

• Sept/October 1990 pp17–18 (extract).