Difetti di progetto hanno causato l’incidente all’LHC?

Benedetta CappelliniArticoli

Intervista a Lucio Rossi (responsabile del team Magneti & Superconduttori dell’LHC al CERN di Ginevra) sulle cause dell’incidente del Settembre 2008, apparsa on-line su Nature il 23 febbraio 2010. 
Il catastrofico guasto per cui due magneti sono tra loro collassati non è stato un fenomeno sfortunato, ma il risultato di un progetto non adeguato di alcune piccole parti e di una mancanza di un’accorta qualità e capacità diagnostica.
Jim Strait del Fermilab (Betavia, Illinois) sostiene che l’analisi tecnica di L. Rossi è fondamentalmente corretta.
Rossi afferma anche che non incolpa nessuno di ciò che è accaduto all’LHC: “Ogni errore tecnico è un errore umano. Ciò che dobbiamo fare è di imparare dai nostri errori e fare sempre meglio”.
Riportiamo qui nel seguito l’articolo/intervista apparso sulla prestigiosa rivista.

Published on Naturenews, online 23 February 2010 (Nature 463, 1008-1009 (2010))
Did design flaws doom the LHC?
Catastrophic failure that caused accelerator shutdown was not a freak accident, says project physicist.
di Geoff Brumfiel

Running more than a year behind schedule and at half its intended energy, the world’s most powerful particle accelerator is slated to begin its first full scientific run this week.     Along with relief, the occasion is bringing some soul-searching.
One senior scientist who helped to build the Large Hadron Collider (LHC) at CERN, Europe’s particle-physics laboratory near Geneva, Switzerland, is claiming that the cause of the delay — a major accident in 2008 — could have been avoided.
“Any technical fault is a human fault,” says Lucio Rossi, a physicist who oversaw the production of the accelerator’s superconducting magnets. In a paper published on 22 February (L. Rossi Superconductor Science Technoogy 23, 034001; 2010), he concludes that the catastrophic failure of a splice between two magnets was not a freak accident but the result of poor design and lack of quality assurance and diagnostics. The project, he says, will be coping with the consequences for many months to come.
On 19 September 2008, just weeks before the LHC was first scheduled to start colliding protons, an electrical short caused massive damage.     A connection between two superconducting cables developed a small amount of resistance, which warmed the connection until the cables — cooled by liquid helium to superconducting temperatures — lost their ability to carry current. Thousands of amps arced through the machine, blowing a hole in its side and releasing several tonnes of liquid helium.     The expanding helium gas created havoc, spewing soot into the machine’s ultraclean beamline and ripping magnets from their stands. Repairs took more than a year, and the LHC successfully restarted last November.
An investigation revealed that technicians had not properly soldered the cables together. With tens of thousands of such connections, it is perhaps inevitable that some were faulty, Rossi says, but design flaws worsened the problem.     The silver–tin solder that was used melted at high temperatures and did not flow easily into the cable joints. Moreover, workers did not adequately check to see if each connection was electrically secure. Sensors to detect an overheating circuit, which might have helped prevent the accident, were not installed until after it happened.

Worse, says Rossi, when the wires were originally joined, the same silver–tin solder was used to connect them to an adjacent copper stabilizer, meant to provide an escape route for current in the event of a failure.     That step risked reheating and destroying the original connection, he says.     Making the second connection to the stabilizer with a different type of solder that had a lower melting point could have avoided the problem.     Lyn Evans, who oversaw the LHC from 1994 to 2009, says that the idea was considered and rejected because the alternative solder contained lead, a hazard to workers.
A detailed analysis last summer revealed several more bad connections, and CERN now says that it will take a year to correct the problem throughout the machine.    As a result, the LHC will not run at its full collision energy of 14 tera-electronvolts (1012 eV) until around 2013.

But Jim Strait, a physicist at Fermilab in Batavia, Illinois, says that Rossi’s analysis is fundamentally right.    The connections between the LHC’s magnets aren’t robust enough, Strait says. “The design looks like one that is optimized to make installation easy,” he says. “These stupid little corners [of the design] get short shrift because they are boring.”     Only constant project reviews and more-integrated management can catch such problems, he says.
Rossi says that he doesn’t blame any one person for what happened at the LHC. “In Italian we say, Chi non fa, non sbaglia: ‘He who doesn’t work makes no mistakes’.
What we have to do is learn from our mistakes and make it better.”

Riportiamo i link ad alcuni articoli, relativi all’LHC, pubblicati su questo sito:
Riparte il super-acceleratore LHC del Cern
– LHC: alla ricerca del Bosone di Higgs
LHC: Large Hadron Collider