From ALICE Matters: Heavy Ion Beams

Amy Dusto
11 November 2011

On Monday November 14th the LHC begins heavy ion physics, the process of colliding lead ions, to learn about conditions in the primordial universe. The accelerator is expected to perform 5 to 10 times better than it did in its first run of these collisions last November. Although the heavy ion program will last only from now until CERN’s annual winter shutdown on December 8th, preparations began months in advance. Amy Dusto, from the blog symmetry breaking, reports for ALICE Matters on what it really takes to put lead beams in the LHC.

The source

Making heavy ions is more complicated than preparing the protons used in regular LHC collisions, which come from hydrogen gas. Since hydrogen atoms have only one proton and one electron each, applying a voltage to them is sufficient to rip off their electrons, leaving a load of beam-ready, positively charged protons. But the source for heavy ions, enriched lead, starts with 208 electrons. Physicists do not have miracle flypaper to grab that many subatomic particles at once, so the process takes a few steps.

Meet Detlef Kuchler, a heavy ion expert who tends the lead source, the first part of the heavy-ion acceleration process, by hand. He helped develop the method of extracting lead ions decades ago and can explain from memory its hundreds of associated, unlabeled diagrams. Although several people work on the source, a flowchart of what to do when things go wrong at this stage dead-ends everywhere with, “Call the expert.” It may as well say, “Call Detlef.” He spends a lot of nights and weekends at CERN during heavy ion season.”

From 2010 Heavy Ion season

Event display from a lead-lead collision recorded by ALICE (6.11.2011)

Read the full post here.