"Studying the Infinitely Small through Infinitely Large Machines"
This sentence is undoubtedly an oversimplified yet fitting description of the work of a particle accelerator.
Nowdays, there are approximately 30,000 accelerators on the planet, but only a few of them delve into the secrets of the universe. Their origin can be traced back to the Austrian physicist Bruno Touschek, who in the 1960s had the first two particle accelerators built: the Accumulation Ring (Ada) and Adone at the National Laboratories of Frascati of INFN. These two accelerators are no longer in operation.
In just a few decades, science has made enormous strides. Literally...
The largest particle accelerator in the world today is the Large Hadron Collider (LHC) at CERN, which boasts a circumference of 27 kilometers and is located in an underground tunnel approximately 100 meters deep on the border between France and Switzerland. It was inside the LHC in 2012 that one of the greatest discoveries of the 21st century took place: the Higgs boson. This particle is named after its discoverer, physicist Peter Higgs, who in the 1960s hypothesized the existence of a missing particle. When it was discovered 50 years later, Higgs was awarded the Nobel Prize in Physics (2013). This boson is valuable because it completes the missing piece of the famous Standard Model (a physical theory that describes three of the four fundamental interactions). Its characteristic is that it imparts mass to all other particles. Its peculiarity is that it is a particle that decays very quickly and is therefore difficult to observe, even in the most sophisticated detectors. This is why, outside of scientific contexts and against Higgs's own wishes, many refer to it as the "God particle."
How does the world's largest accelerator work, and what is it made up of?
In this article, we will focus on two accelerators: the LHC at CERN and the synchrotron at CNAO in Pavia.
Starting with the LHC, its notable components include over 1,000 superconducting magnets operating at extremely low temperatures (-271.3°C, nearly as cold as interstellar space), producing a magnetic field intensity of 8 tesla (200,000 times stronger than Earth's magnetic field).
It's evident that an accelerator of this scale requires significant support to operate, which is why a vast area near the Swiss border was chosen.
To make the accelerator function, several processes must take place even before the detectors (which we will examine in more detail shortly) can begin collecting data.
It all begins with a hydrogen cylinder, from which, after removing electrons, only protons (hydrogen nuclei) remain. These protons are injected into the linear accelerator (LINAC), which accelerates them to an energy of 50 MeV. These protons are then sent to a small proton synchrotron, the PS Booster (PSB), which accumulates them in four overlapping rings and accelerates them to 2.0 GeV (in the past, the units of various measurements were smaller, but over time, power has gradually increased). The beam is then transferred to the Proton Synchrotron (PS), which increases its energy to 26 GeV before directing it to the Super Proton Synchrotron (SPS), where it is accelerated to reach 450 GeV.
Only at this point is the beam injected into the Large Hadron Collider.
The figure below illustrates what has been explained so far.
This procedure is repeated multiple times to accumulate as many protons as possible in the two starting rings. Once filled, the beam's energy must be raised to the maximum value, which reached a record of 13.6 trillion electronvolts (TeV) in July 2022.
The acceleration of the two beams launched in opposite directions occurs simultaneously, but the actual collision has to wait. At the end of the phase analyzed so far, the beams are made to intersect, with the help of specialized magnets, at the four locations where LHC's main experiments are located (ATLAS, CMS, ALICE, and LHCb), serving as the "eyes" of the accelerator.
Under normal conditions, protons can circulate in LHC's tubes for several hours, allowing experiments to collect data for extended periods through sophisticated detectors present in the four aforementioned experiments. The task of these experiments is to capture images of the infinitely small particles produced by proton collisions and then present them in graphs that, through a complex computer system, will be analyzed by researchers. The amount of data produced after each collision is immense, which is why computers are capable of filtering the data, allowing only those of greatest interest to pass through.
The proton beams travel at a speed of 99.999999% of the speed of light. To give you an idea, the beams complete 11,245 laps per second.
The goal is to search for new particles and discover more about the origin of the universe. The work of such a large accelerator relies on millimeter-level precision, which CERN describes as follows: "The particles are so tiny that the task of making them collide is like shooting two needles 10 kilometers apart with such precision that they meet halfway" (translated from the original article on www.cern.ch).
But the appeal of accelerators extends beyond the world of nuclear physics. Within an accelerator, various types of charged particles can be accelerated, such as electrons, protons, and carbon ions. Thanks to this, accelerators are indispensable tools in a range of fields, including nuclear physics, electronic industry, and medicine.
In the medical field, accelerators are essential for oncology research. Take, for example, the treatment of tumors through hadron therapy. It requires the use of an accelerator no less complex than the one used at CERN, called a synchrotron.