The Large Hadron Collider (LHC) reigns as the world’s most powerful particle accelerator. Its detection system used in one of the four major experiments, A Large Ion Collider Experiment (ALICE), is about to get a computer chip upgrade.
The chips, dubbed SAMPA, were designed at Brazil’s University of São Paulo’s Engineering School (Poli-USP). After extensive testing across the globe from a team of international experts, SAMPA was approved for large-scale fabrication. ALICE will receive all of its 88,000 units from Taiwan Semiconductor Manufacturing Company Limited (TSMC).
“The new chips will be used to instrument two of ALICE’s detectors: the TPC [Time Projection Chamber] and the MCH [Muon Chamber],” says Marcelo Munhoz, associate professor with habilitation at USP’s Physics Institute (IFUSP), and one of the research leaders. “The TPC tracks the charged particles produced in the LHC. The MCH specifically measures muons.”
According to Munhoz, ALICE’s TPC acts as the main detection system for tracking charged particles and particle identification. It consists of an inner and outer cylinder, with a gas-filled region between the two structures.
During experimentation, the ends of the cylinders are coated with a grid of 500,000 pads and channels. This helps determine the position of collisions and the incident charge values. Every set of 32 channels will be fitted with a SAMPA chip. Although slightly different, the MCH will roughly follow the same design.
“The job done by each chip is to read out the incident charges, transform the readout into a voltage signal, convert the signal from analog to digital, perform internal digital processing, and send the information to external processors,” says Munhoz. “All the chips operating together will produce those famous images of collisions showing jets of thousands of particles, each of which follows a specific path.”
SAMPA will replace ALICE’s current generation of chips. Right now, each set of 16 channels use two computer chips. One is in charge of reading out the charges, and creating the matching voltage signal. The other converts the analog signal into bits, and then puts the bits through digital preprocessing.
SAMPA consolidates both functions into one design, and bumps up the processing from 16 channels to 32. The upgrade will allow for an increase of collision rate, and thus expand research capabilities. Specifically, the rate of collisions between lead nuclei will jump by a factor of 100.
“This itself makes SAMPA necessary because the existing equipment wouldn’t be able to handle such a huge increase in the collision rate,” says Munhoz. “Today, ALICE is operating at 500 collisions per second. In 2021, it’s expected to operate at 50,000 collisions per second. The scientists foresee that this will increase the probability of rare events such as the production of heavier quarks or the formation of light-element anti-nuclei.”
After its TSMC production, the chips will be individually tested in Sweden. SAMPA will then head to ALICE, with a projected installation timeline between 2019 and 2020.