The Fermilab particle accelerator complex set a record beam power on March 11, 2021, thanks to the high-quality work of numerous teams and individuals. The Main Injector delivered 803 kilowatts of proton beam on the NuMI target system for one hour, producing more neutrinos than it ever has before.
The successful completion of the NuMI 2020 shutdown work prepared the NuMI target facility for this achievement. Back in 2018, the Accelerator Division Target Systems Department developed ambitious plans to complete upgrades in the NuMI target facility during the 2019 and 2020 summer accelerator shutdowns. The goal was to make the NuMI target facility capable of accepting higher beam power: 6.5×1013 protons per spill at 120-giga-electronvolt beam energy with a cycle time of 1.2 seconds. Future improvements to the Fermilab accelerator complex will eventually lead to the actual delivery of this proton beam power. And the more protons hit the NuMI target, the more neutrinos are produced.
The NuMI target system efficiently converts the intense proton beam into a focused neutrino beam aimed at the NOvA experiment’s detectors. The most critical beamline components are the target and horns. Once the accelerated protons smash into the target to create pions and kaons, two magnetic focusing horns immediately focus the the short-lived charged particles before they decay into neutrinos. Without the horns, an experiment would lose 95% of the neutrinos in its beam.
To ready the system for increased beam power, the NuMI target and Horn-1, along with their cooling systems, needed to be upgraded to address the increased heat that the increased beam power brings. Members of the Target Systems Department installed the new target in 2019. Other tasks were completed during the 2020 shutdown, including the installation of the upgraded Horn-1, replacement of transverse motion drives for the horn and upgrade of the HVAC system for horn cooling. These jobs required a combination of remote-handling operations, safety planning and hazard mitigation, engineering, design, fabrication, mock-up practice, installation, safety oversight and local trades. And to make it interesting, the jobs were to be done at least 160-feet underground in the NuMI beamline and target hall.
Targets and focusing horns are custom-designed and built at Fermilab. The scientific specification, engineering, design, fabrication and assembly of these one-of-a-kind devices takes years to complete. The engineering challenges for horn design and fabrication are the heating and mechanical stress that producing millions of magnetic pulses causes. The devices require adequate water and air cooling, and they are installed to a tolerance of 1/200 of an inch (127 micrometers) inside the beam path to provide high-quality beam alignment to the detectors. They must survive in harsh radiation and a corrosive environment.
Prior to beam startup in 2019, we noticed the second horn located in the target station, Horn-2, was slowly leaking cooling water. It ultimately survived the shortened physics run from 2019 to 2020 but was ripe for replacement during the 2020 shutdown. Horn-2 had been in service 12 years and exposed to more than 100 million pulses, well exceeding its predicted lifetime. Replacing Horn-2 added a significant work to an already busy summer, but the team felt they could accomplish it if parts arrived as scheduled. Eventually, everything became even more ambitious than anticipated due to the pandemic.
In early June, technicians, engineers, machinists and welders began working on and off site to fabricate needed components. Technicians across multiple divisions and sections focused on maintenance activities while preparing not one, but two horns for installation. Most jobs in the NuMI target facility are complicated and require much planning and coordination. A talented and dedicated group of technicians, engineers and physicists performed at high levels to safely complete their list of tasks.
To install two new horns, the team also organized two transports of used components from the NuMI target facility to a long-term storage facility located on site. The Fermilab Fire Department, truck drivers, security and ES&H worked with the target systems team to complete these transfers. We produced a four-minute time-lapse video that captures the process.
To help meet the goals for the upgrade initiative, the team enlisted the help of nine accelerator operators who handled various work activities in the target hall over the course of the shutdown. Their contributions helped tremendously, were critical to success and were beyond the excellent job they typically perform in keeping the beam power optimized during normal physics operations.
We thank everyone who helped achieve these aspiring goals over the 2020 summer under adverse circumstances: Accelerator Operations Department, Alignment and Metrology Department, dispatch, ES&H, FESS, Fire Department, Mechanical Support Department, Security Department, Technical Division and our outside contractors.
Thank you to all the people who make the accelerators and associated beamlines work with efficiency and reliability, paving the way for many more beam-power records to come.
Marty Murphy is an engineering physicist in the Main Injector Accelerator Department and was coordinator of the NuMI summer shutdowns from 2018 to 2020. Yun He is a principal engineer in the Target Systems Department and is the project manager for the NuMI Accelerator Improvement Project.