FAST meets design specs

Vladimir Shiltsev

You may have read that recently our FAST accelerator reached a milestone energy, accelerating a beam of electrons to 300 MeV. This energy is above the threshold required to inject beam into the upcoming Integrable Optics Test Accelerator, or IOTA, which is the focus of the FAST facility. With this achievement, we now know that FAST is able to support IOTA, enabling further cutting-edge accelerator research at Fermilab.

The design injection energy for IOTA is 150 MeV, and now that we’ve doubled that, we plan to move to the next stage of the IOTA research program.

That was not all. The 300-MeV beam was the highest-energy beam ever accelerated through an ILC-type superconducting radio-frequency (SRF) acceleration cryomodule at design specifications. The International Linear Collider, or ILC, is a proposed electron-positron collider currently under consideration for construction in Japan. One of its performance goals is the generation of an electron beam with an energy gain of 250 MeV through an eight-cell, 1.3-GHz ILC-type cryomodule at the maximum gradient of 31.5 MV/m. For the first time anywhere, we met the specifications with actual beam acceleration.

On Nov. 15, a group at the Fermilab Accelerator Science and Technology (FAST) facility celebrates the record-high-energy 301-MeV electron beam acceleration all the way to the facility's beam absorber. From left: Vladimir Shiltsev, Jinhao Ruan, Alexandr Romanov, Alexander Valishev, Dean "Chip" Edstrom and Elvin Harms.

On Nov. 15, a group at the Fermilab Accelerator Science and Technology (FAST) facility celebrates the record-high-energy 301-MeV electron beam acceleration all the way to the facility’s beam absorber. From left: Vladimir Shiltsev, Jinhao Ruan, Alexandr Romanov, Alexander Valishev, Dean “Chip” Edstrom and Elvin Harms.

The achievement has naturally become the record one for electron beams at Fermilab’s, as in the past Fermilab was known for mostly its outstanding proton beams.

It was also a testament to the strength of the laboratory’s SRF accelerator program and long-awaited proof of the feasibility of the SRF technology at its frontier.

Fermilab’s involvement in the worldwide efforts toward the development of SRF-based accelerators was begun by the late Helen Edwards in the second half of the 1990s. There was enough promise demonstrated in a smaller-scale AZero photoinjector facility by mid-2000s.

So the accelerator community in the United States and the Fermilab team originally led by Robert Kephart, Richard Stanek, Sergei Nagaitsev and Shekhar Mishra initiated in 2006 a large-scale program to develop SRF technology and, as part of it, to build a major beam facility to test the SRF accelerator elements, what we now know as FAST. That initiative involved many scientists, engineers and technicians from Fermilab’s Accelerator and Technical divisions, as well as people from other divisions and sections, such as FESS, Computing and ESH&Q.

This is an image of the 301-MeV beam at the end of the FAST electron injector beamline.

This is an image of the 301-MeV beam at the end of the FAST electron injector beamline.

It is expected that several future high-energy particle accelerators will be based on SRF, including our own PIP-II linac and the proposed ILC. Meeting the very challenging ILC goals was a formidable task for SRF experts and accelerator physicists worldwide, and several teams were for a long time close to showing that it was possible. It was finally demonstrated at Fermilab.

And now that FAST has demonstrated that it can support the future IOTA ring, we look forward to conducting more advanced high-precision research to better understand and characterize fundamental beam physics phenomena, such as the generation of beam halo, which creates an undesired beam motion through the accelerator, and performance-limiting particle losses, which can result in high-energy release and potential damage to equipment. These phenomena limit the experimental possibilities of all the intensity frontier accelerators, including our own Booster, Recycler and Main Injector. Our FAST research program aims to develop novel accelerator techniques of so-called “integrable optics” and space-charge compensation with electron lenses.The program has a potential to prove innovative design concepts for future Fermilab accelerator complex upgrade aiming at multimegawatt proton beams for neutrino experiments.

Starting in mid-2018, we will inject beams of electrons into the IOTA ring. We expect to inject proton beams into IOTA in 2019.

Congratulations to everyone — going all the way back to the 1990s — who contributed to the achievement!

Vladimir Shiltsev is the head of the Accelerator Physics Center.