SRF - TRIUMF

01 Overview
02 SRF Science Highlights

01 Overview

TRIUMF’s Superconducting Radiofrequency (SRF) facility is Canada’s only centre for the research, design, testing, and assembly of SRF accelerator technologies.

Since 2000 the TRIUMF SRF team has collaborated with university research and laboratory partners worldwide, and designed, assembled and maintained TRIUMF’s two SRF accelerators, the ISAC-II Superconducting Heavy-Ion linear accelerator (SC-linac) and the ARIEL Electron linac (e-Linac).

SRF is at the cutting edge of radio frequency (RF) accelerator technology enabling the operation of more efficient, powerful, compact and cost-effective accelerators.

All RF accelerators use electric fields oscillating within a cavity to accelerate charged particles. While room-temperature RF cavities are typically made from copper, SRF cavities are made from a superconducting metal and operate at ultra-low temperature. The TRIUMF SRF cavities are made from niobium that when cryogenically cooled to below 5 K is a 100,000-times better conductor than copper. As a result, there’s almost no power loss in the SRF cavity and they can be operated with high voltages in a range where which copper cavities would melt, thus enabling much more powerful, compact accelerators.

The SRF facility has become a major international collaborator in the design, fabrication and testing of SRF technologies. Major collaborations include:

The SRF group co-developed the ARIEL e-linac’s injector cryomodule with a team from India’s Variable Energy Cyclotron Centre (VECC) and the SRF group is now designing a heavy ion cryomodule for VECC.
TRIUMF designed, fabricated and tested an innovative SRF cavity as part of South Korea’s new Rare Isotope Science Project. The SRF group also tested the first two prototype cavities for the South Korean facility.
The SRF group will build five new cryomodules to contain SRF cavities for the High Luminosity upgrade to CERN‘s Large Hadron Collide
TRIUMF’s SRF group also collaborates in sample studies of new treatments and materials using TRIUMF’s unique µSR material probe. This includes work with Cornell University, Temple University, Lancaster University, the S. Fermi National Accelerator Laboratory, and Jefferson Laboratory.
TRIUMF also hosted the 2015 International SRF technology conference with 400 participants from around the world.

As Canada’s only centre for university training and research in SRF technologies, the SRF facility also includes a graduate and post-graduate program of research into next-generation SRF technologies. This includes both micro-and macroscopic research topics, from characterizing and optimizing superconducting properties of potential new alloys to more efficient cavity designs and optimization of surface preparation techniques.

02 SRF Science Highlights

A Pathway to Optimizing the Performance of SRF Cavities

Superconducting radio-frequency acceleration involves creating strong electromagnetic fields inside a cryogenically cooled superconducting vessel that can be used to accelerate charged particles. The superconducting state is limited by the ability of the material to repel magnetic flux penetration from the strong surface fields. New materials or new material treatments are being developed to allow higher fields and more efficient acceleration before flux penetrates the material. Recent experiments at the TRIUMF muSR facility have shown that coating niobium with a high Tc material (like Nb³Sn or MgB²) of variable coating thickness can increase the field of first flux penetration by 40% with respect to a non-coated sample. The measurements suggest a path forward to increase the performance of niobium SRF resonators through modification to the surface.

Successful proof of principle test of novel balloon resonator

Superconducting radiofrequency (SRF) technology is the enabling advances in a new generation of proton linacs for discovery science or industrial application. Strong electromagnetic fields created in specially designed resonators are used to accelerate the protons. A class of resonators, termed spoke cavities, is efficient in acceleration but suffers from a phenomenon called ‘multipacting’ wherein a cascade of electrons is released from the surface by the high fields, which can limit the cavity performance. The TRIUMF SRF team has invented a new type of spoke resonator called the `balloon cavity’ with a special shape that virtually eliminates multipacting as an issue for single spoke resonators. A prototype cavity was fabricated and tested at TRIUMF and recent tests confirm the unique capabilities of the new variant.

Investigations of beam-beam effects in HL-LHC

Around the experimental regions of the Large Hadron Collider (LHC), beams travel in a common vacuum chamber and therefore experience the fields of the opposing beams - so-called ‘long-range interactions’. These are unavoidable and, being nonlinear, limit the LHC's luminosity. Studies of this effect are essential for designs crucial for the ongoing high-luminosity upgrade (or HL-LHC; a program to bring a factor-of-10 performance improvement to the LHC), due to begin operating in 2025. The usual method of investigating the effect is by multiparticle simulations, and TRIUMF is part of the international collaboration charged with these calculations. These are compute-power limited, so it is highly desirable that an alternative analytic model be found. Recently, we have discovered such a model. This has the potential of making beam-beam calculations more tractable.

Housed in ISAC-II, the 500m²SRF facility includes all of the capabilities for SRF testing and assembly, including: a cavity processing lab; ultra-clean assembly room; RF test area; cavity testing cryostats; cryomodule assembly area; cryogens on tap including liquid helium and liquid nitrogen; and an overhead crane that enables materials handling.

Cavity Chemical Processing

When a niobium SRF cavity arrives at TRIUMF from the manufacturer, the first stage in processing is a chemical super-cleaning. Even microscopic contaminants on the interior conductive surface of the niobium cavity can cause the niobium to heat-up to above 9 K, at which point superconductivity is lost. The niobium is cleaned using an aggressive chemical etching process that removes the top 100 microns to ensure a pure niobium surface. This is followed by an eight-hour, high-pressure rinse using ultra-pure water to remove all chemical residues and dust particles.

Ultra-Clean Assembly Room

SRF cavities are assembled together with RF feed lines and pick-ups into hermetically sealed units. The assembly is done in an ultra-clean room in order to ensure the cavities are free of dust. Even microscopic dust on the conductive surface becomes a source of electrons under high electric field that when “sucked” from the surface can be accelerated, reducing the accelerators efficiency and producing unwanted x-rays. The hermetic units can be tested individually in test cryostats or assembled into cryomodules for use as a linear accelerator.

Cavity Testing Cryostats and Cryomodule Assembly

Cryostats and cryomodules are high-tech thermoses that maintain the cavities at superconducting temperature below 5K while allowing RF feed lines into the cavity and the ability to tune the cavity to a precise RF frequency. Cryostats are used for testing individual cavity performance; cryomodules are used to assemble multiple cavities together for acceleration. Every cavity is cryogenically tested as a single cavity before being assembled into a cryomodule.