Fermilab is embarking on a major upgrade to its accelerator complex. The new PIP-II particle accelerator will provide greater than a megawatt, upgradeable to multi-megawatt, proton beam power for the laboratory’s experiments. PIP-II is the first U.S. accelerator project that will receive significant contributions from international partners. Institutions in France, India, Italy, Poland, the United Kingdom and the United States are collaborating on the project.
Institutions in India are building major components for the new accelerator upgrade, including radio frequency power amplifiers. These amplifiers power PIP-II components that accelerate the particles. Each of the 119 superconducting cavities in the PIP-II linac has a dedicated power amplifier, and our Indian partner, the Department of Atomic Energy, or DAE, is providing solid-state RF power amplifiers to power 111 of them. In recent testing, the nine power amplifiers DAE has provided so far showed stellar performance for all critical parameters, and enabled beam acceleration in the PIP-II Injector Test Facility, or PIP2IT, at Fermilab.
Fifty-one of the cavities in PIP-II will be single-spoke-resonator-style and operate at 325 megahertz, or MHz; the other 60 cavities will be elliptical-style and resonate at 650 MHz.
There are two types of SSR-style cavities used in the PIP-II linac: SSR1, which requires up to 7 kilowatts, or kW, of power to accelerate the proton beam, and SSR2, which requires 20 kW of power to accelerate the beam further.
There are also two types of elliptical cavities used in the PIP-II linac: the low-energy cavities, which require up to 40 kW of power to accelerate the beam, and the high-energy cavities, which require up to 70 kW of power.
The amplifiers that drive the SSR cavities will be tuned to 325 MHz and are being designed by the Bhabha Atomic Research Centre in Mumbai. They are being constructed in a collaboration between BARC and the Electronics Corporation of India Limited in Hyderabad, both DAE institutes.
The collaboration has already designed, constructed and delivered nine of the 325 MHz, 7 kW RF power amplifiers for SSR1 cavities. These amplifiers were recently used in a test of the low-energy portion of the PIP-II linac, housed in the PIP2IT facility. The team completed the testing of these amplifiers and placed them into service on Dec 17, 2020, and they were operated for over 300 hours until PIP2IT was shut down on April 23, 2021.The amplifiers provided the power to successfully accelerate 2 milliamps of particles through eight SSR1 cavities to a beam energy of up to 17 mega electronvolts, or MeV. The PIP2IT configuration required a peak power level of 4kW from the amplifiers to accelerate the full beam intensity.
All the efforts put into designing, developing, engineering, qualifying and testing of these amplifiers paid off when the amplifiers DAE provided showed stellar performance for all critical parameters. These parameters include wall power to RF efficiency, overall gain, gain magnitude and phase variation, group delay, harmonic contents, spurious outputs and more.
The solid-state RF power amplifiers that DAE provided offer many benefits, such as high reliability, modularity, graceful power degradation, use of lower bias voltages with higher currents and low maintenance.
Industrial grade components, innovative design techniques, direct-current-bias supplies with lower ripple, proper thermal management and appropriate design to reduce thermal drift have resulted in better amplifier-performance parameters, which improve accelerator operation.
The other set of RF power amplifiers provided by DAE, for the elliptical cavities, are tuned to 650 MHz and are being designed by the Raja Ramanna Centre for Advanced Technology in Indore. The laboratory has already delivered a first unit to Fermilab for testing with high-energy cavities at the PIP2IT facility.
While the assembly and testing of components for the PIP-II test accelerator proceeds, the construction of the buildings for housing the new accelerator at Fermilab is also ongoing. Once the construction is complete, the RF power amplifiers will be moved from their PIP2IT test site to the new buildings for the assembly of the new PIP-II particle accelerator.
Manjiri Pande is a scientific officer at Bhabha Atomic Research Centre, or BARC, and is the sub-project coordinator for 325 MHz RF power in IIFC. Jim Steimel is the level-3 manager for high-power RF for PIP-II and is the sub-project manager for 325 MHz and 650 MHz RF Power in Indian Institutes & Fermilab Collaboration, or IIFC.