2. Attachment A - Specifications - NNSA Project.pdf

NNSA Project Cryocooler Procurement

Specification

September 17, 2025 Version 3

NNSA Project Team @ IARC

NNSA Project Cryocooler Procurement Specification NNSA Project Team @ IARC

NNSA Project at IARC

Fermilab is advancing compact, conduction-cooled Superconducting Radio-Frequency (SRF) accelerator technology to support the National Nuclear Security Administration’s goal of reducing reliance on radioactive cobalt-60 sources.

Electron beam systems provide a safe and effective alternative to Co-60 for applications such as sterilization and materials treatment, eliminating risks associated with transport, security, and long-term waste management of radioactive materials.

By leveraging Fermilab’s expertise in SRF technology and cryocooler-based conduction cooling, this project aims to deliver a reliable, scalable electron beam platform that aligns with NNSA’s mission to enhance national security while enabling practical industrial adoption.

Conduction Cooling with Cryocoolers

SRF cavities are used for electron beam accelerators which can be used for a variety of applications. SRF cavities operate at cryogenic temperatures and are conventionally cooled by liquid helium held near 2-4.5K. This requires lots of cryogenic infrastructure which isn’t ideal for industrial applications.

Conduction cooling an SRF cavity by directly connecting to a closed cycle cryocooler with a thermally conductive link will eliminate the need for the conventional helium bath.

This elimination leads to dramatic simplification of the accelerator: a liquid helium inventory, a helium recovery/storage system, and a helium pressure vessel and relief design is no longer needed, the cryogenics becomes very reliable (commercial 4 K cryocoolers have mean time between maintenance of > 20,000hrs (2.3 years), safe (no liquid helium safety and oxygen deficiency hazards), and simple to operate (cryocoolers turn on/off with push of a button), and significantly reduced footprint as well as added option of portability because all of the cryogenics is integrated into the cryomodule.

The SRF cavity for this system will have a Niobium-Tin coating in order to raise the superconducting temperature to around 4.2 Kelvin. This project is integrating pulse-tube cryocoolers into a SRF cryomodule to cool down the cavities to 4.2K to reach these superconducting temperatures.

Heat Load

The cryostat has two thermal intercept stages. The temperature of the first stage is 4.2K and the temperature of the second stage is 45K. The project team performed simulations and analysis to calculate the heat load generated by the accelerator and the cooling capacity needed at each of these stages.

NNSA Project Cryocooler Procurement Specification NNSA Project Team @ IARC

The heat load of the 4.2K stage is primarily made up of heat generated by the RF losses in the cavity and coupler along with other smaller losses from the particle beam. The total cooling capacity needed at this stage is 2.5W.

The heat load of the 45K stage consists of all other heat generated from the system. The total cooling capacity needed at this stage is 40W.

Vibration Sensitivity

As noted above this project must utilize a Niobium-Tin coated cavity in order to achieve a superconducting state at 4.2K. The Niobium-Tin coating is a sensitive thin-film coating on the inside of the cavity that is susceptible to vibrations.

In order to cool these cavities effectively without disturbing the coating a pulse-tube cryocooler must be used as these produce lower vibrations than other configurations.

Standard Gifford-McMahon (GMM) cryocoolers produce a larger amount of vibration, compared to a pulse-tube cryocooler, which is not suitable for this application.

The IARC @ Fermilab team has demonstrated on a previous project that pulse-tube cryocoolers work for Niobium-Tin coated cavities.

Power Consumption

As this system will be used for mobile applications, power consumption of the entire system is a constraining factor. The power consumption of the cryocoolers shall be 30kW per unit or less.

Specifications

The specifications required for the cryocoolers are stated below:

1. Operating temperature of 4.2K or lower

2. First stage capacity of greater than, or equal to, 2.5 Watts @ 4.2K

3. Second stage cooling capacity of greater than, or equal to, 40W @ 45K

4. Quantity: 1 unit

5. Pulse-Tube configuration is required to limit vibrations on SRF Cavity

6. Size constraints:

a) Diameter of mounting flange: 10in diameter maximum

b) Height of room temperature side: 30in maximum

c) Height of cold side: 20in maximum

d) Compressor dimensions: 6ft x 6ft x 4ft maximum

7. Power Requirements: 15kW maximum

The vendor shall include the following in the quote:

1. Cold head

2. Compressor

NNSA Project Cryocooler Procurement Specification NNSA Project Team @ IARC

3. Gas lines

4. Vibration Dampening Bellows

5. Instrumentation Cables

6. Power Cables