Supplying Ultra-High Vacuum (UHV) Grade Stainless Steel Precision Components for the ITER Project

Project Overview

Location: Saint-Paul-lès-Durance, France
Client: ITER Organization and associated research member institutions.
Products Supplied: Special 316LN Low-Magnetic Stainless Steel, seamless vacuum bellows, and UHV flange components.
Supply Scope: High-precision customized modules for the cryostat system and diagnostic vacuum chambers.

The Challenges

The ITER project aims to harness nuclear fusion, presenting what is widely considered the “ultimate challenge” for materials:

UHV Stability: The system must maintain vacuum levels of $10^{-9}$ Pa. Any microscopic outgassing or leakage caused by impurities would disrupt the fusion environment.
Ultra-Low Magnetic Permeability: In a high-magnetic confinement environment, structural materials must have extremely low magnetic permeability ( $\mu \leq 1.005$ ) to avoid interference with the plasma control fields.
Extreme Cryogenic & Radiation Conditions: Materials must remain mechanically stable at liquid helium temperatures ( $-269$ °C) under high-energy neutron radiation without brittle failure.

Our Detailed Solution

To support this peak scientific endeavor, we provided systemic support from metallurgy to precision machining:

A. 316LN Electroslag Remelting (ESR) Process

We utilized ESR technology to drastically purify the material, ensuring high density and eliminating non-metallic inclusions. Precise Nitrogen (N) alloying increased cryogenic strength while ensuring the material remained non-magnetic even after cold working.

B. Vacuum Annealing & Outgassing Treatment

All components underwent high-temperature vacuum annealing to pre-exhaust internal hydrogen and other impurities. This ensures an exceptionally low outgassing rate, significantly reducing the pre-pumping time for the client’s vacuum systems.

C. Helium Leak Detection & 100% X-Ray Inspection

We implemented the most rigorous NDT protocols. Every welded assembly passed Helium Mass Spectrometer Leak Detection, guaranteeing leak rates below $10^{-11}$ $Pa \cdot m^3/s$ . High-resolution X-ray scans ensured weld seams were free of any micro-pores.

D. UHV Cleaning & Precision Machining

Using multi-axis CNC centers, we achieved tolerances within $\pm 0.005$ mm. All parts were cleaned in a Class 10,000 cleanroom using a 5-step UHV-specific cleaning process and sealed in nitrogen-purged packaging.

Results & Customer Value

The products have demonstrated outstanding performance in core subsystem tests:

Zero Leakage Integrity: During 500 cycles of cryogenic-thermal shock testing, all components maintained zero leakage, ensuring the safety of the superconducting magnet system.
Perfect Magnetic Transparency: Field monitoring showed that our structural components had negligible impact on the confinement fields, fully meeting ITER’s strict EMC criteria.
Accelerating Scientific Progress: Our rapid delivery and superior quality saved valuable time for the research teams, earning us the reputation of a “trusted partner in precision manufacturing.”

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