Case Study: Cryogenic Lens Cooling System for High‑Powered Laser Applications
Overview
GRE was awarded a public tender by the Science and Technology Facilities Council to design and manufacture a mobile, helium‑based, amplifier lens cooling system for the Di‑Pole ‘S’ laser at the Rutherford Appleton Laboratory in Didcot, UK.
The Central Laser Facility required a cooling system that could be moved into position easily within a laboratory and set up quickly, while still maintaining sub‑millimetre accuracy (due to the fact that any misalignment could have reduced cooling performance and potentially caused the laser lens to overheat).
Scientific & Technical Challenges
- Achieving Precision Mobility
Initial research into off‑the‑shelf casters, roller balls, and levelling systems showed that none could deliver the accuracy required and what appeared to be a simple part of the project quickly became considerably more complicated. GRE tested multiple options, but each fell short in terms of precision and stability.
To overcome this, GRE worked with a specialist local engineering company to explore custom bearing and sliding mechanisms. After numerous prototypes and in‑house trials, GRE developed a hybrid movement and levelling system, combining:
- Locking roller balls for initial coarse positioning
- Custom sliding plates with interference‑fit materials for ultra‑fine adjustment
- Multi‑axis levelling capability (left/right, front/back, up/down)
- A “floating” plate mechanism to meet strict floor load requirements
This solution delivered the precision the client needed while preserving mobility.
- Designing a Bespoke Heat Exchanger
One of the largest uncertainties centred on the need to create a custom heat exchanger capable of transferring cooling energy from liquid nitrogen to circulating gaseous helium—while meeting strict pressure‑drop limits.
Because no commercially available heat exchanger met the specification, GRE:
- Calculated helium mass‑flow requirements
- Selected an appropriate cryogenic fluid
- Used finite element analysis (FEA) to model heat transfer performance
- Designed a thin‑wall stainless steel helical tube for maximum efficiency
The unit also needed to operate below –80°C to prevent the nitrogen from boiling. This requirement added further design constraints.
- Managing Extreme Thermal Expansion & Contraction
The heat exchanger and vacuum‑insulated vessel were subject to temperature swings of approximately 220°C. GRE engineers carried out detailed analysis on:
- Material strength
- Weld joint performance
- Expansion/contraction behaviour
- Long‑term cycling resilience
Following extensive calculations and simulation, GRE implemented structural design features to accommodate these changes safely, with plans for post‑build X‑rays, pressure testing, and leak testing to validate performance.
- Creating an Automatic Cooling Control System
The cooling process needed to be fully automated. GRE designed:
- An automated liquid nitrogen top‑up system
- A dynamic bypass loop to regulate helium temperature
- Automated valves and control logic to achieve the client’s precise –196°C requirement
Only the necessary amount of helium was diverted through the heat exchanger, ensuring stable and efficient cooling.
GRE’s Engineering Approach
To overcome the project’s scientific and technical uncertainties, GRE:
- Conducted extensive research and prototype testing of mobility components.
- Collaborated with specialist engineers to refine sliding and levelling mechanisms.
- Developed a hybrid movement system that balanced mobility with sub‑millimetre precision.
- Engineered a bespoke heat exchanger after exhaustive modelling and analysis.
- Designed a vacuum‑insulated vessel to maintain cryogenic conditions and eliminate nitrogen boil‑off.
- Validated structural integrity through modelling and planned real‑world testing.
- Built an automatic process system to ensure reliable temperature control.
This combination of research, modelling, and innovative engineering enabled GRE to deliver a high‑performance solution for a deeply challenging cryogenic application.
Outcome
GRE successfully developed a compact, mobile, precision‑aligned cryogenic cooling system that met the client’s demanding performance requirements. The hybrid levelling mechanism and bespoke heat exchanger represented major engineering achievements, and elements of the design have since been reused in other projects—demonstrating the system’s long‑term value and impact.