# [SCI] Cryogenics

**Cryogenics** is the science and technology of producing and using very low temperatures (below −150°C / 123 K), enabling the study of materials at the quantum mechanical limit and the infrastructure for superconducting devices.

## Overview

James Dewar liquefied hydrogen (1898) and Heike Kamerlingh Onnes liquefied helium (1908, 4.2 K) — the last and most difficult permanent gas to liquefy. In doing so, Onnes discovered superconductivity in mercury (1911), opening a new domain of physics. The Joule-Thomson effect (throttling expansion cools a gas) and the Linde refrigeration cycle (1895) provided the industrial basis for cryogenic gas production.

Cryogenics is the experimental prerequisite for:
- **Superconductivity** — most superconductors require temperatures below ~20 K (achieved by liquid helium or modern cryocoolers)
- **Clinical MRI** — superconducting magnets operating at 4 K or 20 K create the 1.5–7 Tesla fields needed
- **Quantum computing** — superconducting qubits require millikelvin temperatures (achieved by dilution refrigerators reaching ~10 mK)

## Key Figures & Recognition

- **Heike Kamerlingh Onnes** (1853–1926): Helium liquefaction, discovery of superconductivity. **Nobel Prize 1913**.
- **Carl von Linde** (1842–1934): Industrial gas liquefaction (Linde process), 1895.
- **James Dewar** (1842–1923): Dewar flask (vacuum-insulated container), hydrogen liquefaction.

## Seminal Papers

- Kamerlingh Onnes, H. "The Superconductivity of Mercury." *Comm. Phys. Lab. Univ. Leiden* 120b (1911).
- Linde, C. "Verfahren zur Verflüssigung atmosphärischer Luft." DE Patent 88,824 (1895).

## What This Enables

- **[SCI] BCS Superconductivity** — Cryogenic experiments revealedKamerlingh Onnes discovered superconductivity in 1911 via cryogenics; BCS theory (1957) is the explanation ofexplains what cryogenics discoveredrevealed.
- **[TECH] MRI (Magnetic Resonance Imaging)** — Clinical MRI magnets use superconducting NbTi wire cooled bythat requires liquid -helium or cryocoolers to achieve the necessary field strengthscryocooler operation at 4–20 K.
- **[TECH] Quantum Computing Hardware** — Superconducting qubits (IBM, Google) operate at ~15 mK in dilution refrigerators, only achievable with cryogenic technology — the coldest human-made environments.

# Parents

* [SCI] Classical Thermodynamics
* [SCI] Classical Thermodynamics
* [TECH] Chemical Industry