Nuclear fusion is fundamentally a reaction in which light atomic nuclei combine under extreme temperatures and pressures to form heavier nuclei, releasing vast amounts of energy. As humanity’s ultimate solution to the energy crisis, controlled nuclear fusion presents unprecedented engineering challenges. Leveraging decades of expertise in vacuum electronic devices, GLVAC has developed critical components—including hydrogen thyratrons, high-power klystrons, and vacuum capacitors—that serve as indispensable elements in fusion devices. These components provide precise control and efficient energy handling throughout the processes of energy storage, conversion, and transmission, acting as a vital bridge between macro-scale power systems and the micro-scale plasma world.

High-Power Klystron – The Efficient Generator of Microwave Energy

A klystron is a vacuum electronic device that generates high-power microwaves through velocity modulation. By converting the kinetic energy of an electron beam into electromagnetic radiation, klystrons can deliver continuous or pulsed microwave power at the megawatt level.

In magnetically confined fusion devices, klystrons are central to Electron Cyclotron Resonance Heating (ECRH) and Lower Hybrid Current Drive (LHCD) systems. They supply microwave energy to assist in plasma heating and current drive—key enablers of high-confinement operational modes.

These high-power microwaves pass through vacuum windows and are injected into the plasma. Through precise frequency matching, they fulfill two critical functions:

Plasma Heating:

When the microwave frequency matches the electron cyclotron frequency, energy is efficiently absorbed, heating the plasma to temperatures exceeding 100 million degrees Celsius.

Current Drive:

By transferring directional momentum, microwaves drive toroidal currents within the plasma, maintaining stable magnetic confinement.

Hydrogen Thyratron – The Precision Switch for High-Power Pulses

The hydrogen thyratron is a hot-cathode, low-pressure gas-filled (hydrogen or deuterium) switching tube capable of withstanding extremely high voltages and pulsed currents. It can conduct thousands of amperes within microseconds—a capability essential for plasma initiation and pulsed power delivery in magnetic confinement systems.

In tokamak devices, hydrogen thyratrons are primarily used in the power supplies for ohmic heating coils. At startup, a massive current pulse must flow through the central solenoid in an extremely short time to generate the initial plasma and induce the toroidal current. Acting as the main switch, the hydrogen thyratron precisely controls the timing of this process—ensuring the current pulse peaks (often reaching tens of kiloamperes) within milliseconds and then rapidly turns off to prevent energy waste and overheating.

Vacuum Capacitor – Efficient Storage and Delivery of Pulsed Energy

Vacuum capacitor uses vacuum as the dielectric medium, offering extremely high insulation strength and exceptionally low dielectric loss. They can store large amounts of electrical energy and release it in an extremely short time. Compared to conventional capacitors, vacuum capacitors provide higher voltage ratings, greater current-carrying capacity, and significantly longer service life.

In controlled fusion systems, vacuum capacitor banks perform three essential roles:

Energy Storage and Pulse Formation

Fusion experiments require enormous pulsed power far beyond what the grid can supply directly. Vacuum capacitor banks act as intermediate energy reservoirs—slowly charging over tens of seconds from the grid to store tens to hundreds of megajoules, then discharging within milliseconds to deliver instantaneous high power for plasma initiation and heating.

Rapid Response for Plasma Control Systems

Active control is crucial in modern fusion devices to suppress plasma instabilities. Vacuum capacitor banks supply fast-response energy to control systems—such as those powering vertical stability coils—delivering precisely timed current pulses within milliseconds to dynamically adjust plasma position and shape.

Energy Diversion for Magnet Protection

During a plasma disruption, immense electromagnetic energy stored in superconducting magnets must be safely extracted within milliseconds to avoid catastrophic damage. Vacuum capacitors, working in tandem with power electronic switches, form rapid energy transfer systems that safely dissipate this energy in just a few milliseconds.

Integrated Operation: Synergy in Fusion Devices

In a typical tokamak, these three devices work in concert to form a complete energy management system:

Startup Phase:

Vacuum capacitor banks charge and store energy; hydrogen thyratrons precisely trigger its release into the magnet system to generate the initial plasma.

Heating Phase:

Klystron systems convert electrical energy into millimeter-wave microwaves, which penetrate the vacuum vessel to heat the plasma and drive current.

Sustainment Phase:

Vacuum capacitors support active control systems with rapid energy delivery; hydrogen thyratrons regulate power distribution across subsystems; klystrons maintain optimal plasma temperature and current profiles.

Termination and Protection Phase:

Hydrogen thyratrons and vacuum capacitors collaborate to safely terminate the discharge and protect equipment from disruptions caused by plasma instabilities.

Driving Toward Commercialization

Future fusion systems will demand even higher performance: greater efficiency, longer lifespans, enhanced reliability, and lower costs. The ongoing innovation of these core vacuum electronic devices will go hand-in-hand with advances in fusion technology—accelerating humanity’s journey toward the ultimate clean energy solution.