Product Category
Vacuum Capacitors
Fixed and variable vacuum capacitors offering ultra-low RF losses at high voltages. Capacitance range 10 pF–5000 pF, voltage ratings up to 60 kV. Essential for RF matching networks, plasma systems, and particle accelerators.
What Is a Vacuum Capacitor?
A vacuum capacitor is a precision capacitive component that uses vacuum as the dielectric medium between its electrodes. Unlike conventional capacitors that use ceramic, film, or electrolytic dielectrics, the vacuum dielectric has virtually zero dielectric loss — making vacuum capacitors the lowest-loss, highest-Q capacitors available for RF power applications.
The electrodes are sealed inside a glass or ceramic envelope from which the air has been evacuated to a pressure of 10⁻⁶ torr or lower. This vacuum environment also provides excellent voltage standoff capability, allowing vacuum capacitors to handle tens of kilovolts that would cause breakdown in air-dielectric or solid-dielectric designs.
Fixed Vacuum Capacitors
Fixed vacuum capacitors have a predetermined, non-adjustable capacitance value set during manufacturing. The concentric cylindrical electrodes are fixed in position within the vacuum envelope. Fixed vacuum capacitors are characterized by:
- Very high Q factor (low losses) at RF frequencies
- Excellent voltage handling (5 kV to 60 kV)
- High current capability (up to 500 A RMS for large types)
- Long service life with no mechanical wear
- Capacitance range: 10 pF to 5000 pF (standard types)
Variable Vacuum Capacitors
Variable vacuum capacitors allow continuous, smooth adjustment of capacitance by mechanically moving the inner electrode relative to the outer electrode using a bellows seal that maintains the vacuum while allowing movement. Features include:
- Continuous tuning from minimum to maximum capacitance
- Typical capacitance ratios of 10:1 (e.g., 10–100 pF, 25–250 pF)
- Motorizable versions available for remote or automatic tuning
- Smooth, backlash-free operation
- Capacitance range: 5 pF to 1000 pF (variable types)
Specifications Overview
| Type | Capacitance Range | Max Voltage (DC/Peak RF) | Max Current (RMS) | Typical Q | Application |
|---|---|---|---|---|---|
| Fixed (small) | 10–100 pF | 5–15 kV | 50–150 A | >5000 | RF circuits, tuning, impedance matching |
| Fixed (medium) | 100–1000 pF | 15–40 kV | 150–300 A | >3000 | Industrial RF heating, broadcast |
| Fixed (large) | 1000–5000 pF | 20–60 kV | 300–500 A | >1000 | High-power RF matching, accelerators |
| Variable (small) | 5–100 pF | 5–15 kV | 30–100 A | >3000 | Tunable RF networks, antenna tuners |
| Variable (medium) | 10–500 pF | 15–30 kV | 100–200 A | >2000 | Plasma matching, industrial heating |
| Variable (motorized) | Custom | Up to 30 kV | Up to 200 A | >2000 | Automatic impedance matching systems |
Applications
RF Matching Networks
Fixed and variable vacuum capacitors form the tuning and matching elements in high-power RF amplifier output networks for broadcast and industrial equipment.
Plasma Generators
Variable vacuum capacitors in automatic matching units (AMUs) tune the impedance between the RF generator and plasma chamber in semiconductor etching and deposition systems.
Particle Accelerators
Fixed vacuum capacitors tune the RF resonant cavities in cyclotrons, synchrotrons, and linear accelerators at research and medical facilities.
Industrial RF Heating
High-voltage vacuum capacitors in the tank circuits of dielectric heaters and sealers operating at 13.56 MHz and 27.12 MHz ISM frequencies.
NMR / MRI Systems
Precision vacuum capacitors in the RF coil matching networks of NMR spectrometers and MRI scanners where ultra-low loss is critical.
Fusion Research
High-power variable vacuum capacitors in the RF heating systems (ICRF/ICRH) of experimental fusion reactors such as JET and ITER.
Frequently Asked Questions
Why use a vacuum capacitor instead of a ceramic capacitor?
Vacuum capacitors offer significantly lower losses (higher Q) at RF frequencies compared to ceramic capacitors of the same value. They also handle much higher voltages and currents. For high-power RF applications above a few kilowatts, or where heating losses in the capacitor itself would be problematic, vacuum capacitors are the preferred choice. Ceramic capacitors lose their advantage at high power due to self-heating from dielectric losses.
How do I select the right vacuum capacitor?
Key selection parameters are: (1) capacitance value (pF), (2) peak voltage rating — must exceed the maximum RF peak voltage in the circuit, (3) RMS current rating — must exceed the maximum circulating current, (4) frequency of operation, and (5) fixed vs. variable. PartnerTubes' application engineers can help you calculate the correct ratings for your circuit and select the appropriate component.
What brands of vacuum capacitors do you supply?
PartnerTubes sources vacuum capacitors from leading manufacturers including Comet (Switzerland), Jennings (USA), Meiden (Japan), IXYS (formerly Directed Energy), TESLA (Czech Republic), and others. We can cross-reference to equivalent types across brands and source A-series, B-series, C-series, D-series, and RE-series Czech types (50–5000 pF, 4.5–21 kV).
Can you supply vacuum capacitors for plasma etching (semiconductor FAB)?
Yes. We supply motorized variable vacuum capacitors compatible with automatic matching units (AMUs) used in semiconductor plasma etch, CVD, and PVD equipment from manufacturers including AE, ENI, Comdel, and Dressler. Contact our team with the equipment make/model and current capacitor part number.