Insulator Seal - RF Power Introduction

RF Power
Introduction

RF Power Feedthroughs are specifically designed for the transmission of Radio Frequency power into the vacuum environment. Differences between ISI’s conventional DC Power Feedthroughs and RF Power Feedthroughs are found in the construction materials used at ceramic to metal interfaces. High conductivity, non-magnetic materials are utilized in the construction of RF Power feedthroughs as they are less susceptible to the effects of current induction.
A common application of ISI RF Power Feedthroughs is in-vacuum induction heating. Designs having power ratings as high as 35kW and frequencies up to 13.56MHz are available.

ISI RF Power feedthroughs are divided in catalog a follows:

8000 Volts DC / 10 kW / 450 kHz
	Del-Seal™ CF Kwik-Flange™ KF Weldable

10,000 Volts DC / 20 & 35 kW / 13.56 MHz
	Del-Seal™ CF Kwik-Flange™ KF Weldable

RF Power Feedthroughs are constructed using copper alloys; high conductivity non-magnetic materials, which are not susceptible to the effects of RF coupling. Both RF and DC power feedthroughs can be water cooled to allow increased currentcarrying capacity, while maintaining relatively small conductor sizes. On the other hand, DC Power Feedthroughs are constructed using nickel-iron alloys, materials ideal for joining to alumina ceramics because of their low thermal coefficient of expansion. However, nickel-iron alloys are magnetic, and therefore highly susceptible to RF coupling.

High frequency current is conducted along the outer surface or “skin” of an electrical conductor. A feedthrough’s current carrying capacity is based on the conductor’s effective cross sectional area, electrical resistivity and heat dissipating capacity. Since solid conductors have a fixed cross-sectional area, their current and heat dissipating capacity are therefore finite values. If applied currents exceed a solid conductor’s maximum current rating, temperature in the conductor will rise. Tubular conductors
can provide enhanced heat dissipation by means of continuous water cooling, therefore increasing the current-carrying capacity. As with other water cooled electrical feedthroughs, RF Power Feedthroughs must also be installed with properly grounded cooling systems. For example, a coolant flow rate of 4
gallons/hour was determined to be the minimum allowable rate in a test of the 35kW feedthrough.

When installing two 35kW/13.56MHz RF power feedthroughs side by side, their center-to-center spacing must be greater than 2.00 inches. RF Power Feedthrough users must allow adequate clearance between the feedthrough and any surrounding hardware in order to avoid RF coupling.

ISI offers RF Power Feedthroughs on three standard vacuum mount styles: Weldable; Conflat® compatible Del-Seal Flanges; and ISO NW compatible Kwik-Flanges.

INTENDED OPERATING CONDITIONS
Electrical ratings are determined by various factors, including dielectric strength, geometry and system operating pressure. Please note that all ISI catalog products are electrically rated for operation with one side in dry atmospheric conditions and the other side in a vacuum environment with a maximum system
pressure of 1 x 10-4 Torr. We advise that users make allowances for deviations from stated operating parameters and take adequate safety precautions when feedthroughs are operated at high voltages or high currents.