Thallium and xenon filled thyratron was developed that operates at tube envelope temperatures up to 750 C. This tube performs at peak voltage ratings of 2000 V forward and reverse and at an average current rating of 15 A for up to 11,000 hours

Baum, E. A.

Jones, N. D.

English

NASA Technical Reports Server

Ceramic-To-Metal 
Butt-Type 
Anode Seal 
Graphite Anode 
and Grid 
Tungsten 
Heater 
Ceramic-To-Metal 
Butt-Type
Cathode Seal 
Matr 
Cathode Dis
ihite 
ie Shield 
Grid 
Connection 
Ceramic-To-Metal 
Butt-Type 
Grid Seals 
Alumina 
Envelope 
Cathode 
Connection 
May-1972	 B72-10134 
•	 NASA TECH BRIEF 
Lewis Research Center 	 A 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
High-Temperature, Long-Life Thyra tron 
The problem: 
Thyratrons require the use of materials which provide 
long life operation at high temperatures. 
The solution: 
A thallium and xenon filled thyratron was developed 
that operates at tube envelope temperatures up to 750°C. 
This tube performs at peak voltage ratings of 2000V 
forward and reverse and at an average current rating of 
ISA for up to 11,000 hours.
How it's done: 
Thallium was chosen as the basic working fluid be-
cause of its favorable equilibrium-vapor-pressure versus 
temperature characteristic, its comparatively low ioni-
zation potential, and its high work function. The xenon 
in the initial thallium-xenon mixture is present only dur-
ing the breaking-in period and early life of the tube 
(usually several hundred hours or less). Afterward, the 
xenon is lost through sputtering, and the tube operates 
or, thallium alone. A reservoir, as shown in the figure, 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the
	 - 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000134 2020-03-17T03:30:52+00:00Z
is a one-inch extension of the exhaust tubulation that 
contains approximately 80 milligrams of liquid thallium 
which is more than ample to supply the tube require-
ments during the life of the tube. Thallium vapor is pre-
sent effectively only when temperatures throughout the 
tube interior are above 600°C. The pressure of the 
thallium vapor within the tube is controlled by varying 
the temperature of this small reservoir by external 
means (not shown). 
The tube envelope is a high-purity (99.9 17o) alumina 
ceramic. The seal flanges are an alloy of iron, nickel, and 
cobalt. The ceramic-to-metal, butt-type seals are fabri-
cated by first preparing the ceramic by applying a 
tungsten-based metallizing coating to the abutting sur-
faces. The ceramics thus coated are then furnace brazed 
(at 1260°C) to the metal flanges using a palladium-
cobalt brazing alloy. 
Material sputtered from the anode structure by ion 
bombardment is usually the major factor leading to gas 
cleanup for inert gas filled tubes. The anode, grid, and 
shields are fabricated from graphite which has the 
lowest sputtering rate among the suitable materials. 
The matrix cathode consists of a porous tungsten 
sponge impregnated with barium-calcium aluminate. 
This structure has much better resistance to cathode 
sputtering than the conventional oxide cathode. The 
cathode proper consists of two discs (12 cm  each) 
area-brazed to a tantalum core which is heated indirectly. 
Test results show that thallium is successful as a 
working fluid in that arc drop was low, recovery time 
was low, and sputtering and'contamination of electrodes 
and insulators was not serious. 
Major advances achieved during development of this 
tube include: 
(1) Ceramic-to-metal seals capable of long life in 
the temperature range to 800°C.
(2) Inter-electrode design to minimize anode and 
grid emission at high operating temperatures. 
(3) Gas clean-up rates under high frequency con-
ditions and associated sputtering. 
(4) Cathode structures capable of high emission 
currents and long life. 
Notes: 
1. These new tubes can be used in power conditioning 
circuits where switching, rectifying, inverting, etc., 
functions are required in a high temperature environ-
ment. 
2. Underlying work in high temperature tubes is de-
scribed in Tech Brief 69-10376, "High Temperature, 
Gas-Filled Ceramic Rectifiers, Thyratrons, and Volt-
age-Reference Tubes." 
3. The following documentation is available from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: NASA CR- 1684 (N70-42577), 
4. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B72-10134 
Patent status: 
No patent action is contemplated by NASA. 
Source: E. A. Baum and N. D. Jones of

General Electric Corp.

under contract to
Lewis Research Center

(LEW. l 1327) 
Category 01


High-temperature, long-life thyratron

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