In-line, quarter-wave thermal short cools the center conductor of the signal-input coaxial transmission line to a cryogenically cooled traveling wave maser. It reduces both the thermal noise contribution of the coaxial line and the heat leak through the center conductor to the maser at 4.4 degrees K

Clauss, R. C.

English

NASA Technical Reports Server

I	 80°K L_ 
Center 
Conductor	 A'A 
Outer Conductor 
SIGNAL INPUT COAXIAL LINE ASSEMBLY
To Maser (440 K) 
Copper Rod 
IN-LINE QUARTER-WAVE THERMAL SHORT 
- /	 290°K 
Vacuum 
Seal with 0-Ring
AA 
Copper Shorting Rod 
March 1968	 Brief 68-10059 
NASA TECH BRIEF	
-I& 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Thermal Short Improves Sensitivity of Cryogenically Cooled Maser 
First Stage of CCR 
Coax to Waveguide Flange Mounts to CCR 
Flange	 Vacuum Jacket
	
jFiner Stock Provides	 Finger Stock 
Heat Transfer Through 	 Contact for Heat Transfer 
Center Conductor 
An in-line, quarter-wave thermal short has been de-
signed to cool the center conductor of the signal-input 
coaxial transmission line to a cryogenically cooled 
traveling wave maser. This device has two important 
advantages in that it reduces both the thermal noise 
contribution of the coaxial line and the heat leak 
through the center conductor to the maser at 4.40K. 
The ambient insertion loss of the short is 0.011 dB. 
When cooled to 80° K, the device contributes less than 
0.1° K to the maser noise temperature. 
The first figure shows the thermal short installed in 
the transmission line and the manner in which heat is 
transferred through the center conductor. into the 
closed-cycle refrigerator (CCR). Refrigeration at the 
first stage is sufficient to cool the center conductor 
from ambient temperature (290° K) to 80°K along a 
4-inch length. The thermal short (second figure) which 
is inserted into the transmission line, is of such config-
uration that the heat from the inner conductor is 
conductively transferred (at the rate of 400 mw) 
through copper shorting rods to a finger stock contact 
to the outer conductor. The addition of the thermal 
short does not change the electrical characteristics of
the line,having little effect on the VSWR over a 25°,<, 
bandwidth. 
Notes: 
I. The entire center conductor can be removed (to 
replace the vacuum seal) in the field without dis-
assembly of the refrigerator. 
2. Additional technical details are contained in JPL 
Space Programs Summary No. 37-40, Vol. Ill, 
pages 90-93. Inquiries may also be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B68-10059 
Patent status: 
This invention is owned by NASA, and a patent ap-

plication has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should be

made to NASA, Code GP, Washington, D.C. 20546. 
Source: Robert C. Clauss

Jet Propulsion Laboratory
(N P0-09975)
Category 01 
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.
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Thermal short improves sensitivity of cryogenically cooled maser

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