System employs pulsed, constricted arc heater capable of multi-MW power, permitting quasi-stationary flow conditions during latter half of pulse of about 5 msec. System description is given

Dethlefsen, R.

Tinkham, J.

English

NASA Technical Reports Server

1972	 B72-10048 
NASA TECH BRIEF 
Ames Research Center
	
A A 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
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Pulsed High-Power Arc Heater with

Improved Cathode and Triggering Mechanism 
The problem: 
The simulation of hypervelocity reentry conditions 
for the performance of critical tests requires con-
stricted arc heaters of the order of 30-MW power 
level. Continuous operation of high-power constricted 
are heaters requires a large investment for the ac-
quisition and maintenance of power supplies and 
water-cooling systems for arc sections. For certain 
applications, however, in which test runs of milli-
second durations are permissible, low-cost lumped-
parameter-line pulse-power supplies may be substi-
tuted for continuously operated water-cooled power 
supplies. In either case, the arc is often initiated by 
an exploding thin wire, but this leads to contamina-
tion of the plasma stream and the inconvenience of
reloading the trigger wire. Moreover, single-attach-
ment cathodes can cause corrosive plasma jets in the 
vicinity of the cathode. 
The solution: 
A system employing a pulsed, constricted are 
heater capable of multi-MW power which permits 
quasi-stationary flow conditions during the latter half 
of a pulse of about 5 msec. Since the power output 
is not continuous, only a modest investment in stor-
age-capacitor power supplies is required, a cooling 
system is not necessary, and the tube containing the 
arc can be made of quartz so that photographic ob-
servations can be made. A cascading trigger circuit 
eliminates the problems connecting with exploding 
Lumped Parameter Pulse Line Power Supply 
L	 L	 L	 L 
Pulse duration, 5 msec. 
Nitrogen flow rate, 5 to 40 9/sec. 
R
	
R 
Gas 
Inlet
Cathode	 Trigger Segments 	 Quartz 
(continued overleaf) 
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C
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wires, and a multi-attachment electrode eliminates 
cathode jets of hot plasma. 
How it's done: 
The constricted arc heater consists of a long tube 
made of fused quartz through which a gas flows. The 
flow of gas (nitrogen, for example) is pulsed on for 
about 0.2 second by electrical actuation of a shutoff 
valve to fill a small plenum chamber, and then is 
metered from the plenum chamber into the arc con-
strictor through four sonic orifices. These orifices 
issue gas jets in a tangential direction; they can be 
aligned so that they all blow in the same direction, 
creating a strong vortex, or can be aligned to create 
a turbulent gas flow without swirl. 
The cathode consists of four parallel 0.3-cm dia-
meter thoriated (2%) tungsten rods pressed into an 
1.27-cm diameter copper slug. The rods are about 
2 cm long and are spaced about 1 mm apart. High-
speed films of the cathode attachment area have 
shown that the arc attaches to the tungsten rods 
simultaneously, which lowers the currents at each 
attachment area and results in a lower cathode ero-
sion rate. If a single cathode is used, Maecker 
cathode jets of hot plasma develop which cause 
destruction near the cathode. 
The arc is initiated by a cascading triggering cir-
cuit as shown in the diagram; the space between the 
first copper segment in the constrictor wall and the 
cathode is broken down electrically when the Igni-
tron switch closes. The arc current drawn by this 
segment is limited to about 40 amperes by a resistor. 
The axial gas stream sweeps hot are gases down the 
contrictor which leads to electric breakdown of the 
following segments in succession until the full arc 
current of some kA starts to flow when the hot gases 
reach the anode. 
A nearly rectangular arc current pulse is obtained 
from the discharge of a lumped parameter transmis-
sion line. Such a line consists of n capacitors, C, and 
inductors, L, connected as shown in the diagram. 
Arc current ranges from 1.8 to 3.6 kA with a flow rate 
of nitrogen from 5 to 40 g/sec. 
Notes: 
1. The cascading trigger circuit works very well ex-
cept at high gas flow rates and low charging 
voltage; it is adaptable to varied conditions. 
2. Other investigators have tried multiple cathodes 
which were balanced with ballast resistors; in the 
present configuration, no ballast resistors were re-
quired - perhaps due to the length and close 
spacing of the thoriated-tungsten rods. 
3. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: NASA CR-1246 (N69-17212), 
Experiments on a High Power, Pulsed, Con-
stricted Arc Heater 
4. No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B72-10048 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. Dethlefsen and J. Tinkham of
Convair Division/General Dynamics 
under contract to

Ames Research Center 
(ARC-10173)
. 
EA 
Category 03
S 


Pulsed high-power arc heater with improved cathode and triggering mechanism

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