Converging, coaxial accelerator electrode configuration operates in vacuum as plasma gun. Plasma forms by periodic injections of high pressure gas that is ionized by electrical discharges. Deflagration mode of discharge provides acceleration, and converging contours of plasma gun provide focusing

Cheng, D. Y.

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November 1971	 I3rici7l-10454 
S	 NASA TECH BRIEF 
Ames Research Center 
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Improved Plasma Accelerator 
The problem: 
A dense, high-energ y
 plasma is required for the 
study of nuclear fusion reactions. Most existing 
plasma accelerators use strong shocks produced h 
Solenoid Puff-
L10 it's done: 
The plasma gun (see fig.) consists of the follos ing 
components: a truncated conical shell (the anode): 
an axially concentric cylindrical or conical rod (the 
rull.	 IIIOWCIL'.fl 
magnetohydrodynaniic techniques to accelerate the 
particles, but the particles can only travel as fast 
as the shock speed (about 2 lO cm/see). In ad-
dition, such accelerators either cannot focus plasmas, 
or can only provide a modicLim of focusing as a 
result of the magnetic pinch effect. 
The solution: 
A converging, coaxial accelerator-electrode con-
fi g uration is operated in a vacuum as a plasma 
gull. The plasma is formed by periodic injections 
of high-pressure gas that is ionized by electrical 
discharges. Acceleration is provided by a deflagra-
tion mode of discharge. and focusing is pro ided by 
the coil\erging coillours of the pI:tsina gull.
cathode): an upstream insulator which provides a 
gas-tight seal and which electricall y insulates the 
anode from the cathode; and a fast-acting solenoid 
valve which injects a controlled amount (pull) of 
gas into a small pocket located at the upstream end 
(large end) of the gull. 
The gun is operated in a chamber evacuated to a 
pressure of lO torr. A charged capacitor bank is 
connected to the gun electrodes. When a gas puff 
is injected into the system, the electrical discharge 
is typically self-triggered, according to the Paschen 
curve for electrical breakdown Alternatively, the 
electrical discharge may be triggered by a switching 
s\ stem	 hich provides a suitable time dela y alter
the gas Pit h:H been inpeeted. flie resulting plasma 
tt'iitiuiucU	 ricO) 
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is accelerated as a deflagration wave. In this mode 
of operation, the plasma particles are accelerated 
in a high-pressure region and are expelled into a 
low-pressure region, where a negligible number of 
collisions occur to impede their progress. This per-
mits the plasma to travel faster then the shock-prop-
agation velocity. 
The pocket of gas at the upstream end of the gun 
supplies gas to the accelerating region for a relatively 
long period of time, and the ionization process 
continues until the bank of stored electrical energy 
is dischar ged. Since the direction of the acceleration 
force E 13 (where E is the electrostatic field vector 
and B
 is the induced magiletic field vector) can be 
controlled by the shape of the electrodes, focus or 
defocus of the plasma pulse is possible. In the il-
lustrated focusing configuration, the accelerated plas-
ma issues from the gun in a converging stream which 
has a focal point at some distance downstream. 
Notes: 
I. Different electrode configurations may be used. 
For example, the length and convergence angle 
ol either electrode or both electrodes may be 
varied.
2. The plasma gun typically provides hydrogen 
or deuterium plasma velocities on the order 
of 10cm/sec. 
3. The plasma gun can be used for rocket propul-
sion. It characteristically provides a specific im-
pulse of 1 0 sec at a thrust density of approxi-
mately 100 kN/ni2. 
4. Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP7I-10454 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code 200-11 A 
Ames Research Center 
Moffett Field, California 94035 
Source: D. Y. Cheng

Anies Research Center

(ARC- 10109)
S 
. 
BrieF 71-10454	 Category 03
	
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Improved plasma accelerator

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