Transcript Document

Plasma Window Performance
Leslie Bromberg
Katie Maurer
Ady Herskovitch*
MIT Plasma Science and Fusion Center
ARIES meeting
Madison, WI
April 23, 2002
*Brookhaven National Laboratory, NY
HIBD-Chamber Vacuum Interface
• Heavy Ion Beam Driver requires high vacuum for operation
• 10-6-10-9 Torr
• Chamber operation requires low to intermediate vacuum
• 10-3 - 10 Torr
• Because of the large openings required for beam propagation, large gas
throughput across the HIB final focus and the chamber exits
• Large vacuum pumping speeds required
• Not clear whether it is possible to maintain that large pressure differential
with the available space for pumps.
• Can Flinabe pump Xe?
Plasma Window
• Experiments at MIT for
supporting work on a
compact neutron source
(Dr. R. Lanza, Dr. A.
Herskovitch)
• Funded in the past
through LLNL
Schematic of
plasma window
operation
Argon viscosity at 1 bar
Throughput calculations
• In the viscous regime (usually p > 100 mTorr), the
throughput through a channel is
 a4
Q
P P2  P1 
8h l
Here, Q is the throughput, h is the gas viscosity, a is the diameter, and
P’s are the pressure
• Increased viscosity and decreased number density results
in decreased flow through the opening.
• If the channel is filled with a thermal plasma, both the viscosity
increases and the number density decreases, decreasing the particle
throughput.
Plasma window
picture as of 1/8/2002
Preliminary results in Argon
diameter of orifice: 6 mm
Plasma windows for applications to HID
•
Demonstrated technology for intermediate pressure (in the viscous regime)
•
•
•
Preliminary experiments with Ar at atmospheric and higher pressures
Minimum pressure at low pressure side is ~ 30 mTorr (down from 100 mTorr)
Not clear how low it can reach with different gases, different size openings and
lowered pressure at high pressure side of window
• Need scaling experiments
•
Additional experiments at lower pressures and with other gases to come in the
summer
•
Power consumption, per window, is probably (?) on the order of 50-200 W for
1 Torr operation with Xe
•
Requires dielectrics (?)
•
Already a conducting media