Plasma Physics Experiments Fundamental Physics and its Applications
Paschen’s law
Introduction
Paschen’s Law
Plasma is usually described as an ionized gas. In fact it is –
The set-up consists of two items: the Plasma Physics
like solids, liquids and gases – a state of aggregation.
Operating Unit (09108-99) and the Plasma Physics
There are many kinds of plasma in nature (well known
Experimental Set (09108-10).
examples are the sun and lightnings) and in technical
In the physical part, the students should verify Paschen’s
applications like plasma TVs or industrial surface treat-
law, i.e. the dependence of the breakdown voltage on the
ments. Nevertheless, students in physics or engineering
distance of the electrodes and the gas (air) pressure. Also
learn nearly nothing about this important topic.
the influence of different gases can be investigated.
So far, hands-on experiments have not been available because the equipment for treating plasmas in a research lab is very expensive and only available at few universities. The PHYWE set-up is designed to enable students to perform plasma experiments and learn about the basics and applications of plasma at an affordable price. The equipment is easy to handle and safe according to all relevant regulations. The set-up allows different kinds of experiments, which can be varied in many ways, e.g. the time, and level of difficulty can be adapted to the needs and ability of the students and
Paschen curve at 4 mbar, measured with the set-up
the supervisors.
PHYWE SYSTEME GmbH & Co. KG · Robert-Bosch-Breite 10 · D-37079 Goettingen · Phone +49/551 604-0 · Fax +49/551 604-107 · www.phywe.com
Plasma Physics Experiments Fundamental Physics and its Applications
Surface Treatment
Surface Treatment In the application part, the students treat surfaces of
By selecting different exposure times, the students
different kinds of materials with plasma and then observe
examine the influence of plasma on surfaces. Another
the effect on the moistening behaviour. Therefore, a
variable is the use of different materials: while for metals or
sample set (09108-30) is supplied. Coloured water is used
plastic the drop of the liquid disperses more with increasing
as liquid so that the wetting behaviour can be easily studied
exposure
by determination of the size of the moistened area. A large
hydrophobic.
time,
wood
for
example
becomes
more
variety of liquids can be applied.
Equipment List for Plasma Physics Experiments: Plasma Physics Operating Unit
Moistened area of a treated (left) and untreated (right) sample (transparent plastic foil)
For advanced studies of the contact angle a webcam or a digital camera is recommended.
09108-99
Plasma Physics Experiment Set
09108-10
Plasma Physics Sample Set
09108-30
Digital Multimeter
07122-00
Safety connecting cable, 50 cm, red
07336-01 (2x)
Safety connecting cable, 50 cm, blue
07336-04 (2x)
Connecting cable, 50 cm, green-yellow
07361-15
Additionally needed: Vacuum pump, Vacuum tube, Pipette (5 µl), Coloured Contact angle of a treated (left) and untreated (right) sample (increased hydrophilicity)
water
PHYWE SYSTEME GmbH & Co. KG · Robert-Bosch-Breite 10 · D-37079 Goettingen · Phone +49/551 604-0 · Fax +49/551 604-107 · www.phywe.com
NEW equipment enables a Practical Course on Plasma Physics
Phywe Systeme GmbH & Co. KG Goettingen, Germany
Plasma in nature
99 % of visible matter in the Universe is in the plasma state!
Plasma in nature - omnipresent The Sun and all the stars consist of plasma. Even the space between the stars is filled with a plasma, although a very sparse one (interstellar medium)
Plasma in nature – “extreme” physics Lightning consists of plasma. Discharges 30,000 A up to 100 million V Plasma temperatures in lightning can approach 28,000 K Electron densities may exceed 1024/m3
Plasma in nature – fascinating
•
Auroras
•
“Northern lights”, “Southern lights”
•
Example for the typical property of radiation emission
Plasma technology – everybody knows
•
Fluorescent lamps
•
Neon signs
•
Plasma display
•
Plasma TV
Plasma technology –applications •
Arc welding
•
Varnishing
•
Surface treatment
•
Plasma used to etch dielectric layers in the production of integrated circuits
•
Analysis technology
•
…
Plasma technology – the future •
Fusion power reactor
•
ITER (International Thermonuclear Experimental Reactor)
Plasma definition Plasma = collection of charged particles •
Quasineutral ¾
•
The plasma approximation ¾
•
Each particle influences many nearby charged particles
Bulk interactions ¾
•
Charge density is very small compared with electron density
Debye length is short compared to the physical size of the plasma
Plasma frequency ¾
Time between particle collisions is big against the period of the plasma oscillation
Plasma parameters Characteristic Size Lifetime Density Temperature Magnetic fields
Lower limit
Upper limit
Plasma parameters Characteristic
Lower limit
Upper limit
1025 m (intergalactic m (lab plasmas) nebula)
Size
10−6
Lifetime
10−12 s (laserproduced plasma)
Density
1032 m-3 (inertial 10 m (i.e., 1) confinement plasma) (intergalactic medium)
Temperature
102
Magnetic fields
10−12 T (intergalactic medium)
1017 s (intergalactic plasma) 0
K (aurora)
-3
108 K (magnetic fusion plasma) 1011 T (near neutron stars)
Plasma physics experiment •
Students produce an effective and controllable but safe plasma
•
Part 1: Learn some basics about plasma (Paschen’s law)
•
Part 2: Learn something about technical applications of plasma - Surface treatment - Cleaning effects
•
Level of the experiment can be varied: simple observation → high-level, PC-based evaluation
Plasma physics experiment set up
Operating unit
Test stand
Plasma physics operating unit
Pulse mode for application
Continues mode for basic experiment
Plasma physics stand
Basic experiment (Paschen’s law)
Application (Surface treatment)
Basic experiment: Paschen’s law Paschen’s law: breakdown voltage U is a non-linear function of the product of the gas pressure p and the gap distance s: U = f (ps)
Basic experiment: Paschen’s law
Variation of: •
Voltage
•
Distance
•
Pressure
Basic experiment: Paschen’s law
Variation of: •
Voltage
•
Distance
•
Pressure
Application: Surface treatment •
Expose a sample to plasma at a fixed distance
•
Observe the moistening behaviour of a liquid (water, oil, …)
?
•
Vary the time of exposure
•
Vary the type of sample (different plastics, glass, wood)
•
Control the time of the experiment by variation
Application: Surface treatment
Examination of the moistening behaviour: Counting squares
Contact angle of a treated (left) and untreated (right)
Application: Surface treatment Examination of the moistening behaviour: Measurement of the contact angle
Contact angle of a treated (left) and untreated (right) Moistening depends on the time of exposure Buy selecting the method (like square counting) you can vary the difficulty level of the experiment!
Conclusions
•
Even plasma is very important topic it is treated only less during teaching and nearly not in a practical manner
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Comparable cheap set up enables demonstration and student experiments
•
Compact design for easy and safe use
•
Both basic theory and applications
•
Paschen’s curve (varying distance, voltage and pressure)
•
Time and difficulty of the experiment can be easily varied