I am using ECR plasma CVD (875 Gauss of magnetic field which generates electron resonance at 2.45 GHz microwave frequency with maximum power 1.2 KW ) for my synthesis. The system is showing MW output power 50 (for example) and reflected output power around 9 . I checked with manual and I couldn't find anything. Can someone help me to calculate the net power of microwave?
that is a difficult question. you need to have a talk with your power supply maker, he should know how his displays were calibrated. if you have spare money, i would recommand to have some good power meter (with the right waveguide coupler: S-Team in slovakia are doing a good job).
magnetron are rate by their anode current, also here there should be a documentation from the maker which calibrates the magnetron ouput power with the anode current (probably a panasonic device, you can find them online)
measuring the anode current by yourself is a dangerous task (high-voltages are around, 2-3-4 kV)
plasma likes the microwave very much, normally all the energy is absorbed by the plasma (well I am not so familiar of the ECR case). Reflection should be tunable to zero..
do your control instrument show your power in percentage of maximum power?
the Xantrex is a DC power supply? what does it control? the magnet?
what is giving the microwave power?
i do not get clever out of those two sheets?
the ECR RR250 is from Roth&Rau? then the microwave is from Muegge.. (must be some MX power supply.. probably 50% of max forward power. 5%reflection..
maximum depending on the MX device, probably 1200W) (so 50 would be 600W, and 5 reflection 60W which is big but not too big, as long as you have an isolator)
if so, this fits to your sheet2
600W is 50%, the reflection is given is % .. so your 9% are not optimal.(need some tuning at the stubs..)
the xantrex should be set to give the right current to your magnet.. some 4-6 Amps.
50%-9% of the total 1200W available goes into the plasma, around 400W
Thanks a lot for your time and information.
Now my question is, what is the net power? Do I have to consider the reflected power in the calculation of net power? That means, shall I tell the net power is 600 W or (600-108)W = 492W (if reflection power 9%)? ,
The reflection power is dependent on gas/gas composition.
Forward - reflection is your power into the plasma.
Yes the reflection may vary with gas and presure, magnetic field, since the plasma impedance is varied (its density). Then you need to tune with the help of the 3-stub tuner to minimise the reflection for a given condition..
This may drift a little..
Grateful to you for useful discussion. Everything is fine. Yes I know about tuning for adjustment of minimum reflected power.
MW power means output power or (output power-reflected power). But kindly tell me in straight forward way, which one is correct?
tuning with the stubs, and may be tuning with the magnetic field strength?
the power into the plasma is forward power (50) minus reflected power (9),
so you have 41% of total 1200W in your plasma.
good luck
Hello Lukas,
I want one more clarification.
Suppose we consider two cases. viz.
1. MW forward power is 50 % and reflected power is 10 %
2. Forward power 42 % and reflected power is 2%
in both the cases the net MW power is 40%.
will there be any difference for both cases in plasma dynamics in terms of ion energy, ion density, plasma potential, etc?
it is starting to get difficult. I am not so familiar with ECR plasmas.
Without ECR , it is so that the plasma absorbs all it can take and the left-over is reflected. The high-plasma density (provided the pressure is high enough) is such that the cut-off density is reached and the plasma just reflects the E-fields (like a conductor, only evanescent waves enter the plasma/material).
With ECR there is a magnetic field which allows the E-fields to penetrate the plasma.
So this self-limiting is not given.
Next question is how do the field strenght influence the plasma, since waves coming from the 50% forward power are stronger than those coming from the 42% forward power. At higher pressure (without ECR) I can not imagine it as any effect. Since the electron collision frequency is... oh..oh.. sorry.. i will need to read the books alsö..
i never asked myself this question.
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