From: roxo@cfn.ist.utl.pt (Roxo)
Newsgroups: sci.physics.plasma
Subject: Re: H alpha line profile
Date: Fri, 06 Feb 98 14:17:05 GMT
Organization: centro de fusao nuclear-ist
Message-ID: <6bf611$208_002@w.cfn.ist.utl.pt>
References: <34D86CEC.1F64@sci.muni.cz> <34D9D01B.322@nrc.ca>


In article <34D9D01B.322@nrc.ca>, louis.st-onge@nrc.ca wrote:
>
>Antonin Brablec wrote:
>>
>> Dear colleagues,
>> we investigate a special type of corona discharge burning in liquid
>> water
>> and we try to estimate electron density and temperature from line shape
>> of
>> H alpha. We try to use the standard Griem's tables (impact broadening by
>> electrons and static broadening by ions) for fitting with the measured
>> line
>> profile in order to verify that such procedure can be also used in this
>> case.
>> However, the measured profile of H alpha is a little bit asymmetrical
>> and
>> so the fitting is not good (especially on wings). It could indicate that
>> other additional broadening effects can play important role.
>> So, we are interested in other broadenings like are resonant, van der
>> Waals,
>> etc. and in effect which can produce asymmetrical line shape. Do you
>> have
>> experience with the matter? We also looking for analytical formula of
>> the mentioned broadenings (or tabulated values or programs).
>> Can somebody advice us?
>
>Dear colleague,
>
>The H alpha line is intrinsically asymmetrical. This is due to the fine
>structure of the levels involved in the transition, not to a broadening
>mechanism. In fact, H alpha is composed of seven separate transitions,
>given below in L-S coupling notation, with the wavelength positions
>(relative to the most intense transition), and the relative intensities:
>
>Transition Wavelength shift (nm) Normalized intensity
>
>3d 2D3/2 --- 2p 2P1/2 -0.01418 0.556
>3d 2D3/2 --- 2p 2P3/2 0.00155 0.111
>3d 2D5/2 --- 2p 2P3/2 0.0 1.0
>3p 2P1/2 --- 2s 2S1/2 -0.00802 0.116
>3p 2P3/2 --- 2s 2S1/2 -0.01267 0.231
>3s 2S1/2 --- 2p 2P1/2 -0.00996 0.0109
>3s 2S1/2 --- 2p 2P3/2 0.00577 0.0217
>
>In the past, I did some work on microwave hydrogen discharges (in the
>1-10 torr range) and determined the gas temperature by measuring the
>Doppler broadening of H alpha (using a Fabry-Perot interferometer). I
>had to take into account the fine structure of the line because
>otherwise I would have overestimated the temperature. Indeed, not only
>does the fine structure cause an asymmetry of the line but also a
>broadening (because of the wavelenght shifts between the different
>components). For example, for a temperature of about 630 K, each
>component of the line has a width of 0.275 cm-1, but the resulting line
>(obtained by adding up the seven components) has a width of 0.55 cm-1.
>In this case, the overestimation would be by a factor of two. Of course,
>the larger the broadening of each component, the smaller is the
>influence of the fine structure on the measured width.
>
>I don't know about broadening mechanisms in corona discharges. You will
>have to determine how important is the influence of the fine structure
>of H alpha in your case.
>
>Finally, a reference I found useful at the time was:
>
>K Matsunaga, K Kadota, M Fujiwara, and J Fujita, Jpn. J. Appl. Phys. 20
>(1981) L615.
>
>Hope this helps,
>
>Louis St-Onge, Ph.D.
>Process Instrumentation
>Industrial Materials Institute
>National Research Council Canada
>75 de Mortagne Blvd.
>Boucherville, Québec J4B 6Y4, Canada
>
>E-mail: louis.st-onge@nrc.ca
>

Hello!
I'm working with Halpha diagnostic for a plasma

this 'tutorial' was very nice and convinient!

Thanks!

Help me a lot!
M.Peres Alonso peres@cfn.ist.utl.pt

Many

---------------
http://www.cfn.ist.utl.pt/~peres