----- Original Message -----

From: Jin-Seok Ko

To: jko6@wisc.edu

Sent: Wednesday, August 26, 2009 1:35 PM

Subject: Fwd: Spectroscopic measurements of near-MSE spectra during plasmas

----- Forwarded message from sscott@psfc.mit.edu -----
    Date: Wed, 26 Aug 2009 13:18:47 -0400
    From: Steve Scott <sscott@psfc.mit.edu>
Reply-To: Steve Scott <sscott@psfc.mit.edu>
 Subject: Spectroscopic measurements of near-MSE spectra during plasmas
      To: 'Jinseok Ko' <jinseok@MIT.EDU>

Hi Jinseok,



While we're awaiting the resurrection of the DNB, it seems prudent to
consider MSE upgrades to deal with our other major problem:
partially-polarized background light whose magnitude and/or polarization
direction change on a time scale short compared to the usual DNB on/off
cycles.



The really important question for this issue is whether line radiation
(either from impurity charge exchange or molecular D2 emission from the
edge) versus a broad-band noise source (such as a glowing metal structure
inside the torus that emits black-body radiation) is the dominant source of
our background noise.  I fear that both may play a role, depending on
conditions.



* You no doubt remember that there is an immediate drop in the
polarized background light as seen by MSE at an L-H transition, which we
originally attributed to Halpha light that somehow got past our narrow-band
bandpass filters.  This decrease in background light follows exactly the
time history of the decrease in Halpha light, i.e. when the Halpha drops 35%
in magnitude, so does our background signal.  But there was no change in
this behavior when you added additional sharp-edge filters that should have
reduced the Halpha that leaks through our filter assembly by an additional
factor of 100-1000.  So this seems to implicate a noise source that involves
neutrals, but it not Halpha.  So impurity charge exchange is a candidate.



* We also see background light well after a disruption that decreases
on a time scale of 50-100 ms, and also background light that correlates with
glowing structures on the LH launcher.  This seems to suggest that glowing
structures could be a problem also.



To assess the possible contribution of line radiation, it would be great to
have good spectra measurements over the range 658-664 nm, with say a
wavelength resolution of 0.1 - 0.2 nm, and hopefully good time resolution -
100 ms would be OK,  10 ms would be great.



My recollection is that in your thesis you have a considerable amount of
spectra measured during beam-into-gas, but I don't recall seeing anything
relating to beam-into-plasma.  Do you remember what spectral measurements
we've taken through the MSE optics during plasma operation?



Thanks - Steve



Steven D. Scott

Principal Research Physicist

Princeton Plasma Physics Laboratory

presently at:

Plasma Science and Fusion Center, MIT

617-253-8695

fax: 617-253-0627





----- End forwarded message -----

---

Hi Jinseok,

 

While we’re awaiting the resurrection of the DNB, it seems prudent to consider MSE upgrades to deal with our other major problem:  partially-polarized background light whose magnitude and/or polarization direction change on a time scale short compared to the usual DNB on/off cycles. 

 

The really important question for this issue is whether line radiation (either from impurity charge exchange or molecular D2 emission from the edge) versus a broad-band noise source (such as a glowing metal structure inside the torus that emits black-body radiation) is the dominant source of our background noise.  I fear that both may play a role, depending on conditions.  

 

• You no doubt remember that there is an immediate drop in the polarized background light as seen by MSE at an L–H transition, which we originally attributed to Halpha light that somehow got past our narrow-band bandpass filters.  This decrease in background light follows exactly the time history of the decrease in Halpha light, i.e. when the Halpha drops 35% in magnitude, so does our background signal.  But there was no change in this behavior when you added additional sharp-edge filters that should have reduced the Halpha that leaks through our filter assembly by an additional factor of 100-1000.  So this seems to implicate a noise source that involves neutrals, but it not Halpha.  So impurity charge exchange is a candidate.  

 

• We also see background light well after a disruption that decreases on a time scale of 50-100 ms, and also background light that correlates with glowing structures on the LH launcher.  This seems to suggest that glowing structures could be a problem also.

 

To assess the possible contribution of line radiation, it would be great to have good spectra measurements over the range 658-664 nm, with say a wavelength resolution of 0.1 – 0.2 nm, and hopefully good time resolution – 100 ms would be OK,  10 ms would be great.

 

My recollection is that in your thesis you have a considerable amount of spectra measured during beam-into-gas, but I don’t recall seeing anything relating to beam-into-plasma.  Do you remember what spectral measurements we’ve taken through the MSE optics during plasma operation?

 

Thanks - Steve

 

Steven D. Scott

Principal Research Physicist

Princeton Plasma Physics Laboratory

presently at:

Plasma Science and Fusion Center, MIT

617-253-8695

fax: 617-253-0627