Updates On THE Optical Emission Spectroscopy AND Thomson Scattering Investigations on the Helicon Plasma Experiment (HPX)*

Presented By:1/c Omar Duke-Tinson2/c Jackson Karama

*Supported by U.S. DEPS Grant [HEL-JTO] PRWJFY13

ABSTRACT 

Now that reproducible plasmas have been created on HPX at the Coast Guard Academy Plasma Laboratory (CGAPL) we have set up spectral probes to help verify plasma mode transitions to the W-mode. These optical probes utilize movable filters, and ccd cameras to gather data at selected spectral frequency bands. Raw data collected will be used to measure the plasma's relative density, temperature, and the plasma’s structure and behavior during experiments. Direct measurements of plasma properties can be determined with modeling and by comparison with the state transition tables, both using Optical Emission Spectroscopy (OES). The spectral probes will take advantage of HPX’s magnetic field structure to define and measure the plasma’s radiation temp as a function of time and space. The spectral probe will add to HPX’s data collection capabilities and be used in conjunction with the particle probes, and Thomson Scattering (TS) device to create a robust picture of the internal and external plasma parameters. TS internal temperature and density data will track HPX plasma transitions through the capacitive and inductive modes as it develops into helicon plasma. Once achieved, the system will be invaluable in making quantitative plasma observations in conjunction with the Optical Emission Spectroscopy (OES) System. Recently CGAPL, has focused on building its laser beam transport and scattered light collection optical systems. The high energy laser (HEL) will be configured to directly enter the side port of the chamber, with collection optics mounted on the top port. HPX has acquired and will employ an Andor ICCD spectrometer in a setup similar to HBTEP at Columbia University, for the spectral analysis of the scattered light. Data collected by the TS system will then be logged in real time by CGAPL's Data Acquisition (DAQ) system with remote access to under LabView. Further additions and progress of the OES probe, TS alignment, installation, and calibration on HPX will be reported.

*Supported by U.S. DEPS Grant [HEL-JTO] PRWJFY13

Complete TS Detection System: Radiation Collection

http://www.aa.washington.edu/research/ZaP/images/Thomson_Schematic.png

Example Thomson Scattering System in Plasma

• Refracted light is absorbed though a set of fiber optic wires per spatial point ~ 4X Magnification

• Spectrometer separates the wavelengths of scattered light

Collection Optics Allow Light to be Transferred to Spectrometer

• Photomultiplier reduces gain loss and transforms photons

• Fiber Lenses Diverge Volume

Incoherent Scattering Requires Probe Collection

• Electric Field is used to determine Energy of Scattered Light

• Probes Detect Energy Levels via Wavelengths from a distant point

• Scattered Light is coherent [directional] when collected by spectrometer

• Accuracy is Increasedhttp://www.kosi.com/Holographic_Gratings/vph_ht_overview.php

Volume Phase Holographic (VPH) Grating Produces

Coherent Signal• Transforms Incoherent Scattering light to

Coherent Form

• Deflects Unwanted wavelengths and transmits selected wavelengths at desired angles

• Up to 6000 lines/mm

• Compact Setup to Spec.

• Ultrafast Laser – signal amplification

Dichromated Gelatin Coated on Glass http://www.kosi.com/Holographic_Gratings/vph_ht_overview.php

Recently Acquired Andor iStar DH334T Image Intensified Charge Coupled

(ICCD) Spectrometer

Specification Detail

1024 x 1024 Sensor Resolution

13 μm2 Pixel Size

Near Infra-Red Photocathode Type

114,800 Electrons / Pixel

380 – 1090 nm Wavelength Range

Calculating Interference from Noise

Quality Components are Delicate and Expensive!

Electron Energy Distribution Function

Particle in a box wave function. Determine the eigenvectors to correlate the wave function

Can only determine energy function at a moment in time.

Coherent vs. incoherent results of a relativistic particle

• Full Automated Spectrometer Control ~ remote resolution

• 2D & 3D Models• Data exported to LabView GUI• Input Equations

Solis Software Package Controls iStar in Real Time

Most Essential Equation:

New Laser

HPXRF Plasma Ignition

Next Steps?

Build Collection Optics

Configure / Demo Spectrometer

Assemble

Acquire New Laser

NEXT UP: Jackson Presents OES

Keeping updated on the latest development and research of all things plasma

Visit CGA PLASMA LAB Online!

http://cgaplasma.wordpress.com/

Optical Probes on HPX Verify TS & Particle Probe Data

•Helicon Plasma Ignited in Pyrex Tube•Optical Probes Installed •Spectrometers Record Emissions & Send to DAQ

OES - Currently Main Data Collection SourceMeasures Relative Plasma Density & Temperature

•Recorded wave length corresponds to specific energy transitions - ID density and temp

Optics Used to Explore Neutrals– Filters change collected wavelength – Fiber optic cable collects & transmits signals to spectrometer

• CCS Spectrometer

Courtesy of Thor Labs

• Visible – Wide range, low resi. range: 200 – 1000 nmii. resolution: < 2nm FWHM @633 nm

• NIR– Smaller range, Higher resolutioni. range: 500 – 1000 nmii. resolution: < .6 nm FWHM @633 nm

Long Term Experimental Goals for OES

1. Measure Plasma Density & Temp to Compare with Thompson scatteringA) Apply Ar Kinetic Code to HPX

i. particle properties from energy transitionsB) Compare Transitions to Get intensity Ratios

i. Calculate transition probabilities to determine measured ne & Te values

Long Term Experimental Goals for OES

1. Measure Plasma Density & Temp to Compare with Thompson scatteringA) Apply Ar Kinetic Code to HPX

i. particle properties from energy transitionsB) Compare Transitions to Get intensity Ratios

i. Calculate transition probabilities to determine measured ne & Te values

2. Internal Mode Structure

A) Ar neutrals: create ‘map’ with 694.3 nm Interference filter

A) D-alpha: same internal mode investigation, just with D2

Mode structure data from D emissions on HBT-EP -Courtesy of Columbia University

Cadet Summers