Hananiel Setiawan
The BLAST-TNG Project
Repurposing the SPARO Cryostat for HWPr Cold Testing
Hananiel Setiawan, Prof. Giles Novak (adviser), Peter Ashton
Star Formation
  • Stars form in molecular clouds when gas and dust collapse due to gravity.


    • Star Formation Process

  • Theoretical predictions based only on pure gravitational collapse and gas pressure over-estimate the star formation rate by a factor of 100. [1]
  • Why? Interstellar Turbulence and Interstellar Magnetic Fields may have affected the process.
  • The role of magnetic fields in the star formation process is still poorly understood.


    • Molecular Clouds

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BLAST Collaboration and BLAST-TNG


    BLAST logo BLASTPol

  • BLAST (Balloon-borne Large Aperture Submillimeter Telescope) is an international collaboration studying the roles of magnetic fields in star formation processes by observing polarized light from molecular clouds.
  • The group has successfully launched two telescopes from Antarctica: BLAST (2005, 2006) and BLASTPol (2010, 2012).
  • BLAST-TNG (“The Next Generation”) is currently in-development and testing in preparation for a 2016 launch.
  • The telescope will capture light with submillimeter wavelengths (250, 350, and 500 µm).


    • Electromagnetic Spectrum

  • The telescope has polarization capability, using a rotating Half Wave Plate (HWP) and polarization-sensitive detectors.


    • BLAST TNG and its Optics Box

  • The light we are seeking to observe is blocked by Earth’s atmospheric water vapor. The telescope’s float altitude is above 99.5% of the Earth’s atmosphere.


    • Atmosphere Spectrum

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Polarimetry Method and HWPr
  • Polarization states of the incoming light waves will be measured. The detectors at the end of the path have 4 different configurations: horizontal, vertical, and the two 45 degrees diagonals. HWP will be rotated in four 22.50 steps using a HWP rotator (HWPr), which was designed and manufactured at Northwestern University.
  • The differences in signal power in different detectors will determine the polarization angle. Data from different HWPr angles will be compared to minimize systematic errors.


    • HWP and Polarization explained

  • To reduce noise in data, HWPr will operate at 4 K to avoid thermal radiation.
  • Thus, we need to cold test HWPr and make sure that thermal contraction due to the low temperature will not affect the system.


    • Polarization Map

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Cold Testing Preparation
    HWPr

    SPARO and Cryogenics

  • The SPARO (Submillimeter Polarimeter for Antarctic Remote Observations) cryostat was repurposed to be the new HWPr test cryostat. SPARO was operated at South Pole station during 1998-2003. The cryostat was designed to cool to 4 K temperature. We will use Liquid Nitrogen (to 77 K) and Liquid Helium (to 4 K) as our cryogens.


    • SPARO modifications, before and after

    Electronics and Software

  • To make sure that the inside of the cryogenic chamber reaches the desired temperature of 4 K, we calibrated a Silicon-diode thermometer and programmed an EDAS-CE (Ethernet Data Acquisition System) computer system to track the temperature inside over time. The EDAS-CE reads analog voltage signal, digitizes it, calculates the temperature associated with the voltage, and allows user to access the data remotely.


    • Electronics

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The Next Step
  • Once all the parts of HWPr are manufactured, we will assemble and perform the cold-testing.
  • The HWP from Cardiff University (UK) will be installed in HWPr at UPenn.
  • Finally, the HWP and HWPr will be assembled inside the optics box of BLAST-TNG for the 2016 launch.
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Acknowledgements
  • NASA Grant No. NNX13AE50G S04, NNX09AB98G
  • NSF Grant No. AST-1359462
  • Northwestern University, NU Infrared Group & the Instrument Shop


    • NASA NSF Northwestern University CIERA at NU



    This material is based upon work supported by the National Science Foundation (NSF) under grant AST-1359462, a Research Experiences for Undergraduates grant awarded to CIERA at Northwestern University. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF, NASA, or the Northwestern University



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