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Cryocooled Sapphire Oscillator Frequency Standards for the shortest VLBI Wavelengths

Cryocooled Sapphire Oscillator Frequency Standards for the shortest VLBI Wavelengths. (or improving sensitivity by reducing coherence losses). Maria Rioja, Richard Dodson Yoshiharu Asaki John Hartnett Steven Tingay. Contents. Why need to improve frequency standard?

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Cryocooled Sapphire Oscillator Frequency Standards for the shortest VLBI Wavelengths

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  1. Cryocooled Sapphire Oscillator Frequency Standards for the shortest VLBI Wavelengths (or improving sensitivity by reducing coherence losses) Maria Rioja, Richard Dodson Yoshiharu Asaki John Hartnett Steven Tingay

  2. Contents Why need to improve frequency standard? Description of Simulation Studies Comparative Performance: Coherence losses for H-maser and CSO 4. Other Strategies to improve sensitivity: 4.1 WVR (co-located independent technique), 4.2 Frequency Phase Transfer (FPT) (simultaneous dual frequency observations)

  3. Why? The Quest for Sensitivity… H-maser Good Weather Very Good=ALMA-type weather More Stable VW=WVR@ALMA Cryocooled Sapphire Oscilator Trop phase fluctuations  site with stable weather conditions H-maser instabilities  ultra stable Cryogenic Sapphire Oscilator (CSO)Clock

  4. Ultra-stable Cryocooled Sapphire Oscillator (CSO) Hartnett & Nand, 2010 Hartnett et al. 2012

  5. Simulations: Parameter Space (Asaki+2007) CLOCK only TRP only CLOCK & TRP

  6. Synthetic Datasets generated with ARIS Visibility Phases (86 GHz, Good Weather,) (Worse weather)

  7. Simulations: Data Analysis (x 11) MAP (x 11) Solint: 0.1, 0.2,… 6 minutes MAP Simulated Dataset MAP

  8. Flux loss 4% Flux loss 20% MAPS Figure of Merit Uncompensated residual phase fluctuations leads to Flux loss. Use Flux loss as a measure of coherence loss for comparative studies.

  9. RESULTS:CLOCK noise only, all freq. H-maser CSO

  10. RESULTS:CLOCK noise only, all freq. 0% CSO 0% 0.5% 10% 86 GHz 175 GHz H-maser 350 GHz 40%

  11. RESULTS:CLOCK noise only, all freq. RESULTS: ATM noise only, all weathers, all freq. G V VW ASD_V=3*ASD_VW ASD_G = 2*ASD_V ASD_T = 2*ASD_G ASD_P = 2*ASD_T

  12. RESULTS: ATM noise only, all weathers, all freq. RESULTS: ATM noise only, all weathers, all freq. VW V 20% G T P 80% 86 GHz

  13. RESULTS: ATM noise only, all weathers, all freq. RESULTS: ATM noise only, all weathers, all freq. VW V 20% G T P 80% 86 GHz 175 GHz 20% 50% 80%

  14. RESULTS: ATM noise only, all weathers, all freq. RESULTS: ATM noise only, all weathers, all freq. VW V 20% G T P 80% 86 GHz 350 GHz 20% 175 GHz 20% 80% 80%

  15. SUPERIMPOSED H-Maser vs. ATM noise, all weathers, all freq(zoomed). VW H-maser Significance of H-maser noise Expected to increase at highest frequency (350 GHz) and with best quality weather conditions (V,VW); the CSO noise remains negligible in all Circumstances. V G 86 GHz T 10% P 350 GHz 10% H-maser 10% H-maser 175 GHz

  16. RESULTS: CLOCK (H-maser/CSO-100MHz) + ATM (Very Good), all freq. 20% + CSO x H-maser 86 GHz 175 GHz CSO Significant Benefit (i.e. increased sensitivity) @ 350 GHz with V quality weather conditions. Comparative Performance 20% change 6% change 2% change 350 GHz

  17. INTERPRETATION of RESULTS: SENSITIVITY @ 350 GHz, V weather 20% increase sensitivity with CSO wrt H-maser + H-maser + CSO Thermal only

  18. RESULTS: CLOCK (H-maser/CSO-100MHz) + ATM (VW), all freq. + CSO x H-maser 20% 86 GHz CSO Very Significant Benefit (i.e. increased sensitivity) @ 350 GHz with VW quality weather conditions. 175 GHz 40% change 10% change 2% change 350 GHz

  19. RESULTS: CLOCK (H-maser/CSO-100MHz) + ATM (G), all freq. 20% + CSO x H-maser 86 GHz 175 GHz CSO moderate benefit (i.e. increased sensitivity) @ 350 GHz with G quality weather conditions. Comparative Performance 8% change 3% change 1% change 350 GHz

  20. Other Strategy(1): WVR to “upgrade” weather quality IMPROVEMENTS WRT H-maser, G weather, @350 GHz (G trop. loss) +CSO+WVR, 70% (V tropospheric loss) H-maser+WVR, 50% (V tropospheric loss, H-maser loss) +CSO, 8% (G tropospheric loss)

  21. Other Strategy(2): Multi Frequency Observations + FPT analysis FPT & Hybrid Analysis, Very Good Weather Hybrid analysis: FPT @low freq (0.5’) + SC@high freq (3’, 6’). FTP: Use Low Freq. Analysis to Guide High Frequency (“disciplined phases”). 0-5% 86, 350 GHz 175, (175x2) 350GHz FPT & Hybrid Analysis, Good Weather 86 GHz (87x2) 175GHz 175 GHz 350 GHz 20% (43x2) 86GHz Extended (hours!) coherence Time at all frequencies also with G Quality weather conditions.

  22. Summary • The stability of typical H-masers introduce significant coherence losses • at submmwavelengths. • Most noticeable in very best weather conditions. • A CSO based frequency standard for submm VLBI benefits from superior stability which results in Increased coherence time. • Our estimates are 20% increase in sensitivity at 350GHz with “Very Good” (i.e. ALMA-type) weather conditions; along with WVR, 40% increase is possible. • WVRhave the potential to upgrade `Good’ sites into `VeryGood’ sites, ideal for submmobservations (maximum benefits along with CSO). • Including Freq. Phase Transfer has great potential to increase coherence time (i.e. sensitivity) at submmwavelengths • - requires dual frequency observations. Master Title

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