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Hg Microwave Ion Clock Technologies for Fundamental Physics in Space John Prestage JPL, Pasadena

Hg Microwave Ion Clock Technologies for Fundamental Physics in Space John Prestage JPL, Pasadena. In Lab: Sang Chung Thanh Le Robert Tjoelker Eric Burt Rob Thompson Nan Yu John Prestage. Flight Design: Armond Matevosian Saverio D’Agostino Eric Archer Larry Epp Paul MacNeal

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Hg Microwave Ion Clock Technologies for Fundamental Physics in Space John Prestage JPL, Pasadena

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  1. Hg Microwave Ion Clock Technologies for Fundamental Physics in SpaceJohn PrestageJPL, Pasadena In Lab: Sang Chung Thanh Le Robert Tjoelker Eric Burt Rob Thompson Nan Yu John Prestage Flight Design: Armond Matevosian Saverio D’Agostino Eric Archer Larry Epp Paul MacNeal Talso Chui John Prestage Lamp Exciter Electronics: William Riley

  2. Space Clock Outline 2-3 kg atomic clock,10-16 stability for under $10M Technology Overview Compact physics package layout Reliability for in-space operation Magnetic Design, Shielding Factors Mechanical design for launch vibration

  3. AAA Battery USO Flights Topex Grace Mars Global Surveyor Cassini New Horizons (Pluto)

  4. Graphic 1E-13 GPS Cs GLONASS Cs Galileo Rb (10-13/day drift) GPS Rb ( 10-13/day drift) GP-A H-Maser 1E-14 Galileo Passive H-Maser Aces H-Maser (ISS) 1E-15 JPL Ion Clock (Prototype) ESA NASA/SAO H-Masers 1E-16 0 10 20 30 40 50 60 70 80 Mass of Atomic Clock (kg) Space-Based Clocks (LEO, MEO)** GALILEO Atomic Clocks **Only Atomic Clock to leave Earth Orbit was a pair of Rb clocks on Cassini-Huygens Probe for Doppler Winds measurement in Atmosphere of Titan

  5. Hg microwave Ion clock Physics Overview No Lasers, No Cryogenics, No Microwave cavities No Light Shift ! No gas load, not a gas ‘flow-thru‘ architecture, no consumables 106-107199Hg+ trapped ions Clock Transition: 40,507,347,996.8 Hz No wall collisions, high Q line State selection via optical pumping from 202Hg+; 1-2 photons/s scattered Plasma UV light source is radiation tolerant, PMT’s have flown many times. Ion Shuttling from Quad to Multi-pole, “Reversible, lossless atomic beam” Ions are buffer-gas (Ne) cooled to ~300K Very low tempco - 0.1C temp change only pulls frequency by ~6x10-17

  6. Breadboard Liter Clock Results • Clock stability to 10-15 in 1 liter physics package • Sealed Tube operation with no active pumps (no power required) for more than 2 years, no degradation of signal size.

  7. ~4x10-13/ Cryogenic Cavity Ultra-high vacuum leads to ultra-high Q With cryogenic local oscillator, will deliver 3x10-14/

  8. ~4x10-13/ Ultra-high vacuum leads to ultra-high Q With quartz USO, will eliminate Dick effect degradation with modified trap architecture See: Local Oscillator Induced Degradation of Medium –Term Stability in Passive Atomic Frequency Standards, Dick, Prestage, Greenhall, Maleki

  9. Physics Package Design Summary • Mass of package shown ~1 kg • w/ Ti tube, 2 layers Mu-metal, Mg baseplate, 4 FS lens,.. • Trap layout same size as lab breadboard, • Optical system collection ~ 2x improved, • Additional outer shield + electronics will add 1-2 kg.

  10. Sealed Tube uses getters to maintain Vacuum (No Consumables) Titanium- Titanium Weld VUV Sapphire to Titanium Seal 450 C Rated Titanium-Titanium Welds Trap rods Alumina Ceramic Bake-Out de-gas rate is exponential Tantalum Tubes - Molybdenum Wires Electron Emitter ~ 1 mA @ 1-2 Watts heater

  11. Getter Pumping used in prototype demo (~3 years with no degradation of ion signal) Estimated Lifetime (from typical outgassing and measurable leak rates)  100 yrs/gram of getter material Getter Reservoir 50 grams >50 years Huygens/Cassini MS used Titanium, Molybdenum getter material

  12. Time (in hours) Tube Materials for 400 C Bakeout Improve vacuum 1000-fold Ultra-clean vacuum is essential for clock stability and tube lifetime. Ion lifetime limited by residual gases, eg., Hg+ + H2O  Hg + H2O+ Gettering action not diminished by presence of weak Hg vapor.

  13. …Optical Design…

  14. G10 Thermal Standoff Al Oven Shell Hg Lamp Lamp Holder (Indium Solder) UV Light Source – 202Hg Lamp • Designed, Fabricated Ovenized Hg Lamp exciter following GPS Rb technology.

  15. Sapphire bulb material for longer lifetime • UV Sterilization/ Water purification Industry uses high power Hg UV Lamps • (~185 nm Ozone production) • Bulb Lifetime Problem Identified: Hg reacts with glass SiO2 to form HgO • Light level falls, Hg leaves the vapor, shortens bulb life • Sapphire Material will extend bulb lifetime by 2-4 • Conclusion: Build bulbs from Sapphire

  16. ….Magnetic Design…. 3 layer shields, each 0.020” thick Mount Tube through 2 shields and coil

  17. Reference Magnetic Field (Quantization Axis for Microwave polarization) • Inherently Low magnetic field sensitivity (35x less than Rb) Transverse magnetic field allows Doppler-free probe of Clock and Zeeman transitions

  18. Shielding Factor and Frequency Shift 1 gauss external pulls frequency ~ 10-15 • Measure μ for real single layer shield • (μ de-rated from 80K to 20K) • Enter shields layout in Maxwell field simulator • Apply 1G (80A/m) field along each of 3 axes • Determine SF = Hext / Hin • Single layer Shield Factor ~

  19. 5x10-16 Shielding Factor and Frequency Shift More useful calculation is the clock frequency shift when external field (1 Gauss) is applied These directions are perpendicular to reference field • Can estimate frequency shift at any position inside shields • μ adjusted from 80K to 20K • BC-field= 50 mGauss • Apply 1G (80A/m) field along each of 3 axes • Determine frequency shift vs position (Plotted at right) This leakage is parallel to reference field

  20. …Vibration Design and Test…

  21. Completed Physics Package Vibration Modal Analysis for TRL 6 vib spec • Modal analysis ~3000 mesh points to find resonant frequencies, all above 200 Hz • Loads are based generic random vibration level, 9.2 Grms • Equivalent quasi-static loads • G peak  100 G’s • Factors of safety • Yield factor of safety is 1.25 • Ultimate factor of safety is 1.40

  22. Shake Test for UV Photo-Multiplier Tubes R6354 R7154 O: Original Data R: Retest Data

  23. Summary - Ion Space Clock Teamed with flight engineers (JPL, GPS) to design small Ion clock for in-vacuum operation and vibration hardening __________________________________________________________________________________________________ Tube design based on other space vacuum tubes with 10+ years life ___________________________________________________________________________________________________ Lamp lifetime expected to exceed 10 years with VUV sapphire bulb material ___________________________________________________________________________________________________ 10-15 stability in (2-3 kg) small package feasible (1 ns at ~ 2 weeks autonomous TK)

  24. ICP, Inductively Coupled Plasma Lamp Lighting Industry uses cylindrical coil exciter • Plasma deposition and Ion thruster industries • use planar coil plasma exciter. • Creates uniform plasma region Two turn inductive exciter coil, 1 Amp at ~200 Mhz In vacuum operation, temperature rises to 170 C, higher than in-air optimum by 70 C Thermal base with indium heat conduction at ~60 C Hybrid Planar-Cylindrical Coil

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