Rockets, Stars & Jars

1. Rockets, Stars & Jars Hot on the trail of cosmic plasma accelerators Dr. Robert Sheldon February 19, 2003

2. Talk Outline • Mass Spectrometers • How I became a space physicist • Two mass spectrometers • Space Plasma Physics • The stochastic dipole cyclotron • The spinning magnet linac • Laboratory Plasma Physics • Field-aligned voltages • Dusty plasmas

3. Why Space Plasma Physics? I started out as an experimentalist in high school (with the box of disassembled Timex watches…) I switched from pre-med to physics at Wheaton College. In grad school, the prof with the MBE (molecular beam epitaxy) machine had too many students, so instead I worked on a Time-Of-Flight Mass Spectrometer for space. Space MS led to launching on a rocket & an Earth orbiting satellite, NASA/AMPTE/CHEM. Plasma physics theory was needed to explain the data. A lab experiment was needed to explain the theory. Moral: Follow the Physics, not the method

4. I. Mass Spectrometers

5. VMASS: The 1st TOF MS [1987]

6. HELIX: The 2nd TOF MS [1999]

7. NASA patent disclosure [2003]

8. Mass Market Mass Spec? Mass Spectrometers are so versatile, they can be used in place of other medical diagnostics. Nature (Feb 2003) reports using MS for malaria diagnosis. (diabetes, etc...) But the scientists agree it needs to be cheaper. HELIX is simple enough to be built by undergraduates! My own goal is to put a M/dM=10,000 Dalton resolution MS into a cell-phone. Already the cell phone is a digital ear and digital eye. Soon it will be a digital nose. Applications: Bomb detection, anti-terrorism, home safety, drug testing, medical tests, or everything a german shepard could tell you if he could talk. (During Spring Break I will be attending PittCon`03 )

9. II. Space Plasma Physics

10. Space Physics • Unfortunately, one cannot get a physics PhD by designing instruments, so I needed data to complete my PhD in 1987. This was provided by an earlier instrument flown by the UMd group, based on a much simpler MS. • This data analyzed the 1-300 keV/q energetic ions trapped in the magnetosphere. So perhaps a little introduction to this region is in order. • The magnetosphere was discovered in 1959 by James VanAllen...

11. The Magnetosphere in 1965 Trapped energetic particles have 3 conserved “adiabatic” motions: 1) Gyration (t=msecond) 2) Bounce (t=second) 3) Drift (t=ksecond)

12. NASA/POLAR satellite orbit [1996] Many satellites had explored the radiation belts building up this picture: Trapped particles on inner & outer belts; untrapped outside. POLAR had cameras to take pictures while over the polar caps. It also had an energetic particle instrument vintage 1970. It wasn’t supposed to find anything new... UNTRAPPED

13. A keV detector’s view of M’sphere POLAR Energy-time color intensity spectrograms 15-1500keV protons. Radiation belts get hotter as s/c flies closer. Except on the 2nd pass...

14. Trapped H+ 43keV O+ Beams! B-field aligned “beams”

15. MeV electrons in the wrong place! Outer Radiation Belt Electrons MeV electrons in the Cusp!

16. Where are these energetic particles coming from? • Not the solar wind! (too energetic) • Can they be trapped particles? (wrong pitchangles, wrong place) • Are they just locally accelerated? W/O drift? • What are the mechanisms for accelerating particles to high energy very quickly? • How do we do it on Earth? Cyclotron & Linear accelerators or stochastic vs. resonant. Can the magnetosphere be doing the same thing? • Cyclotrons & Linacs

17. A. Space Plasma Cyclotrons

18. The Synchro-Cyclotron • A cyclotron traps the electron, then accelerates it. It operates at resonanceand therefore needs to be synchronized. • The maximum energy is determined by maximum gyroradius allowed by the pole magnet. It is efficient, center fed, rim exit. • The Earth is an inside-out cyclotron. But how does it trap?

19. Drift Motion in B-field Gradients x Trap ions w/ gyro-orbit Two other ways to trap ions –using a B-gradient: Gradient IN or Gradient OUT Dipole CUSP

20. 1 MeV electrons in Cusp Trapped, but how does it accelerate?

21. Stochastic Cyclotron Acceleration • The ions are trapped in a gradient B trap. (discovered theoretically by Singer in 1957.) • Waves that compress the trap with the same frequency as ion drift will accelerate the ions by betatron acceleration (1st order). • But solar wind fluctuations are thought to be random—thus the ions diffuse through energy space—stochastic 2nd order accel. • Perhaps not as fast as 1st, but accel. nonetheless

22. But SDC doesn’t explain Earth Although the radiation belts of the earth have 10’s MeV particles, either GeV’s precipitate into the center, or keV’s adiabatically escape, cooling off. From a Mars vantage point, the Earth dipole is a weak source of keV particles and atoms. Nor does adiabatic heating explain power law tails. The Dipole is a better trap than accelerator.This has been known for 30 years at Earth, but doesn’t explain the origin of the Earth’s radiation belts, especially the outer electrons. What then is the origin of the Earth’s MeV e- ?

23. But The Quadrupole Cusp... • 2-Dipole interactions = Quadrupole. A Dipole embedded in flowing plasma creates a quadrupole cusp trap. • How likely? About like binary stars. • Quadrupole is both a drift+bounce+gyro trap. • Q is center feed, rim exit. Hi E escape. Efficient! • Q has no center magnet permitting higher maximum energies. • Q is NOT adiabatic==> chaotic (fast) accel!

24. Quadrupole Cosmic Scales keV (Mercury) to MeV (Jupiter) 10 - 100 MeV as observed at Sun 1-10 GeV 10-100 GeV ? TeV? • Planetary Magnetospheres • Stellar Heliospheres • Binary stars • Galactic magnetic fields • Galaxy clusters This range of energies may explain Fermi’s question about the origin of cosmic rays.

25. B. Space Plasma Linacs

26. Nature abhors charge separation: Parallel Electric Field Theory Whipple, JGR 1977. Ne = Ni, quasi-neutrality (Wheaton grad 1953?) Different pitchangles for Ions and electrons n F E kT || e Wouldn’t E-field bring ions back to electrons?

27. Heuristics for Parallel-E Formation: Bouncing keeps H+ & e- apart. Bouncing motion of ion in a magnetic mirror B-field (dipole) looks like marble rolling in a bowl. E-field

28. Necessary Conditions for E|| in Space • Inhomogeneous strong B-field such that grad-B drifts dominate over ExB • Dipole field! Ubiquitous • Source of hot plasma • Injected directly (accretion disks) • Convected from elsewhere (plasmasheet) • Spinning central magnet? • Result: • Rim feed, axial exit accelerator. Efficient • Hot, non-thermal Xray source.

29. Herbig-Haro Objects: YSO Stars with Accretion Disks HH30

30. Blazar Galaxies and Schematic Jet

31. Visible vs Xray : HST deep field Deep field image taken by HST, showing galaxies as far as the eye can see. Some percentage of these are x-ray emitters. This suggests that the Xray continuum is really discrete Xray objects in the sky.

32. Can SLINAC power blazar jets? • The maximum electric field of such a system is limited by 2nd order forces ((F x B) x B). Using some typical numbers for YSO for magnetic field strength, we get limiting energies of keV - MeV. • Applying same formula to blazar jets, we get ~1 GeV. Precisely the value that explains observations! But black holes power blazars. • Q: What does a black hole magnetosphere look like? How does plasma affect equilibrium? General Relativity theorists don’t know yet.

33. Stochastic Cyclotron & SLINAC Accelerator Conclusions • Both mechanisms are topological • Ubiquitous. We should see them everywhere • Scale to all sizes. • Quadrupole cyclotrons = 2 dipoles • Planets embedded in flowing plasma • Opposing magnetic fields, e.g. binary stars • Stars (galaxies) moving through a plasma background • Jets =accretion disks + spinning B-fields. • YSO, blazar, micro-quasars,Herbig-Haro • Earth has half an accretion disk=plasmasheet

34. III. Laboratory Plasma Accelerators

35. 1st Experimental Setup w/electrode • Bell jar, oil roughing pump, HV power supply, Nd-B ceramic magnet (low Curie temp!) • Needle valve used to control the pressure from 10-400 mTorr • Simple • Cheap

36. Arcs and Sparks=> Equator Potential Arc completely around! 40s exposure Arcs follow B-field lines Electrode spinning stationary

37. 2nd Lab Setup w/Biassed Magnet 1) N & e 2) Saturated 3) - 400VDC 4) 0.5Tesla 5)10 - 200mT

38. Characteristics of Discharge • KeV of Voltage • Discharge lasts 30 microseconds • Calculated milliCoulombs of charge • Estimated nF capacitance of magnetic field • In better vacuum (or collisionless plasma) potentials are limited by 2nd order plasma drifts • Result: Space charge accelerator • (How do I know for sure? Dust tracer...)

39. 3rd Lab Setup w/ Pyrex Bell Jar Laser Plasma

40. Saturn’s Rings in the Lab? Dust Ring 3 SiO2 dust

41. The 4th Wheaton Belljar Setup • Built in Experimental Physics class by Geoff Poore & Ben Noonan [2002] • Moderate vacuum (10mTorr) oil-roughing pumped Pyrex bell jar • Exploring toroidal magnetized DC glow discharge plasma geometry

42. Toroidal DC-glow discharge 2/17/03 • Annular disk forming at dipole minimum • Central jet forming at toroidal minimum • Asymmetric jet possibly due to spontaneous symmetry breaking • Stellar jets?

43. Conclusions • Space MS have applications to Earth as well • Novel acceleration mechanisms are found in space corresponding to cyclotrons & linacs • These acceleration mechanisms may solve outstanding questions from astrophysics. • Several of these mechanisms can be demonstrated in the laboratory with DC glow discharges in the presence of strong B-fields. • Dust provides a novel tracer of plasma E-fields

44. Some References • Sheldon & Spurrier, "The Spinning Terrella Experiment", Phys. Plasmas, 8, 1111-1118, 2001. • Sheldon, "The Bimodal Magnetosphere", Adv. Sp. Res., 25, 2347-2356, 2000. • Sheldon, Spence & Fennel, "Observation of 40keV field-aligned beams", Geophys. Res. Lett. 25, 1617-1620, 1998. • All at: http://bex.nsstc.uah.edu/RbS/

45. The Magnetosphere in 1990