1 / 17

Measurement of Screening Enhancement to Nuclear Reaction Rates using a Strongly-Magnetized, Strongly-Correlated Nonneutr

An example of High Energy Density Physics at Low Energy Densities. Measurement of Screening Enhancement to Nuclear Reaction Rates using a Strongly-Magnetized, Strongly-Correlated Nonneutral Plasma. Dan Dubin, UCSD Experimental collaborators:

nira
Download Presentation

Measurement of Screening Enhancement to Nuclear Reaction Rates using a Strongly-Magnetized, Strongly-Correlated Nonneutr

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. An example of High Energy Density Physics at Low Energy Densities Measurement of Screening Enhancement to Nuclear Reaction Rates using a Strongly-Magnetized, Strongly-Correlated Nonneutral Plasma Dan Dubin, UCSD Experimental collaborators: John Bollinger, Marie Jensen NIST Boulder Supported by the NSF/DOE partnership

  2. How can a nonneutral plasma have anything to do with nuclear reaction rates?? Nonneutral plasma: collection of charges of like sign : eg. pure ion plasma (Be+) pure ion plasmas can be confined for days in the static electric and magnetic fields of a Penning trap • B ~ 4 Tesla • E ~ 10Volt/cm • ~ 30 kHz n ~ 108 cm-3 T ~ 0.001K - 104 K Nuclear reactions are NOT happening. But something analogous to nuclear reactions IS happening!

  3. Relative EnergyE required for close encounter: n is dominated by superthermal nuclei with E >> T Gamow peak: 1/2 s(E) ~ e-c/E e-E/T E EGamow [ c2 ~ Nuclear Rydberg ~ 105 eV] Bethe (1939), Gamow and Crutchfield (1949), … Nuclear reactions in the sun Reaction rate n : Required distance of closest approachb ~ a few Fermi, ~10-12 cm (nuclei tunnel the rest of the way through the Coulomb barrier)

  4. E +E|| E No exchange of parallel and cyclotron energy E|| time B Higher parallel energy: Cyclotron freq. Wc >> all other dynamical frequencies E +E|| Energy E of cyclotron motion is an adiabatic invariant E Adiabatic invariant is broken in close collisions E|| time Low parallel energy (strongly-magnetized collision): B Ion-Ion Collisions in a strong magnetic field

  5. Adiabaticity parameter In cold, strongly-magnetized plasma, most collisions have Only superthermal ions release the cyclotron energy Higher parallel energy collision: B Release of cyclotron energy requires close collisions to break the adiabatic invariant : or Collision timescale So K is internal energy, like nuclear energy. Close collisions release this energy Gamow peak in equipartition rate will occur if Eg. B=1 Tesla, m=mBe, T<< 3 K

  6. 3/2 s(E||) ~ e-c/E e-E /T || || E|| EGamow mean adiabaticity parameter ^ Equipartition rate n of cyclotron temperature T and parallel temperature T is analogous to nuclear reaction rate: O’Neil + Hjorth ‘85

  7. Theory and experiment for equipartition rate (measured on pure electron plasma) k-1 Beck, Fajans and Malmberg Phys. Plasmas ‘96, Glinsky, O’Neil and Rosenbluth Phys. Fluids B ‘93

  8. No screening: Debye screening: less energy needed to get the same differential rate enhancement factor f rate for no shielding What effect does Debye screening have on the rate (nuclear or equipartition)? Debye screening decreases energy required for a given distance of closest approach b Salpeter ‘55

  9. Eg. in solar interior: n~1023 cm3 T ~106 K G~0.1, f ~1.05 Screening Enhancement factor f for equipartition is identical to enhancement factor for nuclear reactions Release of cyclotron energy in a close collision of guiding centers is analogous to release of nuclear energy in close collision of nuclei Both nuclear and equipartition rates are enhanced by screening: because close collisions are more probable when they are screened

  10. G >>1 in a white dwarf, a giant planet interior, or a nonneutral plasma: interparticle spacing 1<< G << k2/5 (Proof: see Dubin, PRL in press) Rate is still given by n = f(G) no Ichimaru and Iyetomi: DeWitt and Slattery: Pycnonuclear regime: G > k2/5 :theory TBD f is very large (Salpeter and van Horn, 1969) and has never been verified experimentally I. Strong shielding regime: close collisions still dominate:

  11. Rate enhancement due to screening is huge at large G, Predictions for it differ (dynamical screening controversy: J. Bahcall 2002) f has never been tested experimentally in the strong shielding or pycnonuclear regime.

  12. n = f(G) no no Rapid equipartition when T ~ 0.2 MD Simulations of equipartition can measure the rate enhancement factor f(G) N=200 ions, Wc/wp = 12.4. Parameters chosen so that G =1.25/T Start with T >> T. Increase T instantaneously, twice.

  13. Simulation with T < T As T decreases, n decreases and equilibration is suppressed

  14. f = n/no Measured equipartition rate for several simulations: no : theory for 2-body equipartition rate n = f(G) no Wc/wp=12.4 • = 1.25/T, k = 42.4/T3/2 Dubin, PRL in press

  15. Ion-neutral collisions Causes slow heating Dirty cloud, dark ions (BeH+ etc) Experimental evidence of enhanced equipartition Laser-cooled Be+ ion cloud, initial T~ 0.001 K. At time t=0 turn off laser cooling. Pure Be+

  16. Parallel Temperature jump due to coupling to hot cyclotron motion of dark ions Rapid heating in a dirty cloud ~ 1-10 hertz ~ 1010 0 Marie Jensen et al. PRL in press

  17. Proof that heating step is due to to dark ion cyclotron motion Add rf noise to trap electrode at dark ion cyclotron freq. Parallel energy is heated resonantly but only when T is sufficiently large T(t) T at 1 sec

More Related