1. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Production of cold positronium S.N. Gninenko INR, Moscow

2. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Outline   introduction   Ps production in porous films   set up for cold Ps study   laser Ps cooling   conclusion

3. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Why cold Ps antihydrogen production rate: R = N(p) n(Ps)  (p+Ps*->H) L  Ps density: n(Ps)=N(Ps)]/Vol n(Ps) ~ 1/Vol ~ (1/L) 3 ~ (1/v Ps ) 3 ~ (1/T) 3/2 n(Ps) ~ 1/Vol ~ (1/L) 3 ~ (1/v Ps ) 3 ~ (1/T) 3/2 for charge exchange  (p+Ps*->H) is enhanced if v Ps =(3kT/m Ps ) 1/2 <  c/2n R (velocity in Rydberg state n) for n R ~ 40 v Ps ~25 km/s and T ~10 K Can we create and manipulate cold Ps’s in a vacuum under controlled conditions? L p Ps

4. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Sample (Moscow IME)    L~ 1  m thick MSSQ film  spun on Si wafers from porogen+ MSSQ solution porogen+ MSSQ solution  highly interconnected pore network network  pore size ~ a few nm possible  intensive PAS study: pore size, distributions, interconnectivity, … distributions, interconnectivity, … Ps formation in porous SiO 2 in reflection mode e+ low-k dielectric films for microelectronics

5. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Ps formation in porous SiO 2 in reflection mode PRL90(2003)203402 T= 300 K D.Gidley, o-Ps lifetime study  e+’s stop, thermalized, form o-Ps  o-Ps yield:~30-40% emitted into vacuum vacuum  mean free path ~ 3 nm, diffusion length L>> film diffusion length L>> film thickness thickness  number of collisions with pore walls 10 4 – 10 6 pore walls 10 4 – 10 6 (depending on implantation (depending on implantation depth/energy) depth/energy)  well thermalized E(o-Ps) ~ kT  thermalization time t~R/V n t~1 ns << t (o-Ps) t~1 ns << t (o-Ps)  E = 40 meV, V=1.2 10 7 cm/s, R ~ 1 cm/lifetime R ~ 1 cm/lifetime

6. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Positron implantation profile vs energy Film density is 1.0 g/cm3 Typical depth resolution  ~10% of the mean stopping distance Z 0 Typical depth resolution  ~10% of the mean stopping distance Z 0 e.g. for beam energy E=2.1. keV, in polymer Z 0 ~1000 A ->  ~ 100 A e.g. for beam energy E=2.1. keV, in polymer Z 0 ~1000 A ->  ~ 100 A http://positrons.physics.lsa.umich.edu/

7. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko o-Ps spectrum from porous silica T= 300 K o-Ps temp. vs implantation energy two different films

8. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Other works  A.P. Mills (1989) TOF method. Ps thermalization in SiO 2 powder ( r=3.5 nm) in reflection Ps thermalization in SiO 2 powder ( r=3.5 nm) in reflection geometry. For 19 keV positrons ~2% of Ps are thermalized geometry. For 19 keV positrons ~2% of Ps are thermalized at 4.2 K. Londer contact with the powder grains would be at 4.2 K. Londer contact with the powder grains would be better. better.  K.G. Lynn (2005). 2  /3  method, reflection. Ps at low temps in Si porous films. Ps at low temps in Si porous films. Surprise: large amount 40 % of o-Ps produced at 50 K. Surprise: large amount 40 % of o-Ps produced at 50 K. ( even more at lower temps). ( even more at lower temps). No o-Ps out of films (trapped) No o-Ps out of films (trapped)  R. Suzuki (2003, 2005). TOF, reflection, 300 K. Ps study of porous low-k films. Clear Ps emission peaks. Ps study of porous low-k films. Clear Ps emission peaks. Strong dependence of o-Ps energy on film porosity, Strong dependence of o-Ps energy on film porosity, pore interconnectivity. pore interconnectivity.

9. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko A.P. Mills (1989) o-Ps energy reduces as the temp. drops

10. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Ps formation in in transmission mode (very little known) type of the porous film we would need (talk to experts) e+  o-Ps have to diffuse through a thick layer: o-Ps yield ? a thick layer: o-Ps yield ?  o-Ps could be well thermalized due to increase of interaction time to increase of interaction time  film could be porous SiO 2 or metalic (e.g. Al(100) or Al 2 O 3, metalic (e.g. Al(100) or Al 2 O 3, see D.Sillou proposal) see D.Sillou proposal)  effective source of cold o-Ps ?

11. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Set up for cold Ps study moderator moderator Na-22 T T TTTT Continuous beam e+ e+ high efficiency pulsing system Target Target  detector Pulse beam or accumulator?   intensity > 10 5 e+/s   beam size ~ 5 mm   bunch duration ~ few ns   energy up to 10 keV Porous films   thickness ~ 1-5  m   different (open) porosities   temps 300 K, 77 K, 4 K   ………………. Photon detection system   Ge detector   NaI, BGO counters   electronics, DAQ,…   ……………… Few techniques   2  /3    PALS   TOF   ……………….

12. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko VACUUM SYSTEM MODERATOR CHAMBER CHAMBER  DETECTOR PULSING SYSTEM MAGNETIC COILS Beam prototype: NIM A560(2006)224

13. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Compression of ~300 ns and 120 ns

14. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko TOF study of o-Ps emitted into vacuum o-Ps energy, eV Examples of TOF spectra, R.Suzuki(2003)

15. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko o-Ps laser cooling E.P. Liang, C.D. Dermer, Opt. Commun. 65(1988)419   1S-2P transition, 243 nm, lifetime 3.2 ns   photon recoil limit ~ 0.1 K   ~50 cylces, ~ 200 ns duration Laser specification (Cr:LiSAF):   wavelendth 243 nm   pulse length ~200 ns   bandwidth 150 pm   power ~100  J   rate ~ 100 Hz

16. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko o-Ps laser cooling Experiments in progress

17. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Possible scenario for cold Ps study  start at room temps in reflection geometry. Use a ~ 1 micron porous film with high pore interconnectivity (or another target). porous film with high pore interconnectivity (or another target). Ps yield and energy (TOF) spectra from porous films Ps yield and energy (TOF) spectra from porous films  cool film to liquid N. See, if we get thermalized Ps in vacuum.  check if ~ 10 K is ok for good thermalization (might be too low), if not - play with implantation energy, films properties, etc.. if not - play with implantation energy, films properties, etc..  the same steps for Ps production in transmission mode.  if thermalization is not good enough, think on additional Ps laser cooling cooling

18. Antihydrogen Workshop, June 14 2006, CERN S.N.Gninenko Conclusions  Limited data on Ps yield and energy (TOF) spectra in vacuum from porous films at low temps in reflection geometry. porous films at low temps in reflection geometry. No data on transmission mode. No data on transmission mode.  Some estimates exist ( SiO 2 ), but no theory for Ps thermalization (solid state, phonons, etc). Would be good to thermalization (solid state, phonons, etc). Would be good to have (even naive) simulations. In general: the longer interaction have (even naive) simulations. In general: the longer interaction time with the film the better for Ps cooling (but cannot be time with the film the better for Ps cooling (but cannot be too much longer than a few 142 ns). too much longer than a few 142 ns).  Not enough info to make definitive conclusions on a porous film we would need. Experimental study needs to be done. film we would need. Experimental study needs to be done.  Measurements are not simple. Construction of an intense pulse beam or positron accumulator (two birds in one shot?), availability beam or positron accumulator (two birds in one shot?), availability of porous film samples, cryogenic sample chamber and  -detection of porous film samples, cryogenic sample chamber and  -detection system for TOF, PALS,.. techniques is required. system for TOF, PALS,.. techniques is required. Steps could be at 300, 77 and 4 K temps. Steps could be at 300, 77 and 4 K temps.  Contacts with experts on porous film are important. Possible feedback: Films characterization could be done with the Possible feedback: Films characterization could be done with the constructed apparatus. constructed apparatus.