Muon Catalyzed Fusion CF - Recent progress and future plan

1. Muon Catalyzed Fusion (µCF) - Recent progress and future plan K. Ishida (RIKEN) Introduction ddm formation: wider range of temperature, phase and ortho/para ratio of D2 dtm formation: first experiment with T2/ortho-D2 mixture mCF with intense muon beam in collaboration with K. Nagamine1,2,3, T. Matsuzaki1, N. Kawamura2, H. Imao1, M. Iwasaki1, Y. Matsuda1, S. Nakamura1**, A. Toyoda2, M. Kato4, H. Sugai4, A. Uritani5, H. Harano5, G.H. Eaton6 1RIKEN, 2KEK, 3UC Riverside, 4JAEA, 5AIST, 6RAL present address *U. Tohoku , **RIKEN

2. muon catalyzed fusion (µCF) - principle and motivations After injection of muons into D/T mixture (or other hydrogen isotopes) Formation of muonic atoms and muonic molecules In small dtµ molecule, Coulomb barrier shrinks and d-t fusion follow Muon released after d-t fusion - muon works as catalyst - History 1947 Hypothesis of µCF (Frank) 1957 observation of pdµ fusion (Alvarez) 1966 observation of resonant ddµ formation 1967 hypothesis of resonant formation Vesman) 1979-82 observation of large dtµ formation rate 1987 observation of x-rays from (aµ)+ (PSI,KEK) 1993 large ddµ formation rate in solid 1995 study with eV beam of (tµ) 1996 systematic study starts at RIKEN-RAL

3. Maximizing µCF efficiency .Motivations Atomic physics in small scale rich in few body physics problems Prospect for applications (fusion energy, neutron source) muon production cost (~5 GeV) vs fusion output (17.6 MeV x 120) Observables (1) Cycling rate lc (h) (vs l0: muon life) dtµ formation tµ + D2 g[(dtµ)dee] (2) Muon loss per cycle W (i) muon sticking to a-particle, etc Fusion neutron disappearance rate : ln = l0 +Wflc Number of fusion per muon: Yn = flc/ln = 1 / [(l0/flc)+W] (h)

4. Outstanding problems in ?CF Main ?CF processes are understood, however still discrepancies … 1. Muonic atom acceleration during cascade, hyperfine transition, transfer 2.Molecular formation rates temperature dependence non-linear density (3-body?) effect ortho/para 3. Muon to alpha sticking initial sticking ?? atomic process, muon reactivation 4. Helium effect muon transfer process helium in solid D/T Progresses are being made in each of the problems. Focus is given to molecular formation rate in this talk.

5. Key process of µCF - dtµ formation Auger formation : 106 /s (as slow as muon decay rate 0.45 x 106/s) tµ + D2 g (dtµ) + D + e- Resonant molecular formation : 106-109 /s tµ + D2 g ((dtµ) dee) (dtµ binding energy ~ excitation of complex molecule) (tµ energy to match the small energy difference) Thus, dependence on temperature dependence on initial states such as tµ spin state, D2 states We could change (enhance) µCF by controlling initial D2 states. For the muon to complete one fusion cycle, there occur many reactions. Among them, the key processes is the formation of dtµ bound state, since it is usually the slowest. When the idea of mCF appeared, it was first estimated to occur by Auger formation and the rate was only comparable to the muon life, and thus there was little hope to produce many fusions. However, this rate was later measured to have a large temperature dependence and was understood to occur via resonant molecule formation.For the muon to complete one fusion cycle, there occur many reactions. Among them, the key processes is the formation of dtµ bound state, since it is usually the slowest. When the idea of mCF appeared, it was first estimated to occur by Auger formation and the rate was only comparable to the muon life, and thus there was little hope to produce many fusions. However, this rate was later measured to have a large temperature dependence and was understood to occur via resonant molecule formation.

6. Present understanding of dtµ formation dtµ molecule formation large formation rate (~109/s) by resonant formation mechanism is established (temperature dependence, etc) still many surprises non-trivial density dependence even after normalization three-body effect : tµ + D2 + D2’ g ((dtµ)dee) + D2’’ low temperature & solid state effect

7. How about ddµ ? Same resonant formation process applies for ddµ formation in pure D2 Slower compared to dt-µCF, and with lower energy output per fusion Still, study should be done in parallel with study of dtµ No need of tritium Simpler cycling process (pure D2) dµ + D2 g [(ddµ)dee] In analogy to dtµ case, temperature dependence dµ Hyperfine effect (F=1/2,3/2) D2 molecule effect

8. ddm formation: understanding before 2000 Resonant ddµ formation is nearly established in gas fitting by theoretical curve gives precision determination of shallow state binding energy in ddµ (-1.97 eV) [Petitjean et al] which is comparable to the value by precise three-body calculation However, in liquid and solid, large deviation from the theoretical curve was observed [Knowles et al, Demin et al] Theoretical prediction of ddm formation rate dependence on D2 ortho-para state.

9. New parameter: Ortho- and para-D2 in mCF D2 populates several rotational states (J=0,1,2,3,4,…) With normal D2, the resonance condition for all these are mixed. Ortho-D2 (dd nuclear spin coupled with 0,2, y spin yJ,v symmetry under dd exchange allows only J=even) Para-D2 (similarly, for coupling with 1, J=odd allowed) Normal mixture is ortho:para=2:1 (for H2, para H2 has J=even) Resonance condition for each state should be separately measured. First measurement with normal- and ortho-D2 at 3.5K Toyoda et al (2000) @ RAL, TRIUMF (fusion proton)

10. E968/E1061 Experiment @TRIUMF Measure dd mCF in D2 target (Since 2003) ortho/para controlled low temperature target (5K - 36 K) gas/liquid/solid phase several densities (0.03 to 1.2 of LHD) detectiong fusion neutrons TRIUMF M9B muon channel decay m- beam from 500 MeV x 200 mA proton cw beam was necessary for ddm fusion 1) good time resolution (<1 ns) 2) suppression of muon capture neutrons background by coincidence with delayed me-decay 10 ms beam gate limits the beam rate (50 k/s) 50 MeV/c muon beam (cryogenic Cu target cell, 1.5 Mbar)

11. Experimental setup @TRIUMF (E968/E1061) D2 (ortho, normal or para) preparation ortho-para ratio analysis with Raman spectroscopy Target cell (30cc liquid/solid, or 200cc pressurized gas) muon beam counters B1+B2 µe-decay electron counters E1-E8 (>50% solid angle) neutron detectors(NE213) N1-N4

13. Ortho/para-D2 preparation and analysis Ortho D2 (established) ortho-para conversion with Al2O3/Cr2O3 catalysis Para D2 (some success in Jun06 RUN) preferential adsorption on Al2O3 at ~20K 99% para D2 had been reported [D.A. Depatue and R.L. Mills, 1968] our case 55% para large gas quantity (30 liter), temperature control etc Analysis by laser Raman spectroscopy

14. Fusion neutron time spectra: gas D2 (36K) Fusion from resonant ddm formation (f=0.17, 36K) increased for ortho-rich D2 However, some structure in very early timing.

15. Understanding non-exponential time structure Resonance calculation [by Adamczak]

16. RUN in Jun 2006 Gas data at f=0.03 (28K and 36K), 0.07(36K), 0.17(36K) were recently obtained for normal-, ortho-, and para-rich(55%) D2 to see temperature effect, density effect, non-exponential e\ffect (para) analysis is still in progress (signal selection, b.g. subtraction etc)

17. Typical fusion neutron time spectra: liquid D2

19. ddm summary Data for gas D2 (f=0.17, 35K) was consistent with calculations based on idealistic gas model Non-exponential structure of fusion neutron time spectra is qualitatively understood by slow thermalization In liquid and solid phases, the observed ortho-para dependence of ddm formation rate was opposite to the prediction based on a simple gas model in all the temperature range measured (3K - 36K) Target D2 density (rather than temperature) is responsible for the reversal Theory is being developed to include density and phase effect resonance energy shift, broadening

20. dtm case: theoretical calculations 1. Idealistic gas model tµ + D2 g [(dtµ)dee] low temp. resonance only for para-D2 2. with Condensed matter effect under development [Adamczak] Even larger effect of ortho-para D2 expected!

21. Expected effect in D/T(50%) mixture Prepare ortho-D2 or para-D2 and mix with T2 Very high cycling rate could be expected (>2 of normal rate) followed by decay due to 1. molecular equilibration process D2 + T2 D 2DT (~68 hour in D/T(50%)) tµ + D2 g [(dtµ)dee] tµ + DT g [(dtµ)tee] (ldtµ0,D2>>ldtµ0,DT) 2. ortho-para equilibration by radiation effect o-p conversion by paramagnetic T atom ~16 hours in D/T(50%) at 14K Cycling Rate lc = 1/(td+tt) =1/[ q1sCd/(ldtCt) + (3/4)/(ltm1,0Ct) + 1/(l0dtm-D2(o,p)CD2(o,p) + ldtm0,DT CDT)]   As a summary, we observed the fusion neutrons and muonic atom x-rays from muon sticking successfully at 0, 1.2, 2.4 and 3.3 T with a accuracy of 5 % for neutrons and 10 % for x-rays. The result indicate the cycling rate and muon los does not have a large dependence on the magnetic field, while there can be increase of mu-to-alpha sticking x-ray at high field. For the solid case, it is similar to the liquid, while only the data at 2.4T and 8K shows smaller cycling rate and larger muon loss. As a summary, we observed the fusion neutrons and muonic atom x-rays from muon sticking successfully at 0, 1.2, 2.4 and 3.3 T with a accuracy of 5 % for neutrons and 10 % for x-rays. The result indicate the cycling rate and muon los does not have a large dependence on the magnetic field, while there can be increase of mu-to-alpha sticking x-ray at high field. For the solid case, it is similar to the liquid, while only the data at 2.4T and 8K shows smaller cycling rate and larger muon loss.

22. µCF at RIKEN-RAL Muon Facility RIKEN-RAL Muon at ISIS Intense pulsed muon beam (70ns width, 50 Hz) 800MeV x 200µA proton 20~150MeV/c µ+/µ- muon 5x104 µ-/s (55MeV/c) and tritium handling facility

23. µCF target and detectors Cryogenic target : 1 c.c. liquid or solid D-T Detectors with calibration fusion neutrons, X-rays, µe decay 120 muon stops per pulse 106 fusions/s . .

24. Preparation of ortho-D2+T2 target 1) Production of ortho D2, analysis of ortho/para ratio 2) Evacuation of TGHS 3) Charge ortho D2 into target through TGHS and solidify 4) Extraction of T2 from getter and solidify into target 5) mix D2 and T2 by melting, start mCF measurement 6) after several days, turn to gas to force equilibration, restart mCF with equilibrated gas

25. Preliminary result of the first RUN: Cycling rate: lc

26. Result: Muon loss probability W

27. Why the ortho-D2 effect was not clearly seen? Possible reasons 1) fast ortho-para conversion (?) in the D2 inlet path, in D2/T2 liquid masked by impurity effect (first few hours) 2) ortho-para effect is small (?) non-thermalization change of resonance condition in condensed matter, similarly to ddm case Near future plans measurement with reduced impurity and para D2 study of ortho-para conversion rate at tritium lab. in JAEA in situ Raman analysis with new D/T target with optical window

28. Other ongoing studies of µCF Understanding mechanism and parameters of key processes Muon-to-alpha sticking loss [my talk in NuFact04] muon-to-alpha sticking x-rays 2. Muon loss to accumulated 3He from tritium decay [my talk in NuFact04] tHem molecule formation and decay 3. dtm formaiton in wider and exotic target conditions low temperature solid D/T, high density D/T, ortho-para D2 4. fusion in ttm particle correlations in 4He-n-n exit channel

29. Use of intense muon beam in mCF Intense muon beams will definitely contribute to the study of µCF 1) efficient search of more and more target conditions 2) short-lived extreme conditions (laser, plasma etc) 3) better S/N 4) exotic beams from µCF 5) intense neutron source

30. Summary A clear effect of ortho-para ratio was observed for ddµ formation in D2 In gas case, effect was consistent with theoretical prediction. (need to include thermalization process) In the liquid/solid case, the effect was opposite, possible modification of resonance condition by density effect Even larger effect was predicted for dtµ formation This opens up possibility for enhancement of µCF The first measurement failed to give conclusive result. Further study is planned. There are also other ongoing studies on mCF. Intense muon beam is indispensable for the study of mCF. II