Nuclear Reactions in Z-Pinch Gas Discharge
Investigation of Reactions Between Light Nuclei at Ultralow Energies Using Z-Pinch
Tech Area / Field
- PHY-PLS/Plasma Physics/Physics
- PHY-ANU/Atomic and Nuclear Physics/Physics
3 Approved without Funding
Joint Institute of Nuclear Research, Russia, Moscow reg., Dubna
- VNIIEF, Russia, N. Novgorod reg., Sarov\nSiberian Branch of RAS / Institute of High Current Electronics, Russia, Tomsk reg., Tomsk
- University of Florida, USA, FL, Gainesville\nLawrence Livermore National Laboratory, USA, CA, Livermore\nUniversity of California / Department of Physics, USA, CA, Irvine
Project summaryThe investigation of strong interactions between light nuclei at ultralow energies (~eV – keV) is of great interest due to the following reasons. This is stipulated that it can provide a possibility on verification of fundamental symmetries in strong interactions at ultralow energies (such as charge symmetry, isotopic invariance), that established for MeV energy region so and permits of number of problems, existing in the astrophysicist (discovered in stars and Galaxy a deficit of light nuclei (with the exception of 4He) in contrast with predictions, basing on theories of thermonuclear reactions and usually accepted star models).
Because of very small magnitude of cross sections 10-38 – 10-43 cm2 for the collision energies range of ~ keV, application of classical accelerators becomes problematic due to low intensity of accelerated particles beams.
Therefore, now information on characteristics of strong interaction among light nuclei can only be obtained with a nontraditional method for formation of accelerated particle fluxes.
In the context of this in papers [1-5] we suggested a new method for measuring cross sections of dd, pd, dHe reactions at ultralow energies – to use high intensity, radially converging ion flows, generated during the implosion of the current carrying liner plasma. In this approach the intensity of the accelerated ion flow could reach ~ 1020 particles in the pulse in given energy region.
The purpose of the project is to carry out a program consisting of three stages:
1) investigation of the dd reaction in the energy range 0.5 -3.0 keV;
—> 3He + n (2.45 MeV) (1)
d + d —> p + t + 4.03 MeV (2)
—> 4He + g (23.8 MeV) (3)
2) investigation of the pd reaction in the energy range 0.5-3.0 keV;
p + d —> 3He + g (5,5 MeV) (4)
3) investigation of the d3He reaction in the energy range 2-10 keV.
The experimental program is planned to be carried out at a powerful pulsed accelerator MIG of IHCE (Tomsk).
The goal of the present project is to measure both the astrophysical S-factors in dd and pd interactions and the effective dd and pd reaction cross sections in the ultralow collision energy range 0.5-3.0 keV with the use of powerful pulsed accelerators allowing high-intensity proton (deuteron) fluxes generated in the course of liner plasma implosion also as its electrodynamic running in the direction from liner axes. With this technique it is possible to gain for the first time quantitative information on astrophysical S-factors and dd and pd interactions and on effective dd and pd reaction cross sections in the above ultralow energy range.
It is planned to carry out the experiments at the accelerator MIG in the Institute of High Current Electronic of the Russian Academy of Sciences . In this case the maximum level of measured dd and pd reaction cross sections will be 10-38 cm2.
The experimental set up for the efficient cross section measurement of the dd and pd-reactions, as well as astrophysical S-factors in dd and pd-interactions at ultralow energy of collision 0,5-3,0 keV includes: 1) high current generator; 2) load module (liner and target); 3) nucleus reactions product detectors; 4) recording electronics; 5) diagnostic equipment to monitor dynamics of the compression of the liner (see fig. 1).
The neutrons from dd fusion (reaction (1)) are registered by two types of detectors: the time-of-flight scintillation spectrometers and thermal neutron detectors .
The detection of g-quanta (reactions (3), (4)) is realized by detectors NaI(Tl), but the charged components (reactions (2), (3) are recorded by CR-39 (PM-355) polymer track detectors , practically non-sensitive to powerful electrical and magnetic fields.
In 1995-1996 the first phase of a setup built at the accelerator SGM (ISE) was used to measure the dd reaction cross section at the average energy of accelerated liner plasma deuterons Ed = 440 eV .
At the beginning of 1997 the second phase of the setup for the study of the dd reaction was completed.
The dd reaction cross sections were measured  at the average deuteron energies Ed = 0.1, 0.38, 0.44, 2.07 keV.
Taking into account the energy dispersion of deuterons (protons) in one shot (~20 %), the dispersion of average deuteron energies between shots (~10%) and Coulomb energy losses of deuterons (protons) interacting with the target, we introduce the effective target thickness l and the effective neutron-production dd reaction cross section at the 90 % confidence level upper limits of the effective cross sections of dd the reaction corresponding to the interval of the deuteron collision energy mentioned above:
sndd < 3.1ґ10-32 cm2 (Ed = 100 eV); sndd < 1.6ґ10-33 cm2 (Ed = 0.38 keV);
sndd < 1.1ґ10-33 cm2 (Ed=0.44 keV); sndd < 1.5ґ10-34 cm2 (Ed = 2.07 keV).
Agreement is observed between the experimentally estimated effective dd reaction cross sections and their calculated values.
The results of our first experiments [9, 10] carried out by this method indicate that it allows effective investigation of the properties of reactions between light nuclei in the region of ultralow energies.
According to the calculations, the following results can be expected from the scientific program to be carried out at the accelerator MIG.
With 200 pulses of the accelerator MIG, the smallest measured cross section for the dd reaction yielding a neutron or a proton is 10-38 cm2, which corresponds to the deuteron collision energy 0.8 keV.
At collision energies below 0.8 keV one can obtain only the upper limit for the dd reaction cross section and S-factors.
As to the dd reaction channel yielding a g-quantum, only the upper limit for this process (at a level of 10-39 cm2) and S-factor can be determined.
When studying the pd reaction one can measure the yield of g-quanta which will be as large as Ng = 20 for 200 “shots” (accelerator pulses).
The background is negligibly small in this experiment. It is 10-3 for 200 “shots” of MIG. It follows from these estimates that
(1) it is possible to measure for the first time the pd reaction cross section at the collision energy Ecol > 1.5 keV;
(2) the upper bound for the pd reaction cross section and S-factors can be found at collision energies Ecol > 1.5 keV.
To gain precision information on cross sections for the reactions in question, it is necessary to have reliable information on velocity distribution of accelerated liner particles in a shot and fluctuations of the average particle energy from shot to shot. This is due to exponential dependence of the cross sections for processes (1)-(4) on the energy of collision of liner ions with the target. Therefore, to carry out correct measurements of cross sections for reactions (1)-(4) it is necessary to develop such liner implosion conditions which eliminate the possibility of instabilities (sausage-type instabilities) in the Z-pinch that could be recorded by very sensitive instruments: dB/dt probes, soft X-ray detectors, optical methods involving the Doppler effect, electronic sweep.
For the suppression of instabilities in the process of acceleration of the liner it is worthy of attention of methods basing on the use “inverse” Z-pinch [11,12]. In this scheme a plasma accelerates up radial from the liner axis electrodynamically. Such scheme of acceleration has, on our glance, number of advantages in contrast with “direct” Z-pinch (plasma of liner accelerates up radial to the axis). The radial fly apart plasma after dispersal allows:
1) to reduce the plasma density of the flow incident on the target;
2) “disperse” on time processes of the electrodynamics acceleration of plasma and its interaction with the target;
3) greatly simplify a problem of the velocity measurement of a plasma under its flying to the target.
The experimental program to be carried out under the project requires not only higher-current pulsed accelerators than those used in the 1995-1998 experiments but also a recording system with extended capabilities.
Implementation of the project will undoubtedly allow answers to the fundamental questions related to mechanisms of nuclear reactions in the ultralow energy range, which are still open questions
Fig. 1. Experimental set up:1 - high current generator; 2 - load module; 3 - diagnostic chamber; 4 - electromagnetic valve; 5 - Laval nozzle; 6 - liner; 7 - target; 8 - time-of-flight scintillation spectrometers (8 pieces); 9 - thermal neutron detectors (3 pieces); 10 - NaI(Tl) detectors; 11 - CR-39 (PM-355) polymer track detectors; 12 - Pb shield.