The key requirement of the LENR reaction is the chiral polarization of matter and energy. All particles can be Chiral polarized including photons. This polarization principle is most notably and purely demonstrated in the Papp fuel preparation process. The goal of that process is the left handedness polarization of the spins of 5 types of noble gases.
Most hopeful Papp engine replicators do not spin chiral polarize the noble gas mix. Nobody understands the purpose of the Papp fuel preparation process.
Generally, in the Papp fuel preparation process, radioactivity from thorium and x-rays are used to chiral polarize the spins of the five noble gases with left handed chiral spins. Radioactivity produces subatomic particles and photons that are always left handed chiral spin polarized. The use of radioactive materials loaded into the hollow electrodes (aka buckets) in the Papp engine maintains the left handed chiral polarization of the noble gases during the operation of the engine.
When Papp developed the Papp engine, laser tech was not known, so Papp used radioactivity as the means to spin polarize the noble gases that powered the Papp reaction.
Today, noble gas chiral spin polarization can be done without the need for radioactive material. Optical pumping is a very efficient method to control the atomic spin state through interaction with a resonant light beam carrying angular momentum. In the presence of a magnetic guiding field B and of weak relaxation processes, the net result of the repeated light absorption and re-emission cycles is a change in the relative populations of the involved atomic sublevels, i.e. creation of spin orientation. For chiral spin polarizing of noble gases currently used in industry, two routes are possible: spin exchange optical pumping (SEOP), with indirect transfer of angular momentum from a polarized laser beam to the noble gas nuclei via alkali metal atoms (usually rubidium), and metastability exchange optical pumping (MEOP), with direct transfer of angular momentum from resonant laser light to He atoms. Each technique has its own advantages and limitations.
For instance, SEOP directly operates at high pressure but is a slow process (several hours are required to polarize helium), while MEOP is a much faster process (it only takes seconds to polarize 100 cm3 of gas at 1 mbar), but only operates at low pressure (mbar). SEOP has been used for several imaging experiments, but MEOP is preferred because of its faster production rates and higher nuclear polarizations.
An example of a He Polarizing Industrial Method
The polarization apparatus is based on the method of optical pumping of metastable He atoms in a weak gas discharge at a gas pressure of about 1 mbar. The whole equipment is located in a homogeneous magnetic field B0 of 1 mT, which serves as a holding field and as quantization axis for the polarized He-nuclei. The polarizing and compressing system consists of three parts: The first part contains the He reservoir and getters for gas purification. The second part consists of the optical pumping volume. The optical pumping itself is done by two 15 W fiber lasers at 1083 nm. The five OP-cells have a length of 2.20 m. In order to maximize the light absorption the circularly polarized laser light is back-reflected at dichroic mirrors. The nuclear polarization of the He gas can be monitored during the OP-process by measuring the circular polarization of the 668 nm-light emitted by the discharge. The third part contains a mechanical polarization-conserving compressor driven by hydraulics.
In my own way of thinking, a linearly polarized laser vertical photon beam produced by a diode laser can be conditioned by an organic chiral spin filter (aka karo syrup) to convert the photon stream from a laser into a left handed chiral state. All organic matter is polarized left handed. A clear solution of d-glucose can convert the photon polarization in the required left handed polarization. The required photon stream must be linearly chiral spin polarized left handed. This conditioned laser beam could irradiate a small hole in a container from which a noble gas mix is flowing. The hole is small enough for the laser beam to cover the entire hole.
In the picture, an intense source of light is polarized filtered into the LENR required left handed spin state.