The invention relates to processes for photo detaching negative ions in a magnetic field and, more particularly, relates to a process for achieving selective neutralization of a given population of negative hydrogen ions in a magnetic field in order to produce an intense negative hydrogen ion beam with spin polarized protons.
There has been an increasing demand in the last several years for spin polarized protons that are useful in a number of different applications for high energy research. The development of fusion reactors may also create the need for intense "high" energy neutral deuterium beams that have polarized nuclei. A number of different processes presently exist for producing such spin polarized protons and high energy neutral deuterium beams; however, all such present prior art methods known to the applicant are initiated by either polarizing an electron of the hydrogen atom, or by producing nuclear and electron spin polarized atomic gas. In such prior art processes, a necessary subsequent step is to either polarize the nuclear spin in one case, or to eject a particular spin state from a gas in an alternative case. Finally, the nuclear polarized atomic beam thus produced needs to be converted to either a positive or negative ion beam before it is entered into a suitable accelerator. All of these known prior art methods have certain major drawbacks. One such drawback is that considerable difficulty is encountered in attempting to produce a proper polarized atomic beam which has both high density and high velocity, as is necessary in order to avoid space charge effects and collisional destruction. A further significant disadvantage of such prior art methods is that the efficiency of converting polarized H to polarized H.sup.-, or even to H.sup.+, is rather poor in currently available processes.
One known process for achieving neutralization of accelerated ions by photo-induced charge detachment involves the employment of a laser beam that is directed across the path of a negative ion beam to effect photodetachment of electrons from the beam of ions. An example of that type of prior art process is disclosed in U.S. Pat. No. 4,140,577, which issued Feb. 20, 1979. A related U.S. Pat. No. 4,140,576, which also issued Feb. 20, 1979, discloses a cavity that is useful with a relatively efficient strip diode laser that emits monochromatically at an approximate wavelength equal to 8,000 .ANG. for H.sup.- ions, in order to strip excess electrons by photodetachment with increased efficiency and reduced illumination required to obtain approximately 85 percent neutralization. Such prior art processes do not use selective neutralization of H.sup.- ions in a magnetic field as is done in the process of the invention as disclosed in the present application. Accordingly, no polarized ions or even neutrals result from such prior art processes.
Other types of processes are known in the prior art wherein isotope separation is achieved by selectively ionizing given isotopes with polarized laser light. For example, U.S. Pat. No. 3,959,649, which issued May 25, 1976, and U.S. Pat. No. 4,020,350, which issued Apr. 26, 1977, disclose methods in which polarized laser light is used in laser isotope separation processes that are employed to selectively ionize given isotopes. Although such prior art methods employ polarized laser light, they do not result in the production of any spin polarized nuclei. Accordingly, except insofar as such prior art processes provide an awareness and understanding of the uses of polarized laser light, they appear to be of minimal relevance with respect to the process of the present invention disclosed herein.
A somewhat more relevant prior art photodetachment method is described by W. A. M. Blumberg, W. M. Atano and D. J. Larson in an article entitled "Theory of the Photodetachment of Negative Ions in a Magnetic Field", which appeared at pp. 139-148 of Vol. 19, (No. 2) of the Jan. 15, 1979 issue of Physical Review. That paper presents a theory of a process for achieving photodetachment of atomic negative sulfer ions in a magnetic field. A basic element of the theory considered in that paper involves the confinement of the motion of the detached electron in the directions transverse to an applied magnetic field. Such confinement leads to the quantization of the transverse kinetic energy into the familar cyclotron, or Landau levels. As a result of the theoretical and experimental work reported by those authors, the theory discussed in the paper was said to predict the dependence of the photodetachment cross section upon magnetic field strength and upon light frequency. The experiments to confirm the theories discussed, were performed on ions that were confined in a trap of the Penning type, in which a uniform magnetic field and a quadrupolar static electric potential are present. The authors concluded that their theory, which was developed for S.sup.- atomic photodetachment, should also be equally valid for photodetachment of O.sup.-.
In light of the shortcomings and disadvantages of all known prior art methods, as explained above, it remains desirable to provide a simple, essentially one-step photodetachment process that is operable to produce a multi-ampere beam of H.sup.- ions and to achieve laser neutralization of the H.sup.- ion beam with essentially 100 percent efficiency.