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Neutral Particle Beam [NPB]

Contrasted to charged particle beams, neutral particle beams have several inherent properties that make them very attractive for space based applications. In particular, high energy neutral particles propagate in straight lines unaffected by the earth's magnetic field and have a very brief flight time to targets even at extended ranges. In addition, the neutral particles become high energy charged particles upon interaction with the surface of a target and penetrate deeply into the vehicle, thus making shielding relatively ineffective. In the case of a nuclear warhead, these particles are capable of heating the nuclear material by fission processes, neutron generation and ionization. For non-nuclear material, heating is produced by ionization, possibly producing kill by thermal initation of the weapon's high explosive.

Thus, interest in space based systems was revitalized when experiments, at the Los Alamos Clinton P. Anderson Meson Physics Facility (LAMPF), on the proton linear accelerator showed several orders of magnitude improvement in accelerator performance. Extensive measurements of beam properties at energies of 211 and 500 MeV showed that the energy spread of the beam was better than 0.5% and the emittance of the beam was better than 0.66pcm-mrad. In addition, the LAMPF accelerator was used to accelerate H - ions to energies above 100 MeV and, as expected, their behavior is similar to that of protons. These achievements prompted Knapp and NcNally to write a LASL report titled SIPAPU Rpt. LA-5642-MS, Los Alamos Scientific Laboratory, July 1974, in which they proposed a satellite-based high energy neutral hydrogen weapon. An intense, high quality beam of H - ions is generated and accelerated to an energy of approximately 250 MeV. After acceleration the beam is expanded, and passed through final focusing and steering magnets. The beam is subsequently neutralized by stripping the weakly bound electron from the H - ion and the resulting hydrogen beam propagates toward the target unaffected by the earth's magnetic fields. Both the system and the target must remain above approximately 250 kilometers in order to minimize the beam degradation by collisions with residual gases.

Improvements in the state of the art for producing intense high quality ion beams, for lightweight efficient accelerators, for high current negative ion beams stripper techniques without excessive scattering, and for compact lightweight power systems are necessary before this device can be considered viable. Methods for neutral beam detection, signatures for closed loop tracking and kill assessment, and techniques for rapidly steering the beam over large angles are also needed.

Although, there are many of these practicle issues to be considered, there did not appear, in principle, to be any inherent limitations that deem the device inviable. But the solutions for the neutralization of the H - ion beams all had serious adverse systems implications. Once the H - beam has been accelerated, aimed, and focused on the target it can be neutralized. This can be accomplished by a number of techniques. For example, photo detachment, a plasma or gas stripping have been considered. Photo detachment causes less degradation in beam quality and can result in the largest friction of the ion beam being converted to a neutral beam. Unfortunately, extremely high energy cw lasers at wavelengths that are not currently available are required for this purpose, and, even if they become available, they would probably be as large and as expensive as the rest of the system. Since open-ended plasma strippers with quiescent plasmas cause less beam degradation than a gas stripper they have also been considered; but, because of the necessity of allowing the plasma to escape, the power requirement for the plasma stripper alone in equal to or greater than that for the rest of the system. Also, it is problematical that a sufficiently quiescent plasma could be produced. Therefore, considerable work both theoretical and experimental has been devoted to the development of a gas stripper. The fractions of the initial beam which survives as H - , which is stripped to H o , and which is stripped to H + is given as a function of the stripper thickness. As a result of this work a gas stripper was included in the SIPAPU system.

Sipapu was named after a Native American word said to mean "sacred fire", but then altered to protect ethnic sensibilities. Sipapu is the place of emergence from the underworld (where the spirits and ancestors of the Hopi live). The passage between the World Below and the earth is the sipapu. The Grand Canyon, which is the Hopi Sipapu or Emergence Hole, and it is where legend says the Hopi came up from the under world. In Hopi mythology, Sipapu is the entryway through which all souls must enter and exit the spirit world. The circular kivas found in Anasazi ruins are said to be symbolic of this emergence, i.e. underground ceremonial chambers with a roof entrance/exit, called the sipapu. The tepali, the ritual hole covered by a stone disc at the center of the tuki, is a variant of the sipapu (Hopi sipaapuni), the mythical place of emergence of the Pueblo peoples, which is architecturally represented as a hole in the center of the kiva.

For the Army, Sipapu was a neutral beam, space-based weapon, ranked second in priority to Chair Heritage and is receiving in excess of $10 million in 1980. This Army program, being conducted at the Los Alamos Scientific Laboratory in New Mexico, is based on advanced Soviet technology demonstrated in a Russian-designed plasma generating device. The US version was tested to determine compatibility with a Meson Physics Accelerator, located at Los Alamos. The two devices were coupled to form a test apparatus for follow-on experiments on beam propagation and lethality. The Sipapu program reached a stage where weapons packaging designs could be initiated. If Sipapu were developed in a less sophisticated, antisatellite configuration, it could be launched in three to five years with adequate funding.

In its 1984 directed energy plan, SDIO planned to build a space-based neutral particle beam (NPB) and test it on the ground by the end of fiscal year 1992 at an estimated cost of $747 million through fiscal year 1989. Through fiscal year 1993, SDIO allocated $794 million to this program and it had not completed all of the ground and space tests included in the 1984 plan. SDIO estimated in 1993 that it would take 4 more years and $421 million to complete the ground and space testing and the development of a lightweight power source for NPB (power source for NPB was initially to be developed under another program). These actions would exceed the objectives included in the 1984 plan. At that point, SD10 could decide whether to propose entering the demonstration and validation phase of development and doing an integrated system level demonstration.

According to SDIO's 1984 plan, NPB development was to have advanced by 1992 to a point enabling a decision on whether to fund an integrated system level demonstration in space. As a basis for this decision, SDIO planned to have demonstrated beam generation/conditioning feasibility and scalability with an accelerator, lightweight magnetic optics for steering the beam, concepts for sensing the beam and boresighting it, propagation of a beam from a spacecraft into a space environment, feasibility of growth technology that could provide higher brightness beams, and integration on the ground of key subsystems of a space-based NPB weapon.

The plan specified that about $747 million would be required from fiscal years 1986 through 1989 to achieve these objectives. The power system and the ATP system for NPB were to be developed under separate programs. Four of the 1984 program plan's eight major objectives for NPB had been completed by 1993. SDIO said that significant progress had been made on completing the other four. Through fiscal year 1993, SD10 spent about $794 million to develop NPB, or $47 million more than it estimated was needed for fiscal years 1986 through 1989 to do the planned research.

SDIO'S 1984 program goals were to generate a particle beam in the burst mode with a power of 50-million electron volts and a beam in the continuous mode with a power of 5 million electron volts. The 50-million electron volt goal was replaced in 1987 by a 24 million electron volt goal. SD10 said the change was prompted by concept studies that indicated the 24 million electron volt experiment would demonstrate the requisite weapon relevant objectives. SDIO said that considerable progress has been made toward achieving these goals. Final completion of the 1984 goals will occur with operation of the beamline components that are now fabricated and being installed on the Ground Test Accelerator and the continuous wave deuterium demonstrator.

The Ground Test Accelerator at Los Alamos National Laboratory produced a 3.2~million electron volt beam in the burst mode by 1993. Additional components to increase the accelerator's beam energy to 24 million electron volts were added to the accelerator. 1, SDIO plans to perform the 24 million electron volt demonstration during fiscal year 1994, which accomplished the first objective. According to SDIO, the results of this demonstration were scalable to higher levels.

The continuous wave deuterium demonstrator, located at Argonne National Laboratory, was used to demonstrate the continuous operation of a particle beam accelerator to produce a beam with an energy of up to 7 million electron volts. This demonstration will address not only issues related to the continuous operation of an accelerator such as cryogenic operation and thermal management but also the use of deuterium particles to enhance lethality. Over 90 percent of the hardware needed for this accelerator had been fabricated by 1993. SDIO completed this demonstration during fiscal year 1994.

SD10 developed lightweight foil neutralizers for stripping the electrons from hydrogen or deuterium ions to produce a beam of neutral atoms. Neutral atoms are unaffected by magnetic fields, so once accelerated and pointed at a target, they will proceed in a straight line. Foil neutralizers are lightweight, have no power requirements, and have been fabricated to weapon-level size.

A lightweight magnetic beam-expander telescope has been developed to focus and control the size of the beam at the target, In addition, a weapon level beam sensing technology has been developed and tested to sense the direction in which the neutral beam is pointed. The beam sensor can detect the direction of the beam at a very precise level and make corrections to ensure the beam is properly directed at the target.

SDIO reported that NPB'S primary mission, interactive discrimination, requires that detectors be developed and placed on a separate space platform to detect the emissions induced when the beam penetrates targets. This data is needed so NPB cm determine the mass of the target or assess the extent of damage to the target if NPB is used to destroy missiles. SD10 has investigated several different detector technologies such as multiwire proportional counter detectors, scintillating fiber optics, advanced ionization chambers, and solid state silicon detectors. The multiwire proportional counter detector and the scintillating fiber optics are the preferred concepts because of their proven operational capabilities and low sensitivity to gamma rays. Detector modules based on these technologies have been developed and are scalable to weapon level specifications.

The 1984 program plan objectives for resolving issues related to operating an NPB in space have been partially completed by three experiments. In 1989, SDIO completed a suborbital NPB space experiment, called Beam Experiment Aboard Rocket, at a cost of about $60 million at the White Sands Missile Range. This experiment achieved its primary objective of generating an NPB in space and its secondary objective of resolving a number of space physics issues that were potential obstacles to operating an NPB in space. The second experiment, the Army Background Experiment, successfully measured the natural neutron background of the earth with a neutron detector module developed for NPB applications. The third experiment consisted of three separate shuttle-based space experiments of neutralizer material interactions with atomic oxygen and the space environment. SDIO said the neutralizer material was not adversely affected by the space environment.

SDI0 also spent about $78 million planning another space experiment, called the integrated space experiment, which was to be a shuttle launched experiment to demonstrate NPB technologies on-orbit. This experiment, however, was canceled in 1988 because it was too expensive and the NPB technology was not mature enough to support the specified performance.

A complete NPB system must be demonstrated in space to resolve the space-related technology problems, The space demonstration is to determine the system's ability to propagate a beam to distant targets and is to also resolve other issues such as spacecraft charging, atomic oxygen effects, and control of effluents. By 1993 SDIO was considering two options for the space experiment: an experiment called far-field optics experiment and a larger experiment called Lunar Resource Mapper. The far-field optics experiment would cost about $260 million and could be launched on a Delta II vehicle and completed in 4 years. According to SDIO, the Lunar Resource Mapper experiment was of greater interest to the scientific community due to its ability to identify mineral resources on celestial bodies at much higher geographic resolution than possible with passive means.

SDIO developed a lightweight system to provide the power needed for the space platform. Such a power system must be capable of providing 20 kilowatts of housekeeping power on a long-term basis as well as megawatt levels of burst power to operate the NPB during a battle. SDI0 estimates in 1993 that it would cost $40 million to complete this program.

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