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The effects of buried-well potential perturbation under the buried-oxide (BOX) layer are studied in both a heavy-ion single event upset (SEU) test and a high-energy proton-SEU test of a silicon-on-insulator (SOI) dual interlocked storage cell (DICE)-based flip-flop. Their dependence on incident angle and back bias is discussed. We fabricated both DICE-based flip-flop and conventional flip-flop, which are designed as 80 000-stage shift-register chains. In a heavy-ion test, a considerable number of SEUs were observed at back bias exceeding 2.4 V, and a ten-times larger SEU-cross section was finally recorded at back bias of 3.0 V compared with the total active area of a DICE-based flip-flop cell. This marks the first case where DICE topology was found to be broken by buried-well potential perturbation on an SOI DICE-based flip-flop. In a proton test, one error was observed at back bias of 2.0 V. The SEU rate in the Van Allen belt at an altitude of 2300 km and an inclination of 90° was estimated as being once every 5 years.

Background Selective biliary cannulation (SBC) is the first challenge of endoscopic retrograde cholangiopancreatography (ERCP), especially for trainees, and a rotatable sphincterotome may be useful to guide the directional axis of the scope and SBC. Methods We performed a prospective randomized single-center trial, enrolling 200 patients with a native papilla who required therapeutic biliary ERCP. Patients were randomly assigned to the rotatable sphincterotome group (n = 100) or the conventional sphincterotome group (n = 100). The primary endpoint was successful SBC by the trainees within 10 minutes. Results The early and late cannulation success rates did not differ significantly between the groups (P = 0.46 and P > 0.99, respectively). For the patients in whom trainees failed to achieve SBC, the rotatable sphincterotome was used as a rescue cannulation technique in four patients from the conventional group; in no patients in the rotatable group was the conventional sphincterotome used for SBC. Post-ERCP pancreatitis (PEP) occurred in 11 patients (5.5 %; 6 mild, 5 moderate); the incidence did not differ significantly between the two groups (rotatable group 3 %, conventional group 8 %; P = 0.21). The two groups were thus combined for evaluation of the factors relating to cannulation difficulty for trainees, which revealed that orientation of the papilla was a significant factor (P Conclusions The type of sphincterotome used did not affect the success of SBC by trainees. However, orientation of the papilla was revealed to be a significant factor relating to cannulation difficulty for trainees overall.

Characteristics of ripples generated as transient responses with idealized current patterns in synchrotrons are studied along with practical applications. The ripples intrinsically occur in synchrotron magnets as a driven harmonic oscillation whenever ramp pattern currents are applied to the magnets. In realistic synchrotron magnet circuits, additionally, damping resistors and interconnection types should be taken into account, because they largely change such circuit parameters as resistance and capacitance. In this paper, effects of damping resistance and conductor types, such as cables and bus-bars, on intrinsic ripples are studied. Simulated results are obtained within realistic circumstances of J-PARC Main-ring Synchrotron in the present 30 GeV operations.

The acceleration of intense and high-energy muon beams is one of the challenge of future neutrino factories. The acceleration of such beams using the synchrotron motion inside stationary rf buckets of scaling fixed field alternating gradient (FFAG) rings is considered in this paper. Possible parameters of a 3.6–12.6 GeV muon ring using 200 MHz rf cavities is presented. Detailed particle tracking simulations are used to demonstrate the large 6D acceptance as well as the relatively good tolerance to errors of this scheme. The improvement of the current neutrino factory baseline scenario, using this type of FFAG ring, is finally discussed.

An RF accelerating system was developed for the 150 MeV FFAG accelerator to demonstrate rapid cycling acceleration. The 150 MeV FFAG accelerator has been developed as a prototype for various applications, such as proton cancer therapy. To achieve rapid cycling acceleration, a high-field gradient and a broadband impedance of the RF cavity were necessary. Therefore, we employed a magnetic alloy (MA) for a core material. The required field gradient and the bandwidth were 35 kV/m and 3.0 ± 1.5 MHz , respectively. Because of the strong fringing field of the focusing magnets of the FFAG accelerator, the RF cavity had to be magnetically shielded. An effective cooling system for the MA cores was also needed because of the large power dissipation of more than 1 W / cm 3 . We have developed an RF system satisfying these requirements and successfully demonstrated a rapid cycling acceleration of 100 Hz.

Fixed Field Alternating Gradient (FFAG) synchrotron was revived recently with modern accelerator technologies. Quite a few projects using FFAG synchrotrons have been proposed and some of them are under construction. One of the most interesting applications with FFAG synchrotron is an intense neutron source with emittance recovery internal target.

A superconducting magnet for the Fixed Field Alternating Gradient (FFAG) accelerator has been proposed. The static magnetic field is required to be proportional to the k-th power of the orbit radius where k is the geometrical field index of the accelerator. A left/right asymmetric coil with elliptical aperture is utilized to maximize the horizontal aperture with a compact design. The saddle shaped coil configuration is designed to fulfil the design requirement in terms of integral magnetic field along an arc orbit. In a beam tracking simulation, a particle was circulated and accelerated with the magnetic field generated by the designed coil. A prototype superconducting coil with a cylindrical bore was developed and the field quality was evaluated at warm field measurement

A new type of beam chopper has been developed and installed at HIMAC (Heavy Ion Medical Accelerator in Chiba) in NIRS (National Institute of Radiological Sciences). The chopper has only 11.6 cm length and has been set between the ion sources and the RFQ. It is similar to a beam transformer, and modulates the beam kinetic energy by 10%. The beam is successfully chopped because the RFQ has a rather small energy acceptance. A chopped beam was injected into the synchrotron and a beam study has been performed. A very short bunch was formed and accelerated to the top energy. The behavior of the short bunch shows that a dipole oscillation was excited because of an unexpected frequency error of the RF system. It was caused by noise in the B-clock (Gauss Clock) circuit. The dipole oscillation caused by the frequency error was significantly reduced and the acceleration efficiency was improved by replacing the B-clock module.

The fast extraction kicker magnets of the 50 GeV synchrotron are now in an intensive R&D stage. In the 50 GeV ring, the fast extraction system is designed to deliver the 50 GeV beam to the downstream neutrino oscillation experiment beam line with the Super-Kamiokande detector. At the same time, the fast extraction line is required to function as a beam abort, in case of hardware failure during acceleration of the beam from 3 GeV to 50 GeV. In order to fulfill both demands, the extraction system is designed to accommodate bipolar beam extraction. A new technology to make the bipolar kicker magnet system, using a symmetric Blumlein pulse forming network (SBPFN) system, has been introduced. Its validity is being investigated, both theoretically and experimentally. R&D programs aimed at establishing some of the important technical elements in the fast extraction kicker system are presently in progress. This R&D includes experimental studies of the bipolar kicker principle and the development of IGBT switching modules that satisfy full switching capability of the designed current and voltage.

The Japan Hadron Facility (JHF) accelerator complex comprises a 50-GeV main synchrotron, a 3-GeV rapid-cycling synchrotron, and a 400-MeV linac. The accelerators provide high-intensity, high-energy proton beams for various scientific fields. These high-intensity, high-energy accelerators, especially the 50-GeV main synchrotron, impose tight demands on the injection/extraction septum magnets for a thin structure, large aperture and high operating field. But to manufacture high field septum magnets on the condition of a large aperture is very difficult because of its extraordinarily strong electromagnetic force due to the self-field. To cope with these tight demands, new design concepts of septa are required. An opposite-field septum magnet system is one of the solutions to realize a thin septa or very high-field septum magnets.

Fixed field alternating gradient (FFAG) focusing synchrotron is attractive as a proton driver for the generation of intense secondary particles such as muons. The magnetic field of the FFAG synchrotron is static, therefore, the repetition rate of acceleration could be increased more than ten times larger, such as 1 kHz, than that of an ordinary rapid cycling synchrotron (RCS) if an efficient high-voltage rf accelerating system becomes available. Recently, a new type of high gradient and broad-band rf cavity using a high-permeability magnetic alloy (MA) has been developed and the FFAG focusing becomes very promising. In this paper, a design of 1.5 GeV and 10 MW beam power of proton driver is presented. In order to clarify the feasibility of rapid cycling FFAG synchrotron experimentally, a proof-of-principle (POP) machine, which accelerates protons up to 1 MeV with 1 kHz repetition, is under development.

In the replica-exchange molecular dynamics method, where constant-temperature molecular dynamics simulations are performed in each replica, one usually rescales the momentum of each particle after replica exchange. This rescaling method had previously been worked out only for the Gaussian constraint method. In this letter, we present momentum rescaling formulae for four other commonly used constant-temperature algorithms, namely, Langevin dynamics, Andersen algorithm, Nos\'{e}-Hoover thermostat, and Nos\'{e}-Poincar\'{e} thermostat. The effectiveness of these rescaling methods is tested with a small biomolecular system, and it is shown that proper momentum rescaling is necessary to obtain correct results in the canonical ensemble., Comment: 6 pages, (Revtex4), 4 figures

An ERIT (Emittane/energy Recovery Internal Target) scheme for generating intense secondary particles such as neutron, unstable nuclei, muon etc. with ionization cooling has been proposed. Intense neutron source based on ERIT with FFAG proton storage ring is under construction.

Beam blowup due to a half-integer resonance was observed in the HIMAC synchrotron with a nondestructive two-dimensional beam-profile monitor. As the betatron tune approached a half-integer, the vertical beam size became larger by about 13%. The measured rms beam size is in good agreement with a space-charge-included numerical simulation.

Recent simulation results imply that the number of particles in a high intensity synchrotron is limited by the resonance crossing of coherent mode oscillations, not by the incoherent one. In order to verify it, we measured the tune shift of quadrupole mode oscillations in HIMAC at National Institute of Radiological Sciences (NIRS) to show the connection with beam loss. In this paper, we discuss signals observed in a coasting beam. We also present the numerical calculation of envelope motion for a bunched beam.

The 150 MeV proton FFAG (fixed field alternating gradient) synchrotron has been developed for aiming to investigate the possibilities of various applications such as proton beam therapy. The construction started in September 2002, and almost completed recently. In the proceedings, the overview of construction and status of commissioning is to be reviewed

A preliminary design of the heavy ion collider (PS collider), which has been recently proposed at KEK PS, is described. The PS-Collider (PSC) aims to accelerate and collide various ions from protons (polarized) to gold an energy of 5-7 GeV/u and with a luminosity of 10/sup 25/ cm/sup -2/ s/sup -1/ in order to create high nuclear density matter ( rho approximately=10 rho /sub 0/) and high-energy spin physics. >

The present status of the design and R&D works for the accelerators of Japanese Hadron Facility (JHF) are expressed.

An antiproton accumulation and deceleration ring in the KEK proton synchrotron (KEK PS) complex has been designed. The KEK PS top energy is 12 GeV and it is enough to produce 2 GeV/c antiprotons. As many as 10/sup 5/ of them would be collected each synchrotron cycle, that is 2 second. After stacking and stochastic cooling of the beams, 10/sup 7/ to 10/sup 8/ antiprotons per hour should be available for physics experiments. There are several R&D items such as compression of the nine bunch train in the PS. Preliminary simulation has been done to look at single turn transfer of antiprotons to the proposed ring whose circumference is 1/3 of the PS.

The TRIUMF optically-pumped polarized H/sup -/ ion source (OPPIS) produces in excess of 150 /spl mu/A DC of H/sup -/ ion current at 85% polarization within a normalized emittance of 0.8 pi mm mrad. A 20 /spl mu/A beam was accelerated to 500 MeV through the small acceptance of the injection line and the cyclotron. A feasibility study of higher current production for application to multi-GeV accelerators has been performed. A polarized H ion current of 1.6 mA within a normalized emittance of 2.0 pi mm mrad was obtained after upgrading the ECR primary proton source. The source performance now well exceeds the original design parameters and clearly confirms the potential of the OPPIS technique for other accelerators.

A new type of fast beam chopper was developed and installed at the HIMAC facility. Test operations of the chopper have been carried out. The chopper is basically a periodic beam-energy transformer that performs 10% modulation of beam's kinetic energy. The modulated fraction of the beam is chopped off by the downstream RFQ due to the relatively narrow injection energy window of the RFQ. Some of the recent test results with the chopper are presented. Measured chopped beams show sharp spikes at the pulse edges. Their origin is studied by numerical calculations. Another topic is the beam injection studies at the HIMAC's main-ring with the use of the chopped beams.

The first acceleration of protons in a FFAG (Fixed Field Alternating Gradient) synchrotron was demonstrated at KEK in June 2000. Since the magnetic field in the FFAG is static, therefore the repetition rate depends only on the acceleration frequency. We have developed a high gradient rf cavity using the 'FINEMET' magnetic alloy cores. With this new type of rf cavity, the, cycle time of the synchrotron can become very high, 1 kHz or more, which is more than 100 times of the ordinary synchrotron. Thus, the FFAG is an attractive machine for accelerating intense beams. Moreover, the FFAG can accelerate not only single bunch, but also several bunches each having a different energy, by changing the rf frequency for each bunch. The new type rf cavity using the FINEMET cores has a low Q-value which easily enables the coexistence of different frequencies. We have demonstrated this multi-energy, multi-bunch acceleration at the KEK POP FFAG machine.

The 150 MeV proton FFAG (Fixed Field Alternating Gradient) synchrotron is under construction at KEK to investigate the possibilities of various applications such as proton beam therapy after the success of the POP FFAG synchrotron. One of distinguished features of this machine compared with the PoP FFAG is to use a new type of magnet, "Return-Yoke Free" magnet. Because there is no return-yoke in the median plane in this magnet, the beam injection and extraction become easier.

Beam losses due to half-integer resonance have been observed in the Heavy Ion Medical Accelerator in Chiba synchrotron, along with exciting the harmonic component of gradient field errors. During operation, while varying the defocusing quadrupole to cross a half-integer tune in the vertical space, the region of bare tunes which causes the half-integer resonance was evaluated. When the initial beam intensity was high, the bare tune where the beam loss occurred became higher. The beam loss occurred rapidly when the half-integer tune was crossed upward, but gradually when it was crossed downward. Those results mean that the half-integer resonance is affected by space-charge-induced tune shifts. This fact was verified experimentally for the first time. The results from a one-dimensional multiparticle simulation agreed with those characteristics. Finally, the beam-size growth and the change in distribution were studied by a simulation.

One of the frontiers of accelerator science is the path toward the highest beam power. Many new accelerators are based on this philosophy. In proton accelerators, the high beam power allows production of a variety of intense secondary particle beams such as kaons, neutrons , muons, neutrinos, antitprotons , and short-lived radioactive nuclear beams. In nuclear and particle physics, an example using these secondary beams is to measure rare processes such as neutrino oscillations and CP violations. In addition, sciences and technologies other than particle and nuclear physics can be carried out by using these secondary beams. These sciences and technologies include a) material and life sciences with neutron and muon beam, b) accelerator -driven nuclear transmutation of long-lived nuclides in nuclear waste, and others related to the various secondary particles. In order to realize these requirements, the new high intensity proton facility is under construction in Japan as a joint project of the Japan Atomic Energy Research Institute (JAERI) and the High Energy Accelerator Research Organization (KEK). The location of the facility is the JAERI/Tokai site. The project has evolved from the Neutron Science Project (NSP) of JAERI and the Japan Hadron Facility (JHF) project of KEK. In Fig. 1, expected beam powers in the present facility are compared with those available in the world.

The acceptance of the KEK booster has large side value (272 /spl pi/ nm mrad in the horizontal plane and 61/spl pi/ mm mrad in the vertical plane). To increase the beam intensity we have been trying to achieve painting injection in the horizontal plane. The intensity-dependent emittance exchanges in the horizontal and vertical plane were measured by a method using a scraper and bump magnets method. In order to clarify the experimental results, multiparticle tracking was performed with self-consistent space-charge forces. The experimental and simulation results imply that a space-charge potential of a beam-induced coupling exists between the horizontal and vertical planes.

Beam commissioning of the new proton therapy system for University of Tsukuba was started in September 2000. The present system employs a synchrotron with a maximum energy of 250 MeV and two rotating gantries. The beam was successfully accelerated up to 250 MeV and transported to the irradiation nozzles. The position of the beam extracted from the synchrotron was confirmed to be very stable and sufficient flatness for the irradiation area was realized by using the dual ring double scattering method developed at University of Tsukuba. Furthermore, synchrotron operation triggered by patient respiration signal was succeeded.

Longitudinal beam emittance should be controlled to alleviate space charge effects and to avoid beam instabilities by rf manipulations at proton synchrotrons in JAERI-KEK Joint High Intensity Proton Accelerator Project. Furthermore, heavy beam loadings should be compensated for stable acceleration. The cures for them are reported with particle tracking simulations.

We designed an impedance tuner consisting of an inductive material, FINEMET, to cancel the space charge impedance in the longitudinal direction. It was installed in the KEK Proton Synchrotron (PS) main ring. We observed the frequency shift of the coherent quadrupole oscillations and inferred the shift of the incoherent synchrotron oscillation. The total reactive impedance can be estimated as the coefficient between the shift and the beam intensity. The measured impedance is reduced from −j2475Ω to −j1182Ω by the impedance tuner which consists of 12 pieces of FINEMET cores. We demonstrated that the space charge impedance is compensated by the impedance tuner. This is the first time for FINEMET to be equipped with an accelerator component. One may think that the characteristics of FINEMET deteriorate under an environment with strong radiation generated by unavoidable beam loss. We have proved that the radiation dose not affect FINEMET even with a total neutron dose of 1.83×1012(n cm−2), which is considered ...

This paper introduces a new type of chopper, which is similar to a beam transformer first discussed by R. Wideroe (1928). It is based on the fact that the RFQ has a rather small energy window. A pulsed beam transformer that provides 10% energy modulation to the beam in front of an RFQ can effectively chop the beam. It has fast rise- and fall-time and a short physical length. A prototype, which consists of a cavity and a high voltage pulsed power supply, has been constructed and tested. Two types of magnetic materials were tried for making the core of the cavity-the Finemet and the ferrite Philips 4M2. While the former gave good performance, the latter failed the test. Results from the bench measurements and a plan for beam tests are briefly described.

In collaboration with KEK two barrier cavities, each generating 40 kV per turn have been installed in the Brookhaven AGS. Machine studies are described and their implications for high intensity operations are discussed.

A multi-orbit synchrotron (MOS) with fixed field alternating gradient (FFAG) focusing is attractive for acceleration of high intensity hadron beams because acceleration cycle could be increased. The magnetic field of MOS is static, therefore, the repetition rate of acceleration could be increased more than 10 times larger than that of ordinary rapid cycling synchrotron (RCS) if an efficient high voltage RF accelerating system becomes available. Recently, a new type of high gradient RF cavity (HGC) using high permeability magnetic alloy (MA) has been developed and MOS with FFAG focusing becomes very promising. In order to clarify the feasibility of rapid cycling MOS (RCMOS) experimentally, proof-of-principle (POP) machine, which accelerates protons up to 1 MeV with 1 kHz repetition, is under development. We have also made several designs on high intensity proton accelerators with RCMOS for various applications such as an accelerator driven system (ADS) as an energy breeder, a spallation neutron source and a proton driver for a muon collider.

Fixed Field Alternating Gradient (FFAG) is a strong candidate for muon accelerators of the neutrino factory because fixed field allows essential fast acceleration for muon. Roughly speaking, we have two schemes to design FFAG optics, scaling and non-scaling [1]. Scaling FFAG has constant betatron tunes, in principle, with the magnetic field having nonlinear components. However, tunes slightly change during acceleration because of imperfection of the field. On the other hand, a condition of constant tunes is given up in non-scaling FFAG to obtain other advantages such as simple lattice composed of only linear elements. Then, beam dynamics of resonance crossing has become an important issue for both scaling and non-scaling FFAG. Since keeping constant tunes is basic strategy to avoid resonance, dynamics of resonance crossing has not been studied sufficiently. There are especially not many experimental studies. We performed beam studies of third order resonance crossing at PoP FFAG and HIMAC synchrotron. Their main results are described in this paper.

Acceleration of the polarized proton beam at the KEK PS up to 3.5 GeV is described. In the booster synchrotron, 75% of the linac beam polarization was preserved without any correction for the depolarizing resonances. In the main ring, almost 100% of the booster beam polarization was preserved at 3.5 GeV by the fast passage method for the intrinsic resonances and by the closed orbit correction for the imperfection resonances. The KEK PS is the first cascaded synchrotron which has demonstrated acceleration of a polarized beam.

Faraday rotation of optically pumped sodium atoms in a weak magnetic field, which is lower than the critical field of hyperfine splitting, was obtained theoretically. The estimated rotation angles were compared with the experiments for various magnetic fields. The measured values showed good agreement with the values calculated from the theory.

Optically pumped polarized H- ion source has been developed at KEK. Various improvements have been made for stably long term operation. Among them, efforts were concentrated to develop a control system for pumping dye lasers with a personal computer and an ECR ion source. We also examine polarizing effect of dissociated hydrogen atoms from H2+ ions and show that it could be possible to use H2+ ions instead of H+ ions in this type of polarized ion source.

The effect of radiation trapping in an optically pumped sodium target was measured with a Faraday rotation method. The experimental results were compared with calculations based on recent theoretical work, and good agreement was found between the two.

An Alvarez linac is being built to increase the injection energy of the booster synchrotron from 20 MeV to 40 MeV. Its drift tubes are equipped with quadrupole permanent magnets. It has post couplers and still inherits the two feed system. Two TH 516 RF high power amplifiers, which have excited the 20 MeV linac, are modified so that one excites the old linac and the other the new one. 40 MeV H- beams will be supplied to the booster in November of 1985.

Depolarization resonance in a strong‐focusing synchrotron is discussed. Correction of the depolarization resonance is performed at the booster synchrotron and at the main ring. Using these methods the KEK PS has delivered a polarized proton beams at 3.5 Gev to physics experiments from May 1987.(AIP)

A multi‐cusp H− ion source was built for the charge‐exchange multiturn injection project in the KEK 500 MeV booster proton synchrotron. More than 20 mA H− ion beam was extracted from the ion source, 18 mA was injected in the linac and 8.5 mA was accelerated up to 20 MeV. Beam was successfully injected in the booster and a new intensity record of 500 MeV proton beam was obtained.

Optically pumped polarized H− ion source has been developed for the 12 GeV proton synchrotron at KEK. Sodium atoms are electron‐spin polarized by two single frequency dye lasers. Protons, which are yielded by an ECR ion source, receive the polarized electrons from the sodium atoms and are polarized by conventional zero‐crossing method. The hydrogen atoms become H− ions by charge‐exchange reaction with sodium vapor. Beam intensities and polarizations so far achieved are 15 μA with 60 % and 25 μA with 40 % at 350 keV. The intensity increases recently to 30 μA and the beam is accelerated to 20 MeV by the linac and injected in the 500 MeV booster synchrotron. The polarization is 45∼56 % at 20 MeV.

Due to their finite lifetime, muons must be accelerated very rapidly. It is challenging to make the magnets ramp fast enough to accelerate in a synchrotron, and accelerating in a linac is very expensive. One can use a recirculating accelerator (like CEBAF), but one needs a different arc for each turn, and this limits the number of turns one can use to accelerate, and therefore requires significant amounts of RF to achieve the desired energy gain. An alternative method for muon acceleration is using a fixed field alternating gradient (FFAG) accelerator. Such an accelerator has a very large energy acceptance (a factor of two or three), allowing one to use the same arc with a magnetic field that is constant over time. Thus, one can in principle make as many turns as one can tolerate due to muon decay, therefore reducing the RF cost without increasing the arc cost. This paper reviews the current status of research into the design of FFAGs for muon acceleration. Several current designs are described and compared. General design considerations are also discussed

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides continued work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (CoM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay ($��\to ����_��$) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. We also present theoretical and experimental R & D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the R & D since the Feasibility Study of Muon Colliders presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)]., 95 pages, 75 figures. Submitted to Physical Review Special Topics, Accelerators and Beams

The electron-spin polarization of optically pumped sodium atoms for a polarized H− ion source was measured by a Faraday rotation method. This paper presents the theory of this scheme and some experimental results which have been obtained so far. When two pumping lasers were used, a sodium electron-spin polarization of about 90% was obtained at a target thickness of 1 × 1013n/cm2.