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In preparation for an experiment with a laser-generated intense proton beam at the Laser Fusion Research Center at Mianyang to investigate the 11B(p,α)2α reaction, we performed a measurement at very low proton energy between 140 keV and 172 keV using the high-voltage platform at the Institute of Modern Physics, Lanzhou. The aim of the experiment was to test the ability to use CR-39 track detectors for cross-section measurements and to remeasure the cross-section of this reaction close to the first resonance using the thick target approach. We obtained the cross-section σ = 45.6 ± 12.5 mb near 156 keV. Our result confirms the feasibility of CR-39 type track detector for nuclear reaction measurement also in low-energy regions.

The laboratory generation and diagnosis of uniform near-critical-density (NCD) plasmas play critical roles in various studies and applications, such as fusion science, high energy density physics, astrophysics as well as relativistic electron beam generation. Here we successfully generated the quasistatic NCD plasma sample by heating a low-density tri-cellulose acetate (TCA) foam with the high-power-laser-driven hohlraum radiation. The temperature of the hohlraum is determined to be 20 eV by analyzing the spectra obtained with the transmission grating spectrometer. The single-order diffraction grating was employed to eliminate the high-order disturbance. The temperature of the heated foam is determined to be T = 16.8 ± 1.1 eV by analyzing the high-resolution spectra obtained with a flat-field grating spectrometer. The electron density of the heated foam is about N e = 4.0 ± 0.3 × 10 20 cm − 3 under the reasonable assumption of constant mass density.

We report on charge state measurements of laser-accelerated carbon ions in the energy range of several MeV penetrating a dense partially ionized plasma. The plasma was generated by irradiation of a foam target with laser-induced hohlraum radiation in the soft X-ray regime. We used the tri-cellulose acetate (C$_{9}$H$_{16}$O$_{8}$) foam of 2 mg/cm$^{-3}$ density, and $1$-mm interaction length as target material. This kind of plasma is advantageous for high-precision measurements, due to good uniformity and long lifetime compared to the ion pulse length and the interaction duration. The plasma parameters were diagnosed to be T$_{e}$=17 eV and n$_{e}$=4 $\times$ 10$^{20}$ cm$^{-3}$. The average charge states passing through the plasma were observed to be higher than those predicted by the commonly-used semiempirical formula. Through solving the rate equations, we attribute the enhancement to the target density effects which will increase the ionization rates on one hand and reduce the electron capture rates on the other hand. In previsous measurement with partially ionized plasma from gas discharge and z-pinch to laser direct irradiation, no target density effects were ever demonstrated. For the first time, we were able to experimentally prove that target density effects start to play a significant role in plasma near the critical density of Nd-Glass laser radiation. The finding is important for heavy ion beam driven high energy density physics and fast ignitions., Comment: 7 pages, 4 figures, 35 conferences

Intense particle beams generated from the interaction of ultrahigh intensity lasers with sample foils provide options in radiography, high-yield neutron sources, high-energy-density-matter generation, and ion fast ignition. An accurate understanding of beam transportation behavior in dense matter is crucial for all these applications. Here we report the experimental evidence on one order of magnitude enhancement of intense laser-accelerated proton beam stopping in dense ionized matter, in comparison with the current-widely used models describing individual ion stopping in matter. Supported by particle-in-cell (PIC) simulations, we attribute the enhancement to the strong decelerating electric field approaching 1 GV/m that can be created by the beam-driven return current. This collective effect plays the dominant role in the stopping of laser-accelerated intense proton beams in dense ionized matter. This finding is essential for the optimum design of ion driven fast ignition and inertial confinement fusion., A detailed understanding of particle stopping in matter is essential for nuclear fusion and high energy density science. Here, the authors report one order of magnitude enhancement of intense laser-accelerated proton beam stopping in dense ionized matter in comparison with currently used models describing ion stopping in matter.

The X-ray emissions in the interaction of 3–6 MeV Xe23+ ions into thick solid In target are measured. The projectile-to-target and target Lα/Lβ X-ray production intensity ratios are observed to strongly depend on the projectile energy. The dependence deviates from Coulomb ionization predictions, which implies the important roles of coupling between subshells and the activation of 4fσ rotational couplings for projectile energy larger than 5 MeV.

The proton-boron (p 11 B) reaction is regarded as the holy grail of advanced fusion fuels, where the primary reaction produces 3 energetic α particles. However, due to the high nuclear bounding energy and bremsstrahlung energy losses, energy gain from the p 11 B fusion is hard to achieve in thermal fusion conditions. Owing to advances in intense laser technology, the p 11 B fusion has drawn renewed attention by using an intense laser-accelerated proton beam to impact a boron-11 target. As one of the most influential works in this field, Labaune et al. first experimentally found that states of boron (solid or plasma) play an important role in the yield of α particles. This exciting experimental finding rouses an attempt to measure the nuclear fusion cross section in a plasma environment. However, up to now, there is still no quantitative explanation. Based on large-scale, fully kinetic computer simulations, the inner physical mechanism of yield increment is uncovered, and a quantitative explanation is given. Our results indicate the yield increment is attributed to the reduced energy loss of the protons under the synergetic influences of degeneracy effects and collective electromagnetic effects. Our work may serve as a reference for not only analyzing or improving further experiments of the p 11 B fusion but also investigating other beam-plasma systems, such as ion-driven inertial confinement fusions.

The hydrodynamic behavior of a cylindrical solid target, heated by the intense heavy-ion beams, was simulated. The target was of the LAboratory PlAnetary Science (LAPLAS)-type geometry, as described by Tahir (LAPLAS). An iron target irradiated by the intense heavy-ion beams, with parameters available from the planned High Intensity Accelerator Facility or Facility for Antiproton and Ion Research, Society for Heavy Ion Research, Darmstadt, Germany, will transform to the warm-dense state, similar to the situation that exists in the planet interior. The dependence of the achievable state of iron on the outer-shell material and beam location was investigated with Medusa-code simulations. The simulation results show that the compression of inner iron is significantly influenced by the density-to-mass ratio of the outer-shell material and the location of the beam heating. Using the LAPLAS geometry, a uranium beam of 800 MeV/u, and 1.5 × 10 11 particles per pulse, our simulations show that the warm-dense-matter regime for iron is obtained. Details depend on the yet unknown equation of state and will be measured when this beam intensity is available in a couple of years.

We report on a precision energy loss measurement and theoretical investigation of $100\text{ }\text{ }\mathrm{keV}/u$ helium ions in a hydrogen-discharge plasma. Collision processes of helium ions with protons, free electrons, and hydrogen atoms are ideally suited for benchmarking plasma stopping-power models. Energy loss results of our experiments are significantly higher than the predictions of traditional effective charge models. We obtained good agreement with our data by solving rate equations, where in addition to the ground state, also excited electronic configurations were considered for the projectile ions. Hence, we demonstrate that excited projectile states, resulting from collisions, leading to capture-, ionization-, and radiative-decay processes, play an important role in the stopping process in plasma.

We studied the explosive evaporation of high energy density matter generated by irradiation of intense heavy ion beams and the resulting effect on the dynamic vacuum of the accelerator beamlines. High Energy Density Physics (HEDP) experiments are proposed at the plasma physics terminal at the Facility of Antiproton and Ion Research (FAIR), which is currently under construction. The target response to irradiation by intense beam was simulated by HEIGHTS (High Energy Interaction with General Heterogeneous Target Systems) simulation package. The vacuum deterioration resulting from the target evaporation was simulated with the Molflow+ Monte-Carlo simulator. Experimentally we measured the pressure wave propagation at the HTD beamline at GSI in order to benchmark the simulation. The pressure wave was generated through ohmic heating of a cold surface.

The research activities on warm dense matter driven by intense heavy ion beams at the new project High Intensity heavy-ion Accelerator Facility (HIAF) are presented. The ion beam parameters and the simulated accessible state of matter at HIAF are introduced, respectively. The progresses of the developed diagnostics for warm dense matter research including high energy electron radiography, multiple-channel pyrometer, in-situ energy loss and charge state of ion detector are briefly introduced. Keywords: Warm dense matter, Intense heavy ion beams, HIAF, Electron radiography, PACS Codes: 34.50.Bw, 94.20.Fg, 52.40.Mj, 87.59.B-, 41.75.Lx

We summarize our theoretical studies for stopping power of energetic heavy ion, diatomic molecular ions and small clusters penetrating through plasmas. As a relevant research field for the heavy ion inertial confinement fusion (HICF), we lay the emphasis on the dynamic polarization and correlation effects of the constituent ion within the molecular ion and cluster for stopping power in order to disclose the role of the vicinage effect on the Coulomb explosion and energy deposition of molecules and clusters in plasma. On the other hand, as a promising scheme for ICF, both a strong laser field and an intense ion beam are used to irradiate a plasma target. So the influence of a strong laser field on stopping power is significant. We discussed a large range of laser and plasma parameters on the coulomb explosion and stopping power for correlated-ion cluster and C60 cluster. Furthermore, in order to indicate the effects of different cluster types and sizes on the stopping power, a comparison is made for hydrogen and carbon clusters. In addition, the deflection of molecular axis for diatomic molecules during the Coulomb explosion is also given for the cases both in the presence of a laser field and laser free. Finally, a future experimental scheme is put forward to measure molecular ion stopping power in plasmas in Xi'an Jiaotong University of China. Keywords: Molecules, Stopping power, Coulomb explosion, Vicinage effect, Laser, PACS Codes: 34.50.Bw, 52.40.Mj, 61.85.+p, 34.50.Dy

This paper reports the measurement of the energy loss of protons at the energy of 100 keV penetrating a partially ionized hydrogen plasma. The plasma of ne≈ 1015–16cm−3; Te≈ 1–2 eV and lifetime of about 8 µs is created by the hydrogen gas discharge. The experimental results show an increase of a factor of 2.8 in the energy loss, which are in good agreement with the Bethe, Standard Stopping Model, Li–Petrasso and Vlasov models’ predictions within the error limit. The Bethe–Bloch Coulomb logarithm term is found to increase by a factor of 4.0 for free electrons as compared with the situation where bound electrons prevail. The potential application of protons energy loss for diagnosing the electron density in plasma is proposed too.

The hydrodynamic response of solid target heated by heavy ion beams at High Intensity Accelerator Facility (HIAF) project was simulated with 1-D computer code. The energy deposition was benchmarked by a 2-D program. The work serves to show the prospect of HIAF project for High Energy Density Physics (HEDP) study, and provide helpful information for the future experiments. Various target materials and schemes are used in the calculation. The results show that in the first phase of HIAF project, the available ion beam is already a powerful tool to generate HED matter with specially designed target, and the second phase of the project will extend the accessible state of matter a big step further. What’s more, the hydrodynamic behavior of the target under direct heating indicates that the beam parameter design for HEDP research should come to a compromise, which means, for example, with higher intensity or smaller focal spot, the beam pulse length must be compressed short enough to avoid the target dispersal before the end of the pulse.

In this paper, we report visible light emission from 320 keV Krq+ (4 ≤ q ≤ 9) ions on the Cu target. The wavelength range measured is from 300 nm to 656 nm. Two Cu I spectra deriving from different initial states and one Kr I line are detected. Specifically, the two Cu I lines belong to transitions 3d104p(2P03/2) − 3d104s (2S1/2) at 324.78 nm (A) and 3d104p(2P01/2) − 3d104s(2S1/2) at 327.42 nm (B), respectively, and the photon yield ratio of spectra lines (A) and (B) are about 2:1. The Kr I line belongs to transition 4s24p5(2P03/2)11d 2[3/2]0 − 4s24p5(2P03/2)5p 2[1/2] at 486.12 nm (C). In addition, the experimental results show that the photon yields of all lines are increasing with the charge state increase.

Secondary electron emission yield from the surface of SiC ceramics induced by Xe17+ ions has been measured as a function of target temperature and incident energy. In the temperature range of 463–659 K, the total yield gradually decreases with increasing target temperature. The decrease is about 57% for 3.2 MeV Xe17+ impact, and about 62% for 4.0 MeV Xe17+ impact, which is much larger than the decrease observed previously for ion impact at low charged states. The yield dependence on the temperature is discussed in terms of work function, because both kinetic electron emission and potential electron emission are influenced by work function. In addition, our experimental data show that the total electron yield gradually increases with the kinetic energy of projectile, when the target is at a constant temperature higher than room temperature. This result can be explained by electronic stopping power which plays an important role in kinetic electron emission.

In this work, we studied the photon emission in the visible light range for Xeq+ ions of different charge states (10 ≤ q ≤ 21) bombardment on an aluminum target at 410 keV. During the interactions, the spectra in wavelength range 300–500 nm are recorded, including the photons from Al atoms and neutralized Xe+ ions. The yield of the visible light strongly depends on the projectile charge states. Its variation tendency with the charge states is similar to that of the potential energy variation. In addition, the experimental results also indicate that when the incident charge state is less than the critical charge state, it obeys the staircase classical-over-barrier model.

We present a scheme of electron beam radiography to dynamically diagnose the high energy density (HED) matter in three orthogonal directions simultaneously based on electron Linear Accelerator. The dynamic target information such as, its profile and density could be obtained through imaging the scattered electron beam passing through the target. Using an electron bunch train with flexible time structure, a very high temporal evolution could be achieved. In this proposed scheme, it is possible to obtain 1010 frames/second in one experimental event, and the temporal resolution can go up to 1 ps, spatial resolution to 1 µm. Successful demonstration of this concept will have a major impact for both future inertial confinement fusion science and HED physics research.

K-shell X-ray emission of Silicon induced by near-Bohr-velocity ions was systematically investigated in collision systems for which the ratio of projectile-to-target atomic numbers (Z1/Z2) ranged from 0.07 to 3.79. The results show that, in asymmetric collisions, the measured K-shell X-ray production cross sections of Silicon fit very well with the predictions of different direct ionization models depending on the atomic number of projectile. In the case of near-symmetric collisions (Z1/Z2 ∼ 1), an obvious enhancement of the X-ray production cross section was observed, which can be attributed to the vacancy transfer within the framework of quasi-molecular model.

The generation of highly polarized high-energy brilliant γ-rays via laser–plasma interaction is investigated in the quantum radiation-reaction regime. We employ a quantum electrodynamics particle-in-cell code to describe spin-resolved electron dynamics semiclassically and photon emission and polarization quantum mechanically in the local constant field approximation. As an ultrastrong linearly polarized (LP) laser pulse irradiates a near-critical-density (NCD) plasma followed by an ultrathin planar aluminum target, the electrons in the NCD plasma are first accelerated by the driving laser to ultrarelativistic energies and then collide head-on with the laser pulse reflected by the aluminum target, emitting brilliant LP γ-rays via nonlinear Compton scattering with an average polarization of about 70% and energy up to hundreds of MeV. Such γ-rays can be produced with currently achievable laser facilities and will find various applications in high-energy physics and laboratory astrophysics.

High-energy-density physics (HEDP) deals with the study of matter under extreme conditions with an energy density higher than 1011 J/m3, corresponding to a pressure of 100 GPa. Such matter exists in abundance in deep interiors of the planets and stars. It also exists for a short duration during nuclear explosion and the loading of high-power-pulsed machines. HEDP is the international frontier of national security, astrophysics and fusion science, and it is also one of the main scientific goals of the high-power laser-facilities, Z-machines and heavy-ion-accelerators. Herein, the HEDP research based on High Intensity heavy-ion Accelerator Facility (HIAF), which is the “12th Five-Year Plan” national major science and technology infrastructure, will be introduced. The HIAF is advocated to provide the world with a heavy-ion beam with utmost high power. The energy and power of one beam pulse is about 100 J and several TW, respectively. With such a high-power heavy-ion beam, heating a solid-state lead sample, for example, could generate homogenous high-energy-density matter with a spatial scale from mm to cm and a temperature of 10 eV, near-solid density, and energy density of 1013 J/m3. Thus, through the HIAF, the generation, properties and evolution of high-energy-density matter can be investigated. This paper also reports the state of the art in the field of HEDP based on HIAF, including the generation and development of high-energy-density matter driven by a high-intensity heavy-ion beam, micro mechanism of interaction between the ion beam and dense matter or plasma, and key diagnostics of the high-energy-density matter driven by a hevy-ion beam.

In near Bohr velocity ion-atom collisions, a dependence of target K-shell ionization cross sections upon the ionic charge states has been observed. Experiments were performed in silicon solid target with 2–5 MeV iodineq+ ions incident in charge states +20 to +25. K-shell ionization cross section of silicon for q = 20 and 22 iodine ions impact with the same incident energy are almost equal, and are well described by the theory of binding-energy-modified BEA. However, for q = 25 iodine ions collisions, 3d vacancies of projectile transfer to the 1s orbit of target atom via rotational coupling of 3dπ, δ-3dσ molecular orbits in the framework of quasi-molecular model, which results in an increase of the K-shell ionization cross section of silicon.

We have measured the L-shell X-rays of iodine from the collisions of 3 MeV Iq+(q=15,20,22,25,26) ions with an iron target. It is found that the X-ray yield decreases with the increasing initial charge state. The energy of the subshell X-ray has a blue shift, which is independent of the projectile charge state. In addition, the relative intensity ratios of Lβ1,3,4 and Lβ2,15 to Lα1,2 X-ray are obtained and compared with the theoretical calculations. That they are larger than for a singly ionized atom can be understood by the multiple ionization effect of the outer-shell electrons.

The K-shell X-rays of argon from the collisions of 1–3 MeV Ar 11+ ions with V target were measured. It was found that the Kα X-ray shifts to the high energy by 52 eV, and the intensity ratio of Kβ/Kα was larger than the atomic data, owing to the presence of 2p multiple vacancies. The X-ray production cross sections were obtained and compared with BEA, PWBA and ECPSSR theoretical predictions. The BEA model, taking into account the ionic binding energy, coulomb repulsion and multiple ionization effect on fluorescence yield, presented a better agreement with the experimental cross section data.

Highly charged ( 129 Xe q+ , q = 10–30) ion-induced secondary electron emission and formation of nanostructure on the surface of highly oriented pyrolytic graphite (HOPG) have been studied on the 320 kV ECR platform for Highly Charged Ion Beam at IMP-CAS, Lanzhou. The experimental data of the total secondary electron yields are used to separate contributions of kinetic and potential electron yields. The estimated kinetic electron yields are about 17 and 35 electron/ion by ions with kinetic energies of 600 keV and 5 MeV, respectively. The potential electron yield increases linearly with increasing potential energy of the incident ion. The total electron yield, however, does not depend significantly on kinetic energy. AFM analysis of the HOPG surface bombarded with Xe 30+ ions revealed regular hillock like nanostructure. The relationship between hillock size (height and width) and ion’s energy (including potential energy and kinetic energy) shows the same trend with the total electron yield which increases with potential energy and is independent on incident kinetic energy.

The L-shell X-ray emission of Xenon was measured for 6 MeV Xe20+ ions impacting on V, Fe, Ni, Cu and Zn targets. The distinct L-subshell X-rays and the energy shift were observed. The L-shell ionization and the multiple ionization of the outer-shell were investigated. In addition, the relative intensity ratios of Lα1,2 to Lβ1,3,4 and Lβ2,15 were obtained, which approximately decrease linearly with the increasing target atomic number. That was interpreted by considering multiple ionization of the outer-shell electron.

The electron emission yield γ induced by Ne2+ and O2+ impacting on a clean tungsten surface has been measured. The range of projectile energy is from 3 keV/u to 14 keV/u. The total electron yield gradually increases with the projectile velocity. It is found simultaneously that the total electron yield for O2+ is larger than the total electron yield for Ne2+, which is opposite to the results for higher projectile velocity. After considering the contribution from recoiling atoms to the energy distribution and electron emission yield, we find that recoiling atoms are of crucial importance in electron emission in our energy range. Thus, the unexpected results in our experiment can be explained successfully.

In this work, we review current trends in China to investigate beam plasma interaction phenomena. Recent progresses in China on low energy heavy ions and plasma interaction, ion beam-plasma interactions under the influences of magnetic fields, high energy heavy ion radiography through marginal range method, energy deposition of highly charged ions on surfaces and Raman spectroscopy of surfaces after irradiation of highly charged ions are presented.

M-shell ionization of tungsten by Ar12+ ions were investigated in the energy range of 1.2–3.0 MeV. The measurements were also implemented for H, He and Xe ions as a comparative study. A significant shift of the M X-ray lines to the higher energy side caused by multiple ionizations, which was verified by the analysis of the intensity ratios of M γ and M α β , was observed. The total experimental cross sections of tungsten were compared with the PWBA and ECPSSR theoretical predictions, which are based on two extreme assumptions, namely, single ionization and full ionization.

The observation of the extensive air showers has been carried out since 1990 by Tibet air-shower array to study the origin of the cosmic-rays. In order to investigate the chemical composition around the knee, air-shower core detector was used in two experimental phases aiming to separate light primary elements (proton and helium). In a first phase experiment made in 1996-1999, primary proton and helium spectra were measured using a hybrid detector consisted of Tibet II air-shower array, emulsion chambers, and burst detectors. The result indicated that the fraction of light elements among the all particle spectrum is less than 30%. We performed the second phase experiment in 2002-2005 to measure proton + helium together to confirm the previous result with higher statistics by improving the detection efficiency for the air-shower cores. The P + He spectrum was obtained in a good agreement with previous result by several times higher statistics. The flux of the light elements, together with the all-particle energy spectrum, indicates the dominance of nuclei heavier than helium in the energy range around the knee. We also present the outline of the next phase experiment, which is to measure the heavy elements around the knee, using low threshold air-shower core detector named YAC. (C) 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.

The hydrodynamic behavior of metal targets when heated by intense proton beams was simulated numerically. The dependence of the achieved warm dense matter state for targets with different materials was investigated by means of a computer code based on two-dimensional fluid models with quantum corrections. Under the irradiation of a proton beam with an energy of 10 MeV, a particle number of 7.9 × 107, and a pulse duration of 10 ps, the numerical simulation results show that the achieved state is significantly influenced by the Winger-Seitz radius rs of materials.

The Tibet-III air shower array, consisting of 789 scintillation detectors, has been operating successfully at Yangbajing in Tibet since 1999. Some recent results on gamma-ray observation by the Tibet-III air shower array are introduced and its future prospects of gamma-ray observation will be discussed.

Recent results and future prospects of the Tibet air-shower experiment are reported on the all-particle energy spectrum and the chemical composition of cosmic rays around 10 15 eV energy range. The knee of the all-particle energy spectrum has been clearly observed at the energy around 4 ×10 15 eV by Tibet III air-shower array located at Yangbajing, Tibet, China (atmospheric depth 606 g/cm 2 , area 37,000 m 2 ). The energy spectrum of light components (protons and helium) measured by air-shower-core detector exhibits steeper power index than that of direct measurements below 10 14 eV, leading to decreasing fraction of the light component toward the knee. Hence, it is strongly suggested that the origin of the knee is related with the change of the chemical composition of cosmic rays. A new air-shower-core detector called `YAC' is under the preparation for explicit measurement of the heavy component.

We present an updated all-particle energy spectrum using data collected in the period from 2000 November through 2004 October by Tibet III air-shower array. The energy determination of the air showers is made by fitting the lateral density distribution of the shower particles to the modified NKG function which is optimized by simulation calculation using interaction models of QGSJET01c and SIBYLL2.1 taking into account of the detector configurations. It is shown that the model dependence in the energy determination is not significant, being less than 5% in the absolute flux value, and we obtained the cosmic ray energy spectrum in a wide range over 3 decades between 10(14) eV and 10(17) eV, in which the position of the knee is clearly seen at around 4 PeV. The spectral index is -2.68 +/- 0.02(stat.) below 1PeV, while it is -3.12 +/- 0.01(stat.) above 4 PeV. The various systematic errors are under study now.

We are planning to build a large water-Cherenkov-type muon detector array around the Tibet air shower array for Gamma-ray astronomy in the 100 TeV Region. In this paper, we describe the design of the Tibet MD array and details of the Monte Carlo simulation to demonstrate the sensitivity of the Tibet AS+MD array.

The Tibet air shower array with effective area 37,000 m 2 located at 4300m in altitude, in Tibet, China, is sensitive to celestial gamma rays with energies above a few TeV. We have a plan to add a large underground muon detector array to it in order to discriminate cosmic gamma rays from cosmic-ray hadrons and to increase its sensitivity by approximately one order of magnitude to cosmic gamma rays in the 100 TeV energy region. The overview of the plan will be briefly described.

We searched for steady 100 TeV gamma-ray point sources from −10° to +70° in declination based on six year data obtained from Nov. 1999 to Nov. 2005 by the Tibet air shower array. No new source was found and no significant excess of events could be detected from known TeV sources. We set flux upper limits above 100 TeV on several nearby objects located inside Our Galaxy. All of them are slightly higher than extrapolation from lower energies by a factor of 1 to 20. Our new project named Tibet MD will improve our sensitivity by a factor of ∼10 in this energy region. We would discover ∼10 new sources and be able to measure cutoff energy of known and unknown sources, which might lead to identification of the origin of cosmic rays.

We report on the spectral index of cosmic rays around 10 TeV energy region obtained by observation of the Compton-Getting anisotropy due to the terrestrial orbital motion around the Sun with the Tibet III air shower array during the period from 1999 to 2005. The spectral index has turned out to be 2.99 ± 0.54 , which is consistent with 2.74 by the direct energy spectrum measurement. This method is a new approach to measure the spectral index and is complementary to the conventional energy spectrum measurement.

Simultaneous observation of gamma-families and their accompanying air showers was performed at Yangbajing (4300 m above sea level) in Tibet with the emulsion chambers and burst detectors which were linked with the Tibet-II air-shower array. For three years operation, we observed 177 gamma-families (Sigma E-gamma > 20 TeV) accompanying air showers with the size N-e > 2 x 10(5). Using this data and the simulation code CORSIKA, we obtained the primary proton spectrum in the energy range of 10(15)-10(16) eV. The slope of the observed spectrum is steeper than that extrapolated smoothly from the lower energy region below 10(14) eV, irrespective of the interaction models assumed in the simulation. The uncertainty of the absolute flux of protons due to the interaction model dependence involved in the simulation codes is at most 30%, which is much weaker than results of other air-shower experiments. Our experiment shows low intensity of light components (proton and helium) independent of the interaction models suggesting that the main component responsible for making the knee structure of the all-particle spectrum is composed of nuclei heavier than helium. This is the first measurement of the differential energy spectra of primary protons by selecting them event by event at the knee energy region.