Hot Mode Research Articles

High Power ECH Experiments for Direct Bulk Electron Heating in Central-Cell Region Plasmas on GAMMA 10 Tandem Mirror

High power electron cyclotron heating (ECH) experiment for the central-cell region in GAMMA 10 has been started in the hot ion mode operation (Ti = several keV). Transmission system for the central-cell ECH, including a taper, mirrors and polarizers, has been designed and installed for efficient direct bulk electron heating. ECH system with a twister and a circular polarizer for central-cell region has the advantages for controllable polarization of incident wave. Recently, a high power gyrotron of ~500 kW at 28 GHz has been developed in collaboration with Japan Atomic Energy Agency (JAEA) and this high power gyrotron was installed in central-cell region of GAMMA 10. This high power and efficient ECH system was applied to central-cell electron heating and significant increment of soft X-ray and diamagnetism signals during a pulse of ECH operation was obtained. In this paper, central ECH experimental results in the hot ion mode operation are reported.

Transformer recharging with alpha channeling in tokamaks

AbstractTransformer recharging with lower hybrid waves in tokamaks can give low average auxiliary power if the resistivity is kept high enough during the radio frequency recharging stage. At the same time, operation in the hot ion mode via alpha channeling increases the effective fusion reactivity. This paper addresses the extent to which these two large cost-saving steps are compatible.

Galaxies in a simulated ΛCDM Universe - I. Cold mode and hot cores

We study the formation of galaxies in a (50 Mpc/h)^3 cosmological simulation (2x288^3 particles), evolved using the entropy conserving SPH code Gadget-2. Most of the baryonic mass in galaxies of all masses is originally acquired through filamentary "cold mode" accretion of gas that was never shock heated to its halo virial temperature, confirming the key feature of our earlier results obtained with a different SPH code (Keres et al. 2005). Atmospheres of hot, virialized gas develop in halos above ~2.5e11 Msun, a transition mass that is nearly constant from z=3 to z=0. Cold accretion persists in halos above the transition mass, especially at z>=2. It dominates the growth of galaxies in low mass halos at all times, and it is the main driver of the cosmic star formation history. Satellite galaxies have accretion rates similar to central galaxies of the same baryonic mass at high redshifts, but they have less accretion than comparable central galaxies at low redshift. Relative to our earlier results, the Gadget-2 simulations predict much lower rates of "hot mode" accretion from the virialized gas component of massive halos. At z<=1, typical hot accretion rates in halos above 5e12 Msun are below 1 Msun/yr, even though our simulation does not include AGN heating or other forms of "preventive" feedback. The inner density profiles of hot gas in these halos are shallow, with long associated cooling times. The cooling recipes typically used in semi-analytic models can overestimate the accretion rates in these halos by orders of magnitude, so such models may overemphasize the role of preventive feedback in producing observed galaxy masses and colors. A fraction of the massive halos develop cuspy profiles and significant cooling rates between z=1 and z=0, a redshift trend similar to the observed trend in the frequency of cooling flow clusters.

STUDY OF LASER BEAT-WAVE INTERFEROMETRY FOR LASER TRACKING OF MOVING BODY

In order to increase more greatly the measurement accuracy for the laser tracking system in measuring the moving body, a laser beat-wave interferometry method is approached based on the absolute measuring distance. The He – Ne laser with the two hot steady frequency modes is used as the light source for the laser tracking system. The light source developed by us not only has the advantages of steady frequency, high precision and strongly anti-interference capability, but also it mainly has the same character in the shoot stability degrees and laser frequency stability degrees. By using the laser beat-wave interferometry method, we can realize the absolute distance measurement of the moving body, and the laser tracking system has very high measurement precision, fast tracking speed and anti-interference capability.

Optimization of Plasma Production Using Hα Emission Detector and CCD Camera in the GAMMA 10 Tandem Mirror

Detailed behavior of plasmas has been investigated in the course of an optimization phase of wall conditioning in the central-cell of GAMMA 10 tandem mirror. The results are described based on the visible image measurements using CCD camera together with Hα line-emission measurements in the central-cell. Three limiters are installed in the central-cell and the behavior of the plasmas near the each limiter is precisely observed in response to electron cyclotron heating (ECH) for potential formation. In an early stage of wall conditioning in GAMMA 10, plasma parameters obtained in standard hot ion mode plasmas are compared in cases of sustained plasma in ECH pulses and of collapsed one simultaneously with ECH. Dependence of gas puffing from the mirror throat in the central cell and of the diameter of limiters is also investigated on the plasma behavior in ECH. From the measured results, it is recognized that a significant upward shift of the plasma column and imbalance of the Hα intensity between east and west Iris-limiters cause the plasma collapse in ECH. A systematic analysis of the dependence on plasma durability in the number of wall conditioning shots, the position of the plasma just before the ECH injection and suitable quantity of gas puffing is necessary for stably sustaining the plasma during potential formation by ECH.

Galaxies in a simulated ΛCDM universe - II. Observable properties and constraints on feedback

We compare the properties of galaxies that form in a cosmological simulation without strong feedback to observations at z=0. We confirm previous findings that models without strong feedback overproduce the observed galaxy baryonic mass function, especially at the low and high mass extremes. Through post-processing we investigate what kinds of feedback would be required to reproduce observed galaxy masses and star formation rates. To mimic an extreme form of "preventive" feedback (e.g., AGN radio mode) we remove all baryonic mass that was originally accreted via "hot mode" from shock-heated gas. This does not bring the high mass end of the galaxy mass function into agreement with observations because much of the stellar mass in these systems formed at high redshift from baryons that originally accreted via "cold mode" onto lower mass progenitors. An efficient "ejective" feedback mechanism, such as supernova driven winds, must reduce the masses of these progenitors. Feedback must also reduce the masses of lower mass z=0 galaxies, which assemble at lower redshifts and have much lower star formation rates. If we monotonically re-map galaxy masses to reproduce the observed mass function, but retain the simulation's predicted star formation rates, we obtain fairly good agreement with the observed sequence of star-forming galaxies but fail to recover the observed population of passive, low star formation rate galaxies. Suppressing all hot mode accretion improves agreement for high mass galaxies but worsens the agreement at intermediate masses. Reproducing these z=0 observations requires a feedback mechanism that dramatically suppresses star formation in a fraction of galaxies, increasing with mass, while leaving star formation rates of other galaxies essentially unchanged.

Comparative Investigation of Fusion Reactions for Space Propulsion Applications

A space propulsion system based on the acceleration of fusion ash is discussed by use of the energy balance equation and a hypothetic ash extraction and acceleration system. The fusion reactions D-T, D-3He, p-11B and 3He-3He are investigated under the condition of thermal generation of high energy ions and equal plasma system conditions in terms of Ti/Te relation and plasma beta. External plasma heating is defined by an equal efficiency concerning thermal energy conversion and energy transfer back into the plasma. There is no additional external heating applied to the fusion system. Power losses are based on neutrons, bremsstrahlung, synchrotron radiation and convection. We compare the plasma pressures, volumetric power densities, magnetic field strengths, heat waste, exhaust velocities and thrust density levels depending on the temperature and the hot ion mode. We show that, based on the fusion products, the exhaust velocity may reach several percent of speed of light in the case of 3He-3He. The temperature driven radiation losses of the 3He-3He reaction puts the purely aneutronic property into perspective. The mass flow rate densities of the considered fusion products are very low leading to very low thrust power densities. Considering the supposed system masses of a fusion based space vessel the thrust density levels are negligible and reach the order of 1 N/m3 near the optimum in the case of 3He-3He. We conclude that a propulsion system based on the acceleration of fusion products or ash is unfeasible for typical manned missions e.g. to Mars.

Bimodal gas accretion in the Horizon-MareNostrum galaxy formation simulation

The physics of diffuse gas accretion and the properties of the cold and hot modes of accretion on to proto-galaxies between z= 2 and 5.4 is investigated using the large cosmological simulation performed with the ramses code on the MareNostrum supercomputing facility. Galactic winds, chemical enrichment, ultraviolet background heating and radiative cooling are taken into account in this very high resolution simulation. Using accretion-weighted temperature histograms, we have performed two different measurements of the thermal state of the gas accreted towards the central galaxy. The first measurement, performed using accretion-weighted histograms on a spherical surface of radius 0.2Rvir centred on the densest gas structure near the halo centre of mass, is a good indicator of the presence of an accretion shock in the vicinity of the galactic disc. We define the hot shock mass, Mshock, as the typical halo mass separating cold dominated from hot dominated accretion in the vicinity of the galaxy. The second measurement is performed by radially averaging histograms between 0.2Rvir and Rvir, in order to detect radially extended structures such as gas filaments: this is a good proxy for detecting cold streams feeding the central galaxy. We define Mstream as the transition mass separating cold dominated from hot dominated accretion in the outer halo, marking the disappearance of these cold streams. We find a hot shock transition mass of Mshock= 1011.6M⊙ (dark matter), with no significant evolution with redshift. Conversely, we find that Mstream increases sharply with z. Our measurements are in agreement with the analytical predictions of Birnboim & Dekel and Dekel & Birnboim, if we correct their model by assuming low metallicity(≤10−3Z⊙)for the filaments, correspondingly to our measurements. Metal enrichment of the intergalactic medium is therefore a key ingredient in determining the transition mass from cold to hot dominated diffuse gas accretion. We find that the diffuse cold gas supply at the inner halo stops at z= 2 for objects with stellar masses of about 1011.1M⊙, which is close to the quenching mass determined observationally by Bundy et al. However, its evolution with z is not well constrained, making it difficult to rule out or confirm the need for an additional feedback process such as active galactic nuclei.

3.4: Invited Paper: A Novel Use of MEMS Switches in Driving AMOLED

AbstractAs the current thin film transistors (TFTs) for driving AMOLED have been made of amorphous silicon, poly‐Silicon, or organic materials, they have suffered from carrier mobility‐related problems. We proposed in this work a new idea of using MEMS switches as the TFTs, for achieving a better switching characteristic capable of conducting large current with high uniformity and stability. Using simulation and initial experiments with the metallic MEMS switches, we successfully demonstrated that the digital driving of OLED using MEMS switches was possible with gray scale. The fabricated 50μm × 10μm‐Sized switch conducted current of up to 15mA and it operated up to 1.3×105 Cycles in a hot switching mode in air when the current was 57μA and switching pulse frequency was 100Hz. Complete active‐matrix driving of multiple OLED pixels is to be done.

Investigation of hot carrier degradation in asymmetric nDeMOS transistors

Abstract Hot carrier degradation in asymmetric nDeMOS transistors is investigated in this paper. It is found that the worst case hot carrier stress condition in asymmetric nDeMOS transistors is at Ig,max, and not at Ib,max and hot-electron injection (HE, i.e. Vgs = Vds). Further, the damage regions in transistors upon various hot carrier stress modes are located by using variable amplitude charge pumping technique. It is found that the interface traps generation in the gate/n-type graded drain (NGRD) overlap and spacer/NGRD regions is the dominant mechanism of hot carrier degradation in transistors upon Ig,max stress mode. Moreover, both the interface trap generation and the electron trapping are two important factors to induce the electrical parameters shifts of asymmetric nDeMOS transistors under Ib,max and HE stress.

2617 CO_2を用いる業務用ヒートポンプ給湯機の開発(S32 高効率ヒートポンプの要素技術とその応用,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

New heat pump water heater system using CO_2 has been developed to spread the electrical heat pump water heater from the point of view of the global warming prevention. The developed system consists of a water tank, the refrigeration circuit with a suction line heat exchanger (SLHX), a bypass line and heat recovery heat exchanger (HRHX) for the defrost. This system has three operating modes; hot water storage mode, heating up mode and defrost mode using HRHX. The SLHX can make the inlet quality of the evaporator lower than the conventional cycle without the SLHX, therefore amount of excessive refrigerant can be stored in the air side heat exchanger (evaporator) without accumulator under the various condition. In the defrost mode, the HRHX makes defrosting capacity increase and the air heat exchanger are used as the condenser.

Locating hot carrier degradation in asymmetric nDeMOS transistors by gated diode technique

In this paper, hot carrier degradation in asymmetric nDeMOS transistors is investigated. For the first time, we found that the worst hot carrier stress condition is at Ig,max, and not at Ib,max and HE stress conditions. The damage regions in transistors upon various hot carrier stress modes are located by using gated diode technique. It is found that the interface traps generation in the gate/n-type graded drain (NGRD) overlap and spacer oxide regions is the dominant mechanism of hot carrier degradation in asymmetric nDeMOS transistors upon various hot carrier stress modes. Furthermore, the bulk silicon damages locating at the p-well and NGRD regions during hot carrier stress must be taken into account, because they lead to a series of issues, such as the increase in Ioff current, the off-state breakdown voltage decrease, and so on.

Performance analysis of ammonia absorption GAX cycle for combined cooling and hot water supply modes

An ammonia Generator–Absorber heat eXchange (GAX) absorption cycle with combined cooling and hot water supply modes is developed in this study. This paper proposes new multi-modes GAX cycles which function in three different modes (case 1, case 2 and case 3) of cooling and hot water supply with one hardware (ammonia/water GAX absorption heat pump), and finds the best cycle for performance improvement by the parametric analysis. The key parameters are the outlet temperature of hot water and the split ratio of the solution. It is found that the COP c values for case 1, case 2 and case 3 are 60%, 42% and 87% of COP c for case 0, respectively, which is the standard cooling mode for the conventional GAX cycle. From the viewpoints of hot water supply, case 1 gives the best performance. However, during the summer season when the cooling mode is the primary purpose rather than the hot water supply, case 3 is the most desirable cycle. The split ratio of the solution should be carefully determined depending on the primary application of the modified GAX cycle; cooling or hot water supply applications. It is also recommended that the optimum design values of UA SCA and UA HCA for case 3 should be less than those for case 1.

Investigation of Electron Distribution Functions in the Plug Region of the GAMMA 10 Tandem Mirror

Generalized scaling laws for the formation of plasma confining potentials are investigated to find the physics essentials common to representative tandem-mirror operational modes in GAMMA 10. These modes are characterized in terms of (i) a high-potential mode and (ii) a hot-ion mode. The potential-formation scalings in these modes are consolidated and generalized on the basis of the consistency with finding of the wider validity of Cohen’s strong electron-cyclotron heating (ECH) theory covering over both modes. A plateau-shaped electron distribution function is observed when a plug electron-confining potential is formed in the hot ion mode of GAMMA 10, as predicted in terms of the strong ECH theory.

Aspect ratio dependencies of D– 3He fueled tokamak reactors

Ignition capability is studied and compared for two types of D– 3He spherical tokamak (ST) and medium aspect ratio tokamak (MT) reactors. The required power fraction to ions for maintaining the hot ion mode, which is indispensable for D– 3He fusion, is smaller in a ST reactor than that in a MT reactor due to the lower synchrotron radiation loss. It is found that the nuclear elastic scattering capable of supplying 40% of the fusion energy to ions is enough to maintain the hot ion mode in the D– 3He ST reactor with the high wall reflectivity. For achieving the D– 3He MT reactor, the power fraction to ions should be additionally increased.

Bimodal fission in binary and ternary spontaneous fission of 252Cf

The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the “hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.

Crustal flow modes in large hot orogens

Abstract Crustal-scale channel flow numerical models support recent interpretations of Himalayan—Tibetan tectonics proposing that gravitationally driven channel flows of low-viscosity, melt-weakened, middle crust can explain both outward growth of the Tibetan Plateau and ductile extrusion of the Greater Himalayan Sequence. We broaden the numerical model investigation to explore three flow modes: homogeneous channel flow (involving laterally homogeneous crust); heterogeneous channel flow (involving laterally heterogeneous lower crust that is expelled and incorporated into the mid-crustal channel flow); and the hot fold nappes style of flow (in which mid-/lower crust is forcibly expelled outward over a lower crustal indentor to create fold nappes that are inserted into the mid-crust). The three flow modes are members of a continuum in which the homogeneous mode is driven by gravitational forces but requires very weak channel material. The hot fold nappe mode is driven tectonically by, for example, collision with a strong crustal indentor and can occur in crust that is subcritical for homogeneous flows. The heterogeneous mode combines tectonic and gravitationally driven flows. Preliminary results also demonstrate the existence and behaviour of mid-crustal channels during advancing and retreating dynamical mantle lithosphere subduction. An orogen temperature—magnitude (T-M) diagram is proposed and the positions of orogens in T-M space that may exhibit the flow modes are described, together with the characteristic positions of a range of other orogen types.

Dynamic Assimilation of MODIS-Retrieved Humidity Profiles within a Regional Model for High-Latitude Forecast Applications

Abstract A “hot start” technique is applied to the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) to dynamically assimilate cloud properties and humidity profiles retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on board the NASA Earth Observing System polar-orbiting satellites. The assimilation approach has been studied through extensive numerical experimentation for high-latitude rain events to demonstrate the feasibility and the benefit of the approach on the model cloud and precipitation simulation/forecast. The ingestion of MODIS-retrieved cloud and clear-air humidity information impacts MM5 cloud fields on both a microphysical and macrophysical level. From short-term (6–12 h) forecast experiments conducted for a preliminary test case and 16 extensive summer and winter experiments, the following primary conclusions have been reached. 1) It is feasible to introduce MODIS-retrieved cloud-top properties and humidity profiles into the MM5 model in a hot start mode without disrupting model stability and evolutionary continuity. 2) The introduction of high-resolution MODIS information produced more accurate humidity fields and resulted in increased mesoscale structure in the cloud and precipitation fields. 3) The opportunistic ingestion of MODIS data at its observation time into the model leads to improved 6–12-h model precipitation forecasts with respect to not only the frequency of occurrences, but also the magnitude of precipitation amounts. 4) Verification with three-dimensional analyses indicates some improvement in model forecasts of temperature, wind, pressure perturbation, and sea level pressure as well. 5) Verification with surface station observations indicates that model forecasts of 2-m temperature, 2-m relative humidity, 10-m winds, and sea level pressure are also improved, most notably for the summer cases. The largest improvement in forecast skill is for 2-m relative humidity (12%).

Measurements of the anode temperature in a vacuum arc with an asymmetric hot refractory Mo anode

The temperature of an asymmetric anode was measured at three points in the anode body of a Hot Refractory Anode Vacuum Arc (HRAVA) using high temperature thermocouple probes placed near the front and rear surface. Different anode geometries with inclined front surfaces were used for arc currents in the range 125-225 A and for gaps with electrode separations of 5-18 mm. The measurements show that the transition period to the Hot Anode mode in the HRAVA decreased with arc current. Photographic study of the interelectrode region indicated that the plasma plume in the transition period expands from the anode toward the cathode and filled the gap. The plasma plume was asymmetrically distributed on the asymmetric anode surface, resulting in an asymmetric anode surface temperature distribution. Asymmetry of the anode surface temperature distribution increased for more asymmetric anodes and gap geometries. Molybdenum anode temperatures increased with arc current and decreased with electrode separation. The anode surface steady state temperature exceeded 2200/spl deg/K-2300/spl deg/K when the arc currents were larger than 145 A. The observed surface temperature variations were caused by fluctuations of the heat flux to the anode.

How do galaxies get their gas?

We examine the temperature history of gas accreted by forming galaxies in smoothed particle hydrodynamics simulations. About half of the gas follows the track expected in the conventional picture of galaxy formation, shock heating to roughly the virial temperature of the galaxy potential well (T ∼ 106 K for a Milky Way type galaxy) before cooling, condensing and forming stars. However, the other half radiates its acquired gravitational energy at much lower temperatures, typically T < 105 K, and the histogram of maximum gas temperatures is clearly bimodal. The ‘cold mode’ of gas accretion dominates for low-mass galaxies (baryonic mass Mgal ≲ 1010.3 M⊙ or halo mass Mhalo ≲ 1011.4 M⊙), while the conventional ‘hot mode’ dominates the growth of high-mass systems. Cold accretion is often directed along filaments, allowing galaxies to efficiently draw gas from large distances, while hot accretion is quasi-spherical. The galaxy and halo mass dependence leads to redshift and environment dependence of cold and hot accretion rates, with the cold mode dominating at high redshift and in low-density regions today, and the hot mode dominating in group and cluster environments at low redshift. The simulations reproduce an important feature of the observed relation between the galaxy star formation rate (SFR) and the environment, namely a break in star formation rates at surface densities σ∼ 1 h275 Mpc−2, outside the virial radii of large groups and clusters. The cosmic SFR tracks the overall history of gas accretion, and its decline at low redshift follows the combined decline of cold and hot accretion rates. The drop in cold accretion is driven by the decreasing infall rate on to haloes, while for hot accretion this slower mass growth is further modified by the longer cooling times within haloes. If we allowed hot accretion to be suppressed by conduction or active galactic nuclei feedback, then the simulation predictions would change in interesting ways, perhaps resolving conflicts with the colours of ellipticals and the cut-off of the galaxy luminosity function. The transition at Mhalo∼ 1011.4 M⊙ between cold-mode domination and hot-mode domination is similar to that found by Birnboim & Dekel using one-dimensional simulations and analytic arguments. The corresponding baryonic mass is tantalizingly close to the scale at which Kauffmann et al. find a marked shift in galaxy properties, and we speculate on possible connections between these theoretical and observational transitions.