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Study of the Effects of Neutrals in Alcator C-Mod Plasmas

Description: Recently, much effort has been dedicated to understanding the bifurcation involved in the transition from a low to high confinement regime. While several theories have been brought forward, many factors remain to be elucidated, one of which involves the role played by neutral particles in the evolution of a transport barrier near the edge of the plasma. Alcator C-Mod is especially well suited for the study of neutral particle effects, mainly because of its high plasma and neutral densities, and closed divertor geometry. Alcator C-Mod employs ICRF as auxiiiary heating for obtaining a high confinement regime, although ohmic H-modes are routinely obtained as well. The neutrals can enter the edge dynamics through the particle, momentum and energy balance. In the particle balance, the source of neutrals has to be evaluated vis-8-vis the formation of the edge density pedestal. It is widely believed that plasma rotation is an important factor in reducing transport. In this case, neutrals could act as a momentum sink, through the charge-exchange process. That same process can also modify the energy balance of the plasma near the edge by increasing the cross-field heat flux. These effects are quite difficult to measure experimentally, in large part because neutral particle diagnosis is not an easy task, and because of the inherent 3-dimensional aspect of the problem. Consequently, the neutral�s spatial and energy distributions are usually not well known. In Alcator C-Mod, we recently implemented a series of diagnostics for the purpose of measuring these distributions. They include measurements of the neutral pressure at many locations around the tokamak, and spatially resolved measurements of Lyman-a and charge-exchange power emission. A high-resolution multichord (20 channels) tangential view of neutral deuterium emission (Lyman-a) has been recently installed near the midplane. The viewing area covers approximately 4 cm across the separatrix, with a ...
Date: June 14, 1999
Creator: Boivin, R.L.; Boswell, C.; Goetz, J.A.; Hubbard, A.E.; Irby, J.; LaBombard, B. et al.
Partner: UNT Libraries Government Documents Department


Description: The lifetime for the decay of a {pi} meson into {mu} meson and neutral particle was first measured by Richardson and later by Martinelli and Panofsky. The method was the same in both cases: The fraction of {pi} mesons surviving various times of flight is measured by placing photographic detectors at various path lengths from the target. In the experiment reported here we observe the time lag between the two bursts of fluorescence due to mesons decaying in a scintillation crystal. The first burst is due to the stopping of the entering {pi} meson, the second to the {mu}-meson. As is shown in Fig. 1, a particle penetrating the first and into the second crystal starts the sweep (10{sup -8} sec/mm) of an oscilloscope. The pulses in the second crystal are delayed 0.5 x 10{sup -6} sec to allow the sweep to start and brighten and are then photographed. If the responsible particle is a {pi}{sup +} meson which stops in the crystal, it undergoes {pi}-{mu} decay and two pulses appear on the trace. The {mu}{sup +} meson has a range of only 2 mm in the crystal. If its decay electron is detected some time (.5-2.5 x 10{sup -6} sec) later; a neon light flashes and is photographed together with the scope trace. Only such marked traces are measured. Of these marked traces, 650 or roughly one-half, show the two pulses of the {pi}-{mu} event. Five percent are calculated to be due to random delayed coincidences, and another 3 percent due to {pi} mesons which have decayed in flight and come to rest in the second crystal as {mu} mesons. The remaining traces are due to {pi}{mu} decays which are too fast to be resolved. The sweep speed of the oscilloscope is calibrated periodically with an oscillator of known ...
Date: May 10, 1950
Creator: Chamberlain, O.; Mozely, R.F.; Steinberger, J. & Wiegand, C.
Partner: UNT Libraries Government Documents Department

Instrumentation for the absorbers in the low Beta* Insertions of the LHC

Description: Concepts are examined for the measurement of luminosity, beam-beam separation and transverse beam shape and size using the high flux of forward neutral particles produced at the low {beta}* (high luminosity) interaction points (IP's) of the LHC. At design luminosity 10{sup 34} cm{sup -2}sec{sup -1} the flux of neutrals striking the neutral beam absorbers (TAN) in front of the D2 beam separation dipoles is high enough ({approx} 8 neutrons per bunch crossing with mean energy 2.3 TeV) to allow measurement of luminosity with 1% precision in {approx} 1.8 x 10{sup 3} bunch crossings and measurement of beam-beam separation at the collision point with 0.1{sigma}* precision in {approx} 3 x 10{sup 4} bunch crossings. An Argon ionization chamber placed near the shower maximum {approx} 22 cm inside the Cu neutral beam absorber is analyzed as a possible detector. Background effects due to beam-gas interactions, beam-halo scraping, beam crossing angle modulation and transverse drift of the IP are estimated and found to be small compared to the anticipated signals. Extending these concepts to the front quadrupole absorber (TAS) and segmenting the ionization chambers into four quadrants allows additional measurements of the beam-beam crossing angle and the transverse position of the IP.
Date: August 1, 1998
Creator: Turner, W.C.
Partner: UNT Libraries Government Documents Department

Channeling collimation studies at the Fermilab Tevatron

Description: Bent crystal channeling has promising advantages for accelerator beam collimation at high energy hadron facilities such as the LHC. This significance has been amplified by several surprising developments including multi-pass channeling and the observation of enhanced deflections over the entire arc of a bent crystal. The second effect has been observed both at RHIC and recently at the Tevatron. Results are reported showing channeling collimation of the circulating proton beam halo at the Tevatron. Parenthetically, this study is the highest energy proton channeling experiment ever carried out. The study is continuing.
Date: August 1, 2006
Creator: Carrigan, Richard A.; Drozhdin, Alexandr I.; Fliller, Raymond P., III; Mokhov, Nikolai V.; Shiltsev, Vladimir D.; Still, Dean A. et al.
Partner: UNT Libraries Government Documents Department

MCNP(TM) Version 5.

Description: The Monte Carlo transport workhorse, MCNP, is undergoing a massive renovation at Los Alamos National Laboratory (LANL) in support of the Eolus Project of the Advanced Simulation and Computing (ASCI) Program. MCNP Version 5 (V5) (expected to be released to RSICC in Spring, 2002) will consist of a major restructuring from FORTRAN-77 (with extensions) to ANSI-standard FORTRAN-90 with support for all of the features available in the present release (MCNP-4C2/4C3). To most users, the look-and-feel of MCNP will not change much except for the improvements (improved graphics, easier installation, better online documentation). For example, even with the major format change, full support for incremental patching will still be provided. In addition to the language and style updates, MCNP V5 will have various new user features. These include improved photon physics, neutral particle radiography, enhancements and additions to variance reduction methods, new source options, and improved parallelism support (PVM, MPI, OpenMP).
Date: January 1, 2002
Creator: Cox, L. J. (Lawrence J.); Barrett, R. F. (Richard F.); Booth, Thomas Edward; Briesmeister, Judith F.; Brown, F. B. (Forrest B.); Bull, J. S. (Jeffrey S.) et al.
Partner: UNT Libraries Government Documents Department

Neutral particle production in pi- d reactions at 200 GeV/c

Description: Characteristics of {pi}{sup o} production and K{sup o}, {Lambda}, {bar {Lambda}}, production in {pi}{sup -}d interactions at 200 GeV are presented. The data are obtained from a 70,000 picture exposure of the FNAL 30-inch deuterium-filled bubble chamber. Comparison with pion proton data at similar energies and pion deuterium data at lower energies are made.
Date: April 1, 1975
Creator: Csorna, S.; Dunn, L.; Kocsis, A.; Lubatti, H.J.; Moriyasu, K.; Tressel, P. et al.
Partner: UNT Libraries Government Documents Department

Contemporary Instrumentation and Application of Charge Exchange Neutral Particle Diagnostics in Magnetic Fusion Experiments

Description: An overview of the developments post-circa 1980's of the instrumentation and application of charge exchange neutral particle diagnostics on Magnetic Fusion Energy experiments is presented.
Date: July 21, 2007
Creator: S.S. Medley, A.J.H. Donné, R. Kaita, A.I. Kislyakov, M.P. Petrov, and A.L. Roquemore
Partner: UNT Libraries Government Documents Department

Negative particle planar and axial channeling and channeling collimation

Description: While information exists on high energy negative particle channeling there has been little study of the challenges of negative particle bending and channeling collimation. Partly this is because negative dechanneling lengths are relatively much shorter. Electrons are not particularly useful for investigating negative particle channeling effects because their material interactions are dominated by channeling radiation. Another important factor is that the current central challenge in channeling collimation is the proton-proton Large Hadron Collider (LHC) where both beams are positive. On the other hand in the future the collimation question might reemerge for electon-positron or muon colliders. Dechanneling lengths increase at higher energies so that part of the negative particle experimental challenge diminishes. In the article different approaches to determining negative dechanneling lengths are reviewed. The more complicated case for axial channeling is also discussed. Muon channeling as a tool to investigate dechanneling is also discussed. While it is now possible to study muon channeling it will probably not illuminate the study of negative dechanneling.
Date: December 1, 2009
Creator: Carrigan, Richard A., Jr.
Partner: UNT Libraries Government Documents Department

Precision measurement of the {Sigma}{sup 0} hyperon mass

Description: The research that is described in this paper is part of a program to study strong interaction mechanisms in proton proton collisions. The program consists of two experiments: Brookhaven E766 in which we studied the reactions pp {yields} p+ all charged particles with 27.5 GeV/c incident protons and Fermilab E690 in which we studied the reactions pp {yields} p+ all charged particles with 800 GeV/c incident protons. In these experiments, we employed state-of-the-art data acquisition sys- tems and acquired large samples of data: at Brookhaven we amassed 300 million high multiplicity events and at Fermilab, 5.5 billion events. Our uncertainty in the {Sigma}{sup 0} mass is more than 7 times smaller than the best previous result and was based on 16 times the statistics. Likewise, the {Sigma}{sup 0} - {Lambda}{sup 0} mass difference is more than 14 times more accurate than the previous best result. Finally, we note that this measurement is the first direct measurement of the {Sigma}{sup 0} mass.
Date: February 17, 1998
Creator: Wang, M.H.L.S.; Hartouni, E.P. & Kreisler, M.N.
Partner: UNT Libraries Government Documents Department

RIBE Flux vs. Position Monitor

Description: Recent work at SNL has demonstrated unique capabilities to experimentally measure a variety of ion and neutral particle parameters inside surface features being etched, including ion energy, angular distributions, ion and neutral species measurements. This report details the construction of one recent laboratory tool designed to measure ion beam uniformity over the wafer surface in a reactive ion beam etch system, (RIBE). This information is critical to the development of accurate plasma processing computer models and simulation methods, and is essential for reducing the cost of introducing new processing technologies.
Date: October 1, 2000
Partner: UNT Libraries Government Documents Department

Determination of the Z` Mass and Couplings Below Threshold at the NLC

Description: We investigate the capability of the NLC to indirectly determine both the mass as well as the couplings to leptons and b-quarks of a new neutral gauge boson below direct production threshold. By using data collected at several different values of the collide center of mass energy, we demonstrate how this can be done in an anonymous and model- independent manner. The procedure can be easily extended to the top and charm quark couplings.
Date: August 1996
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Low energy neutral atom imaging: Remote observations of the magnetosphere

Description: Recent developments in detection of neutral atom imaging should enable imaging the global structure and dynamics of the terrestrial magnetosphere. The inherent technical challenge of imaging low energy neutral atoms (LENAs) with energy < 30 keV is their separation from the tremendous UV background, to which LENA detectors are sensitive, without loss of information of LENA trajectory and energy. Three instrument concepts for separating LENAs from the background UV are presented: LENA charge conversion via transmission through an ultrathin carbon foil and subsequent electrostatic deflection, EUV grating polarizers and attenuators, and high frequency shutters. Each of these concepts can be mated to a detector section that provides both LENA imaging capability and coincidence/time-of-flight.
Date: February 1, 1995
Creator: Funsten, H. O.; McComas, D. J.; Scime, E. E. & Moore, K. R.
Partner: UNT Libraries Government Documents Department

Modeling of Localized Neutral Particle Sources in 3D Edge Plasmas

Description: A new edge plasma code BoRiS [1] has a fully 3D fluid plasma model. We supplement BoRiS with a 3D fluid neutral model including equations for parallel momentum and collisional perpendicular diffusion. This makes BoRiS an integrated plasma-neutral model suitable for a variety of applications. We present modeling results for a localized gas source in the geometry of the NCSX stellarator.
Date: May 23, 2002
Creator: Umansky, M V; Rognlien, T D; Fenstermacher, M E; Borchardt, M; Mutzke, A; Riemann, J et al.
Partner: UNT Libraries Government Documents Department

Simulations of the LHC high luminosity monitors at beam energies from 3.5 TeV to 7.0 TeV

Description: We have constructed two pairs of fast ionization chambers (BRAN) for measurement and optimization of luminosity at IR1 and IR5 of the LHC. These devices are capable of monitoring the performance of the LHC at low luminosity 10{sup 28} cm{sup -2}s{sup -1} during beam commissioning all the way up to the expected full luminosity of 10{sup 34} cm{sup -2}s{sup -1} at 7.0 TeV. The ionization chambers measure the intensity of hadronic/electromagnetic showers produced by the forward neutral particles of LHC collisions. To predict and improve the understanding of the BRAN performance, we created a detailed FLUKA model of the detector and its surroundings. In this paper, we describe the model and the results of our simulations including the detector's estimated response to pp collisions at beam energies of 3.5, 5.0, and 7.0 TeV per beam. In addition, these simulations show the sensitivity of the BRAN to the crossing angle of the two LHC beams. It is shown that the BRAN sensitivity to the crossing angle is proportional to the measurement of crossing angle by the LHC beam position monitors.
Date: March 28, 2011
Creator: Matis, H.S.; Miyamoto, R.; Humphreys, P.; Ratti, A.; Turner, W.C. & Stiller, J.
Partner: UNT Libraries Government Documents Department

Proposal to study neutral particle production in 250-GeV p p interactions in the Fermilab 15 foot bubble chamber

Description: We propose a small exposure (25K pictures) of the hydrogen-filled FNAL 15-foot bubble chamber to a 250 GeV proton beam. Our main physics objectives are: (1) To study the dependence of neutral particle production ({pi}{sup 0}, K{sup 0}, {Lambda}) on the charged multiplicity in diffractive and non-diffractive processes. (2) To measure integrated correlations (f{sub 2}{sup {+-}0} and f{sub 2}{sup 00}) for neutral pions in a ''clean'' experiment. To make these measurements reliably requires neutral particle detection in both CM hemispheres and the CM symmetry of the pp system. For example, we will determine f{sub 2}{sup 00} to {+-} 0.2. The event analysis of the neutral secondaries together with the measurement of the slow laboratory protons in pp {yields} p{sub slow} + X for the distinction between diffractive and non-diffractive events will be done in 1/2 year. Further objectives are: (3) To measure differential neutral-charged correlations. (4) To measure multiplicities, spectra and correlations (''inclusive program'') inside the mass M{sub X} in pp {yields} p{sub slow} + X{sup -}.
Date: October 1, 1974
Creator: Jaeger, K.; /Argonne; Ammar, R.; Davis, R.; Loos, L.; Stump, R. et al.
Partner: UNT Libraries Government Documents Department

Simulation of the LHC BRAN luminosity monitor for high luminosity interaction regions

Description: The BRAN (Beam RAte of Neutrals) detector monitors the collision rates in the high luminosity interaction regions of LHC (ATLAS and CMS). This Argon gas ionization detector measures the forward neutral particles from collisions at the interaction point. To predict and improve the understanding of the detector's performance, we produced a detailed model of the detector and its surroundings in Fluka. In this paper, we present the model and results of our simulations including the detectors estimated response to interactions for beam energies of 3.5, 5, and 7 TeV.
Date: May 23, 2010
Creator: Miyamoto, R.; Matis, H.; Ratti, A.; Stiller, J. & White, S.M.
Partner: UNT Libraries Government Documents Department

Measurement of the sigma^o Lifetime

Description: The Coulomb production of {Sigma}{sup 0} hyperons on uranium and nickel nuclei has been measured in a beam of {Lambda} hyperons at the CERN Proton Synchrotron. The results for the {Sigma}{sup 0} lifetime, {tau}{Sigma}{sup 0} = (0.58 {+-} 0.13) x 10{sup -19} sec, and for the {Sigma}{sup 0}-{Lambda} magnetic transition moment, |{mu}{Sigma}{sub {Lambda}}| = (1.82{sub -0.18}{sup +0.25}) nuclear magnetons, are in agreement with SU(3) predictions.
Date: March 1, 1972
Creator: Devlin, T.J.; U., /Rutgers; March, R.H.; Pondrom, L.G.; U., /Wisconsin; Overseth, O.E. et al.
Partner: UNT Libraries Government Documents Department

Effects of particle exhaust on neutral compression ratios in DIII-D

Description: In this paper, neutral particles in DIII-D are studied via their compression in the plenum and via particle exhaust. The compression of gas in the plena is examined in terms of the magnetic field configuration and wall conditions. DIII-D compression ratios are observed in the range from 1 to {ge} 1,000. Particle control ultimately depends on the exhaust of neutrals via plenum or wall pumping. Wall pumping or outgassing is calculated by means of a detailed particle balance throughout individual discharges, and its effect on particle control is discussed. It is demonstrated that particle control through wall conditioning leads to lower normalized densities. A two-region model shows that the gas compression ratio (C{sub div} = divertor plenum neutral pressure/torus neutral pressure) can be interpreted in relation to gas flows in the torus and divertor including the pumping speed of the plenum cryopumps, plasma pumping, and the pumping or outgassing of the walls.
Date: August 1, 1998
Creator: Colchin, R. J.; Maingi, R.; Wade, M. R.; Allen, S. L. & Greenfield, C. M.
Partner: UNT Libraries Government Documents Department