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Alignment and steering scenarios for the APT linac

Description: The Accelerator for the Production of Tritium (APT) requires a very high proton beam current (100 mA cw). Requirement for hands-on maintenance limits the beam spill to less than 0.2 nA/m along most of the linac. To achieve this, it is important to understand the effects of fabrication, installation and operational errors, establish realistic tolerances, and develop techniques for mitigating their consequences. A new code, PARTREX, statistically evaluates the effects of alignment, quadrupole field, and rf phase and amplitude errors in the linac. This paper reviews the effects of quadrupole misalignments and present two steering algorithms that minimize the potential for particle loss from the beam halo. These algorithms were tested on the 8-to-20 MeV portion of the APT linac.
Date: September 1, 1996
Creator: Stovall, J.E.; Gray, E.R.; Nath, S.; Takeda, H.; Wood, R.L.; Young, L.M. et al.
Partner: UNT Libraries Government Documents Department

IBS and possible luminosity improvement for RHIC operation below transition energy

Description: There is a strong interest in low-energy RHIC collisions in the energy range below present RHIC transition energy. These collisions win help to answer one of the key questions in the field of QCD about the existence and location of a critical point on the QCD phase diagram. For such low-energy RHIC operation, particle losses from the RF bucket are of particular concern since the longitudinal beam size is comparable to the existing RF bucket at low energies. In this paper, we explore an Intrabeam Scattering (IBS) feature below transition energy that drives the transverse and longitudinal beam temperatures towards equilibrium to see whether we can minimize longitudinal diffusion due to IBS and predict some luminosity improvement for the low-energy RHIC project.
Date: May 4, 2009
Creator: Fedotov,A.V.
Partner: UNT Libraries Government Documents Department

Dynamics of beam halo in mismatched beams

Description: High-power proton linacs for nuclear materials transmutation and production, and new accelerator-driven neutron spallation sources must be designed to control beam-halo formation, which leads to beam loss. The study of particle-core models is leading to a better understanding of the causes and characteristics of beam halo produced by space-charge forces in rms mismatched beams. Detailed studies of the models have resulted in predictions of the dependence of the maximum amplitude of halo particles on a mismatch parameter and on the space-charge tune-depression ratio. Scaling formulas have been derived which will provide guidance for choosing the aperture radius to contain the halo without loss.
Date: September 1, 1996
Creator: Wangler, T.P.; Garnett, R.W.; Gray, E.R.; Ryne, R.D. & Wang, T.S.
Partner: UNT Libraries Government Documents Department

Anomalous loss of DT alpha particles in the Tokamak Fusion Test Reactor

Description: An escaping alpha collector probe has been developed for TFTR`s DT phase. Energy distributions of escaping alphas have been determined by measuring the range of {alpha}-particles implanted into nickel foils located within the alpha collector. Results at 1.0 MA of plasma current are in good agreement with predictions for first orbit alpha loss. Results at 1.8 MA, however, show a significant anomalous loss of partially thermalized alphas (in addition to the expected first orbit loss), which is not observed with the lost alpha scintillator detectors in DT plasmas, but does resemble the anomalous delayed loss seen in DD plasmas. None of the candidate explanations proposed thus far are fully consistent with the anomalous loss observations. An experiment designed to study the effect of plasma major radius shifts on {alpha}-particle loss has led to a better understanding of {alpha}-particle dynamics in tokamaks. Intuitively, one might suppose that confined marginally passing {alpha}-particles forced to move toward higher magnetic field during an inward major radius shift (i.e., compression) would mirror and become trapped particles, leading to increased alpha loss. Such an effect was looked for during the shift experiment, however, no significant changes in alpha loss to the 90{degree} lost alpha scintillator detector were observed during the shifts. It is calculated that the energy gained by an {alpha}-particle during the inward shift is sufficient to explain this result. However, an unexpected loss of partially thermalized {alpha}-particles near the passing/trapped boundary was observed to occur between inward and outward shifts at an intermediate value of plasma current (1.4 MA). This anomalous loss feature is not yet understood.
Date: September 1, 1997
Creator: Herrmann, H.W.
Partner: UNT Libraries Government Documents Department

MHD-Induced Alpha Particle Loss in TFTR

Description: MHD-induced increases in alpha particle loss to the wall were observed for both coherent modes and transient reconnection events using an array of scintillator detectors near the wall of Tokamak Fusion Test Reactor (TFTR). The magnitude of the coherent MHD-induced alpha loss as seen by these detectors was normally comparable to the MHD-quiescent first-orbit or toroidal-field ripple loss, but the magnitude of the alpha loss during reconnection events was up to 1000 times higher than this for a short time. Modeling suggest that the coherent MHD loss mechanism will be even less significant for future reactor-scale deuterium-tritium tokamaks due to the smaller ratio of the alpha gyroradius to minor radius.
Date: March 1, 1999
Creator: Darrow, D.S.; Fredrickson, E.D.; Taylor, G.; White, R.B.; Zweben, S.J. & von Goeler, S.
Partner: UNT Libraries Government Documents Department

Alpha-driven magnetohydrodynamics (MHD) and MHD-induced alpha loss in the Tokamak Fusion Test Reactor

Description: Alpha-driven toroidal Alfven eigenmodes (TAEs) are observed as predicted by theory in the post neutral beam phase in high central q (safety factor) deuterium-tritium (D-T) plasmas in the Tokamak Fusion Test Reactor (TFTR). The mode location, poloidal structure and the importance of q profile for TAE instability are discussed. So far no alpha particle loss due to these modes was detected due to the small mode amplitude. However, alpha loss induced by kinetic ballooning modes (KBMs) was observed in high confinement D-T discharges. Particle orbit simulation demonstrates that the wave-particle resonant interaction can explain the observed correlation between the increase in alpha loss and appearance of multiple high-n (n {ge} 6, n is the toroidal mode number) modes.
Date: February 1, 1997
Creator: Chang, Z.; Nazikian, R. & Fu, G.Y.
Partner: UNT Libraries Government Documents Department

Impedance studies - Part 4: The APS impedance budget

Description: This note will wrap up the numerical results that were obtained in our calculations of the wake potentials, the loss factors, and the impedances for a variety of structures in the APS storage ring. It consists of five sections and one appendix. Section 1 is an introduction. Section 2 summarizes the hand calculations. The computer calculations are the subject 1 of Section 3. Section 4 discusses several tests in our numerical methods. Section 5 presents the APS impedance budget, along with some discussion. The appendix contains the figures of the structures, the longitudinal/transverse wake potentials and the real/imaginary part of the impedances of various sorts of geometries that have been included in the budget.
Date: July 1, 1988
Partner: UNT Libraries Government Documents Department

Foil deposition alpha collector probe for TFTR`s D-T phase

Description: A new foil deposition alpha collector sample probe has been developed for TFTR`s D-T phase. D-T fusion produced alpha particles escaping from the plasma are implanted in nickel foils located in a series of collimating ports on the detector. The nickel foils are removed from the tokamak after exposure to one or more plasma discharges and analyzed for helium content. This detector is intended to provide improved alpha particle energy resolution and pitch angle coverage over existing lost alpha detectors, and to provide an absolutely calibrated cross-check with these detectors. The ability to resolve between separate energy components of alpha particle loss is estimated to be {approx} 20%. A full 360{degree} of pitch angle coverage is provided for by 8 channels having an acceptance range of {approx} 53{degree} per channel. These detectors will be useful in characterizing classical and anomalous alpha losses and any collective alpha instabilities that may be excited during the D-T campaign of TFTR.
Date: March 1, 1995
Creator: Hermann, H.W.; Darrow, D.S.; Timberlake, J.; Zweben, S.J.; Chong, G.P.; Pitcher, C.S. et al.
Partner: UNT Libraries Government Documents Department

Shielding estimates for the ANL advanced photon source

Description: Shielding estimates for the Advanced Photon Source (APS) have been computed utilizing presently available design parameters. Calculations of the resulting radiation fields have been made for several considerations involving normal beam loss, as well as for certain postulated accidental beam losses. Whenever available, experimental data from existing accelerators and light sources have been used in lieu of theoretical estimates.
Date: April 1, 1987
Creator: Moe, H.J. & Veluri, V.R.
Partner: UNT Libraries Government Documents Department

Calculations of alpha particle loss for reversed magnetic shear in the Tokamak Fusion Test Reactor

Description: Hamiltonian coordinate, guiding center code calculations of the toroidal field ripple loss of alpha particles from a reversed shear plasma predict both total alpha losses and ripple diffusion losses to be greater than those from a comparable non-reversed magnetic shear plasma in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. High central q is found to increase alpha ripple losses as well as first orbit losses of alphas in the reversed shear simulations. A simple ripple loss model, benchmarked against the guiding center code, is found to work satisfactorily in transport analysis modelling of reversed and monotonic shear scenarios. Alpha ripple transport on TFTR affects ions within r/a=0.5, not at the plasma edge. The entire plasma is above threshold for stochastic ripple loss of alpha particles at birth energy in the reversed shear case simulated, so that all trapped 3.5 MeV alphas are lost stochastically or through prompt losses. The 40% alpha particle loss predictions for TFTR suggest that reduction of toroidal field ripple will be a critical issue in the design of a reversed shear fusion reactor.
Date: March 1, 1997
Creator: Redi, M.H.; White, R.B.; Batha, S.H.; Levinton, F.M. & McCune, D.C.
Partner: UNT Libraries Government Documents Department

Design of a {gamma}{sub t}-jump system for Fermilab Main Injector

Description: In order to control the beam emittance and reduce the particle losses during the transition crossing at high intensity, a conceptual design of a {gamma}{sub t}-jump system for the FNAL Main Injector is presented. It is a first-order system employing local dispersion inserts at existing dispersion free straight sections. The goal is to provide a jump of {Delta}{gamma}{sub t} from +1 to -1 within 0.5 ms. The system consists of 8 sets of pulsed quadrupole triplets. These quads have pole tips of the hyperbolic shape and thin laminations. The power supply uses a GTO as the fast switch and a resonant circuit with a 1 kHz resonant frequency. The elliptical beamtube is made of Inconel 718, which has high electrical resistivity and high strength. Details of the lattice layout and sub- systems design are presented.
Date: June 1, 1997
Creator: Chou, W., Brown, B.C., Fang, S., Leibfritz, J., Ng, K.Y., Pfeffer, H., Terechkine, I.
Partner: UNT Libraries Government Documents Department

Impact of the LHC beam abort kicker prefire on high luminosity insertion and CMS detector performance

Description: The effect of possible accidental beam loss in LHC on the IP5 insertion elements and CMS detector is studied via realistic Monte Carlo simulations. Such beam loss could be the consequence of an unsynchronized abort or � in worst case � an accidental prefire of one of the abort kicker modules. Simulations with the STRUCT code show that this beam losses would take place in the IP5 inner and outer triplets. MARS simulations of the hadronic and electro-magnetic cascades induced in such an event indicate severe heating of the inner triplet quadrupoles. In order to protect the IP5 elements, two methods are proposed: a set of shadow collimators in the outer triplet and a prefired module compensation using a special module charged with an opposite voltage (antikicker). The remnants of the accidental beam loss entering the experimental hall have been used as input for FLUKA simulations in the CMS detector. It is shown that it is vital to take measures to reliably protect the expensive CMS tracker components.
Date: April 13, 1999
Creator: A.I. Drozhdin, N.V. Mokhov and M. Huhtinen
Partner: UNT Libraries Government Documents Department

A water-filled radio frequency accelerating cavity

Description: This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The objective of this project was to study water-filled resonant cavities as a high-energy density source to drive high-current accelerator configurations. Basic considerations lead to the expectation that a dielectric-filled cavity should be able to store up to e/e{sub o} as much energy as a vacuum one with the same dimensions and thus be capable of accelerating a proportionately larger amount of charge before cavity depletion occurs. During this project, we confirmed that water-filled cavities with e/e{sub o} = 60-80 did indeed behave with the expected characteristics, in terms of resonant TM modes and cavity Q. We accomplished this result with numerical cavity eigenvalue codes; fully electromagnetic, two-dimensional, particle-in-cell codes; and, most significantly, with scaled experiments performed in water-filled aluminum cavities. The low-power experiments showed excellent agreement with the numerical results. Simulations of the high-field, high-current mode of operation indicated that charged-particle loss on the dielectric windows, which separate the cavity from the beamline, must be carefully controlled to avoid significant distortion of the axial fields.
Date: December 31, 1998
Creator: Faehl, R.J.; Keinigs, R.K. & Pogue, E.W.
Partner: UNT Libraries Government Documents Department

Sawtooth mixing of alpha particles in TFTR D-T plasmas

Description: Radially resolved confined alpha particle energy and density distributions are routinely measured on TFTR using two diagnostics: PCX and {alpha}-CHERS. The Pellet Charge-eXchange (PCX) diagnostic uses the ablation cloud formed by an impurity pellet (Li or B) for neutralization of the alphas followed by analysis of the escaping helium neutrals. PCX detects deeply trapped alpha particles in the energy range 0.5 - 3.8 MeV. The {alpha}-CHERS technique, were the alpha signal is excited by charge-exchange between alphas and the deuterium atoms of one of the heating beams and appears as a wing on the He{sup +} 468.6 nm line, detects mainly passing alphas in the range of 0.15 - 0.7 MeV. Studies of alpha losses during DT experiments on TFTR have also been conducted using lost alpha detectors located on the walls of the plasma chamber. All of these diagnostics were used for investigating the influence of sawtooth crashes on alphas in high power D-T discharges in TFTR. Both PCX and {alpha}-CHERS measurements show a strong depletion of the alpha core density and transport of trapped alphas radially outwards well beyond q = 1 surface after a sawtooth crash. Lost alpha detectors measure bursts of alpha loss of the previously confined alphas (<1%). Thus, a sawtooth crash leads mainly to radial redistribution of the alphas rather than losses. For modeling of alpha sawtooth mixing, a code is used which is based on the conventional model of magnetic reconnection and the conservation of particles, energy and magnetic flux. The effect of the particle orbit averaged toroidal drift in a perturbed helical electric field generated by the crash has also been included in the code. It is shown that mixing of the passing alphas is dominated by the magnetic reconnection whereas trapped alphas are affected mainly by ExB drift.
Date: December 31, 1996
Creator: Petrov, M.P.; Budny, R.V. & Chang, Z.
Partner: UNT Libraries Government Documents Department

Fast PIN-diode beam loss monitors at Tevatron

Description: The article is devoted to results of fine time structure of particle losses in Tevatron with use of fast beam loss monitors (BLM) based on PIN-diodes. An ultimate goal of the new BLMs is to distinguish losses of protons and antiprotons from neighbor bunches with 132 ns bunch spacing in the Tevatron collider upgrade. The devices studied fit well to the goal as they can recognize even seven times closer - 18.9 ns - spaced bunches` losses in the Tevatron fixed target operation regime. We have measured main characteristics of the BLM as well as studied the proton losses over 10 decades of time scale - from dozen of minutes to dozen of nanoseconds. Power spectral density of the losses is compared with spectra of the proton beam motion.
Date: July 1, 1997
Creator: Shiltsev, V.
Partner: UNT Libraries Government Documents Department

Proton injection and RF capture in the national spallation neutron source

Description: The accelerator system for the 1 to 5 MW National Spallation Neutron Source (NSNS) consists of a linac followed by a 1 GeV proton accumulator ring. Since the ring is a very high current machine, the injection and rf capture of the protons is deeply affected by transverse and longitudinal space charge effects. Results of numerical simulation of the process are presented together with considerations on methods and results of space charge treatment in high intensity proton storage rings.
Date: August 1997
Creator: Luccio, A. U.; Beebe-Wang, J. & Maletic, D.
Partner: UNT Libraries Government Documents Department


Description: The use of a two stage crystal collimation system in the RHIC yellow ring is examined. The system includes a copper beam scraper and a bent silicon crystal. While scrapers were installed in both of the RHIC rings before the year 2000 run, the crystal is installed for the 2001 run in one ring only, forming a two stage collimation system there. We present simulations of the expected channeling through the bent silicon crystal for both protons and gold ions with various beam parameters. This gives a picture of the particle losses around the ring, and the expected channeling efficiency. These results are then used to optimize the beam parameters in the area of the crystal to obtain maximum channeling efficiency, minimize out-scattering in the secondary collimator, and reduce beam halo.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Fast ion loss diagnostic plans for NSTX

Description: The prompt loss of neutral beam ions from the National Spherical Torus Experiment (NSTX) is expected to be between 12% and 42% of the total 5 MW of beam power. There may, in addition, be losses of fast ions arising from high harmonic fast wave (HHFW) heating. Most of the lost ions will strike the HHFW antenna or the neutral beam dump. To measure these losses in the 2000 experimental campaign, thermocouples in the antenna, several infrared camera views, and a Faraday cup lost ion probe will be employed. The probe will measure loss of fast ions with E &gt; 1 keV at three radial locations, giving the scrape-off length of the fast ions.
Date: June 13, 2000
Creator: Darrow, D. S.; Bell, R.; Johnson, D. W.; Kugel, H.; Wilson, J. R.; Cecil, F. E. et al.
Partner: UNT Libraries Government Documents Department

Fokker-Planck Modelling of Delayed Loss of Charged Fusion Products in TFTR.

Description: The results of a Fokker-Planck simulation of the ripple-induced loss of charged fusion products in the Tokamak Fusion Test Reactor (TFTR) are presented. It is shown that the main features of the measured "delayed loss" of partially thermalized fusion products, such as the differences between deuterium-deuterium and deuterium-tritium discharges, the plasma current and major radius dependencies, etc., are in satisfactory agreement with the classical collisional ripple transport mechanism. The inclusion of the inward shift of the vacuum flux surfaces turns out to be necessary for an adequate and consistent explanation of the origin of the partially thermalized fusion product loss to the bottom of TFTR.
Date: August 1, 1998
Creator: Edenstrasser, J.W.; Goloborod'ko, V.Ya.; Reznik, S.N.; Yavorskij, V.A. & Zweben, S.
Partner: UNT Libraries Government Documents Department

Performance and measurements of the Fermilab Booster

Description: We will describe measurements of the beam in the Fermilab Booster during the first five milliseconds. Most of the particle losses in the Booster are over after the first few milliseconds. At high intensity of 4 x 10{sup 12} the transmission is 75%. Such high beam loss can be a limiting factor for future high repetition rate operation of the Booster. The evidence, although indirect, suggests that the losses are the result of incoherent space-charge effects at low energy.
Date: June 1, 1998
Creator: Popovic, M. & Akenbrandt, C.
Partner: UNT Libraries Government Documents Department

Global Alfven eigenmodes in WELDELSTEIN 7-AS

Description: In the presence of fast particle populations marginally stable global modes in the shear Alfven branch can be destabilized by wave particle resonances. This is particularly of concern in future large devices, where losses of resonant particles ({alpha}-particles in a reactor) may then limit the available heating power and also may cause damage of the first wall. In tokamaks TAE modes inside toroidicity induced gaps of the shear Alfven continua have been found. In stellarators with very weak shear like W7-AS low-n TAE-gaps do not occur but gaps below the shear Alfven continua with mode numbers m and n, if the resonant values {tau} = n/m do not exist in the plasma volume (k{sub {parallel}} = (m{sm_bullet}{tau} - n )/R {ne} 0 ). Under these conditions GAE modes with frequencies {omega}{sub GAE} < (k{sub {parallel}}{sm_bullet}V{sub A}){sub min} are the favoured modes. The investigation of GAE modes could also be of relevance in the case of advanced tokamak equilibria with flat or inverted q-profiles in the central region.
Date: September 1, 1995
Creator: Weller, A.; Goerner, C. & Jaenicke, R.
Partner: UNT Libraries Government Documents Department

Calculation of beam neutralization in the IPNS-Upgrade RCS

Description: The author calculated the neutralization of circulating beam in this report. In the calculation it is assumed that all electrons liberated from the background molecules due to the collisional processes are trapped in the potential well of the proton beam. Including the dependence of ionization cross sections on the kinetic energy of the incident particle, the author derived the empirical formula for beam neutralization as a function of time and baseline vacuum pressure, which is applicable to the one acceleration cycle of the IPNS-Upgrade RCS.
Date: January 26, 1995
Creator: Chae, Yong-Chul
Partner: UNT Libraries Government Documents Department

Ion-chamber-based loss monitor system for the Los Alamos Meson Physics Facility

Description: A new loss monitor system has been designed and installed at the Los Alamos Meson Physics Facility (LAMPF). The detectors are ion chambers filled with N{sub 2} gas. The electronics modules have a threshold range of 1:100, and they can resolve changes in beam loss of about 2% of the threshold settings. They can generate a trip signal in 2 {mu}s if the beam loss is large enough; if the response time of the Fast Protect System is included the beam will be shut off in about 37 {mu}s.
Date: May 1, 1995
Creator: Plum, M.A.; Brown, D.; Browman, A. & Macek, R.J.
Partner: UNT Libraries Government Documents Department

Self-consistent beam halo studies & halo diagnostic development in a continuous linear focusing channel

Description: Beam halos are formed via self-consistent motion of the beam particles. Interactions of single particles with time-varying density distributions of other particles are a major source of halo. Aspects of these interactions are studied for an initially equilibrium distribution in a radial, linear, continuous focusing system. When there is a mismatch, it is shown that in the self-consistent system, there is a threshold in space-charge and mismatch, above which a halo is formed that extends to {approximately}1.5 times the initial maximum mismatch radius. Tools are sought for characterizing the halo dynamics. Testing the particles against the width of the mismatch driving resonance is useful for finding a conservative estimate of the threshold. The exit, entering and transition times, and the time evolution of the halo, are also explored using this technique. Extension to higher dimensions is briefly discussed.
Date: December 1, 1994
Creator: Jameson, R. A.
Partner: UNT Libraries Government Documents Department