The LANL/AES normal-conducting radio-frequency injector has been tested at cw cathode gradients up to 10MV/m . Field-emission electrons from a roughened copper cathode are accelerated to beam energy ...as high as 2.5 MeV and impinge on a stainless steel target. The energies of the resulting bremsstrahlung photons are measured at varying levels of injector cavity rf power corresponding to different accelerating gradients. At low cavity power, the bremsstrahlung spectra exhibit well-defined end-point energies at the positions where the number of single-photon events decreases to one (S/Nratio=1 ). Increasing the cavity power raises the probability of two-photon events in which two photons simultaneously arrive at the detector and register counts at twice the photon energy. The end-point energies at high cavity power are recorded at positions where the single-photon events transition to two-photon events. The measured end-point energies using this method are in excellent agreement with PARMELA calculations based on the cavity gradients deduced from the cavity rf power measurements.
The Isotope Production Facility (IPF) at Los Alamos National Laboratory (LANL) is used to produce an array of isotopes for medical, global security, and research applications with an intense beam of ...protons supplied by the linear accelerator at the Los Alamos Neutron Science Center (LANSCE). An Accelerator Improvement Project (AIP) was recently conducted at IPF to improve facility reliability and reduce programmatic risk while increasing general isotope production capacity and flexibility. This was accomplished through the installation of an improved beam window assembly, more robust beam diagnostics, an active and adjustable collimator, and a new beam rastering system. This paper will highlight the four exciting innovations and how they were designed, validated, and installed in parallel as well as the significant operational advantages they provide to IPF. Key experiments and the increased currents achieved in routine production runs demonstrating the enhanced capability from the AIP will be presented. The most notable capability enhancements include irradiations with beam currents ranging from 100 nA experimental runs up to 300 μA on routine production targets and utilization of a range of cylindrical target diameters.
Needlefall, aboveground net primary production (ANPP), canopy light interception and attenuation, and "radiation use efficiency" of five open-pollinated loblolly pine (Pinus taeda L.) families were ...investigated using 10-tree family block plots near Summerville, SC. Family variation in annual needlefall amounts was significant during the fourth (from 4796 to 6191 kg ha-1) and fifth growing seasons (from 4717 to 5721 kg ha-1); needlefall patterns for the poorest performing family were asynchronous from those of the others, with notably higher needlefall rates from April to July. Estimates of ANPP at age 4 yr varied by 16% (from 32.9 to 38.2 Mg ha-1) among families, and were generally commensurate with progeny test rankings based on height growth. The relationship between ANPP and leaf area index (LAI) was both significant and curvilinear, with an apparent optimum level of production (42.6 Mg ha-1) achieved at a LAI of about 13 (all-sided; February). The least productive families had the lowest mean LAI (e.g., 7.9), while the most productive families generally had higher levels of LAI (e.g., 13.6). Significant family differences in canopy light interception were present in every month sampled except June, when photosynthetically active radiation (PAR) interception exceeded 90% for all families. Light extinction coefficients (k) for February differed significantly among the five families, and ranged from 0.28 to 0.38; families with the largest LAIs generally had the lowest values of k and the highest levels of PAR interception. A strong linear relationship (r2 = 0.74) was found between ANPP and intercepted PAR. Estimates of the dry matter:radiation quotient (epsilon; "radiation use efficiency") differed significantly among families, and ranged from 1.33 g MJ-1 to 1.48 g MJ-1. Results of this study suggest that fundamental differences exist in production ecology among loblolly pine families
Data obtained by the associated production of {Lambda} hypernuclei through the ({pi}{sup +},{ital K}{sup +}) reaction are presented for a wide range of mass numbers. The special features which make ...this reaction useful are pointed out. The reaction is shown to be an excellent probe of {Lambda} single-particle states, as demonstrated by the excitation of deeply bound states which are interpreted as the weak coupling of a {Lambda} to neutron-hole states of the core. The {Lambda} binding energies and ground-state production cross sections for {sub {Lambda}}{sup 9}Be, {sub {Lambda}}{sup 12}C, {sub {Lambda}}{sup 16}O, {sub {Lambda}}{sup 28}Si, {sub {Lambda}}{sup 40}Ca, {sub {Lambda}}{sup 51}V, and {sub {Lambda}}{sup 89}Y are presented.
Design of low energy beam transport for new LANSCE H+ injector Batygin, Y.K.; Draganic, I.N.; Fortgang, C.M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2014, Letnik:
753
Journal Article
Recenzirano
The present LANSCE injector utilizes two 750-keV Cockcroft–Walton (CW) based injectors for simultaneous injection of H+ and H− beams into 800-MeV accelerator. To reduce long-term operational risks, ...the new project to replace the existing H+ CW injector with a Radio-Frequency Quadrupole (RFQ) accelerator is underway 1. The new injector requires a Low-Energy Beam Transport (LEBT). An ion source and 2-solenoid magnetic LEBT have been designed and optimized to transport beams over a wide range of space-charge neutralization and transverse emittance, while allowing sufficient space for diagnostics and a beam deflector. The design layout minimizes the beam size in the LEBT and potential emittance growth due to solenoid aberrations and nonlinear space-charge forces. This paper describes the details of the LEBT design activity.
Growth phenology and crown structure of five open-pollinated loblolly pine (Pinus taeda L.) families, planted at two spacings (0.92 and 1.83 m) and grown in pure plots near Summerville, SC, were ...investigated using a split-plot (main plots = spacing, subplots = genotype) field design. Shoot, branch, and foliage characteristics were quantified during the fourth growing season and related to standing volume. Genotype variation in shoot and branch characteristics was generally small and nonsignificant except for differences in annual height increment (from 135 to 152 cm) and current-year branch production (from 11.1 to 14.0). Significant genotype variation in foliage amount, distribution, and longevity was associated with contrasting growth performances and stage of stand development. Foliage biomass differed by as much as 60% among genotypes (from 4.8 to 7.7 Mg ha-1), with 38% of the variation related to family differences in total height. The large range in foliage biomass was the major contributor to leaf area index differences (LAI; from 7.9 to 13.6 m2 m-2), although significant genotype differences in weighted specific needle area (SNA; from 175 to 199 cm2 g-1) were also a factor. Genotype variation in foliage biomass and LAI was related to the vertical distribution of foliage, and both were significantly correlated with standing volume at age 3 yr (r = 0.64 and 0.59). The best performing families (3, 7, and 49 based on progeny testing) held 60% of their total foliage biomass in the middle crown third (nonuniform distribution), whereas the poorest families (37 and 138), had 50% in the same region (more uniform distribution). Compared to the other genotypes, family 37 exhibited reduced foliage longevity, which may have contributed to its low LAI and poor growth performance. Results of this study suggest that foliage display, amount, and duration are the crown characteristics important in conferring differential family performance for loblolly pine
The present LANSCE injector utilizes two 750-keV Cockcroft-Walton (CW) based injectors for simultaneous injection of H super(+) and H super(-) beams into 800-MeV accelerator. To reduce long-term ...operational risks, the new project to replace the existing H super(+) CW injector with a Radio-Frequency Quadrupole (RFQ) accelerator is underway 1. The new injector requires a Low-Energy Beam Transport (LEBT). An ion source and 2-solenoid magnetic LEBT have been designed and optimized to transport beams over a wide range of space-charge neutralization and transverse emittance, while allowing sufficient space for diagnostics and a beam deflector. The design layout minimizes the beam size in the LEBT and potential emittance growth due to solenoid aberrations and nonlinear space-charge forces. This paper describes the details of the LEBT design activity.
A diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies with this diagnostic show that the ...electron flux striking the wall in the quadrupole is comparable to or larger than in an adjacent drift. In addition, the trapped electron signal, obtained using the sweeping feature of diagnostic, was larger than expected and decayed very slowly with an exponential time constant of 50 to 100 mus. Experimental results were also obtained which suggest that a significant fraction of the electrons observed in the adjacent drift space were seeded by electrons ejected from the quadrupole.
A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos national laboratory ...proton storage ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). Evidence obtained from these tests suggests that further improvement in performance is limited by beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback. Here we describe the present system configuration, system optimization, results of several recent experimental tests, and results from studies of factors limiting its performance.
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