arXiv subjects

David Marsden

Publications and source records attributed to David Marsden.

6 recordsLinked to original sources

arXiv2022

High Efficiency, Low Cost, RF Sources for Accelerators and Colliders

Several high efficiency, low cost, RF sources are in development or recently completed. All are designed to provide operating efficiencies exceeding 80% and provide more than 100 kW of output power with a focus on high average power or CW operation. The sources include (1) a magnetron system with amplitude and phase control, a multiple beam, power grid-tube based source, a multiple beam inductive output tube, and a klystron using the core oscillation method. The estimated cost for the magnetron system and multiple beam power grid-tube source are one dollar per Watt and 75 cents per Watt, respectively. Operating frequencies span the range from 300 MHz (power grid tube) to 1.3 GHz (magnetron and klystron). This paper describes the basic operation of the sources, indicates the status and schedule, and provides available experimental results.

physics.acc-ph↗

arXiv2022

SoLAr: Solar Neutrinos in Liquid Argon

SoLAr is a new concept for a liquid-argon neutrino detector technology to extend the sensitivities of these devices to the MeV energy range - expanding the physics reach of these next-generation detectors to include solar neutrinos. We propose this novel concept to significantly improve the precision on solar neutrino mixing parameters and to observe the "hep branch" of the proton-proton fusion chain. The SoLAr detector will achieve flavour-tagging of solar neutrinos in liquid argon. The SoLAr technology will be based on the concept of monolithic light-charge pixel-based readout which addresses the main requirements for such a detector: a low energy threshold with excellent energy resolution (approximately 7%) and background rejection through pulse-shape discrimination. The SoLAr concept is also timely as a possible technology choice for the DUNE "Module of Opportunity", which could serve as a next-generation multi-purpose observatory for neutrinos from the MeV to the GeV range. The goal of SoLAr is to observe solar neutrinos in a 10 ton-scale detector and to demonstrate that the required background suppression and energy resolution can be achieved. SoLAr will pave the way for a precise measurement of the 8-B flux, an improved precision on solar neutrino mixing parameters, and ultimately lead to the first observation of hep neutrinos in the DUNE Module of Opportunity.

hep-ex↗

arXiv2002

Solar Activity and Cloud Opacity Variations: A Modulated Cosmic-Ray Ionization Model

The observed correlation between global low cloud amount and the flux of high energy cosmic rays supports the idea that ionization plays a crucial role in tropospheric cloud formation. We explore this idea quantitatively with a simple model linking the concentration of cloud condensation nuclei to the varying ionization rate due to cosmic rays. Among the predictions of the model is a variation in global cloud optical thickness, or opacity, with cosmic-ray rate. Using the International Satellite Cloud Climatology Project database (1983-1999), we search for variations in the yearly mean visible cloud opacity and visible cloud amount due to cosmic rays. After separating out temporal variations in the data due to the Mt. Pinatubo eruption and El Nino/Southern Oscillation, we identify systematic variations in opacity and cloud amount due to cosmic rays. We find that the fractional amplitude of the opacity variations due to cosmic rays increases with cloud altitude, becoming approximately zero or negative (inverse correlation) for low clouds. Conversely, the fractional changes in visible cloud amount due to cosmic rays are only positively-correlated for low clouds and become negative or zero for the higher clouds. The opacity trends suggest behavior contrary to the current predictions of ion-mediated nucleation (IMN) models, but more accurate temporal modeling of the ISCCP data is needed before definitive conclusions can be drawn.

physics.ao-ph↗

arXiv2001

Propeller vs. Magnetar Concepts for SGR/AXPs

Two lines of thought exist as to the nature of Soft Gamma-ray Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs). On the one hand,we have neutron stars with super-critical magnetic fields, which spin-down the stars and power the gamma-ray bursts. On the other hand, are neutron stars with typical pulsar magnetic fields, which are spun-down by magnetospheric ``propeller'' torques from fallback or fossil disks in addition to magnetic dipole radiation. Many observational facts are available for comparing and contrasting these two concepts. The facts are described and whether or not each is compatible with these concepts is presented.

astro-ph↗

arXiv2001

Fossil Disks and Propellor Spindown of SGR/AXPs

We have shown that the interstellar media which surround the progenitors of SGRs and AXPs were unusually dense compared to the environments around most young radio pulsars. This environmental correlation argues strongly against the current magnetar model for SGRs and AXPs. We suggest instead that they are neutron stars with sub-critical magnetic fields and are spun down rapidly by ``propeller'' torques from fossil disks formed from the fallback of supernova ejecta. We show that this hypothesis is consistent with the observed properties of these enigmatic objects, and we compare the propeller and magnetar models for SGR and AXPs.

astro-ph↗

arXiv1999

Environmental Influences in SGRs and AXPs

Soft gamma-ray repeaters (SGRs) and anomalous x-ray pulsars (AXPs) are young (<100 kyr), radio-quiet, x-ray pulsars which have been rapidly spun-down to slow spin periods clustered at 5-12 s. Nearly all of these unusual pulsars also appear to be associated with supernova shell remnants (SNRs) with typical ages <20 kyr. If the unusual properties of SGRs and AXPs were due to an innate feature, such as a superstrong magnetic field, then the pre-supernova environments of SGRs and AXPs should be typical of neutron star progenitors. This is not the case, however, as we demonstrate that the interstellar media which surrounded the SGR and AXP progenitors and their SNRs were unusually dense compared to the environments around most young radio pulsars and SNRs. Thus, if these SNR associations are real, the SGRs and AXPs can not be ``magnetars'', and we suggest instead that the environments surrounding SGRs and AXPs play a controlling role in their development.

astro-ph↗