arXiv subjects

R. Shah

Publications and source records attributed to R. Shah.

13 recordsLinked to original sources

arXiv2025

Diagnosing the impact of relativistically intense prepulse on few-picosecond timeframes for short scale length laser-matter interactions

With the rapid proliferation of multi-petawatt (MPW) lasers globally, a new era of high-energy density science promises to emerge within the next decade. However, precise control over how light at these ultra-relativistic intensities interacts with matter (especially with solid-density targets) will be crucial to fully realize the cutting-edge scientific advancements and technological breakthroughs that the MPW regime promises to unlock. In this manuscript, we present experimental results, supported by numerical simulations, which show how intense prepulse activity on few-ps ($10^{-12}$ s) timescales leads to rapid shifts in the steepness of the preplasma generated on the surface of ultra-thin nanofoil targets. By combining a single-shot frequency resolved optical gating (FROG) autocorrelation device to diagnose on-shot incident laser pulse contrast, with coherent synchrotron emission (CSE) from relativistic laser plasmas as a probe for evolving plasma-scale length conditions, we provide an experimental benchmark for laser contrast on forthcoming MPW facilities, where high contrast on few-ps timescales will be essential for the next generation of laser-solid interactions.

physics.plasm-ph↗

arXiv2025

A large-momentum-transfer Raman atom interferometer without $k$-reversal

We present a Raman atom interferometer using large momentum transfer without reversing the direction of the effective wavevector ($k$-reversal). More specifically, we use a microwave $\pi$/2 pulse to manipulate the spin state of $^{87}$Rb atoms before applying a Raman light $\pi$ pulse to achieve 4$\hbar k$ momentum transfer per Raman light pulse. A microwave $\pi$ pulse in the middle of the interferometer sequence reverses the spin states, which allows closing of the interferometer arms by the same Raman light $\pi$ pulses without propagation reversal. We present a proof-of-principle demonstration of a 4$\hbar k$ large-momentum-transfer (LMT) atom interferometer and discuss its scalability. Our results extend the scope of using LMT atom optics.

physics.atom-ph↗

arXiv2023

Quantum gas-enabled direct mapping of active current density in percolating networks of nanowires

Electrically percolating nanowire networks are amongst the most promising candidates for next-generation transparent electrodes. Scientific interest in these materials stems from their intrinsic current distribution heterogeneity, leading to phenomena like percolating pathway re-routing and localized self-heating, which can cause irreversible damage. Without an experimental technique to resolve the current distribution, and an underpinning nonlinear percolation model, one relies on empirical rules and safety factors to engineer these materials. We introduce Bose-Einstein microscopy to address the long-standing problem of imaging active current flow in 2D materials. We report on improvement of the performance of this technique, whereby observation of dynamic redistribution of current pathways becomes feasible. We show how this, combined with existing thermal imaging methods, eliminates the need for assumptions between electrical and thermal properties. This will enable testing and modelling individual junction behaviour and hotspot formation. Investigating both reversible and irreversible mechanisms will contribute to the advancement of devices with improved performance and reliability.

physics.app-ph↗

arXiv2022

Optimizing Returns Using the Hurst Exponent and Q Learning on Momentum and Mean Reversion Strategies

Momentum and mean reversion trading strategies have opposite characteristics. The former is generally better with trending assets, and the latter is generally better with mean reverting assets. Using the Hurst exponent, which classifies time series as trending or mean reverting, we attempt to trade with each strategy when it is advantageous to generate higher returns on average. We ultimately find that trading with the Hurst exponent can achieve higher returns, but it also comes at a higher risk. Finally, we consider limitations of our study and propose a method using Q-learning to improve our strategy and implementation of individual algorithms.

q-fin.ST↗

arXiv2021

Background Estimation Studies for Positron Double Beta Decay

The study of neutrinoless double beta decay has attracted much attention as it can provide valuable information about the mass and the nature of the neutrino. The double beta decay (DBD) itself is also of interest in nuclear physics. While DBD has been observed in about a dozen nuclei, the positron double beta decay ($β^{+}β^{+}$/EC-$β^{+}$) continues to be an elusive. An important signature for $β^{+}β^{+}$ decay is the simultaneous emission of four 511 keV gamma rays and the coincident detection of these gamma rays can improve the measurement sensitivity. This paper presents an estimation of sensitivity for EC-$β^{+}$ and $β^{+}β^{+}$ employing coincidence measurement with two high purity Ge (HPGe) detectors. Simulations for coincident detection efficiency ($ε_c$) of 511 keV gamma rays with two HPGe detectors have been carried out using GEANT4 for different source geometries to optimize the mass efficiency product (M$ε_c$). The source of size $55\,mm \times 55\,mm \times 5\,mm$ (thickness) sandwiched between the front faces of the detectors were found to be optimal for 2 pairs of 511 keV gamma rays in the present detector setup. The coincident background is estimated at the sea level with moderate Pb shielding. With this setup, the sensitivity for T$_{1/2}$ measurement of EC-$β^{+}$ in $^{112}$Sn and $β^{+}β^{+}$ in $^{106}$Cd is estimated to be $\sim$10$^{19}$ - 10$^{20}$ y for 1y of measurement time.

physics.ins-det↗

arXiv2021

An Environmental Monitoring Network for Quantum Gas Experiments and Devices

Quantum technology is approaching a level of maturity, recently demonstrated in space-borne experiments and in-field measurements, which would allow for adoption by non-specialist users. Parallel advancements made in microprocessor-based electronics and database software can be combined to create robust, versatile and modular experimental monitoring systems. Here, we describe a monitoring network used across a number of cold atom laboratories with a shared laser system. The ability to diagnose malfunction, unexpected or unintended behaviour and passively collect data for key experimental parameters, such as vacuum chamber pressure, laser beam power, or resistances of important conductors, significantly reduces debugging time. This allows for efficient control over a number of experiments and remote control when access is limited.

quant-ph↗

arXiv2018

Analysis of trends in experimental observables and reconstruction of the implosion dynamics for direct-drive cryogenic targets on OMEGA

This paper describes a technique for identifying trends in performance degradation for inertial confinement fusion implosion experiments. It is based on reconstruction of the implosion core with a combination of low- and mid-mode asymmetries. This technique was applied to an ensemble of hydro-equivalent deuterium-tritium implosions on OMEGA that achieved inferred hot-spot pressures ~56+/-7 Gbar [S. Regan et al., Phys. Rev. Lett. 117, 025001 (2016)]. All the experimental observables pertaining to the core could be reconstructed simultaneously with the same combination of low and mid modes. This suggests that in addition to low modes, that can cause a degradation of the stagnation pressure, mid modes are present that reduce the size of the neuron and x-ray producing volume. The systematic analysis shows that asymmetries can cause an overestimation of the total areal density in these implosions. It is also found that an improvement in implosion symmetry resulting from correction of either the systematic mid or low modes would result in an increase of the hot-spot pressure from 56 Gbar to ~80 Gbar and could produce a burning plasma when the implosion core is extrapolated to an equivalent 1.9 MJ symmetric direct illumination [A. Bose et al., Phys. Rev. E 94, 011201(R) (2016)].

physics.plasm-ph↗

arXiv2016

TITUS: the Tokai Intermediate Tank for the Unoscillated Spectrum

The TITUS, Tokai Intermediate Tank for Unoscillated Spectrum, detector, is a proposed Gd-doped Water Cherenkov tank with a magnetised muon range detector downstream. It is located at J-PARC at about 2 km from the neutrino target and it is proposed as a potential near detector for the Hyper-Kamiokande experiment. Assuming a beam power of 1.3 MW and 27.05 x 10^{21} protons-on-target the sensitivity to CP and mixing parameters achieved by Hyper-Kamiokande with TITUS as a near detector is presented. Also, the potential of the detector for cross sections and Standard Model parameter determination, supernova neutrino and dark matter are shown.

physics.ins-det↗

arXiv2015

Reconstruction of Energy Spectra of Neutrino Beams Independent of Nuclear Effects

We propose a new technique which enables an event-by-event selection of neutrino-hydrogen interactions in multi-nuclear targets and thereby allows application of hydrogen as targets in experiments with neutrino beams without involving cryogenics or high pressure hydrogen gas. This technique could significantly improve the reconstruction of the neutrino energy spectra. Since it allows a separation between hydrogen and the accompanying nuclei, this technique also enables us to measure nuclear effects in neutrino interactions directly.

hep-ex↗

arXiv2014

Scaling of laser-driven ion energies in the relativistic transparent regime

Laser-driven ions have compelling properties and their potential use for medical applications has attracted a huge global interest. One of the major challenges of these applications is generating beams of the required energies. To date, there has been no systematic study of the effect of laser intensity on the generation of laser-driven ions from ultrathin foils during relativistic transparency. Here we present a scaling for ion energies with respect to the on-target laser intensity and in considering target thickness we find an optimum thickness closely related to the experimentally observed relativistic transparency. A steep linear scaling with the normalized laser amplitude a0 has been measured and verified with PIC simulations. In contrast to TNSA, this scaling is much steeper and has been measured for ions with Z > 1. Following our results, ion energies exceeding 100MeV/amu are already accessible with currently available laser systems enabling realization of numerous advanced applications

physics.plasm-ph↗

arXiv2013

160 MeV laser-accelerated protons from CH2 nano-targets for proton cancer therapy

Proton (and ion) cancer therapy has proven to be an extremely effective even supe-rior method of treatment for some tumors 1-4. A major problem, however, lies in the cost of the particle accelerator facilities; high procurement costs severely limit the availability of ion radiation therapy, with only ~26 centers worldwide. Moreover, high operating costs often prevent economic operation without state subsidies and have led to a shutdown of existing facilities 5,6. Laser-accelerated proton and ion beams have long been thought of as a way out of this dilemma, with the potential to provide the required ion beams at lower cost and smaller facility footprint 7-14. The biggest challenge has been the achievement of sufficient particle energy for therapy, in the 150-250 MeV range for protons 15,16. For the last decade, the maximum exper-imentally observed energy of laser-accelerated protons has remained at ~60 MeV 17. Here we the experimental demonstration of laser-accelerated protons to energies exceeding 150 MeV, reaching the therapy window. This was achieved through a dif-ferent acceleration regime rather than a larger laser, specifically a 150 TW laser with CH2 nano-targets in the relativistically transparent regime 18,19. We also demonstrate a clear scaling law with laser intensity based on analytical theory, computer simulations and experimental validation that will enable design of a pro-totype system spanning the full range of therapeutically desirable energies.

physics.plasm-ph↗

arXiv2008

Distal actions and shifted convolution property

A locally compact group $G$ is said to have shifted convolution property (abbr. as SCP) if for every regular Borel probability measure $\mu$ on $G$, either $\sup_{x\in G} \mu ^n (Cx) \ra 0$ for all compact subsets $C$ of $G$, or there exist $x\in G$ and a compact subgroup $K$ normalised by $x$ such that $\mu^nx^{-n} \ra \omega_K$, the Haar measure on $K$. We first consider distality of factor actions of distal actions. It is shown that this holds in particular for factors under compact groups invariant under the action and for factors under the connected component of identity. We then characterize groups having SCP in terms of a readily verifiable condition on the conjugation action (point-wise distality). This has some interesting corollaries to distality of certain actions and Choquet Deny measures which actually motivated SCP and point-wise distal groups. We also relate distality of actions on groups to that of the extensions on the space of probability measures.

math.PR↗

arXiv2004

Discovery of a New Low-Latitude Milky Way Globular Cluster using GLIMPSE

Spitzer Space Telescope imaging as part of the Galactic Legacy Mid-Plane Survey Extraordinaire (GLIMPSE) reveals a previously unidentified low-latitude rich star cluster near l=31.3 degrees, b=-0.1 degrees. Near-infrared JHK' photometry from the Wyoming Infrared Observatory indicates an extinction of A_V ~ 15+/-3 mag for cluster members. Analysis of 13CO features along the same sightline suggests a probable kinematic distance of 3.1 -- 5.2 kpc. The new cluster has an angular diameter of ~1-2 pc, a total magnitude m_{K_0}=2.1 corrected for extinction, and a luminosity of M_K ~ -10.3 at 3.1 kpc. In contrast to young massive Galactic clusters with ages <100 Myr, the new cluster has no significant radio emission. Comparison to theoretical K-band luminosity functions indicates an age of at least several Gyr and a mass of at least 10^5 solar masses. Unlike known old open clusters, this new cluster lies in the inner Galaxy at R_{GC} ~ 6.1 kpc. We designate this object ``GLIMPSE-C01'' and classify it as a Milky Way globular cluster passing through the Galactic disk. We also identify a region of star formation and fan-shaped outflows from young stellar objects in the same field as the cluster. The cluster's passage through the Galactic molecular layer may have triggered this star formation activity.

astro-ph↗