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Christopher Holland

Publications and source records attributed to Christopher Holland.

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Predicting core transport in ITER baseline discharges with neon injections

Achieving self-consistent performance predictions for ITER requires integrated modeling of core transport and divertor power exhaust under realistic impurity conditions. We present results from the first systematic power-flow and impurity-content study for the ITER 15 MA baseline scenario constrained directly by existing SOLPS-ITER neon-seeded divertor solutions. Using the OMFIT STEP workflow, stationary temperature and density profiles are predicted with TGYRO for $1.5 \le Z_{\rm eff} \le 2.5$, and the corresponding power crossing the separatrix $P_{\rm sep}$ is evaluated. We find that $P_{\rm sep}$ varies by more than a factor of 1.7 across this scan and matches the $\sim 100$~MW SOLPS-ITER prediction when $Z_{\rm eff} \simeq 1.6$ or when auxiliary heating is reduced to $\sim 75\%$ of nominal. Rotation-sensitivity studies show that plausible variations in toroidal flow magnitude modify $P_{\rm sep}$ by $\lesssim 20\%$, while AURORA modeling confirms that charge-exchange radiation inside the separatrix is dynamically negligible under predicted ITER neutral densities. These results identify a restricted compatibility window, $Z_{\rm eff} \approx 1.6$--1.75 and $0.75 \lesssim f_{P_{\rm aux}} \le 1.0$, in which core transport predictions remain aligned with neon-seeded divertor protection targets. This self-consistent, model-constrained framework provides actionable guidance for impurity control and auxiliary-heating scheduling in early ITER operation and supports future whole-device scenario optimization.

physics.plasm-ph

Demonstration of atom interrogation using photonic integrated circuits anodically bonded to ultra-high vacuum envelopes for epoxy-free scalable quantum sensors

Reliable integration of photonic integrated circuits (PICs) into quantum sensors has the potential to drastically reduce sensor size, ease manufacturing scalability, and improve performance in applications where the sensor is subject to high accelerations, vibrations, and temperature changes. In a traditional quantum sensor assembly, free-space optics are subject to pointing inaccuracies and temperature-dependent misalignment. Moreover, the use of epoxy or sealants for affixing either free-space optics or PICs within a sensor vacuum envelope leads to sensor vacuum degradation and is difficult to scale. In this paper, we describe the hermetic integration of a PIC with a vacuum envelope via anodic bonding. We demonstrate utility of this assembly with two proof-of-concept atom-interrogation experiments: (1) spectroscopy of a cold-atom sample using a grating-emitted probe; (2) spectroscopy of alkali atoms using an evanescent field from an exposed ridge waveguide. This work shows a key process step on a path to quantum sensor manufacturing scalability

quant-ph

Dynamics of Ion Temperature Gradient Turbulence and Transport with a Static Magnetic Island

Understanding the interaction mechanisms between large-scale magnetohydrodynamic instabilities and small-scale drift-wave microturbulence is essential for predicting and optimizing the performance of magnetic confinement based fusion energy experiments. We report progress on understanding these interactions using both analytic theory and numerical simulations performed with the BOUT++ [B. Dudson et al., Comput. Phys. Comm. 180, 1467 (2009)] framework. This work focuses upon the dynamics of the ion temperature gradient instability in the presence of a background static magnetic island, using a weakly electromagnetic two-dimensional five-field fluid model. It is found that the island width must exceed a threshold size (comparable to the turbulent correlation length in the no-island limit) to significantly impact the turbulence dynamics, with the primary impact being an increase in turbulent fluctuation and heat flux amplitudes. The turbulent radial ion energy flux is shown to localize near the X-point, but does so asymmetrically in the poloidal dimension. An effective turbulent resistivity which acts upon the island outer layer is also calculated, and shown to always be significantly (10x - 100x) greater than the collisional resistivity used in the simulations.

physics.plasm-ph

The rapid dispersal of low-mass virialised clusters

Infant mortality brought about by the expulsion of a star cluster's natal gas is widely invoked to explain cluster statistics at different ages. While a well studied problem, most recent studies of gas expulsion's effect on a cluster have focused on massive clusters, with stellar counts of order $10^4$. Here we argue that the evolutionary timescales associated with the compact low-mass clusters typical of the median cluster in the Solar neighborhood are short enough that significant dynamical evolution can take place over the ages usually associated with gas expulsion. To test this we perform {\it N}-body simulations of the dynamics of a very young star forming region, with initial conditions drawn from a large-scale hydrodynamic simulation of gravitational collapse and fragmentation. The subclusters we analyse, with populations of a few hundred stars, have high local star formation efficiencies and are roughly virialised even after the gas is removed. Over 10 Myr they expand to a similar degree as would be expected from gas expulsion if they were initially gas-rich, but the expansion is purely due to the internal stellar dynamics of the young clusters. The expansion is such that the stellar densities at 2 Myr match those of YSOs in the Solar neighborhood. We argue that at the low-mass end of the cluster mass spectrum, a deficit of clusters at 10s of Myr does not necessarily imply gas expulsion as a disruption mechanism.

astro-ph.SR