Session Q12: Accelerators and Beams

Live

The Muon g-2 Experiment (E989) at Fermilab seeks to measure the anomalous magnetic moment of the muon to high precision for direct comparison with the predictions of the Standard Model at an unprecedented level. Using a precision magnetic field with electrostatic quadrupole focusing, the decaying muons produce positrons which can be tracked and analyzed. During the measurements within each data-taking window, muons can be lost from the storage ring prior to their decay due to a variety of other dynamical processes. If the ``lost muon'' distribution has a different average polarization than the distribution that gets measured by the experimental detectors, then this can lead to a systematic error in the final spin precession frequency analysis and hence an error on the anomalous moment determination. In this talk we investigate possible sources of particle loss, estimates of their respective rates, and the scale of the limits on their contribution to a systematic error.   

Live

The Muon $g$-$2$ Experiment at Fermilab (E989) measures the anomalous magnetic moment of the muon, $a_{\mu}$, with improved precision compared to the previous experiment at Brookhaven National Lab. The new measurement will serve as strong probe of effects of physics beyond the Standard Model (SM) and perhaps validate or disprove other theoretical models outside the SM. Of particular importance is the action of the guide fields of the Muon $g$-$2$ Storage Ring on the stored beam, which affects its overall spin precession frequency relative to the cyclotron frequency. This relative frequency, also known as $\omega_{a}$, plays a crucial role in the determination of the muon magnetic anomaly. Experimental techniques with well-established theoretical backgrounds to characterize the stored beam allow to directly quantify the corrections to $\omega_{a}$ due to such effects. Furthermore, with the support of beam dynamics simulations the associated errors that contribute to the E989 final measurement systematic uncertainty are determined.   

Live

First experiments to produce particle beams on the Multi-Terawatt (MTW) laser at LLE were conducted, utilizing the target normal sheath acceleration (TNSA) mechanism with deuterated titanium foils. In the experiments, a high-power (approx. 10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}})$, short-pulse, (8-ps) laser beam is shone onto a thin (25-$\mu $m) foil previously exposed to varying amounts of deuterium. The electrons in the target are accelerated away from the target by the strong electromagnetic field of the laser, generating an enormous Coulomb field. This field ionizes the atoms at the rear surface of the target and accelerates them to a few hundred keV. This study focused on characterizing the beam composition and energy using a Thomson parabola ion spectrometer (TPIS). For different target finishes, the relative abundance of different ion species originating from surface contaminants, as well as the absolute yield and energy distribution of deuterons in the beam, were measured. Future studies will utilize the optimal target for nuclear reaction experiments with a secondary ``physics'' target. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.   

Live

Coherent Synchrotron Radiation(CSR) is regarded as one of the main sources of emittance growth in the bunch compressor. Current simulations containing CSR wake fields often utilize one-dimensional model assuming a line beam. Despite its good computation efficiency, 1D CSR model can be inaccurate for beams of extreme high current like in FACET II. On the other hand, the existing 3D codes are often slow and have high demands on computational resources. In this paper we propose a new method for calculation of the two-dimensional CSR wakefields in relativistic beams with integrals of retarded potentials. It generalizes the 1D model and includes the transient effects at the entrance and the exit from the magnet. Within given magnetic lattice and initial beam distributions, the formalism reduces to 2D integration along the trajectory and therefore allows fast numerical calculations using 2D matrices.   

Live

Detrimental beam dynamics effects limit performance of high intensity rapid cycling synchrotrons (RCS) such as the 8 GeV Fermilab Booster. He we report the results of systematic study of the Booster beam intensity losses and emittance growth on key important parameters such as the machine tunes, chromaticities and the total number of protons per pulse (PPP). We also cross-check two methods of the beam emittance measurements -- the multi-wires proportional chambers and the ionization profile monitors -- and discuss the ultimate performance of the machine now and after foreseen and proposed upgrades.   

Live

A third-integer resonant slow extraction system is being developed for Fermilab's Delivery Ring (DR) to send protons to the muon production target for the Mu2e experiment. Using bunched beam in the DR, pulses of protons separated by 1.6 $\mu$s (revolution frequency) for a total spill duration of 43 ms provides the proper time structure and required spill intensity of about $3 \times 10^{7}$ protons per pulse. The third-integer resonance is to be achieved using six sextupoles, in conjunction with fast quadrupole magnets to drive the horizontal tune of the DR very close to 29/3. Additionally, a Radio Frequency Knock-out (RFKO) method could be employed to heat up the beam for a finer control of the spill rate. In this talk, the scope of accelerator physics and the challenges of the extraction process from the DR will be briefly reviewed. A preliminary computational analysis of the extraction process shall be discussed, which will include extraction efficiency, spill rate, possible tune-ramp achievable using quads, application of RFKO to heat the beam, the feedback system to regulate the spill rate by choreographing both RFKO and quad tune ramp, and other factors concerning the overall control of the beam.   

On Demand

The SuperKEKB asymmetric electron-positron collider, which provides data for the Belle II experiment in Tsukuba, Japan, is operational and has already reached a luminosity of 1e34 cm-2 s-1. The ultimate target luminosity of 8x1e35 cm-2 s-1 is forty times higher than that achieved by the predecessor KEKB. The large improvement requires an upgraded machine lattice and higher beam currents which lead to increased beam backgrounds. Therefore, a dedicated beam collimation system is crucial to protect Belle II. We present a new simulation procedure, based on the Strategic Accelerator Design (SAD) software framework, used to optimize the collimation system. We aim to optimize the transverse widths of existing collimators, and the longitudinal positions of additional collimators to be installed in the future, in order to maximally and safely reduce interaction region (IR) losses while maintaining acceptable beam lifetime. The developed software allows us to perform a deep analysis of the machine properties, including these collimator optimizations, with greatly reduced computational time. The obtained set of collimator widths (known as the machine mask) serves as a guideline for the experimental setup of collimators.   

On Demand

Generation of betatron radiation is one of the 10 experiments which are proposed at the Facility for Advanced Accelerator Experimental Tests (FACET) II. However, previous works have not considered the effects of ion motion and hosing instability on the radiation spectrum, which may arise due to strongly non-linear wakefields driven by high current beams. We present numerical studies using 3D PIC simulation codes for beams undergoing hosing, seeded by long- and short-wavelength head-to-tail centroid perturbations, including effects of ion collapse due to high-current drive beams. The effects on spectral intensity and photon statistics of the resultant betatron radiation are examined. Our results stand to inform tolerances in input beam quality and potential tunability for betatron radiation experiments due to commence later this year.   

Not Participating

Storage rings and beamline electromagnets with curved longitudinal axes have many applications in accelerator physics, medical physics, fusion \& plasma research, as well as fundamental physics experiments like the Muon g-2 Experiment (E989) at Fermilab. In E989, the magnetic field of the muon storage ring is measured using proton-nuclear-magnetic-resonance spectroscopy, however, this technique only gives the scalar magnitude of the magnetic field, not the full 3 vector components. Here, we use toroidal harmonics and global optimization algorithms to explore a large number of candidate magnetic-field configurations plausibly encountered by muons orbiting in the g-2 storage ring, and we demonstrate that optimal candidate solutions agree well with available magnetic-field data. We also incorporate the reconstructed 3D vector magnetic fields into Geant4-based tracking simulations in order to quantify the effect of different magnetic-field configurations on measurements of the muon magnetic and electric dipole moments. The work presented here is generally applicable to situations in which toroidal harmonics are required to accurately model fields and/or sophisticated numerical techniques are needed to solve complex, high-dimensional optimization problems.