Modelling Plasma Formation and Evolution from Beam Strikes on Advanced Photon Souce Upgrade Collimators

The commissioning of the 360 rf beam position monitors (BPMs) in the Advanced Photon Source (APS) storage ring (SR) is nearing completion. After using the single-turn capability of the BPM electronics in the early ring commissioning phase, resolution measurements versus current and bandwidth were successfully performed. In the standard SR vacuum chamber geometry, the resolution was measured with beam as 0.16 μm⋅mA/Hz. For the insertion device vacuum chamber geometry, the resolution was measured to be 0.1 μm⋅mA/Hz. Since the photon beam stability requirement for the users is only 4.5 microns rms in the vertical direction, invesgations of rf BPM offset versus current and bunch pattern have also been initiated. Both single bunch and multibunch beam patterns with varying intensity were used to determine offset stability for both the global and the local orbit feedback applications.

This article focuses on the current status of the dipole magnet power supply (DMPS) and improvement in the Taiwan Photon Source (TPS) storage ring. The DMPS provides a stable and precise magnetic field for the storage ring operation. Appropriate wiring methods are employed to minimize magnetic field interference across the entire TPS area to meet the demands of high-energy output and overcome the challenges of operating at high currents. The target energy is set at 850 V and 750 A, utilizing a single-pole switching voltage regulator as a high-precision constant current source output structure. The system incorporates a closed control loop that uses the Direct Current Current Transducer (DCCT) to provide current signal feedback to the system. FPGA (Field-Programmable Gate Array) calculates PID (Proportional-Integral-Derivative) compensation values, generating a 2.1 kHz pulse width modulation (PWM) signal to regulate the output current. At the same time, insulated gate bipolar transistor (IGBT) modules are switching components. However, even after several years of practical operation, the stability and performance of the DMPS in the storage ring still require improvements. To enhance long-term output current stability and address peripheral issues, the current TPS utilizes the Beam Orbit Feedback (FOFB) system to suppress and fine-tune the magnetic field and compensate for the impact of temperature drift on the DMPS's output current. This improvement ensures a more stable circulation of the photon beam within the storage ring. By optimizing the temperature control circuit of the main control card, the long-term output current stability has been successfully enhanced to within ± 10 ppm. Simultaneously, the FOFB system reduces uncertainties in adjusting the X-axis beam position, improving beam stability and quality. Furthermore, relevant protective measures have been implemented to ensure robust system operation. Ultimately, these improvement measures have successfully met TPS's stringent requirements for the DMPS, enabling the synchrotron accelerator light source to operate at higher performance levels and fostering advanced scientific research. The results of these upgrades underscore the success of the power supply enhancements, making significant contributions to the overall improvement of the Taiwan Photon Source facility.

Spin precession experiments offer exciting motivations to search for new physics. We propose here an idea of using a modified version of the Muon g-2 storage ring for a potential new scientific program to search for a non-zero muon electric dipole moment (EDM). Using both electric and magnetic dipole fields to produce a "frozen spin" condition for the MDM (all the while enhancing the EDM spin precession), the storage ring would operate at a lower central muon momentum than for the present Muon g-2 measurement. The incident proton beam on target for the muon production can be obtained from the PIP-II high intensity proton beam. Preliminary calculations and simulation results of muon production at 800 MeV PoT, along with the determination of the closed orbit inside the hybrid 'g-2' storage ring configuration, shall be presented. Possibilities of using the 'g-2' storage ring as a test bench to demonstrate the freezing of the MDM spin precession shall be discussed. The operational range of the muon's momentum and energy, and their respective window of electric and magnetic field values to establish the frozen spin condition, shall be presented. We shall also briefly discuss the physics prospects and improvements in muon EDM bounds upon using Fermilab's PIP-II beam.

The behavior of metals in fast rising high (∼100 ns, >1 MG) magnetic fields have attracted attention in connection with designing laboratory-scale superpower pulse generators capable of producing currents of amplitude 50 MA and rise time 100–200 ns. The interaction of a magnetic field with a metal features an extremely fast penetration of the field into the metal in the form of a nonlinear diffusion wave and the formation of surface plasma due to Joule heating. The paper presents results of an experimental study of the propagation of a nonlinear magnetic diffusion wave and its relation to the formation of thermal plasma at the metal surface. The experiment was performed using metal rods and tubes of outer diameter 1–3 mm subject to 2–2.5 MA pulsed currents. The MIG pulse power generator1 (2.5 MA, 100 ns) was used as a driver. With these parameters, the azimuthal magnetic field induction could reach 8 MGs within 100 ns. Surface plasma was detected using VUV detectors and an optical framing camera. The velocity of magnetic field diffusion was measured with a voltage probe inserted axially into the tube.2 Copper, aluminum, titanium, steel, and stainless steel rods were used to prepare test samples.

The generation of strong magnetic fields (∼50 T) using single- or multi-turn coils immersed in water was studied. A pulse generator with stored energy of ∼3.6 kJ, discharge current amplitude of ∼220 kA, and rise time of ∼1.5 μs was used in these experiments. Using the advantage of water that it has a large Verdet constant, the magnetic field was measured using the non-disturbing method of Faraday rotation of a polarized collimated laser beam. This approach does not require the use of magnetic probes, which are sensitive to electromagnetic noise and damaged in each shot. It also avoids the possible formation of plasma by either a flashover along the conductor or gas breakdown inside the coil caused by an induced electric field. In addition, it was shown that this approach can be used successfully to investigate the interesting phenomenon of magnetic field enhanced diffusion into a conductor.

An anomalous damping or growth of transverse coupled bunch modes has long been observed in CESR. The growth rates and tune shifts of these modes are a highly nonlinear function of current. The effect is associated with the operation of the distributed ion pumps, as it disappears when the pumps are not powered. We show that this effect can be explained by the presence of electrons trapped in the CESR chamber by the field of the dipole magnets and the electrostatic leakage field of the distributed ion pumps. Photoelectrons are introduced into the chamber by synchrotron radiation and can be ejected from the chamber by the passage of an e/sup +/ or e/sup -/ bunch. The transverse position of the beam thus modulates the trapped photoelectron charge density, which in turn deflects the beam, creating growth or damping and a tune shift for each coupled bunch mode. Predictions of the dependence of growth rate and tune shift on bunch current, bunch pattern, and mode frequency by a numerical model of this process are in approximate agreement with observations.

Effects of a hybrid superconducting three-pole wiggler on the stored beam at the SAGA-LS storage ring

The detailed understanding of the formation and evolution of plasma from rapidly heated metallic wires is a long-standing challenge in the field of plasma physics and in exploding wire engineering. This physical process is made even more complicated if the wire material is composed of a number of individual layers. The authors have successfully developed both optical and x-ray backlighting diagnostics. In particular, the x-ray backlighting technique has demonstrated the capability for quantitative determination of the plasma density over a wide range of densities. This diagnostic capability shows that the process of plasma formation is composed of two separate phases: first, current is passed through a cold wire and the wire is heated ohmically, and, second, the heated wire evolves gases that break down and forms a low-density plasma surrounding the wire.

Acoustic and optical emission during laser-induced plasma formation

The laser produced plasma generated from an aluminium alloy and expanding across an external steady magnetic field has been studied using atomic emission spectroscopy. Various line emission obtained from different constituents of the aluminium alloy shows an enhancement in its intensity in the presence of ~5 KG magnetic field. Enhancement in the signal was found nearly two times. The maximum enhancement in the emission intensity was noticed between 3-10 μs time delay after the plasma formation in the laser energy ranging from 15-50 my. This enhancement in the emission intensity seems to be due to magnetic confinement of the plasma, when it cools down after expansion. This indicates a type of correlation between the emission intensity and the deceleration in the plasma expansion in the magnetic field.

Plasma formation from thick Al rods ohmically heated during the diffusion of pulsed multimegagauss magnetic field is examined experimentally. Rods in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinch configuration are driven to 1.0-MA peak current. The evolution of the resultant surface plasma is complex yet highly reproducible. Surface plasmas first form at discrete hot spots. As the pulsed current grows, plasma filaments form, first along the current, and then transverse to it. As the plasma temperature rises, emissions become increasingly uniform until instabilities grow and modulate the surface.

Investigation of laser-induced plasma evolution in flexible pad laser shock forming with high speed camera

A muon storage ring for the g-2 experiment at Brookhaven National Laboratory will have a DC superconducting inflector magnet for injection of the muon beam. This inflector locally bucks out the 1.45 tesla storage ring dipole field, so that the muon beam enters the ring tangentially as close as possible to the equilibrium orbit. The g-2 experiment requires the knowledge of the magnetic field over the muon orbits to a precision of 0.1 ppm. The inflector has nested dipole coils of opposite polarity so that it cancels its external magnetic flux and generates very little stray field. Nevertheless the residual field would affect the homogeneity of the storage ring magnetic field. A method of using a multilayer superconducting (SC) composite sheet surrounding the inflector to further reduce the fringe field has been proposed. This sheet should prevent the stray field due to the inflector from affecting the field quality of the muon storage region. In developing this new type of air-core septum magnet, a shortened SC prototype inflector was built in Japan at KEK. It has been used for testing the superconducting performance (in KEK, BNL) and the fringe flux shielding (in BNL). Some of the test results are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Feasibility of dosimetry with optically stimulated luminescence detectors in magnetic fields

The research highlights of synchrotron radiation usage in biology, medicine, chemistry, materials and environmental sciences, pharmacy, electronics and nano-technology, promoted the design and construction of a number of third generation light sources at the intermediate energies of 2.53.5 GeV [1]. The CANDLE general design is based on a 3 GeV electron energy storage ring, full energy booster synchrotron and 100 MeV S-Band injector linac [2, 3]. With nominal machine operation parameters, the horizontal emittance of the electron beam is 8.4 nm-rad. The resulting electron beam lifetime in the ring is 18.6 hours. The magnets design is based on normal conducting technology, although the superconducting wigglers may be installed in the ring to extend the photon spectral range to hard X-ray region. The optimization of the facility performance is based on the following criteria: • The high spectral flux and brightness of the photon beams in 0.01-50 keV range. • The sufficient dynamical aperture to provide stable operation and long beam lifetime; • The flexible operation with reproducible electron beam positioning. For time resolved experiments, the ability to accommodate many different bunch patterns (single and multi-bunch operation) is incorporated into the design.