Rebecca Ramjiawan
A5091866496- Particle Accelerators and Free-Electron Lasers
- Particle accelerators and beam dynamics
- Particle Detector Development and Performance
- Laser-Plasma Interactions and Diagnostics
- Magnetic confinement fusion research
- Photonic and Optical Devices
- Electron and X-Ray Spectroscopy Techniques
- Particle physics theoretical and experimental studies
- Nuclear Physics and Applications
- Radiation Therapy and Dosimetry
- Advancements in Photolithography Techniques
- Advanced Electron Microscopy Techniques and Applications
- Photocathodes and Microchannel Plates
- Advanced X-ray Imaging Techniques
- Advanced Surface Polishing Techniques
- Plasma Diagnostics and Applications
- Experimental Learning in Engineering
- Gyrotron and Vacuum Electronics Research
- Atomic and Molecular Physics
- Advanced MEMS and NEMS Technologies
- Integrated Circuits and Semiconductor Failure Analysis
- Graphite, nuclear technology, radiation studies
- Advanced Neural Network Applications
- Advanced Optical Sensing Technologies
- Advancements in PLL and VCO Technologies
University of Oxford
2018-2025
European Organization for Nuclear Research
2020-2024
Campbell Collaboration
2020-2022
We show in experiments that a long, underdense, relativistic proton bunch propagating plasma undergoes the oblique instability, which we observe as filamentation. determine threshold value for ratio between transverse size and skin depth instability to occur. At threshold, outcome of experiment alternates filamentation self-modulation (evidenced by longitudinal modulation into microbunches). Time-resolved images density distribution reveal grows an observable level late along bunch,...
Plasma wakefield acceleration is a promising technology to reduce the size of particle accelerators. The use high energy protons drive wakefields in plasma has been demonstrated during Run 1 AWAKE programme at CERN. Protons 400 GeV drove that accelerated electrons 2 under 10 m plasma. collaboration now embarking on with main aims demonstrate stable accelerating gradients 0.5–1 GV/m, preserve emittance electron bunches and develop sources scalable 100s metres beyond. By end 2, scheme should...
We show experimentally that an effect of motion ions, observed in a plasma-based accelerator, depends inversely on the plasma ion mass. The appears within single wakefield event and manifests itself as bunch tail, occurring only when sufficient ions suppresses wakefields. Wakefields are driven resonantly by multiple bunches, simulation results indicate ponderomotive force causes ions. In this case, is also expected to depend amplitude wakefields, confirmed through variations drive charge....
A long, narrow, relativistic charged particle bunch propagating in plasma is subject to the self-modulation (SM) instability. We show that SM of a proton can be seeded by wakefields driven preceding electron bunch. timing reproducibility and control are at level small fraction modulation period. With this seeding method, we independently amplitude seed with charge growth rate Seeding leads larger than instability case.
We use a relativistic ionization front to provide various initial transverse wakefield amplitudes for the self-modulation of long proton bunch in plasma. show experimentally that, with sufficient amplitude [$\ensuremath{\ge}(4.1\ifmmode\pm\else\textpm\fi{}0.4)\text{ }\text{ }\mathrm{MV}/\mathrm{m}$], phase modulation along is reproducible from event event, 3%--7% (of $2\ensuremath{\pi}$) rms variations all bunch. The not lower amplitudes. observe transition between these two regimes. Phase...
Multi-objective optimization is important for particle accelerators where various competing objectives must be satisfied routinely such as, example, transverse emittance vs bunch length. We develop and demonstrate an online multi-time scale multi-objective algorithm that performs real time feedback on accelerators. the ability to simultaneously minimize maintain a reference trajectory of beam in electron beamline CERN’s Advanced Proton Driven Plasma Wakefield Acceleration Experiment.
The Advanced Wakefield (AWAKE) Run 1 experiment, which concluded in 2018, achieved electron acceleration to 2 GeV via plasma wakefield driven by 400 GeV, self-modulated proton bunches extracted from the CERN SPS. 2c phase of experiment aims advance these results demonstrating up about 10GeV while preserving quality accelerated beam. For 2c, transfer line will be reconfigured shift first cell 40 m longitudinally and a second added downstream first. In addition, new 150 MeV beamline required...
We study experimentally the longitudinal and transverse wakefields driven by a highly relativistic proton bunch during self-modulation in plasma. show that wakefields' growth amplitude increase with increasing seed as well charge using maximum radius of distribution measured on screen downstream from externally injecting electrons measuring their final energy. Measurements agree trends predicted theory numerical simulations validate our understanding development self-modulation. Experiments...
Self-modulation is a beam–plasma instability that useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing ratio between initial transverse size of bunch and depth, occurs later along bunch, or not at all, over fixed length because amplitude decreases. show cases for which self-modulation does develop, we introduce simple model discussing conditions it would occur after any length. Changing...
Abstract In 2017, AWAKE demonstrated the seeded self-modulation (SSM) of a 400 GeV proton beam from Super Proton Synchrotron at CERN. The angular distribution protons deflected due to SSM is quantitative measure process, which agrees with simulations by two-dimensional (axisymmetric) particle-in-cell code LCODE about 5%. agreement achieved in population scans two selected plasma densities and scan longitudinal density gradient. reached only case wide enough simulation box (several...
We study experimentally the effect of linear plasma density gradients on self-modulation a 400\,GeV proton bunch. Results show that positive/negative gradient in/decreases number micro-bunches and relative charge per micro-bunch observed after 10\,m plasma. The measured modulation frequency also in/decreases. With largest positive we observe two frequencies in power spectrum. are consistent with changes wakefields' phase velocity due to adding slow during growth predicted by theory.
Abstract To improve the performance-critical stability and brightness of electron bunch at injection into proton-driven plasma wakefield AWAKE CERN experiment, automation approaches based on unsupervised machine learning (ML) were developed deployed. Numerical optimisers tested together with different model-free reinforcement (RL) agents. In order to avoid any bias, RL agents have been trained also using a completely state encoding auto-encoders. aid hyper-parameter selection, full synthetic...
A high-resolution, intratrain position feedback system has been developed to achieve and maintain collisions at the proposed future electron-positron International Linear Collider (ILC). prototype commissioned tested with a beam in extraction line of Accelerator Test Facility High Energy Research Organization Japan. It consists stripline monitor (BPM) analogue signal-processing electronics, custom digital board perform calculation, kicker driven by high-current amplifier. The closed-loop...
We report the design, operation and performance of a high-resolution, low-latency, bunch-by-bunch feedback system for nano-beam stabilisation. The employs novel, ultra-low quality-factor cavity beam position monitors (BPMs), two-stage analogue signal down-mixing system, digital processing board incorporating an FPGA. FPGA firmware allows real-time integration up to fifteen samples BPM waveforms within measured latency 232 ns. show that this sample improves significantly resolution and,...
Plasma wakefield dynamics over timescales up to 800 ps, approximately 100 plasma periods, are studied experimentally at the Advanced Wakefield Experiment (AWAKE). The development of longitudinal amplitude driven by a self-modulated proton bunch is measured using external injection witness electrons that sample fields. In simulation, resonant excitation causes electron trajectory crossing, resulting in potential outside boundary as transversely ejected. Trends consistent with presence this...
We present numerical simulations and experimental results of the self-modulation a long proton bunch in plasma with linear density gradients along beam path. Simulation agree reported [F. Braunmller, T. Nechaeva et al. (AWAKE Collaboration), Phys. Rev. Lett. 125, 264801 (2020)]: negative gradients, charge modulated is lower than positive gradients. In addition, modulation frequency varies gradient. show that dephasing wakefields respect to relativistic protons main cause for loss charge. The...
Abstract CERN’s North Area comprises several target and experimental systems is a zone of interest for future development. Provision beam to this area relies upon beam-intercepting devices located in various branched transfer lines from the Super Proton Synchrotron. In lines, these include primary production system beryllium plates followed by combined collimation, attenuation dump device made set aluminum, copper iron blocks known as ‘TAX’ (Target Attenuator [for] eXperimental areas). These...
The vertical plane transverse emittance of accelerated electron bunches at the AWAKE experiment CERN has been determined, using three different methods data analysis. This is a proof-of-principle measurement existing spectrometer to validate technique. Large values geometric emittance, compared that injection beam, are observed ($\sim \SI{0.5}{\milli\metre\milli\radian}$ with $\sim \SI{0.08}{\milli\metre\milli\radian}$), which in line expectations growth arising from plasma density ramps and...
A high-precision intra-bunch-train beam orbit feedback correction system has been developed and tested in the ATF2 beamline of Accelerator Test Facility at High Energy Research Organization Japan. The uses vertical position bunch measured two monitors (BPMs) to calculate a pair kicks which are applied next using upstream kickers, thereby correcting both trajectory angle. Using trains electron bunches separated time by 187.6 ns, was optimised so as stabilize offset BPMs better than 350 nm,...
The Advanced Wakefield (AWAKE) Experiment is a proof-of-principle experiment demonstrating the acceleration of electron beams via proton-driven plasma wakefield acceleration. AWAKE Run 2 aims to build on results 1 by achieving higher energies with an improved beam quality. As part upgrade 2, existing proton and beamlines will be adapted second cell new 150-MeV beamline added. specification for this challenging as it required inject bunches micron-level size stability into while being subject...
A low-latency, intra-train feedback system employing cavity beam position monitors (BPMs) has been developed and tested at the Accelerator Test Facility (ATF2) KEK. The can be operated with either information from a single BPM to provide local stabilisation, or by using two BPMs stabilise an intermediate location. correction is implemented stripline kicker custom power amplifier, calculations being performed on digital board built around Field Programmable Gate Array (FPGA). addition of...
In 2017, AWAKE demonstrated the seeded self-modulation (SSM) of a 400 GeV proton beam from Super Proton Synchrotron (SPS) at CERN. The angular distribution protons deflected due to SSM is quantitative measure process, which agrees with simulations by two-dimensional (axisymmetric) particle-in-cell code LCODE. Agreement achieved for populations between $10^{11}$ and $3 \times 10^{11}$ particles, various plasma density gradients ($-20 \div 20\%$) two densities ($2\times 10^{14} \text{cm}^{-3}$...