Speaker Abstracts

Collective High-k Adjustable-radius Scattering Instrument for electron scale turbulence measurement on MAST-U

D. C. Speirs¹, J. Ruiz Ruiz², M. Giacomin³, V. H. Hall-Chen⁴, A. D. R. Phelps¹, R. Vann³,

P. G. Huggard⁵, H. Wang⁵, A. Field⁶ and K. Ronald¹

¹ Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, U.K.

² Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP, U.K.

³ York Plasma Institute, Department of Physics, University of York, Heslington, York, YO10 5DD, U.K.

⁴ Institute of High Performance Computing, A*STAR, Singapore 138632, Singapore

⁵ Millimetre Wave Technology Group, RAL Space, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, U.K.

⁶ CCFE, Culham Science Centre, Abingdon OX14 3DB, U.K.

Plasma turbulence on disparate spatial and temporal scales plays a key role in limiting the level of confinement achievable in tokamaks. Reduced numerical models predicting cross-scale turbulent interactions require experimental turbulence data at both electron and ion scales to inform development. In this paper, we propose a novel, mm-wave based collective scattering diagnostic for measuring high-k (electron-scale) turbulence in the core and edge plasma of MAST-U. Baseline specifications include an operating frequency of 376 GHz, source power of ~100mW and normalised turbulence wavenumber measurement range of k_⊥ρ_e = 0.1 – 0.5 where k_⊥ is the binormal turbulence wavenumber and ρ_e the electron gyroradius.

Millimetre-wave Undulator Research at Strathclyde

Liang Zhang*†, Jim Clarke†**, Craig R. Donaldson*†, Craig W. Robertson*, Kevin Ronald*†, Colin G. Whyte*† and Adrian W. Cross*†

*Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK.

**ASTeC, STFC Daresbury Laboratory, Sci-Tech Daresbury, Keckwick Lane, Warrington, WA4 4AD, UK.

† The Cockcroft Institute, Sci-Tech Daresbury, Keckwick Lane, Warrington, WA4 4AD, UK.

Electromagnetic-wave (EM-wave) undulators have features of a large beam aperture and fast dynamic control. They have great potential to be used in a shorter-undulator-period free-electron laser (FEL) by operating at high frequencies. This paper summarizes the research activities on millimetre-wave undulator (MU) at ABP group, Strathclyde University. Short sections of MU operating at 36 GHz and 94 GHz were designed, manufactured and measured. To achieve a high equivalent magnet field strength, MU require high power, where Gyroklystrons were proposed as the drive sources.

0.2 MW High-Power W-Band Magnetron with Axially Extended Interaction Space

Jin Zhang, Xiaodong Chen

jin.zhang@qmul.ac.uk

Abstract: We have developed a high-power W-band magnetron as the millimetre wave source for plasma heating in the nuclear fusion facilities for clean power generation. In this re-invented magnetron, we use a novel axial output structure to efficiently extract power, and an axially extended interaction space (with long anode and cathode) to realise high beam current to enhance beam-wave interaction. The simulation results using CST Studio Suite show that a high output power of 0.2 MW at 94 GHz has been achieved, and it demonstrates significant potential for applications in nuclear fusion.

Harmonic cavity design for the EIC Cooler Energy Recovery Linac

Sara Toole, Lancaster University

The Electron Ion Collider (EIC) will use Coherent Electron Cooling (CeC) to combat emittance blow-up of proton beams in storage rings over extended storage times (~10 hrs). CeC is achieved using an Energy Recovery Linac, containing four cryomodules of 5-cell, 1773MHz 3rd harmonic cavities. Machine learning and multi-objective optimisation algorithms reveal three optimum geometries of aperture radii 30, 35, and 40mm with trapped TE111 resonances, indicated by dispersion diagrams.   Enlarged beampipes lower the TE11 cut-off, untrapping the TE111 resonance. A 5-cell, 30mm Ra 42.5mm Rbp solution is presented achieves a 14.9MV/m accelerating gradient, operating at peak electric and magnetic fields of 35MV/m and 65mT. A local electric field minimum initiates multipactor in the beampipe at field levels of 18-21MV/m, a multipactor-free design is investigated. Monopole and dipole HOM analyses form the basis of a feasible damping scheme.

Understanding Prediction to Measurement Power Discrepancies for the CERN Double Quarter Wave Crab Cavity Prototype Beam Tests

Conor McFarlane, Lancaster University

As part of the High Luminosity project of the Large Hadron Collider (LHC) at CERN, transverse deflecting RF structures (crab cavities) have been developed to compensate for the luminosity reduction caused by the collision crossing angle. Early beam tests of the prototype cavities demonstrated significant discrepancies between the simulated and measured extracted power of the Higher Order Modes (HOMs). Investigations into bunch-to-bunch variations and intra-bunch charge distributions have allowed for more sophisticated simulations, which help to understand the source of the observed discrepancies.

94GHz Cherenkov radiation source with two-dimensional periodic surface lattice and multistage depressed collector

A. J. MacLachlan, L. Zhang, I. V. Konoplev, A. D. R. Phelps, C. W. Robertson, P. MacInnes, C. G. Whyte, K. Ronald, A. W. Cross and M. A. Henderson

The concept, theory and design of an efficient, megawatt (MW) coherent Cherenkov oscillator exploiting a two-dimensional periodic surface lattice (2D-PSL) interaction structure with a diameter almost 12 times greater than the free-space wavelength is presented. When paired with a novel energy recovery system¹, simulations demonstrate the ability to efficiently (>50% overall efficiency) generate single-frequency radiation in the 80-95GHz range². The capability of these new sources to generate efficient, continuous wave (CW), powerful (>1MW) radiation,   makes them particularly suited to providing heating and current drive in fusion plasmas, with the potential to outperform rival source technologies.

¹UK Atomic Energy Authority and University of Strathclyde, L. Zhang, I. V. Konoplev, A. J. MacLachlan, K. Ronald, A. D. R. Phelps, C. G. Whyte, C. W. Robertson, P. MacInnes, A. W. Cross, Multistage Depressed Collector, GB 2408675.3. Filed 17 June 2024

² A. J. MacLachlan, L. Zhang, I. V. Konoplev, A. D. R. Phelps, C. W. Robertson, P. MacInnes, C. G. Whyte, K. Ronald, A. W. Cross and M. A. Henderson, Sci. Rep., 14, 23906, 2024

Gyro-amplifies for space situational awareness

Space situational awareness describes the generation and management of information on all objects in orbit. It facilitates the operation of the thousands of satellites that provide essential services to millions of people around the world. One information source is Inverse Synthetic Aperture Radar where the orbiting object’s motion is used to generate images. The key enabling technology for ISAR of objects in Low Earth Orbit (LEO) is the final stage amplifier which must provide high power over the frequency range from 92-100GHz. The Gyro-TWA is a good match for this requirement, we will discuss advances in the design aimed at this new requirement.

THz-Driven Acceleration of Subrelativistic Electrons in Dielectric-Lined Waveguides

 Laurence J. R. Nix, Lancaster University & The Cockcroft Institute

We present a design for the acceleration of 100 keV electrons by interaction with a travelling THz pulse in a dielectric-lined waveguide. By tapering the width of the structure, we keep the phase velocity matched with the increasing electron velocity throughout the interaction length. We analyse both the longitudinal and transverse beam dynamics in depth for our simulated design, which will soon be tested at The Cockcroft Institute.  We then consider various routes towards achieving higher gain in future designs. Also presented is a coupler design for delivering the THz pulse into the accelerating waveguide.

Wakefield and impedance studies for the Electron-Ion Collider

Rancheng Bi, Lancaster University

This presentation covers ongoing wakefield and impedance studies for the Electron-Ion Collider (EIC) electron cooler’s energy recovery linac (ERL), a JLab-BNL collaboration. Key topics include benchmarking between analytical equations and simulation tools (CST and ECHO3D) and impedance and thermal simulation results for beamline components, including BPMs and bellows. Notably, the BPMs show simulated loss factors of 0.77 V/nC for a 73 mm aperture (257 BPMs) and 0.45 V/nC for a 121 mm aperture (185 BPMs). While each BPM’s contribution is small, their combined effect significantly impacts the total impedance budget of the machine, crucial for optimizing performance.

Raman Scattering of Microwaves in an RF Plasma

A series of beat-microwave experiments have been carried out using counter propagating signals across an RF. One signal is launched by a magnetron operating at a fixed frequency of 9.4 GHz while a TWT amplifier provides tunability for optimising the beat frequency to match the natural plasma frequency. Both signals are launched by a pair of antennas forming Gaussian beams via mode mixing, while lenses will soon be added to provide focussing and increase the signal intensity in the bulk plasma. The aim is to produce an electrostatic Langmuir oscillation by the parametric scattering of the 2 incident microwaves.

Analysis of Electromagnetic Power Deposition Resonance Condition for Spherical Tokamak Plasma.

M. Higgins1, I. V. Konoplev2, B. Eliasson1, and K. Ronald1.

1. SUPA, Department of Physics, University of Strathclyde, Glasgow, UK

2. Tokamak Science Department, UKAEA, Abingdon, UK

Abstract: Electron Bernstein Waves (EBWs) have been proposed as a complimentary Heating and Current Drive (HCD) method to the conventional Electron Cyclotron (EC) waves in future fusion power plant designs such as STEP. In this study the requirements for efficient power deposition of EBWs in a Spherical Torus (ST) like plasma are investigated. Through the use of GENRAY and CQL3D raytracing and Fokker-Planck codes, a good agreement between the developed analytical model for efficient power deposition and the numerical simulations is shown. This gives the opportunity to better predict the location of power deposition to compliment complex numerical simulations.