Boris Militsyn

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Mogadalai Gururajan

IIT Bombay

Ben Shepherd

Daresbury Laboratory

Nicole Herbots

Arizona State University

Estela Blaisten-Barojas

George Mason University

Maurizio Forte

Duke University

Emmanuel T Rodulfo

De La Salle University

Mohammad Mehdi Firoozabadi

The University of Birjand

Petra Reinke

University of Virginia

Fabio Cuzzolin

Oxford Brookes University

Irina Kolesnik

Moscow State University

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Papers by Boris Militsyn

STFC ASTeC: First run on the electron beam facility VELA

A pulsed polarized electron source for nuclear physics experiments

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Developments in the CLARA FEL Test Facility Accelerator Design and Simulations

7th International Particle Accelerator Conference (IPAC'16), Busan, Korea, May 8-13, 2016, Jun 1, 2016

We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for... more We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. In order to prioritise FEL schemes requiring the shortest electron bunches, the layout has changed significantly to enable compression at higher energy. Four proposed modes of operation are defined and tracked from cathode to FEL using ASTRA. Supplementing these baseline mode definitions with CSR-enabled codes (such as CSR-TRACK) where appropriate is in progress. The FEL layout is re-optimised to include shorter undulators with delay chicanes between each radiator.

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Metal Photocathodes Preparation for Compact Linear Accelerator at Daresbury Laboratory

9th Int. Particle Accelerator Conf. (IPAC'18), Vancouver, BC, Canada, April 29-May 4, 2018, Jun 1, 2018

The photoinjector of the CLARA FEL test facility Front End at Daresbury Laboratory is based on a ... more The photoinjector of the CLARA FEL test facility Front End at Daresbury Laboratory is based on a S-band 10 Hz photocathode RF-gun operating with a copper photocathode which is driven by the third harmonic of a Ti:Sapphire laser (266 nm). The main aim of this study was to establish a procedure to prepare the Cu surface prior to installation so a Quantum Efficiency (QE) of 10-5 or higher can be achieved at laser power density below the ablation threshold of copper. In order to do this Cu test samples with a roughness of 10 nm were prepared using different techniques. The best results have been obtained by ex-situ chemical cleaning. This removed the surface oxide layer whilst at the same time producing a surface buffer layer. This inhibited the regrowth of native oxide for up to a week when exposed to normal ambient atmospheric conditions. With either chemical cleaning or Ar plasma cleaning after heating the sample in-situ to 150 °C for 90 minutes or 250 °C for 40 hours, almost all of the surface oxide was removed. For these surfaces a QE of 4.10-5 or better was measured. Oxygen plasma cleaning at 100% and 20% power produced CuO layer with surface carbon contaminant to 3 atomic %, however in-situ thermal cycling resulted in at best a QE of 3•10-6 .

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Measurements of the Longitudinal Energy Distribution of Low Energy Electrons

5th Int. Particle Accelerator Conf. (IPAC'14), Dresden, Germany, June 15-20, 2014, 2014

The Transverse Energy Spread Spectrometer (TESS) is an ASTeC experiment designed to measure the e... more The Transverse Energy Spread Spectrometer (TESS) is an ASTeC experiment designed to measure the energy of electrons from different cathode materials. It is a dedicated test stand for future light sources. A full particle tracking code has been developed in the QUASAR Group, which simulates particle trajectories through TESS. Using this code it is possible to simulate different operational conditions of the experiment and cathode materials. The simulation results can then be benchmarked against experimental data to test the validity of the emission and beam transport model. Within this paper, results from simulation studies are presented and compared against experimental data as a collaboration within the Cockcroft Institute between ASTeC and the QUASAR Group for the case of measuring the longitudinal velocity distribution of electrons emitted from a gallium arsenide cathode using a grid structure as an energy filter.

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CLARA - A Proposed New FEL Test Facility for the UK

Presented at, 2012

A Free Electron Laser (FEL) test facility, CLARA (Compact Linear Advanced Research Accelerator), ... more A Free Electron Laser (FEL) test facility, CLARA (Compact Linear Advanced Research Accelerator), is proposed to be constructed at Daresbury Laboratory in the UK. The aim of CLARA is to develop a normal conducting test accelerator able to generate longitudinally and transversely bright electron bunches and to use these bunches in the experimental production of stable, synchronised, ultra short photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation of light source facilities. In addition the facility will be an ideal test bed for demonstrating innovative technologies such as high repetition rate normal conducting RF linacs and advanced undulator designs. This paper will describe the design of CLARA, pointing out the flexible features that will be incorporated to allow multiple novel FEL schemes to be proven.

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A plasma wakefield acceleration experiment using CLARA beam

Nuclear Instruments and Methods in Physics Research, Mar 1, 2014

We propose a Plasma Accelerator Research Station (PARS) based at proposed FEL test facility CLARA... more We propose a Plasma Accelerator Research Station (PARS) based at proposed FEL test facility CLARA (Compact Linear Accelerator for Research and Applications) at Daresbury Laboratory. The idea is to use the relativistic electron beam from CLARA, to investigate some key issues in electron beam transport and in electron beam driven plasma wakefield acceleration, e.g. high gradient plasma wakefield excitation driven by a relativistic electron bunch, two bunch experiment for CLARA beam energy doubling, high transformer ratio, long bunch self-modulation and some other advanced beam dynamics issues. This paper presents the feasibility studies of electron beam transport to meet the requirements for beam driven wakefield acceleration and presents the plasma wakefield simulation results based on CLARA beam parameters. Other possible experiments which can be conducted at the PARS beam line are also discussed.

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Characteristics of dark current from an S-band rf gun with exchangeable photocathode system

arXiv (Cornell University), Mar 1, 2024

Field emission or dark current from RF electron guns is problematic for accelerators for several ... more Field emission or dark current from RF electron guns is problematic for accelerators for several reasons, and can be more difficult to predict, measure and understand, compared to the main beam. The work presented here is a study of the dark current emitted from the CLARA 3GHz 2.5 cell electron gun with exchangeable photocathode, which is a type of gun used for single pass high quality low emittance beams for uses such as free electron lasers. The main purpose of these studies was to identify sources of dark current emission within the gun, by examining the dark current distribution and patterns on scintillating screens. It is shown that the features of the patterns can be reproduced qualitatively by finite element simulations. Thus, certain surfaces within the gun and cathode apparatus which contribute most significantly to problematic dark current can be identified, and further development and preparation of the guns and their cathodes can be informed to minimise dark current.

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Parameters stability of S-Band RF gun cavity due to effects of pulsed RF heating

Nuclear Instruments and Methods in Physics Research, Oct 1, 2019

Requirements to high performances of modern Free Electron Lasers (FEL) facilities transform to re... more Requirements to high performances of modern Free Electron Lasers (FEL) facilities transform to requirements of high stability of their electron injectors, which are typically based on photocathode RF guns. To provide high brightness bunches, gun cavities operate in the injector with high pulsed electric, hence, magnetic fields. The effects, related to a pulsed RF heating, result in the change of resonance frequency and quality factor of the cavity even during few 𝜇𝑠 RF pulse that, in turn leads to the amplitude and the phase change of RF oscillations in the gun cavity. Cavity deformations due to pulsed heating are considered and corresponding deviations in the cavity resonance frequency are evaluated. Resulting deviations in the phase and the amplitude of the RF field in the cavity are estimated in dependence on the RF pulse duration.

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Field Flatness and Frequency Tuning of the CLARA High Repetition Rate Photoinjector

28th Linear Accelerator Conf. (LINAC'16), East Lansing, MI, USA, 25-30 September 2016, May 1, 2017

The High Repetition Rate Photoinjector, designed for the CLARA FEL at Daresbury Laboratory, was t... more The High Repetition Rate Photoinjector, designed for the CLARA FEL at Daresbury Laboratory, was tuned at the manufacturers for both field flatness and frequency. Due to the high average power in the gun cavity of 6.8 kW the cavity requires significant cooling, achieved by water channels in the cavity body. These channels prohibit the use of tuning studs to tune the cavity. The cavity was tuned by taking pre-braze clamped low power RF measurements and using the data to trim the cavity cells to the optimum length for both field flatness and frequency. The optimum field flatness is 100% and the design frequency is 2998.5 MHz. Both cells were trimmed in 4 stages, resulting in a post-braze frequency of 2998.51 MHz and field flatness of 98%.

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A Velocity Bunching Scheme for Creating Sub-Picosecond Electron Bunches from an RF Photocathode Gun

Sub-picosecond electron bunches are in demand for various applications including Free Electron La... more Sub-picosecond electron bunches are in demand for various applications including Free Electron Lasers and electron diffraction experiments. Typically, for Free Electron Lasers, a multiple picosecond scale bunch is produced from a photoinjector with compression achieved via one or more magnetic chicanes by providing an appropriate energy chirp to the bunch in the preceding linac sections. This approach is complex, requiring many components, often including a higher harmonic linac section to linearise the longitudinal phase-space, and careful tuning in order to minimise emittance blow-up due to coherent synchrotron radiation. We present a scheme to deliver sub-picosecond electron bunches, based on a normal conducting RF gun and two short linac sections, one for providing velocity bunching and the second to capture the compressed bunch and accelerate to tens of MeV where the beam properties are then essentially frozen.

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Bunch Length Measurements using a Transverse Deflecting Cavity on VELA

7th International Particle Accelerator Conference (IPAC'16), Busan, Korea, May 8-13, 2016, 2016

The VELA facility at Daresbury Laboratory in the UK includes a 5 MeV/c 2.5 cell S-band photoinjec... more The VELA facility at Daresbury Laboratory in the UK includes a 5 MeV/c 2.5 cell S-band photoinjector gun. This gun operates in the "blow-out" regime with a sub-200 fs length drive laser: the resulting bunch length is determined by space-charge effects. We present measurements made with an S-band transverse deflecting cavity to characterise the bunch length as a function of charge, and as a function of the gun operating phase.

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Front End Simulations and Design for the CLARA FEL Test Facility

We present the design and simulations of the Front End for CLARA (Compact Linear Accelerator for ... more We present the design and simulations of the Front End for CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. This is based around an S-band RF photocathode gun. Initially this will be the 2.5 cell gun, currently used on VELA facility at Daresbury, which is limited to 10 Hz repetition rate. Later, this will be upgraded to a 1.5 cell gun, currently under development, which will allow repetition rates of up to 400 Hz to be reached. The beam will be accelerated up to 50 MeV with a booster linac which will be operated in both bunching and boosting modes for different operating regimes of CLARA. Simulations are presented for a currently achieved performance of the RF system and drive laser with optimisation of the laser pulse lengths for various operational modes of CLARA.

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Effect of the drift gap between the undulator sections on the operation of the Fusion-FEM

Nuclear Instruments and Methods in Physics Research, May 1, 2000

The &Fusion-FEM' is a free electron MASER based on an electrostatic accelerator. An electron beam... more The &Fusion-FEM' is a free electron MASER based on an electrostatic accelerator. An electron beam of 12 A, 1.35}2 MeV is injected into a step-tapered undulator to generate 1 MW of radiation in the range 130}250 GHz. The undulator is built from two sections with di!erent "eld strength (step-tapering), separated by a "eld-free gap. Tapering enhances the e$ciency at high output power. Proof of principle has been demonstrated in the short-pulse regime, without a beam-and energy recovery system. The latter is now being installed and will allow long-pulse operation. The experiments have shown that high output power can be generated and that the FEM has the tendency to lock onto a single longitudinal mode. The in#uence of the length of the gap between the undulator sections has been investigated and is the subject of this paper. The experimental results are reasonably well explained by simulations.

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The photocathode gun of the Polarized Electron Source at NIKHEF

Nucleation and Atmospheric Aerosols, 1998

ABSTRACT

FELICE—the free electron laser for intra-cavity experiments

Elsevier eBooks, 2003

At the FOM Institute "Rijnhuizen" a new Free Electron Laser for Intra-Cavity Experiments (FELICE)... more

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Clara Accelerator Design and Simulations

We present the accelerator design for CLARA (Compact Linear Accelerator for Research and Applicat... more We present the accelerator design for CLARA (Compact Linear Accelerator for Research and Applications) at Daresbury Laboratory. CLARA will be a testbed for novel FEL configurations. The accelerator will consist of an RF photoinjector, S-band acceleration and transport to 250 MeV including X-band linearisation and magnetic bunch compression. We describe the design of the accelerator. Beam dynamics simulations are then used to define an operating working point suitable for the seeded FEL scheme.

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Gallium Arsenide Photocathode Research at Daresbury Laboratory

Presented at, 2011

Significant effort has been expended over several years by ASTeC to develop and optimise procedur... more Significant effort has been expended over several years by ASTeC to develop and optimise procedures for preparing GaAs photocathodes for use as high-current electron sources in accelerators. We present data showing high levels of Quantum Efficiency (Q.E.) for heterostructure photocathodes when activated with Cs-O and Cs-NF 3 procedures, and that the use of NF 3 delivers higher Q.E., and conveys greater control during activation in that the final Q.E. level can be set more accurately when using NF 3. A limiting factor in the performance of electron accelerators is the transverse energy spread in the photocathode source. We are designing a retarding-field electron calorimeter for the measurement of photoemission current as a function of retarding voltage. From this, we will establish the 2-D energy distribution of the emitted electrons, permitting a comparison of these figures for photocathodes at room temperature and at cryogenic temperatures. The goal is to investigate the possibility of creating an ultrabright electron source based on GaAs technology.

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