Dr Dan Faircloth BEng(Hons) MSc PhD MInstP MIET CEng
Senior Research Engineer
Ion Source Section Head
ISIS,
Rutherford
Appleton Laboratory, Oxfordshire, UK
Dan.Faircloth@rl.ac.uk
35. Multi-beamlet Study of Beam Transport in the ISIS H- Ion Source Analysing Magnet [543 kB]
Proceedings of EPAC08, June 2008
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). The existing 90° analysing magnet on the ISIS H- Penning ion source does not perfectly transport the beam after extraction. The present ion source has a 10 mm x 0.6 mm slit extraction aperture. To understand how the beam is transported in the analysing magnet, new ion source aperture plates are manufactured with 5 individual holes instead of a slit. These holes produce separate beamlets that are used to study transport in the sector magnet. This paper details the experiments with the modified aperture plates on the Ion Source Development Rig (ISDR) at ISIS.
34. Study of the Post Extraction Acceleration Gap in the ISIS H- Penning Ion Source [738 kB]
Proceedings of EPAC08, June 2008
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). The injection energy into the RFQ will be in the range of 50 to 70 keV whereas the standard ISIS H- Penning ion source operates at 35 keV, therefore the post extraction acceleration voltage must be increased. In order to finalise the design of the FETS post extraction system, a study is conducted on the Ion Source Development Rig (ISDR) at ISIS. This study shows how beam transport is affected by different post extraction acceleration voltages and gap lengths. Beam, current, profile and emittance measurements are presented along with theoretical calculations.
33. Installation of the Front End
Test Stand High Performance H- Ion
Source at RAL
[353 kB]
Proceedings of EPAC08, June 2008
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H− beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). This paper details the first stage of construction- the installation of the ion source.
32. Modifications to the Analysing
Magnet in the ISIS Penning Ion Source
[387 kB]
Proceedings of EPAC08, June 2008
A full 3D electromagnetic finite element analysis and particle tracking study has been undertaken of the ISIS Penning surface plasma ion source using CST Particle Studio 2008. The existing 90° analysing magnet is found to have a sub-optimal magnetic field index, causing beam divergence and contributing to beam loss. Different magnet pole piece geometries are modelled and the effect of space charge investigated. Based on this modelling, three new sets of poles are manufactured and tested on the Ion Source Development Rig.
31. Improving the ISIS Emittance
Scanner Software
[157 kB]
Proceedings of EPAC08, June 2008
The software to drive the slit-slit emittance scanners at ISIS has been re-written in C#. The scan routine has been enhanced to improve accuracy, and to allow real-time monitoring of the scanning procedure. A multiple document interface allows quick comparison with other measurements and with data from particle tracking codes. Integrated data processing and emittance calculation removes the need to transfer data between multiple software packages, making experimental work more efficient. A user-friendly and robust interface allows easy scanning and generates publication quality emittance plots for presentations.
30. Status of the RAL Front End
Test Stand
[207 kB]
Proceedings of EPAC08, June 2008
High power proton accelerators (HPPAs) with beam powers in the several megawatt range have many applications including drivers for spallation neutron sources, neutrino factories, waste transmuters and tritium production facilities. The UK's commitment to the development of the next generation of HPPAs is demonstrated by a test stand being constructed in collaboration between RAL, Imperial College London, the University of Warwick and the Universidad del Pais Vasco, Bilbao. The aim of the RAL Front End Test Stand is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational conditions. This paper describes the current status of the RAL Front End Test Stand.
29. Understanding Extraction and Beam Transport in the ISIS H− Penning Surface Plasma Ion Source [391kB]
Review of Scientific Instruments Volume 79, Number 1, 2008
The ISIS particle accelerator H− Penning surface plasma source has been developed to produce beam currents up to 70 mA and pulse lengths up to 1.5 ms at 50 Hz. This paper details the investigation into beam extraction and beam transport in an attempt to understand the beam emittance and to try to improve the emittance. A scintillator profile measurement technique has been developed to assess the performance of different plasma electrode apertures, extraction electrode geometries, and post extraction acceleration configurations. This work shows that the present extraction, beam transport, and post acceleration system are suboptimal and further work is required to improve it.
28.
Status Report on the RAL Front End Test Stand
[266 kB]
Proceedings of PAC07, June 2007
High power proton accelerators (HPPAs) with beam powers in the several megawatt range have many particle accelerator applications including drivers for spallation neutron sources [1], neutrino factories [2], waste transmuters and tritium production facilities. The UK's commitment to the development of the next generation of HPPAs is demonstrated by a test stand being constructed in collaboration between RAL, Imperial College London, the University of Warwick and the Universidad del Pais Vasco. The aim of the RAL Front End Test Stand is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational conditions. This paper describes the status of the RAL Front End Test Stand.
27.
Beam Diagnostics for the Front End Test Stand at RAL
[645 kB]
Proceedings of DIPAC 2007, May 2007
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) is intended to demonstrate the early stages of acceleration (0-3MeV) and beam chopping required for high power proton particle accelerators, including proton drivers for pulsed neutron spallation sources and neutrino factories. The FETS ion source is required to produce a 60 mA beam in pulses up to 2ms long at up to 50 pps with an RMS emittance of 0.3 p mm mrad. A number of different diagnostic systems are currently under development to provide precise measurements of the H- ion beam. A pepperpot emittance measurement system, which is also capable of high resolution transverse beam density measurements, has been designed for use on the ISIS ion source development rig. This system is capable of sub-microsecond time-resolved measurements at a range of positions along the beam axis. Details are given of the improvements to the current design, including extensive tests on suitable scintillators and emittance and profile measurements are presented. Additionally, the designs of two different novel laser diagnostic systems for FETS are also presented.
26.
The Development of the ISIS H- Surface Plasma Ion Source at RAL
[236 kB]
18th Meeting of the International Collaboration on Advanced Neutron Sources, April 25-29, 2007
ISIS H- Penning Surface Plasma Source (SPS) has been a world leading operational H- ion source for 20 years; it routinely produces 35 mA of H- ions during a 200 us pulse at 50 Hz for uninterrupted periods of up to 50 days. This paper details the development of the source that has occurred over the last 5 years. The pulse length has been increased from 200 µs to 1.5 ms and the output current doubled to 70 mA. These developments are required for the new Front End Test Stand (FETS) currently being built at RAL. Extensive three dimensional finite element modeling has allowed the thermal operation of the source to be understood in detail: the temperatures around the discharge region have been calculated and the transient thermal behavior of the pulsed source studied. This has allowed the source duty cycle to be significantly increased.Electromagnetic finite element analysis has allowed the source extraction and beam transport to be investigated. Different extraction geometries have been designed and successfully tested to give higher output currents. An energy analyzer and two emittance measurement systems (slit-slit and pepperpot) have been developed to allow the beam to be fully characterized. Several geometry and infrastructure modifications have been implemented and will be discussed.
25. Particle Dynamics Calculations and Emittance Measurements at the FETS [1334 kB]
Proceedings of LINAC06, August 2006
High power proton particle accelerators in the MW range have many applications including drivers for spallation neutron sources, neutrino factories, transmuters (for transmuting long-lived nuclear waste products) and energy amplifiers. In order to contribute to the development of HPPAs, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK. The aim of the FETS is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. An overview on the status of the project together with the results of numerical simulations of the particle dynamics from the ion source to the RFQ exit will be presented. The particle distributions gained from the particle dynamics simulations will be compared with recent measurements of the transversal beam emittance behind the ion source and the results discussed.
24. Development of Emittance Scanner Software for ISIS [242 kB]
Proceedings of EPAC06, June 2006
Horizontal and vertical Faraday cup and slit scanners are used on ISIS, the 800MeV pulsed neutron source at the Rutherford Appleton Laboratory, to calculate the emittance of the beam. Software has been written in C++ to control the scanners, acquire and display beam data and compute an emittance value for the beam. The software allows the user more control, and has the ability to scan over a wider range, than was previously available.
23. LEBT Simulations and Ion Source Beam Measurements for the Front End Test Stand (FETS) [371 kB]
Proceedings of EPAC06, June 2006
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) is intended to demonstrate the early stages of acceleration (0-3MeV) and beam chopping required for high power proton particle accelerators, including proton drivers for pulsed neutron spallation sources and neutrino factories. Optimisation of the beam focussing within the Low Energy Beam Transport (LEBT) is necessary to minimise beam losses upon acceleration within the FETS RadioFrequency Quadrupole (RFQ). Simulations of the LEBT are currently under way using the General Particle Tracer package (GPT). Previous envelope calculations suggest weak and strong focussing solutions for the LEBT solenoids. Definitive beam dynamics simulations in GPT require further measurements of the transverse emittances and beam profile of the ion source beam, due to the sensitivity of the simulations on the initial beam profile and level of space charge compensation. A pepperpot emittance/profile measurement system has been designed for use on the ISIS ion source development rig. Results from this pepperpot system are used to constrain the initial conditions for the GPT simulations.
22. Energy Distribution of H- Ions from the ISIS Ion Source [170 kB]
Proceedings of EPAC06, June 2006
We have used a specially designed retarding field energy analyzer with a resolution (? E /E) of approximately 2 x 10 -4 in order to measure the energy distribution, under different operating conditions, of the H- beam of the ISIS ion source. The paper presents the details of the analyzer and the first results obtained on the Ion Source Test Facility at RAL.
21. ISIS Upgrades - A Status Report [186kB]
Proceedings of EPAC06, June 2006
Since 2002 several particle accelerator upgrades have been made to the ISIS spallation neutron source at the Rutherford Appleton Laboratory in the UK, and upgrades are currently continuing in the form of the Second Target Station Project. The paper reviews the following programmes: a new extraction straight, replacement of the Cockcroft-Walton by an RFQ, installation of a second harmonic RF system, replacement and upgrading of ageing installed equipment, design and installation of improved diagnostics in conjunction with beam dynamics simulations, the Second Target Station Project, design and construction of a front end test stand, and the MICE programme. The paper also looks forward to possible future schemes at ISIS beyond the Second Target Station Project.
20. The RAL Front End Test Stand [135 kB]
Proceedings of EPAC06, June 2006
High power proton accelerators (HPPAs) with beam powers in the megawatt range have many possible applications including drivers for spallation neutron sources, neutrino factories, waste transmuters and tritium production facilities. These applications typically propose beam powers of 5 MW or more compared to the highest beam power achieved from a pulsed proton accelerator in routine operation of 0.16 MW at ISIS. The UK's commitment to the development of the next generation of HPPAs is demonstrated by a test stand being constructed in collaboration between RAL, Imperial College London and the University of Warwick. The aim of the RAL Front End Test Stand is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational regimes. This paper describes the status of the RAL Front End Test Stand which consists of five main components: a 60 mA H- ion source, a low energy beam transport, a 324 MHz Radio Frequency Quadrupole (RFQ) accelerator, a high speed beam chopper and a comprehensive suite of diagnostics. The aim is to demonstrate production of a 60 mA, 2 ms, 50 pps, chopped H- beam at 3 MeV.
19. Practical Experience in Extending the Ion Source and Injection System H- Ion Source Duty Cycle [381 kB]
Review of Scientific Instruments Volume 77, Number 3, March 2006
The ion source and injection system H- Penning surface-plasma source is currently being developed on the ion source development rig at Rutherford Appleton Laboratory in order to meet the requirements for the next generation of high-power proton drivers for particle accelerators. Finite element modeling has been used previously to study the effect of increasing the duty cycle. The main requirement to allow increased duty cycles is improved cooling. By simply reducing the thickness of a sheet of mica to improve thermal conductance to the cooling system, duty cycles of 1.5 ms at 50 Hz can be achieved. Slight increase in hydrogen flow rate is required as the duty cycle is increased. As the duty cycle is increased the output current reduces, however, there is no change in beam emittance. The source cooling system is described and the heat flows within the source are discussed.
18. Progress at the RAL Front End Test Stand [471 kB]
Nuclear Physics B (Proc. Suppl.) 155 (2006) 309–311
The progress in the design of a proton driver front end test stand at the Rutherford Appleton Laboratory (RAL) in the UK is presented. The aim of the test stand is to demonstrate the availability of well chopped H- beams suitable for future high power proton accelerators.
17. Separating the Penning and Analysing Fields in the ISIS H- Ion Source [281 kB]
Proceedings of PAC05, May 2005
The development of H- ion sources with performances exceeding those achieved today is a key requirement for the next generation of high power proton particle accelerators. The ion source development program at ISIS is now well established. To allow different ion source designs to be fully tested, the ability to vary the Penning field is required. Until now the Penning field has been generated by the same magnetic circuit that creates the analyzing field, giving no practical way of altering the Penning field alone. This paper describes the infrastructure changes required to allow the Penning field to be independently varied. The effect the Penning field has on beam current, emittance and discharge stability are discussed.
16. Testing, Installation, Commissioning and First Operation of the ISIS RFQ Pre-Injector Upgrade [453 kB]
Proceedings of PAC05, May 2005
Situated at the Rutherford Appleton Laboratory (Oxon., UK), ISIS is currently the world's most intense pulsed spallation neutron source, delivering 160 kW of 800 MeV protons to a tungsten target at 50 Hz. A major facility upgrade programme involves the construction of a second, 10 Hz target and an increase in the total beam power of up to 50% (i.e. up to 240 kW). To achieve the planned increase in average beam current to 300 µA whilst maintaining the current manageable levels of beam loss, four 2nd harmonic RF cavities have been installed in the synchrotron and the ageing Cockcroft-Walton preinjector in the linac has been replaced with a 665 keV, 202.5 MHz, 4-rod Radio Frequency Quadrupole (RFQ). This paper describes the extensive testing, installation, commissioning and successful initial operation of the RFQ pre-injector upgrade.
15. Magnet Design for the ISIS Second Target Station Proton Beam Line [144 kB]
Proceedings of PAC05, May 2005
The ISIS facility, based at the Rutherford Appleton Laboratory in the UK, is an intense source of neutrons and muons for condensed matter research. The particle accelerator facility delivers an 800 MeV proton beam of 2.5x1013 protons per pulse at 50 Hz to the present target station. As part of a facility upgrade, it is planned to share the source with a second, 10 Hz, target station. The beam line supplying this target will extract from the existing target station beam line. Electromagnetic Finite Element Modelling techniques have been used to design the magnets required to meet the specified beam line optics. Kicker, septum, dipole, quadrupole, and steering magnets are covered. The magnet design process, involving 2D and 3D modelling, the calculation of ideal shims and chamfers, choice of steel, design of conducting coils, handling of heating issues and eddy current effects, is discussed.
14. The RAL Front End Test Stand [115kB]
Nuclear Physics B (Proc. Suppl.) 149 (2005) 323–325
A design for a proton driver front end test stand at the Rutherford Appleton Laboratory (RAL) in the UK is presented. The aim is to demonstrate the availability of well chopped H- beams suitable for future high power proton accelerators for particle accelerators. Advantage is being taken of existing RAL R&D programmes on H- ion sources and beam choppers, and also of a previous RFQ test stand project at RAL for testing a new preinjector RFQ for the ISIS spallation neutron source.
13. The Effect of Extraction Geometry on the Measured ISIS H Minus Ion Source Beam [624 kB]
Proceedings of EPAC04, July 2004
The ISIS H- ion source is currently being developed on the Ion Source Development Rig (ISDR) at Rutherford Appleton Laboratory (RAL) in order to meet the requirements for the next generation of high power proton drivers for particle accelerators. Recent Finite Element Analysis (FEA) electromagnetic modelling of the extraction region of the ISIS H- ion source has suggested that the present set up of extraction electrode and 90° sector magnet is sub-optimal, with the result that the beam profile is asymmetric, the beam is strongly divergent in the horizontal plane and there is severe aberration in the focusing in the vertical plane. The FEA model of the beam optics has demonstrated that relatively simple changes to the system should produce a dramatic improvement in performance. These changes have been incorporated on the Ion Source Development Rig (ISDR) at Rutherford Appleton Laboratory (RAL), and their effects on the H- beam are presented here.
12. Extending the Duty Cycle of the ISIS H Minus Ion Source, Thermal Considerations [304 kB]
Proceedings of EPAC04, July 2004
The ISIS H- ion source is currently being developed on the Ion Source Development Rig (ISDR) at Rutherford Appleton Laboratory (RAL) in order to meet the requirements for the next generation of high power proton drivers for particle accelerators. One key development goal is to increase the pulse width and duty cycle, but this has a significant effect on ion source temperatures if no other changes are made. A Finite Element Analysis (FEA) model has been produced previously [1] and is used here to understand the steady state and dynamic thermal behavior of the source, and to investigate the design changes necessary to offset the extra heating.
11. Thermal Modeling of the ISIS H- Ion Source [341 kB]
Review of Scientific Instruments Volume 75, Number 5, May 2004
The development of H2 ion sources with performances exceeding those achieved today is a key requirement for the next generation of high power proton accelerators. The ISIS Penning surface plasma source, which routinely produces 35 mA of H2 ions during a 200 ms pulse at 50 Hz for uninterrupted periods of up to 50 days, is regarded as one of the leading operational sources in the world, and should provide an excellent starting point for a development program. One goal is to produce pulse widths of 1.2 ms at 50 Hz and 2.5 ms at 50/3 Hz, thereby increasing the duty factor from 1% to as much as 10%. Increasing pulse widths will necessitate an improved cooling system to offset increased heating. The most effective cooling strategy will be determined by thermal finite element analysis of the ISIS ion source. The modeling will then be extended to find an optimal means of offsetting increased heat loading, and will minimize the amount of engineering required to produce an effective solution. Modeling of the ISIS source has established the temperature profiles of the source components. At the specific locations where temperatures are measured in operation using thermocouples the model values match those seen in practice. Transient modeling has been used to provide temperature variations for the source during the 20 ms period of the 50 Hz cycle.
10. Electromagnetic Modeling of the Extraction Region of the ISIS H- Ion Source [494 kB]
Review of Scientific Instruments Volume 75, Number 5, May 2004
The ISIS Penning surface plasma ion source, which routinely produces 35 mA of H2 ions during a 200 ms pulse at 50 Hz for uninterrupted periods of up to 50 days, is regarded as one of the leading operational sources in the world. The ISIS ion source should provide an excellent starting point for a development program to produce H2 ion sources with performances exceeding those achieved today, which will be a key requirement for the next generation of high power proton particle accelerators. One goal is to produce 60 mA of H2 ions from the source without large departures from the optimum conditions for source lifetime or increased emittance. As the ISIS source operates in the space-charge limited mode it is predicted that an increase in extraction potential from 17 to 25 kV should be sufficient to achieve this, and a suitable pulsed power supply for the ion source extraction electrode has been manufactured. An understanding of how extract geometry changes affect beam transport is essential for operation at higher extraction potential. An examination has been undertaken of the electromagnetic fields in the extract electrode region using MAFIA finite element analysis software. The effects of changing the extraction potential, gap, and electrode geometry are described.
9. Calculations Based on Measurements of Charge Deposited by a Streamer on a PTFE Surface [126 kB]
Surface charge on an insulator’s surface is studied using 3-dimesional finite element modelling. The calculations are based on measurements of surface charge deposited by a streamer on a PTFE surface. The surface electric field strengths associated with uniform surface charge density distributions over a 1mm2 region are calculated for a range of different measured charge densities. The effect of reducing the area of the surface charge whilst keeping the total amount of charge in the region constant, is observed. The surface charge is then modelled with a Gaussian distribution of charge and compared to that of a uniform distribution. By assuming a maximum allowable surface electric field strength an estimation of actual charged path diameter is made.
8. Corona Propagation and Charge Deposition on a PTFE Surface [642 kB]
A description is given of some properties of the corona discharge when propagating over a cylindrical PTFE insulator surface placed along the axis of a rod-plane electrode arrangement. A scanning electrostatic probe has been used to measure the density of charge deposited on the surface; it is shown that the total of net deposited charge is small compared with the total charge injected into the gap. Velocity of propagation has been measured. Effects of preceding coronas on succeeding ones and the nature of deposited charge after breakdown are described. Discussion is given in terms of electron lifetimes and attachment and photoemission processes.
7. High Resolution Measurements of Surface Charge Densities on Insulator Surfaces [859 kB]
The uses and limitations of the electrostatic probe for the measurement of charge densities on insulating surfaces are discussed. A development of the technique is described in which two important limitations have together been overcome: (i) The effects on the probe signal of charges on all points of the surface have been taken into account by means of a matrix inversion procedure. (ii) A robotic control system has been developed which enables the probe to follow and scan a wide range of axi-symmetric insulator profiles. The degree of resolution achieved enables the probe system to display and measure charge densities in individual streamer channels of a corona discharge on a PTFE surface. An example is given and comparison made with a dust figure of the same event.
6. Surface Charge Density and its Influence on Insulator Flashover – PhD Thesis [12246 kB]
A technique is developed to measure high-resolution surface charge density distributions on high voltage insulators. This technique is developed into a piece of laboratory equipment and used to investigate the surface charging of practical axi-symmetric insulators by high voltage discharges and its influence on insulator flashover. The different techniques available for surface charge measurement are discussed and the electrostatic probe is chosen for development. The process of calculating surface charge density distributions from probe voltage measurements is detailed. The probe and the mechanism designed to move it over a range of different sized and contoured axi-symmetric insulators is detailed. The software that automates the entire technique is then described. The Software controls the actual measurement process; calculates the charge density distributions; and allows the user to view and analyse the results. The measurement system is evaluated and tested thoroughly and then used for a series of experiments. The experimental work is based around cylindrical PTFE insulators positioned in a rod-plane gap. Various techniques for neutralising surface charge are evaluated. An impulse generator is used to produce single positive discharge events in the rod-plane gap. Each discharge event is recorded using three photomultipliers and current shunts discharge current measurements. Charge density distributions are also recorded. Three different rod diameters and rod surface separations are investigated. The effect of flashover on surface charge is studied and the charge distributions left by negative impulse, DC and AC test voltages on the rod are recorded. The surface charging of several other materials is then briefly studied along with the decay of surface charge and the surface charging of a contoured insulator with a single shed. A full analysis using three-dimensional finite modelling is undertaken of the electrostatic probe, the electrode arrangement, and of the field produced by surface charge.
5. Simulation of an Early Streamer Emission Air Terminal for Application to Lightning Protection [333 kB]
The ESE concept represents an attempt to improve the zone of protection offered by a conventional Franklin rod air terminal. The premise on which ESE lightning protection relies is this: the earlier an air terminal is able to launch an upward leader, during the attachment phase of a lightning discharge, the larger the zone of protection offered by that air terminal. In this paper, the authors have adopted a methodical approach for examining, under laboratory conditions, the extent to which the discharge emanating from an air terminal can be influenced by voltage application to the tip of the air terminal-since such voltage application is one technique employed by ESE air terminals to expedite upward leader inception relative to a Franklin rod. The experimental method used and the preliminary observations of the study are reported here.
This paper describes the method of operation of a system for measuring high-resolution surface charge density maps on practical insulator specimens using an electrostatic probe. Apparatus is described that can scan the electrostatic probe over the surface of the insulator and record the probe signal. The process of obtaining a charge density map from the probe signal measurements is explained. An example charge distribution is shown.
3. Tests of the `Early Streamer Emission' Principle for Protection Against Lightning
Experiments are described which are designed to test two devices based on the `early streamer emission' (ESE) principle, for lightning protection, against the traditional Franklin rod. In all three cases, the device was subjected to a steady negative electric field from a sphere, simulating the field beneath a thundercloud, prior to application of a superimposed negative impulse field, simulating the field due to the downward leader. The first device consisted of a vertical rod to which a subsidiary 1/50 µs positive impulse voltage, variable up to 40 kV peak, could be applied with varying delays from the start of the negative impulse field. Energising of the rod was thus independent of the applied negative field. The second device was a commercial product, energising of which was controlled by its own power supply. Sparkover voltages in the sphere/device gaps and times to breakdown were measured. It is shown that the ESE devices showed a small advantage, in time to breakdown, over the Franklin rod.
2. Some Factors Relating to the Early Streamer Emission Principle [472kB]
A brief review is given of the means by which additional ionisation has been introduced at the tip of a lightning conductor final, with a view to increasing the probability of attachment to a downward leader. Attention is concentrated, in present work, on the "early streamer emission" principle, in which corona is initiated by either a steady or pulsed high voltage applied to a finial. The field of an approaching downward leader is simulated, in these experiments, by application of a negative impulse voltage to a sphere, located above the finial. It is shown that a steady corona does not improve the finial performance, under the conditions used, and that a pulsed corona must be applied within a critical time range, in order to be effective. The implications for lightning protection are briefly examined.
1. Lightning Protection of Buildings Using Active Finials – MSc Dissertation [727 kB]
UMIST Manchester September 1996
This dissertation investigates the efficacy of active lightning finials. The active lightning protection method studied involves the application of a voltage to the finial. An active finial working on this principle is simulated experimentally. The field experienced by a lighting finial during a lightning strike is analysed and simulated to allow investigation of the artificial active device in the laboratory.
