Browsing by Author "Wyndham Hodder, Edmund Sydenham"

Now showing 1 - 19 of 19
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    Characteristics of a small plasma focus device
    (IET, 1996) Favre Domínguez, Mario Benjamin; Silva, P.; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham; Choi, P.; Dumitrescu-Zoita, C.
    We report on experimental observations in PFP-I, a small 3.8 kJ plasma focus, which is operated in Hydrogen-Argon mixtures to investigate the effect of parameter modifications on the overall performance of the device. An extensive array of diagnostics is been used, which includes voltage and current probes in the external circuit, a novel small magnetic probes array located along the cathode rods, filtered PIN diodes located side and end on, and multi-pinhole X-ray camera. EX1ended operated range from below 0.2 Torr upwards has been achieved with the implementation of the auxiliary discharge circuit. Despite the low voltage and low energy operation, energetic beam formation has been observed at the time of the final compression, prior to disruption. Current sheath formation and evolution has been characterised using the magnetic probes array, in correlation with beam formation and plasma emission. Time integrated visible plasma spectroscopy is performed to investigate impurity effects on focus performance and plasma dynamics at the collapse phase.
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    Characteristics of electron beam formation in a hollow cathode triggered fast capillary discharge
    (IET, 2000) Favre Domínguez, Mario Benjamin; Choi, P.; Dumitrescu, C.; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham; Krisch, I.; Larour, J.; Rous, J.; LeBlanc, C.; Rutkevich, I.; Mond, M.
    The fast pulsed capillary discharge has been shown to be an efficient source of radiation in the XUV range. Two main conditions are required to operate a pulsed capillary discharge as a fast XUV radiation source. First, initial formation of an on-axis conducting plasma column detached from the capillary wall, and second, application of a high rate of current rise to an inductive load, to heat the capillary plasma. To satisfy these requirements we have developed a pulsed capillary discharge device which combines the features of a transient hollow cathode discharge (THCD) with the inherent characteristics of the capillary discharge, to obtain XUV radiation with ns rise time. The discharge operates in the nanosecond regime with current in the kA region into a millimeter diameter capillary. The initial breakdown process is controlled by the physics of the THCD, with hollow cathode emitted electron beams, which assist the formation of an on-axis ionization channel. In this paper we present a theoretical model of breakdown formation in the capillary which is compared with experimental measurements of ionization growth. The properties of the electron beams are quantified and their influence on the subsequent breakdown formation is considered through time-resolved measurements on the plasma emission properties and VUV spectroscopy.
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    Comparative studies of ion emission characteristics in a low energy Plasma Focus operating with different gas fillings
    (IEEE, 2004) Bhuyan, Heman; Favre Domínguez, Mario; Kauffmann, Karla; Chuaqui Kettlun, Hernán; Mitchell, Ian H.; Wyndham Hodder, Edmund Sydenham
    The results of an investigation of ion emission from a low energy Plasma Focus (PF), operating at 20 kV, with 1.8 kJ stored energy, using several different gas fillings, including hydrogen, nitrogen, argon and methane, are presented. Graphite collectors, operating in the bias ion collector mode, are used to estimate the energy spectrum and ion flux along the PF axis, using the time of flight technique. The ion beam signals are time correlated with the emission of soft X-ray pulses from the focus plasma. Characteristic duration of the ion beam pulses is found to be in the 10s to 100 s of nanoseconds. Characteristic ion energy is found to be in the 50 to 500 keV range, depending on the operating gas. Ion beam energy correlations for operation in methane indicate that the dominant charge states in carbon ions are C+4 and C+5.
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    Discharge formation in fast pulsed capillary discharges
    (IEEE, 2002) Favre Domínguez, Mario; Choi, Peter; Leñero Marchant, Ana María; Castillo, Francisco; Suzuki Vidal, Francisco Andrés; Chuaqui Kettlun, Hernán; Mitchell, Ian H.; Wyndham Hodder, Edmund Sydenham
    We present a study of discharge formation in a fast pulsed capillary discharge operated in Argon or Methane, in a 50 mm long, 1.6 mm internal diameter capillary, at −15 kV applied voltage. A pressure gradient is used along the capillary, with pressures between 0.2 and 1.0 Torr in the cathode region and a pressure one tenth lower in the anode side. The diagnostics include a capacitive probe array, Faraday cup and beam-target scintillator-photomultiplier detectors. It is found that following the emission of electron beams from the hollow cathode region, a fast ionization wave propagates from the cathode towards the anode, with characteristic velocities of the order of 106 to 107 m/s. The propagation of the ionization front is assisted by the electron beams, which reach a peak current of around 200 mA.
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    Electrical characteristics of a small plasma focus device
    (IET, 1996) Choi, P.; Favre Domínguez, Mario Benjamin; Silva, P.; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham
    Efficient plasma focus operation relies on uniform initial breakdown across the insulator surface. In this paper, we discuss basic plasma focus electric circuit, in order to highlight circuit modifications that produce high voltage oscillation at initial breakdown time. Superimposed on the main discharge voltage such oscillating voltage has been found in real systems to enhance the initial gas breakdown by localizing the initial current path across the insulator surface. PSpice circuit simulations are compared with electric signals from different operational plasma focus devices.
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    Electron beam measurements in a pulsed capillary discharge
    (IEEE, 1998) Favre Domínguez, Mario; Choi, P.; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham; Dumitrescu-Zoita, C.; Larour, J.; Rous, J.
    In this work we present experimental observations of the XUV and electron beam emission properties of an ultrafast pulsed capillary discharge, which combines the features of a transient hollow cathode discharge with the inherent characteristics of the capillary discharge.
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    High current electron beam generation in a vacuum transient hollow cathode discharge
    (1993) Chuaqui Kettlun, Hernan; Favre Dominguez, Mario Benjamín; Soto Norambuena, Leopoldo Alejandro; Wyndham Hodder, Edmund Sydenham
    Experimental observations are presented of prebreakdown electron beam generation in a transient hollow cathode discharge (THCD) in a vacuum. The discharge driver consists of a 400-kV maximum voltage, 25-nF Marx operated at 450-J stored energy coupled to a 120-ns, 1.5- Omega coaxial line. Electron beams with peak currents up to tens of kA are observed when a pulsed Nd:YAG laser is used to produce a plasma at the back of the cathode surface, inside the hollow cathode region (HCR). It is found that a plasma density of a few 10/sup 18/ cm/sup -3/ in a volume of a few mm/sup 3/ is required to generate intense electron beams. Optimal conditions are determined by varying the position of the laser focal spot inside the HCR and the time delay between the laser and the applied voltage. The main features of the electron beams are similar to those observed in conventional THCD at pressures in the 10-200 mtorr range.<>
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    Hollow Cathode Ionization Processes In The Breakdown Phase Of A Transient Hollow Cathode Discharge
    (IET, 1998) Favre Domínguez, Mario Benjamin; Choi, P.; Zambra, M.; Moreno Martinez, José Alberto; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham
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    Ion beam measurements in a small plasma focus operating in hydrogen/gas mixtures
    (IEEE, 1998) Silva, P.; Favre Domínguez, Mario; Choi, P.; Dumitrescu-Zoita, C.; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham
    Dense transient plasmas of high energy density, can be easily produced in a plasma focus device, on a cost effective basis. High energy ion beam emission is one, among several others, of the very interesting transient plasma phenomena observed in plasma focus discharges. Although some of the properties of these ion beams have been investigated in the past, the physical mechanisms involved in their generation are still not clear, and further investigations are required on order to establish the exact correlations of the ion beam emission with other plasma focus phenomena. We present a preliminary series of measurements on ion beams in a plasma focus operating with hydrogen/gas mixtures, using an XRD probe array, which allows the characteristic ion energy to be determined from the time of flight across the probe array, and the time of the ion beam emission to be correlated with plasma emission events associated with the soft X-ray pulses detected by the probes.
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    Laser initiated hollow gas-embedded Z-pinch
    (IEEE, 2004) Chuaqui Kettlun, Hernán; Aliaga Rossel, Raul; Veloso Espinosa, Felipe; Pavez Morales, Cristian Arturo; Favre Domínguez, Mario; Mitchell, Ian H.; Wyndham Hodder, Edmund Sydenham
    Results of new optical method of generating a precursor plasma for a shell gas embedded Z-pinch are presented. Experiments were performed on a pulse power generator using a peak current up to 150 kA with a rise time of 70 ns, 120 ns pulse length. The optical precursor plasma was generated by using a Nd-Y AG laser, 200 ml, 8 ns at 1.06 μm. Two different optical schemes were used, one consists of a combination of lenses capable of producing a hollow beam; while the other uses an axicon to generate the hollow beam. In both cases the hollow beam was focused at the cathode surface where metallic ring plasma, of either 2 or 6 mm diameter, is created. The annular preionization is created immediately before or during the first 30 ns after the line voltage is applied. The discharge was carried out in a chamber filled with hydrogen gas at 1/3 atm. Flat electrodes were used with 10 mm separation. The anode has a 6 mm diameter central hole to allow the passage of the preionizing laser. Optical diagnostics (schlieren, shadowgraphy and interferometry) were performed using the second harmonics of the same laser used to preionize. Preionizing using an axicon results in better formed hollow discharges.
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    Observations of Ablation Dynamics in Wire-Array Z-Pinch Experiments on the Llampüdkeñ Generator
    (2012) Veloso Espinosa, Felipe; Suzuki Vidal, Francisco Andres; Molina, Francisco; Mitchell, Ian H.; Chuaqui Kettlun, Hernán; Favre Dominguez, Mario Benjamin; Wyndham Hodder, Edmund Sydenham
    Wire-array Z-pinch experiments have been performed on the Llampüdkeñ generator (~470 kA in ~410 ns) [Chuaqui et al., Laser Part. Beams 15, 241 (1997)] using an overmassed load of aluminum wires. Time-resolved optical laser schlieren and extreme ultraviolet imaging were used in order to study the plasma ablation dynamics. The results show the formation and subsequent ablation of plasma from the wires, followed by the appearance of a precursor plasma column on the axis. According to these results and to the rocket model of wire ablation, an ablation velocity of (1.7-2.6) × 105 m/s is estimated, which is larger than those obtained in faster generators. Additionally, the main resemblances and differences with previous experiments are presented, allowing in this way to open the study of this configuration in smaller scale machines.
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    Properties of a laser-initiated pseudospark discharge
    (1989) Chuaqui Kettlun, Hernán; Favre Dominguez, Mario Bejamin; Wyndham Hodder, Edmund Sydenham; Arroyo González, Luis Orlando; Choi, P.
    A short-pulse Nd:YAG laser is used to illuminate the back electrode surface in the hollow cathode region of a pseudospark discharge. A fast rising step voltage pulse is applied across the electrodes at various times relative to the pulsed laser illumination. The delay and jitter to the onset of gas breakdown at various filling gas pressures are measured for different laser energies and wavelengths. It is observed that the millijoule range of a green laser applied to illuminate the hollow cathode surface at up to tens of microseconds before the application of voltage would significantly reduce both delay and jitter to discharge initiation. Higher laser energy applied after voltage rise is observed to cause gas breakdown in under 100 ns.<>
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    Space and time resolved observations of plasma dynamics in a compressional gas embedded Z-pinch
    (IET, 1996) Soto, L.; Chuaqui, Hernán; Favre Domínguez, Mario Benjamin; Saavedra Sanchez, Renato Alejandro; Wyndham Hodder, Edmund Sydenham; Aliaga-Rossel, R.; Mitchell, I.
    Recent experiments in a gas embedded compressional Z-pinch are presented. The experiments have been carried out in H2 at 1/3 atm, using a pulse power generator capable of delivering a dI/dt > 1012 A/s. The pinch is initiated by a focused laser pulse, which is coaxial with a cylindrical DC rnicrodischarge. This configuration results in double column pinch at early times, which at current rise evolves into a gas embedded compressional Z-pinch. Diagnostics used are Rogowskii coil, single frame holographic interferometry and holographic shadowgraphy, visible streak camera images from which, current, density, line density, pinch radius and plasma motion are obtained. The pinch is characterized by a maximum on axis density which is much higher than the expected value from filling pressure, with a Bennett temperature of 40 eV at 130 kA‥ Results shown confirm the high degree of compression achievable with the composite preionization scheme.
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    Studies of current sheath evolution in a small plasma focus device
    (IET, 1996) Silva, P.; Favre Domínguez, Mario Benjamin; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham; Choi, P.
    We present preliminary time and space resolved studies of current sheath formation in Plasma Focus discharges, using a novel array of non invasive magnetic field probes. The experiments are performed in a Mather type plasma focus, which is powered by a 9 µf capacitor bank, operating at 30 kV. The discharge is formed between a hollowed anode and six symmetrically arranged cathode rods. The array of small magnetic probes is located along the cathode rods. The probes are of millimeter size. They are shielded behind the rods, as to minimize capacitive coupling to the anode electrode, and allow nonperturbing measurements to be made. The array probe signals are recorded simultaneously, with 2 ns time resolution. Other available diagnostics include voltage and current probes in the ex1emal circuit, filtered PIN diodes located side and end on, and a multi-pinhole x-ray camera. A simple analytical model of current sheath evolution is used to interpret the probe signals. The experiments have been performed in pure Hydrogen and Hydrogen with Argon mixture, at pressures from below 0.2 Torr upwards. The effect of the Argon mixture on the current sheath structure is investigated with the probe array. It is found that at constant mass density operation, the increase in the percentage of Argon results in a thinner sheath, with steeper current profile.
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    Studies on pulsed hollow cathode capillary discharges
    (IET, 1996) Choi, P.; Dumitrescu-Zoita, C.; Larour, J.; Rous, J.; Favre Domínguez, Mario Benjamin; Zambra, M.; Moreno Martinez, José Alberto; Chuaqui, Hernán; Wyndham Hodder, Edmund Sydenham; Wong, C. S.
    We present preliminary results on radiation characteristics of pulsed hollow cathode capillary discharges. The device combines the on axis electron beam assisted ionization capabilities of the transient hollow cathode discharge with a novel high voltage low inductance geometrical design, which integrates the local energy storage into the electrode system. A nanosecond regime high temperature plasma is produced in a long, high aspect ratio capillary, with light emission in the UV to XUV region. The discharge is operated from near vacuum to pressure in the 1000 mTorr range
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    Study of titanium nitride film growth by plasma enhanced pulsed laser deposition at different experimental conditions
    (2021) Escalona Álvarez, Miguel Benito; Bhuyan, Heman; Ibacache, S.; Retamal Ponce, María José; Saikia, P.; Borgohain, C.; Valenzuela Ahumada, Julio César; Veloso Espinosa, Felipe Eduardo; Favre Domínguez, Mario; Wyndham Hodder, Edmund Sydenham
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    Time resolved observations of plasma evolution in the hollow cathode region of a transient hollow discharge
    (1996) Favre Domínguez, Mario Benjamin; Zambra Yañez, Marcelo Cristian; Moreno Martinez, Jose Alberto; Chuaqui, F.; Wyndham Hodder, Edmund Sydenham; Choi, P.
    It is known that in a transient hollow cathode discharge (THCD), the formation of a moving virtual anode in the A-K space is causally linked to the emission of high energy electron beams originated in the hollow cathode region (HCR). In this work we report on time and space resolved observations of the formation and evolution of plasma inside the HCR which are time correlated with ionization processes inside the A-K gap. The experiments have been performed in Hydrogen, at pressures between 50 to 500 mTorr, at 30 kV applied voltage. Capacitive probes are used to monitor ionization growth in the A-K gap, in conjunction with time and space resolved spectroscopic observations in the HCR. High energy electron beams are also measured. Stark broadening observations of the Hβ line indicate that the electron density inside the HCR increases up to a few times 1015 cm−3 some time before breakdown in the A-K gap. This time is also related with the electron beam activity
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    X ray emission from X pinch experiments on the Llampudken Generator
    (IEEE, 2002) Mitchell, Ian H.; Aliaga Rossel, Raul; Gómez Luna, Jorge Antonio; Chuaqui Kettlun, Hernán; Favre Domínguez, Mario; Wyndham Hodder, Edmund Sydenham
    The results from the first plasma physics experiments on the Llampüdkeñ Generator (1MA, 250 ns) are presented. X Pinch experiments have been undertaken at current levels of 400 kA with a rise time of ∼250 ns. X pinches were produced mainly from aluminium wires of different diameters and with varying numbers of wires. Results from X-ray diagnostics characterising the emitted radiation are presented. The diagnostics include filtered PIN diodes and a pinhole and slit-wire camera. Radiation of energy greater then 2.5 keV was emitted from hot spots in timescales of a few nanoseconds. Using the results from the slit-wire camera, the diameter of the hot spots is shown to be less than 5 µm.
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    X-ray and plasma dynamics of an intermediate size capillary discharge
    (2002) Wyndham Hodder, Edmund Sydenham; Aliaga Rossel, Raul; Chuaqui Kettlun, Hernán; Favre Dominguez, Mario Benjamin; Mitchell, Ian H.; Choi, Peter
    A small pulsed power generator, 150 kA and 120 ns, is used to form a plasma in a 5-mm diameter alumina ceramic tube. A hollow cathode geometry is used and a preionized plasma is formed in an initial vacuum background by focussing a pulsed Nd:YAG laser onto a metallic target in the hollow cathode volume. The evolution of the preionizing plasma and its expansion into the main discharge volume may be assisted by applying a current of order Amps for a variable time before the main discharge current is applied. Strong electron beams are observed both during the preionizing stage and during the start of the main current. The plasma species and temporal evolution during the main discharge is observed using X-ray spectroscopy and X-ray pinhole imaging. On varying the rate of rise of the current in the pinching phase, the transient hollow cathode effect was found to be significant at early times in the discharge in the case of the lower value of dI/dt. Both the pinch temperature and diameter depend on varying the dI/dt from 1.5 to 3 /spl times/ 10/sup 12/ A/s. The implications of plasma injection for metal vapor capillary discharges are discussed.