Browsing by Author "Choi, P."

Now showing 1 - 20 of 23
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    A Capacitive Probe Array for Measurements of Ionization Growth
    (1994) Choi, P.; Favre Domínguez, Mario
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    A Compact Ultrafast Capillary Discharge for EUV Projection Lithography
    (2000) Krisch, I.; Choi, P.; Larour, J.; Favre, Mario; Rous, J.; Leblanc, C.
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    A Fast Capacitive Voltage Monitor for Low Impedance Pulse Lines
    (1998) Choi, P.; Favre Domínguez, Mario
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    An Observation of Energetic Electron Beams in a Low Pressure Linear Discharge
    (1987) Choi, P.; Chuaqui, Hernán; Favre Domínguez, Mario; Wyndham, Edmund
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    Breakdown Formation in a Transient Hollow Cathode Discharge-A Statistical Study
    (1995) Choi, P.; Chuaqui, Hernán; Favre Domínguez, Mario
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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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    Denoising of gamma-ray signals by interval-dependent thresholds of wavelet analysis
    (2006) Zhang, Qidao; Aliaga-Rossel, R.; Choi, P.
    Fast Fourier transform and wavelet analysis methods were used to denoise electrical signals by a soft thresholding technique. A neutron pulse of 14 MeV is sent over a sample; as a consequence of the interaction between the sample and the neutrons, multi-spectral gamma rays are emitted by the sample. The gamma-rays were measured using three photo multiplier tubes, which detect optical signals coming from three filtered detectors made of plastic scintillator material. Applying wavelet analysis was possible to realize that the signal can be divided into three different regions. Each region has different thresholds; therefore, different frequency components can be used independently in each region. Comparisons of this method with the fast Fourier transform are presented. In this particular application, it was found that the wavelet transform produces a much better way of denoising the signals in terms of keeping the characteristic high frequency at the start of the signals; this feature allows the differential classification of the signals and the consequent identification of the component of the sample. The preliminary results presented here are the first attempt to identify the chemical composition of samples using this method.
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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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    Experimental and theoretical investigation of the gas embedded Z-pinch
    (1988) Choi, P.; Favre Domínguez, Mario
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    Experimental investigations of hotspots in a low energy plasma focus operating in hydrogen-argon mixtures
    (IEEE, 1998) Favre Domínguez, Mario; Silva, P.; Choi, P.; Chuaqui, Hernán; Dumitrescu-Zoita, C.; Wyndham, Edmund
    We present experimental results on the investigation of hotspot formation in PFP-I, a small 3.8 kJ plasma focus device operating in hydrogen-argon mixtures, at pressures from below 0.2 torr upward. A combination of multipinhole and slit-wire X-ray photography is used to measure the characteristic size and temperature of the hotspots, over a range of pressure and gas mixing ratios. Filtered p-i-n diodes and a beam-target detector are used to investigate the time evolution of the hotspots. Typical size for the hottest emitting region, at temperatures between 200 and 400 eV, is found to be around 150 /spl mu/m, with a typical duration of the high temperature phase of the order of 10 ns. In general, the temperature in the final phase of the time evolution of the hotspots reaches values which are nearly twice those of the plasma column where they are formed. Characteristic size of the hotspots is about half of that of the initial plasma column.
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    Experimental observations in compact capillary discharges
    (2008) Favre Domínguez, Mario; Wyndham, Edmund; Leñero Merchant, Ana María; Suzuki, F.; Valenzuela Ahumada, Julio César; Avaria Saavedra, Gonzalo Felipe; Ruiz, M.; Bhuyan, Heman; Chuaqui, Hernán; Choi, P.
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    Fast pulsed hollow cathode capillary discharge device
    (1998) Choi, P.; Favre Domínguez, Mario
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    High brightness EUV light sources for actinic metrology
    (2010) Choi, P.; Zakharov, S.V.; Aliaga R., Raúl; Bakouboula, A.; Bastide, J.; Benali, O.; Bove, P.; Cau, M.; Duffy, G.; Kezzar, W.; Lebert, B.; Powell, K.
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    High performance next generation EUV lithography light source
    (2009) Choi, P.; Zakharov, S.V.; Aliaga R., Raúl; Benali, O.; Duffy, G.; Sarroukh, O.; Wyndham, Edmund; Zakharov, V.S.
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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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    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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    Silver as a Soft X-ray Filter for Plasma Diagnostics
    (1987) Choi, P.; Favre Domínguez, Mario