S.R. Mohanty

Development of Multi Faraday Cup Assembly for Ion Beam Measurements from a Low Energy Plasma Focus Device

A multiple Faraday cup assembly has been developed for measuring pulsed ion beam of a low energy plasma focus device. The Faraday cups operating in biased ion collector mode have nanosecond response and these have been used to determine the energy spectrum and flux of fast nitrogen ion beam emerging out of the pinched plasma column. The design feature that makes our Faraday cups unique is that they can register ion energy of higher kinetic value (~hundreds of keV) as well as lower kinetic value (~keV). It has been possible to register the ion energy upto a lower kinetic energy threshold of ~5 keV which is a value much lower than that obtained in any previous works. The correlation of the ion beam flux with filling gas pressure is also reported. Angular distribution of ion measurement reveals a highly anisotropic emission indicating an ion dip at the electrode axis.

Comparative study of soft x-ray emission characteristics in a low energy dense plasma focus device

An investigation on the soft x rays emitted in a 2.2 kJ Mather-type dense plasma focus device using a multichannel diode spectrometer and a simple pinhole camera is reported. Emitted x rays associated with different shapes (hollow, solid, and hemispherical) of anode and in hydrogen/nitrogen gas medium are compared. The structure of x-ray emitting sites as well as x-ray yields were found to be strongly influenced by the shape of the anode and the filling gas pressure. The maximum yield of 2.2 J into 4π sr was obtained in the case of hemispherical anode in hydrogen gas medium. The x-ray pinhole images of the collapsed plasma with the hemispherical anode indicated spot-like structure having 500–800 μm in diameter. On the contrary, other anode shapes showed columnar pinched structure of 8–10 mm in length and 1–2 mm in diameter. Results indicated that an appropriate design of the anode could enhance the x-ray yield by more than tenfold in a conventional low energy dense plasma focus device.

Anode length optimization in a modified plasma focus device for optimal x-ray yields

The effect of anode length and operating gas pressure on the x-ray emission from a nitrogen-filling modified plasma focus device has been investigated. The time-resolved investigation of x ray was carried out by using a five-channel photodiode x-ray spectrometer. The maximum x-ray yield is seen to increase with the increase in the anode length from 110 to 125 mm. Further increase in the anode length to 130 mm causes the x-ray yields to decrease. The highest x-ray yield of 4.5 J into 4πsr was found for 125 mm anode length, which is 0.2% of the input energy. The average x-ray photon energy was estimated by using half-value thickness method and found to be 8.4 keV. The electron temperature of the plasma was estimated to be around 3 keV by x-ray intensity ratio method. The space-resolved x-ray-emitting zones for all the anodes were captured by a pinhole-based x-ray imaging camera and the images were scanned for different gray levels by using a MATLAB computing software. These gray level spectra show that the ...

Effect of Anode Designs on Ion Emission Characteristics of a Plasma Focus Device

A comparative study on the ion emission characteristics such as flux and energy, and their variation in angular positions and operating gas pressures has been carried out in a nitrogen-filling plasma focus device. Three different designs of cylindrical anode (central electrode) having hollow, solid and hemispherical tip have been tested for this study. The ion emission characteristics were investigated by employing three Faraday cups at various angular positions. The ion flux depends on the operating gas pressure irrespective of the anode designs and the maximum ion flux is found to be in the pressure range 0.3 to 0.5 Torr for all the anode designs. The hemispherical anode yields highest ion flux while the hollow anode emits lowest ion flux. The angular variation of ion flux is seen to be anisotropic irrespective of the anode designs with an ion dip at 0° (axis of the device) and maximal at 5° angular positions. The anisotropic character of ion emission is less in the case of the hemispherical anode than the hollow anode. The ion energy, measured by the time of flight method, shows its dependence on the anode designs. The maximum ion energy is found to be around 830 keV at an angular position 5° in the case of the hemispherical anode design. The most probable ions are found to be with energy less than 100 keV irrespective of the anode designs and the angular positions. This study indicates that the plasma focus device could be optimized to a great extent for optimal ions yield by using an appropriate anode design.

Miniature hybrid plasma focus extreme ultraviolet source driven by 10 kA fast current pulse

A miniature hybrid plasma focus device, operated in xenon gas medium and driven by a 10kA fast current pulse, has been used to generate extreme ultraviolet radiation in the range of 6–15nm. At present the radiation characteristics from xenon plasma were mainly assessed qualitatively using standard tools such as visible light framing camera, extreme ultraviolet (EUV) pinhole camera, and EUV photodiode. Strong pinching of xenon plasma is indicative from both visible and EUV imagings. The maximum size of the EUV emitting zone is estimated to be of the order of 0.21×1.55mm and the estimated value is within the accepted value as benchmarked by industries. The EUV intensity measurement by photodiode showed fairly isotropic radiation at least in a half solid angle. This device can be developed further as a competent source for EUV metrology or lithography applications.

Magnetic probe measurements of current?sheet dynamics in a coaxial plasma accelerator

A high-frequency multiple magnetic probe assembly has been specifically fabricated for the study of current sheet dynamics in the axial acceleration phase of a low-energy dense plasma focus (DPF) device operated in a nitrogen gas medium. The response time of each probe is of the order of 1 ns and the tiny structure of the probe is well suited to sense the magnetic field associated with a pulsed plasma without perturbing the plasma unduly. The magnetic probes were calibrated using a simple, novel and reliable calibration technique and the calibration factor is found to be 0.34 ± 0.028 T V−1. Our study reveals that the parabolic current sheet accelerates as it propagates through the electrode assembly, reaching a rundown velocity of ~6.1 cm µs−1. The average current sheet thickness in the axial acceleration phase is found to be ~3 cm. In our case, the current shedding and mass loss factors are estimated to be 32% and 40% respectively. Our approach of using a high-frequency multiple magnetic probe assembly for the study of current sheet dynamics in a DPF device is highly effective in obtaining precise and accurate measurements.

A comparative study on the performance of a xenon capillary Z-pinch EUV lithography light source using a pinhole camera

A pinhole camera has been employed to study the performance of a xenon capillary Z-pinch extreme ultraviolet (EUV) lithography light source driven by different dI/dt discharge current pulses. The performance of the EUV source in terms of dimension, intensity, collection efficiency and stability was specifically investigated by varying the experimental conditions such as the supplying gas pressure and dI/dt of the discharge current. Specific features, such as ring shape (annular profile) pinhole images and symmetrical and stable emission in the high dI/dt discharge current, have been observed or confirmed experimentally. Our results support the fact that the high dI/dt and short discharge currents have better EUV emission characteristics for EUV lithography compared with the low dI/dt discharge current.

Influence of electrode separation and gas curtain on extreme ultraviolet emission of a gas jet z-pinch source

Extreme ultraviolet (EUV) emission from a gas jet z-pinch source has been examined by employing a photodiode and pinhole camera. Visible images of the pinched plasma have been also recorded. A current pulse of 10kA is used to heat the gas jet, which emits radiation around 13.5nm. Experimental parameters such as electrode separation and gas flow rate are varied to optimize EUV emission. The maximum EUV energy is obtained for 12mm electrode separation and 20Torr xenon pressure and it is estimated to 10.95mJ∕sr per 2% bandwidth per pulse. The presence of gas curtain improves EUV emission by 30%.

Characteristics of Xenon Capillary Z-Pinch Extreme Ultraviolet Lithography Source Driven by Different dI/dt Discharge Current Pulses

Next-generation lithography will require an extreme-ultraviolet (EUV) light source that ensures high radiation intensities at a wavelength of around 13.5 nm. The characteristics of pinch dynamics and emission in this spectral range were studied experimentally for xenon capillary Z-pinch plasma driven by different dI/dt discharge current pulses. The pinch dynamics of the capillary Z-pinch plasma were examined by employing a high-speed camera, and the spectral emission from plasma was inspected using an EUV photodiode, a mini calorimeter and spectrometers. Our results confirm that high-dI/dt discharge current has better performance in comparison with the low one in terms of plasma dynamics, EUV power output and debris generation.

Extreme Ultraviolet Light Emission from Z‐Pinch Discharge Plasma Source

A capillary Z‐pinch discharge light source for EUV lithography has been developed. Our device is equipped with a water‐cooled ceramic capillary and electrodes, and a solid state pulsed power generator. A stacked static induction thyristors are used as switching elements, which enable high repetition rate operation of pulsed power supply. A magnetic switch is connected in series, which not only assists the semiconductor switch but also provides a preionization current. In the present study, EUV radiation emitted from pinching plasma in a xenon‐filled capillary was quantitatively measured using an in‐band calorimeter. Time‐integrated in‐band source image was also observed using a pinhole camera system. Furthermore, new electrode system using plasma jet has been developed.