G. Kirkman-Amemiya

A study of the high current back lighted thyratron and pseudospark switch

High-current operation of the back-lighted thyratron (BLT) switch is reported. The cathode emission mechanism and discharge formation characteristics common to BLT and pseudospark switches are described. The BLT switch is an optically triggered low-pressure diffuse discharge closing switch that operates at high currents with a self-heated cathode. Operation for square 150 ns pulses of 1-10.5 kA, 2.5-20 kV, <25 Hz, 45 ns risetime and a 500 ns capacitor discharge up to 82 kA at 25 kV including operation at 5 Hz, 17.5 kV, 60 kA is reported. The switch exhibits a risetime and peak current limit at low currents but no high current limit (up to 82 kA). The low current limit is explained as being due to an insufficient heating of the self-heated cathode.<<ETX>>

High current back lighted thyratron switch

High current operation of the back lighted thyratron, an optically triggered, low pressure diffuse discharge closing switch that operates with a self heated, super‐emissive cathode, is reported. Repetitive operation at 5 Hz, 17.5 kV, 60 kA, with 500 ns pulse length has been achieved. The switch exhibits no high current limit up to 82 kA. High dI/dt≳1011 A/s and <45 ns rise times have been obtained. The high current and short rise time capabilities make this switch a possible replacement for spark gaps and multiple parallel thyratron switches in accelerator and laser applications.

Electron beam generation from a superemissive cathode

An experimental study of electron beams produced by a superemissive cathode in the Back-Lighted Thyratron (BLT) and the pseudospark is presented. This work is motivated by experiments demonstrating very high current densities (>or=10 kA/cm/sup 2/ over an area of 1 cm/sup 2/) from the pseudospark and BTL cathode. This high-density current is produced by field-enhanced thermionic emission from the ion beam-heated surface of a molybdenum cathode. This work reports the use of this cathode as a beam source, and is to be distinguished from previous work reporting hollow cathode-produced electron beams. An electron beam of more than 260 A peak current has been produced with 15 kV applied voltage. An efficiency of approximately=10% is estimated.<<ETX>>

An Analysis of the High Current Glow Discharge Operation of the BLT Switch

High current operation of the BLT switch is described. This paper includes a description of the switch structure and several optical triggering methods. Result of experimental observations of high current operation are reported including measurements of peak currents >80kA and rates of current rise >1011A/sec. Observations of the discharge plasma using a streak camera and electrode surface analysis by electron microscope are used to describe the dense glow discharge and the self heated cathode of this switch. Two phases of the discharge are identified, a hollow cathode phase responsible for the fast buildup of the discharge plasma and a dense glow discharge phase with self heated thermionic cathode responsible for the high peak currents obtained.

Fast risetime BLT switches for accelerator applications

A BLT switch with performance capabilities suitable for particle accelerator systems including fast kicker magnets has been demonstrated. With careful design of pulse forming networks and triggering circuits, the performance required by the SSC LEB kickers could be obtained with the BLT switch. The high current capability allows the possibility of driving several systems in parallel, switched by a single BLT. Additional work is required to more accurately define the performance of the BLT switch in the areas of lifetime, average power, and triggering.<<ETX>>

Hermetically Sealed Back Lighted Thyratron Switches for High Power Applications

We report the results of a program to develop hermetically scaled back lighted thyratron switches for high voltage and high current operation. Initial results with a single gap switch include switching >80kA maximum holdoff voltage of 72kV when pulse charged, and 17.5 kV, 60kA, 40kA reverse, 400nsec pulse at 5Hz. Using multiple gap switches we have obtained scaling to voltages > 100kV, 26kA and continuous operation at 78kV, 19kA at 10Hz. The switches are produced in both optically and electrically triggered versions.

Pulsed microwave and millimeter wavelength radiation from the back-lighted thyratron

The authors report experimental results on the production of radiation from approximately=20 GHz to approximately=100 GHz in a pseudospark-type device. Pulsed emission of radiation occurs from a low (neutral) pressure ( approximately=100 mtorr Ar) discharge, during the initial transient phase, as the plasma is being formed and a pulsed electron beam is temporarily present. A high-energy electron beam (15 approximately 20 keV) has been observed along with a high-density plasma in this pseudospark-type device. A beam-plasma interaction is proposed as the mechanism for the radiation generation.<<ETX>>

A plasma-based source of pulsed microwave and millimeter wavelength radiation

Summary form only given. Experimental evidence was obtained for the generation of pulsed microwave and millimeter-wave radiation in the range of 20 to above 100 GHz resulting from a beam-plasma interaction in a back-lighted thyratron or pseudospark. The device supports an intense, low-emittance electron beam and a high-density glow-mode plasma. The back-lighted thyratron and pseudospark were used as a high-current switch for pulsed power applications and produce electron beams with high brightness and low emittance, suggesting a beam-plasma interaction which can produce electromagnetic waves. Time-resolved measurements indicate that the electron beam and radiation occur simultaneously. The beam has ≈120-A peak current with energy 10-20 keV. These devices produce high plasma densities for devices that operate repeatably in a pulsed mode. The plasma is produced in a low-pressure gas (~100-mtorr Ar). The radiation is produced during the transient period when the plasma is being formed. Typical pulse lengths are of the order of the time for the formation of the plasma. which varies with circuit parameters and gas pressure

A study of the high current discharge of the pseudospark and back lighted thyratron switch

Summary form only given. An experimental and theoretical study of the high-current discharge of the pseudospark and back-lighted thyratron switch was performed. These are hollow-electrode low-pressure gas discharge switches that have been operated at voltages up to 100 kV and currents up to 100 kA. They are also a source of electron and ion beams and produce microwave radiation through a beam-plasma interaction. Streak camera observations and electrical measurements have identified two phases of the discharge: a high-impedance formation phase which draws current from a hollow cathode and a low-impedance conduction phase which draws currents from the front surface of the cathode which has been heated during the formation phase by ion bombardment. During the formation phase, ion beams, electron beams and microwaves are produced. During the conduction phase, current densities of ~10 kA/cm2 are conducted through a homogeneous plasma with a large cross-sectional area. Theoretical modeling indicates that a beam component of electrons can contribute to the formation of the discharge and the conduction of high current densities

High-power multiple-gap back-lighted thyratrons

The authors report successful operation of flashlamp-switched multiple-stage back-lighted thyratrons at very high pulsed power levels, including 100 kV stand-off voltage and >70 kA switched peak current. Simultaneous optical triggering of each gap for precision timing and plasma triggering is also discussed. The switch closure generates a highly ionized, very homogeneous plasma in a low pressure static background gas, and thus does not require exchange of high pressure gas for repetition rate operation. The results suggest that fairly simple multiple-gap configurations of the device will be useful for applications such as multiple high-power modulator systems for accelerators.<<ETX>>