Tsuyoshi Oshige

Discharge Processes in a Low-Voltage Microgap Surge Absorber

Discharge processes in the newly developed microgap surge absorber (MSA) are studied using a photomultiplier and image converter camera. The MSA is for the protection of low-voltage circuits from overvoltage surges and consists of a semiconducting thin film coated on a ceramic tube with microgaps which are made by removing annular rings in the coated film by a laser beam. The highly desirable characteristics of the MSA as a surge absorber result from the microgap which supplies initial electrons and triggers a surface streamer to build up a glow discharge.

Temporal evolution of potential formation in a discharge created by pulsed electron beam injection in a low-pressure argon gas

The discharge process is experimentally studied from measurements of the temporal evolution of potential formation when a pulsed electron beam is injected into a DC field in a low-pressure argon gas ((3-5)*10-4 Torr). The V-shaped axial potential profile is found to be formed instantaneously at the moment of beam injection and then collapses at the start of the discharge development. The effective depth of the potential minimum exceeds the ionisation voltage at this moment, resulting in the acceleration of beam electrons with energy enough to ionise the gas. The measured two-dimensional structure of the potential profile reveals that the potential minimum forms a negative potential well in front of the beam source on the central axis.

Dynamics of discharge with electron beam injection in low-pressure gas and weakly ionised plasma

The dynamics of discharge are studied experimentally by applying an impulse voltage to a discharge gap with electron beam injection. Discharge mechanisms in a low pressure gas (0.01-0.27 Pa) and weakly ionised plasma (ion density/neutral gas density approximately=10-7) are found to differ essentially. In the former case, positive space charges are produced locally around the anode. They develop towards the beam source, leading to the collapse of a V-shaped potential profile. Discharge occurs at this moment. In the latter case, the discharge is realised by the collapse of the V-shaped potential caused by the rapid rise of the plasma potential over the whole region at the instant of the application of the impulse voltage.

Discharge time lag with electron‐beam injection in a low‐pressure gas

Discharge time lag is experimentally studied when a single stepped voltage is applied to a gap with a stationary electron‐beam injection in a low‐pressure gas (0.06–2 mTorr). The time lag is found to be almost independent of the electron‐beam density. The beam density does, however, determine a discharge current, which is independent of the applied gap voltage and beam energy. A systematic measurement of the time lag as functions of the gap voltage, beam energy, gas pressure, and gap length is presented. The time becomes extremely short when the beam energy exceeds the ionization energy of the gas. The time lag, when a single pulsed e‐beam is injected into the dc gap field, is also studied. The result is essentially the same in spite of pulsed operation.