R. Menon

Plasma expansion and fast gap closure in a high power electron beam diode

High power electron beam generation studies were carried out in a planar diode configuration to investigate the effect of the accelerating gap, diode voltage, and anode-cathode materials on the electrode plasma expansion. The diode voltage has been varied from 145–428 kV, whereas the current density has been varied from 208–2215 A/cm2 with 100 ns pulse duration. It was found that the diode voltage and current follow the bipolar space-charge limited flow model. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 11 cm/μs for 34 mm anode-cathode gap and the plasma velocity decreases for smaller gaps. It was found that the plasma expansion velocity increases significantly due to the cathode edge contribution and the edge contribution is particularly important during the beginning and the end of the accelerating pulse when the diode voltage and the corresponding electric field are comparatively low. It was also observed that the diode current incre...

Intense relativistic electron beam generation and prepulse effect in high power cylindrical diode

Intense gigawatt relativistic electron beam has been generated in a high power cylindrical diode in the presence of prepulse. A bipolar prepulse voltage, recorded at the diode, varies both in amplitude and time duration with the Marx generator voltage. It was found that only at the accelerating gap ⩽1.65cm there is some shot to shot variation in the diode voltage and current for the same Marx generator voltage. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 5cm∕μs for 1.85cm radial anode-cathode gap and the plasma velocity decreases for smaller gap. It was found that the effect of the prepulse is less pronounced in the cylindrical diode as compared to planar diode that allows one operation of the cylindrical diode with the gap ⩽1.85cm.

Shot to shot variation in perveance of the explosive emission electron beam diode

The shot to shot variation in perveance of a planar diode with explosive emission graphite cathode in a range of accelerating gaps 3–12 mm is investigated experimentally. The typical electron beam parameters were 200 kV, 12 kA, 100 ns, with a few hundreds of A/cm2 current density. The diode perveance remains less than the Child–Langmuir value, indicating that only a fraction of the cathode take part in the emission process. A simple statistical analysis of the diode perveance shows that the shot to shot variation is more pronounced for the later part of the accelerating pulse. The cathode plasma expansion velocity and the effective initial emission area have been calculated from the perveance data. It was found that the plasma expansion velocity varies from 3 to 6.5 cm/μs. The mean expansion velocity and the standard deviation increase with the increase in the accelerating gap. The initial emission areas also varies randomly on a shot to shot basis and at the beginning of the accelerating pulse only 4%–35...

Impedance collapse and beam generation in a high power planar diode

Summary form only given. Intense relativistic electron beam generation studies were carried out in a planar diode configuration to investigate the effect of the plasma expansion on the impedance characteristics of the diode. The diode voltage and current waveforms were analyzed with the bipolar space-charge limited flow model. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 9.5 cm/mus for 31 mm anode-cathode gap and the plasma velocity decreases for smaller gap. It was found that the electron emission is more uniform for 25 mm anode-cathode gap as compared to 31 mm gap. Effect of a nylon sheet on the anode plate has been studied with respect to the impedance characteristic of the diode. It was found that the plasma expand with a faster velocity in the presence of nylon sheet on anode.

Itolizumab – a humanized anti-CD6 monoclonal antibody with a better side effects profile for the treatment of psoriasis

Management of psoriasis is a challenge to the treating physician. The chronic inflammatory state of psoriasis with exacerbations and remissions necessitate “on-and-off” treatment schedules. The safety profiles of drugs and tolerability issues for patients are important factors to be considered during treatment. Various biological agents targeting T-cells and the inflammatory cytokines are available for systemic treatment of psoriasis. However, major causes of concern while using these drugs are risk of susceptibility to infection and development of anti-drug antibodies, which will affect the pharmacokinetic properties, efficacy, and safety profile of the drug. Itolizumab, a humanized anti-CD6 monoclonal antibody, is a new molecule that acts by immunomodulating the CD6 molecule. CD6 is a co-stimulatory molecule required for optimal T-cell stimulation by the antigen-presenting cells. This step is crucial in T-cell proliferation to form Th1 and Th17 cells, which play a major role in the pathogenesis of psoriasis. This article deals with the properties of Itolizumab and its role in the treatment of psoriasis. Based on the available published data, Itolizumab seems to have a better adverse effects profile and at the same time comparatively less efficacy when compared to other biological agents available for treating psoriasis. Larger studies with longer duration are required to clearly depict the long-term side effects profile.

Electron beam current in high power cylindrical diode

Intense electron beam generation studies were carried out in high power cylindrical diode to investigate the effect of the accelerating gap and diode voltage on the electron beam current. The diode voltage has been varied from 130 to 356 kV, whereas the current density has been varied from 87 to 391 A/cm2 with 100 ns pulse duration. The experimentally obtained electron beam current in the cylindrical diode has been compared with the Langmuir–Blodgett law. It was found that the diode current can be explained by a model of anode and cathode plasma expanding toward each other. However, the diode voltage and current do not follow the bipolar space-charge limited flow model. It was also found that initially only a part of the cathode take part in the emission process. The plasma expands at 4.2 cm/μs for 1.7 cm anode-cathode gap and the plasma velocity decreases for smaller gaps. The electrode plasma expansion velocity of the cylindrical diode is much smaller as compared with the planar diode for the same accel...

Influence of Electron-Beam Diode Voltage and Current on Coaxial Vircator

The KALI-5000 pulse power system was utilized to generate high-power microwaves using a coaxial virtual cathode oscillator. The typical electron-beam parameters were 290 kV, 23 kA, and 100 ns, with a few hundreds of amperes per centimeter square current density. Experiments were conducted using a graphite cathode for two different radial anode-cathode gap distances to investigate the dependence of microwave output magnetic field and frequency on diode voltage and current waveform. It was found that the coaxial vircator always has more than one frequency component. It was shown that the microwave B-field and the frequency do not depend on the time-varying impedance and perveance of the diode. Electron-beam emission area, uniformity, and the anode-cathode gap play a major role in deciding the power density and frequency at the point of measurement. The highest microwave power is emitted when all the power is delivered into a single frequency at least for a certain time of the accelerating pulse.

Development and Calibration of Rogowski coils for pulsed power systems

Rogowski coils have been used for decades for non-invasive current measurement when other probe, such as current shunts, current transformers are impracticable. The measurement of diode beam current in pulse power system under vacuum and high voltage are challenging task which requires development of Rogowski coil for specific applications. They operate in large radiation fields, under intense electron bombardment and at high di/dt. The Rogowski coil has been developed and calibrated to detect nano second pulsed currents from 10kA to 100kA with wide bandwidth and sensitivity. This paper describes Calibration of Rogowski coil used for measuring KALI-1000 pulsed power system[1] relativistic electron beam current. Rogowski coi designed and fabricated using damping resistor technique is also described.

High-current density electron beam generation from a polymer velvet cathode

Intense electron beam generation studies were carried out using polymer velvet as a cathode material. The typical electron beam parameters were 250 kV, 15 kA, 100 ns, with a few hundred A cm−2 current density. The cathode plasma expansion velocity and the effective initial emission area have been calculated using the perveance data. It was found that the gap closure velocity and the initial emission areas vary randomly on a shot-to-shot basis. In comparison with a graphite cathode, the gap closure velocity of the velvet cathode is less for lower diode gaps, but is much higher for the larger accelerating gaps. One-way analysis of variance was employed to examine the statistical correlation between the diode voltage, current, plasma velocity and the effective emission area for various diode gaps and for two different cathode materials. It was shown that the mean diode voltage, current, plasma velocity and the effective emission area are different for graphite and velvet cathodes whereas the statistical variations of diode voltage and plasma expansion velocities are not cathode material dependent. However, the mean effective emission area is cathode material dependent as are the variances.

Intense electron beam generation in a high power cylindrical diode with a bipolar pulse

Our previously reported results demonstrated that an intense gigawatt relativistic electron beam can be generated in a cylindrical diode in the presence of prepulse. This article reports intense electron beam generation in a cylindrical electron beam diode when subjected to a high voltage bipolar pulse. The experimental results are compared to the Langmuir–Blodgett law. The diode perveance in the positive voltage pulse linearly increases with time due to the increase in the emission area. It was found that the electron beam can be generated from the diode during the negative voltage pulse due to a very little gap closure during the positive voltage pulse.