J.D. Miller

Pulse shaping a high‐current relativistic electron beam in vacuum

A simple method for shaping the output current pulse of a relativistic electron beam in vacuum is presented. This method has been employed to sharpen the rise time of a high‐current relativistic electron beam produced by a 2‐MV, 7‐kA, 20‐ns pulser. The beam has a pulse shape that is approximately triangular both in voltage and current, with a negligible instantaneous energy spread. The desired pulse shape is nominally rectangular in current. The technique utilizes a magnetic lens with a magnitude of approximately 1.5 kG to focus the beam. Passing beam electrons through the magnetic lens causes them to focus at different axial locations downstream from the lens depending upon their energy. The focal point of the beam current peak (corresponding to maximum energy) is then located furthest downstream. An aperture is used near the focus to select a portion of the beam having the desired parameters.

Cold X-ray simulation technology development at Phoenix

When operated in its plasma radiation source (PRS) mode, the Phoenix simulator employs a 1.6 MJ marx capacitor bank to drive a nominal 3/8 /spl Omega/ diode. During its development, both aluminum wire and puff gas (argon and krypton) loads have been tested. To date, radiation outputs of 50 kJ aluminum and 20 kJ argon K-line radiation have been achieved at 65% of maximum energy storage. This paper emphasizes three aspects of the Phoenix PRS: (1) the operation of the fast rise time gas puff valve, (2) measurements of the implosion dynamics, and (3) the development of a solid deuterium debris shield.

Phoenix multi-terawatt plasma radiation source technology

Summary form only driven, as follows. When configured as a plasma radiation source (PRS), the Phoenix radiation effects simulator, uses its 1.6 MJ marx capacitor bank to deliver over 4 MA to a nominal 3/8 /spl Omega/ diode. As a PRS, the current is used to implode and heat a gas puff or wire array Z-pinch. The goal of the PRS is to generate kilojoules of K-line photons which poses a number of technical challenges. In this paper we will discuss some of the techniques that have been developed to improve energy coupling to the plasma loads. To suppress pre-pulse, the Phoenix diode is electrically isolated from it transmission line power feed by 24 parallel, self-firing gas switches. When operated with a gas puff, this design led to the requirement that the fast-opening-gas-valve, used to form the cold gas distribution prior to the implosion, be remotely operated via fiber optic cables. To form a reproducible gas distribution, the gas valve was designed to open in about 200 /spl mu/sec which allows timing the implosion on the pressure plateau. Gas valve performance data will be presented. The production of intense radiation can lead to early diode voltage collapse. To avoid direct exposure of insulators to the ionizing radiation, the magnetically insulated transmission lines (MITLs) must be carefully designed. Improvements in radiation outputs related to these design changes will be shown. The production of intense radiation pulses is associated with metallic debris. The major sources of debris are: ohmic heating, large magnetic forces and the large surface energy deposition of the soft X-rays. Methods used to limit the debris will be discussed.

Observation of plasma wakefield effects during high-current relativistic electron beam transport

Modulation of the beam current has been observed during ion focused regime (IFR) transport of a high-power relativistic electron beam immersed in a low-density background plasma. In this experiment, a 1.6-MeV, 1-kA, risetime sharpened electron beam is propagated on a KrF excimer-laser-produced IFR channel in TMA gas which is immersed in a low-density plasma filled transport tube. Experimental measurements demonstrating modulation of this high-current relativistic electron beam near the background plasma frequency are presented. >

Modulation of a High-Current Relativistic Electron Beam in a Low-Density Background Plasma

Modulation of the beam current has been observed during ion focused regime (IFR) transport of a high-power relativistic electron beam propagating through a low-density background plasma. In this experiment, a 1.7-MeV, 1-kA, risetime-sharpened electron beam is transported in a KrF excimer laser produced IFR channel in TMA gas. The IFR channel is immersed in a low-density plasma filled transport tube. We present experimental measurements and computer simulations demonstrating modulation of this high-current relativistic electron beam near the low-density background plasma frequency.

Large area electron beam mode for soft X-ray simulation on Casino

A low current density (500-1000 A/cm/sup 2/), large volume (30 cm diameter by 30 cm long) electron beam capability to simulate soft X-ray environments for three-dimensional, cryogenically cooled objects is described.

Argon Z-pinch implosions on Phoenix

Summary form only given, as follows. Upgrades to the Phoenix front end have resulted in a three-fold increase in Argon K-shell X-ray yields. Lack of a transit time isolator between the center conductor and ground necessitated powering the gas-puff hardware with batteries and supplying control via fiber optic cables. A simple gas flow model was developed to optimize the valve/nozzle design. The gas-puff valve and nozzle were modified to produce a 250-/spl mu/s density rise time. This short rise-time allowed firing on the gas plateau which improved reproducibility. Front end power flow was improved by opening the MITL from 8 to 10-mm and by increasing the dog-leg at the nozzle to obstruct UV light. The highest yield shots were achieved with a 4-cm long load using a 3.5-cm mean diameter nozzle with a mean inward tilt of 13.75 degrees. X-ray pulse widths ranged between 7-15 ns and X-ray pinhole photos suggest uniform assembly on axis. Results and documentation of the Phoenix upgrades are presented.

Plasma wakefield effects on high-current relativistic electron-beam propagation in the ion-focus regime

Modulation of the beam current has been observed during ion focused regime (IFR) transport of a high-power relativistic electron beam propagating through a low-density background plasma In this experiment, a 1.7-MeV, 1-kA, risetime-sharpened electron beam is transported in a KrF excimer laser produced IFR channel in TMA gas. The IFR channel is immersed in a low-density plasma filled transport tube. We present experimental measurements and computer simulations demonstrating modulation of this high-current relativistic electron beam near the low-density background plasma frequency.

Plasma Wakefield Effects On High-current Relativistic Electron Beam Transport In The Ion Focus Regime

Abstract : Modulation of the beam current has been observed during ion focused regime (IFR) transport of a high power relativistic electron beam propagating through a low-density background plasma. Injecting a high current, high energy electron beam into an IFR channel immersed in a background plasma induces plasma oscillations. These background plasma oscillations, induced by the risetime portion of the beam ejecting plasma electrons from the vicinity of the beam into the background plasma, give rise to a modulated axial electric field. This field travels with the beam leading to beam energy and current oscillations. In the experiment, a 1.7-MeV, 1-kA, risetime-sharpened electron beam is propagated on a KrF excimer laser produced IFR channel in TMA gas, which is immersed in a low density plasma filled transport tube. We present experimental measurements and computer simulations demonstrating modulation of this high current relativistic electron beam near the low density background plasma frequency.

Fast risetime magnetic field coil for electron beam propagation studies

A new method for detuning the betatron frequency of an intense relativistic electron beam is investigated. The method employs a fast rising magnetic field to decrease the beam radius from the head to the tail of the beam. The magnetic field risetime is on the order of 30 ns with a peak value of about 2 kG. This method may be useful for detuning intense beam instabilities associated with betatron oscillations.<<ETX>>