D. Penache

Experimental investigation of ion beam transport in laser initiated plasma channels

The aim of the presented experiments is to study the transport of a heavy ion beam in a high-current plasma channel. The discharge is initiated in NH 3 gas at pressures between 2 and 20 mbar by a line-tuned CO 2 laser. A stable discharge over the entire electrode gap (0.5 m) was achieved for currents up to 60 kA. Concerning the ion beam transport, the magnetic field distribution inside the plasma channel has to be known. The ion-optical properties of the plasma channel have been investigated using different species of heavy ions (C, Ni, Au, U with 11.4 MeV/u during six runs at the Gesellschaft fur Schwerionenforschungs-UNILAC linear accelerator. The high magnetic field allowed the accomplishment of one complete betatron oscillation along the discharge channel. The results obtained up to now are very promising and suggest that, by scaling the discharge gap to longer distances, the bearn transport over several meters is possible with negligible losses.

Diagnostics of discharge channels for neutralized chamber transport in heavy ion fusion

The final beam transport in the reactor chamber for heavy ion fusion in preformed plasma channels offers many attractive advantages compared to other transport modes. In the past few years, experiments at the Gesellschaft fuer Schwerionenforschung (GSI) accelerator facility have addressed the creation and investigation of discharge plasmas, designed for the transport of intense ion beams. Stable, self-standing channels of 50 cm length with currents up to 55 kA were initiated in low-pressure ammonia gas by a CO{sub 2}-laser pulse along the channel axis before the discharge is triggered. The channels were characterized by several plasma diagnostics including interferometry and spectroscopy. We also present first experiments on laser-guided intersecting discharges.

Plasma channel transport for heavy ion fusion: Investigation of beam transport, channel initiation and stability

For final beam transport in an IFE reactor three alternatives are mainly discussed. These are neutralized ballistic transport, serf-pinched transport, and plasma channel transport. Discharge plasma channels were investigated in the recent years at GSI Darmstadt and at LBNL Berkeley in a number of experiments. Different initiation mechanisms for gas discharges of up to 60 kA were studied and compared. In the Berkeley experiments laser ionization of organic vapors in a buffer gas was used to initiate and direct the discharge while at GSI laser gas heating and ion beam induced gas ionization were tested as initiation mechanisms. Measurements of temperature, electron density, gas density, and magnetic field distribution in the channels are compared with results of beam transport experiments at the GSI UNILAC accelerator and with MHD simulations of the ID-fluidcode CYCLOPS, which was developed in Berkeley. Good agreement between plasma diagnostics results, measured ion optical properties and MHD simulations was found. Parameters that are required for a reactor application are a discharge current of 50 kA, a channel diameter below 1 cm, a pointing stability better than 500 µm, and MHD stability for more than 10 µs. These parameters have been demonstrated in the recent experiments. The results imply that transport channels work with sufficient stability, reproducibility and ion optical properties in a wide pressure range and for various discharge gases.

Stability of gas discharge channels for final beam transport

Discharge plasma channels have been investigated in recent years at Gesellschaft fur Schwerionenforschung-Darmstadt (GSI) and at the Lawrence Berkeley National Laboratory in Berkeley, California, in a number of experiments. A short of the experimental work at Berkeley and GSI is given. Different initiation mechanisms for gas discharges of up to 60 kA were studied and compared. In the Berkeley experiments, laser ionization of organic vapors in a buffer gas was used to initiate and direct the discharge while at GSI, laser gas heating and ion-beam-induced gas ionization were tested as initiation mechanisms. These three initiation techniques are compared and the stability of the resulting discharge channels is discussed. A discharge current of 50 kA, a channel diameter well below 1 cm, a pointing stability better than 200 μm, and MHD stability of more than 10 μs have been demonstrated simultaneously in the recent experiments. These parameters are sufficient or close to the requirements of a reactor application depending on the details of the target design. The experimental results show that transport channels work with sufficient stability, reproducibility, and ion optical properties for a wide pressure range of discharge gases and pressures.

Transport experiments of a 2.2 GeV gold ion beam in a plasma channel at the GSI-UNILAC facility

Charged particle beam transport in plasma channels is a well-established technique for electron and proton beams in the 1 MeV particle energy range. Experiments with heavy ion beams were started at the GSI-UNILAC accelerator facility to explore the applicability of this transport mode to heavy ion beam driven inertial confinement fusion. These experiments investigate the ion optics of a laser-initiated discharges. With the help of a TEA-CO/sub 2/ laser a discharge is initiated in low pressure (5 to 20 mbar) ammonia gas. A capacitor bank (1.33-8 /spl mu/F), charged up to 20 kV, is then triggered and a straight plasma channel is produced along the laser path. The current can be increase up to 45 kA. Fast shutter photography was used to study the stability of the channel. Magnetic field measurements were performed with dB/dt loops. The influence of the magnetic probe on the discharge was checked using an interferometer set-up. A 2.2 GeV gold ion beam was used to probe the ion optical properties of the channel.

Experimental investigation of ion beam transport in a laser initiated high current discharge channel

Summary form only given. The transport of space charge dominated ion beams is of interest to many applications using high power particle beams. The most challenging demands are found in the field of ion beam driven inertial confinement fusion. Motivated by this application the space charge and current neutralized beam focusing and transport in gas discharge plasmas has been under investigation for a number of years. Paralleled by engineering design work of a modified HILIFE II reactor with discharge channel based final beam transport, and by experimental investigations of laser initiated high current discharges at the Lawrence Berkeley National Laboratory (LBNL) the ion optical properties of such a channel will be studied for the first time with a heavy ion beam at GSI.