RSX experiment

Description: Magnetic reconnection refers to the local breaking of magnetic field lines and subsequent change in the global topology of the magnetic field in the presence of plasmas or conducting fluids. During this process, magnetic field lines of opposite polarity are convected toward each other by fluid flow in the so-called diffusion region. This region is centered around a neutral magnetic line, across which the reconnecting component of the magnetic field changes sign. In the diffusion region, the "frozen-in" condition of ideal MagnetoHydroDynamics (MHD) equations is broken. The magnetic field can diffuse through the plasma allowing the annihilation of opposite directed magnetic field lines and conversion of magnetic field energy into Ohmic heating and particle acceleration. During the last four decades, a large effort has been devoted to study magnetic reconnection in plasmas since it is considered to play a crucial role in a variety of different astrophysical and laboratory phenomena. Examples are in the evolution of solar flares, in the dynamics of the earth magnetosphere and in the redistribution of the energy in the universe. In magnetically confined laboratory plasmas for fusion research, a major role is played by magnetic reconnection in determining the dynamics of relaxation processes, such as sawtooth oscillations and major disruptions in tokamaks or dynamo effects in Reversed Field Pinches. Early 3D laboratory experiments on magnetic reconnection provided detailed measurements of the relaxation to a force-free state produced by the coalescence of two current channels in the LPD linear device. Interacting current channels were produced by coating a large cathode source nonuniformly and then biasing it with respect to an external anode. Although 3D features of magnetic reconnection were studied, the Lundquist number of the interacting current channels was limited by the plasma production scheme and ions were not magnetized (EMHD regime). Over the past few years, developments in plasma gun technology have made plasma guns a reliable laboratory source capable of producing plasmas with large Lundquist numbers. The Reconnection Scaling Experiment uses this innovative plasma gun technology to study the coalescence of parallel current channels in a 3D linear geometry. The emphasis will be on using many repetitive plasma discharges to acquire detailed spatial and temporal measurements as the two current channels merge along the axis of the linear device. One major advantage of the plasma gun technology is that it allows a high degree of flexibility in scaling independently the different parameters important in the reconnection process. A view of the RSX device is shown in Fig. 1 (a), (b) together with a schematic view of the linear geometry of two interacting current channels, Fig. 1 (c). For a picture of the actual status of RSX, click here. In this section, the main elements of the RSX device are described together with the plasma production technique. An overview is presented of the control and data acquisition system and main diagnostics. Figure 1. Cross section of RSX device: (a) lateral view, (b) head-on view; and (c) schematics of two interacting current channels along the axis of the device. RSX main elements are shown: (1) plasma guns, (2) head flange accommodating a large window, (3) magnet coils, (4) external anode, (5) stainless steel vacuum vessel, (6) schematics of the vacuum system, and (7) electro-mechanical valve for gas puffing. The RSX vessel consists of a cylindrical vacuum chamber with approximately 4m length and 20 cm radius, Fig. 1 (a), which is formed by 3 sections 48 inches in length recycled from the Field Reversed Configuration experiment FRX-C. Each section is fabricated from stainless steel (SS304) tubing with a 40.6 cm nominal outside diameter, a 0.48 cm wall thickness and has 16 x 2.75 inch and 12 x 6 inch Conflat flanges facing radially.

Magnetic reconnection is a fundamental process in plasma physics, characterized by the breaking and reconfiguration of magnetic field lines. This phenomenon occurs in the presence of conducting fluids, where magnetic field lines of opposite polarity are drawn together by fluid dynamics in a specific area known as the diffusion region. This region is defined by a neutral magnetic line where the magnetic field's polarity shifts. The typical "frozen-in" condition of ideal MagnetoHydroDynamics (MHD) is disrupted in this area, allowing magnetic fields to diffuse through the plasma. This diffusion leads to the annihilation of opposing magnetic field lines, resulting in the conversion of magnetic energy into thermal energy (Ohmic heating) and the acceleration of charged particles.

The importance of magnetic reconnection has been highlighted through extensive research over the past four decades, as it significantly impacts various astrophysical phenomena, such as solar flares, the dynamics of the Earth's magnetosphere, and energy redistribution in the universe. In laboratory settings, particularly in fusion research, magnetic reconnection plays a critical role in governing relaxation dynamics, including events such as sawtooth oscillations and major disruptions in devices like tokamaks and Reversed Field Pinches.

Initial three-dimensional laboratory experiments have provided valuable insights into the dynamics of magnetic reconnection, particularly the transition to a force-free state following the merging of current channels in linear plasma devices. These channels were created by applying a nonuniform bias to a large cathode source relative to an external anode. However, earlier studies faced limitations due to the plasma production methods employed, which restricted the Lundquist number and did not fully magnetize the ions (operating in the EMHD regime).

Recent advancements in plasma gun technology have led to the development of reliable sources capable of generating plasmas with significantly higher Lundquist numbers. The Reconnection Scaling Experiment (RSX) leverages this technology to investigate the coalescence of parallel current channels within a three-dimensional linear framework. The experimental design focuses on conducting numerous repetitive plasma discharges to gather detailed spatial and temporal data on the merging process of current channels along the axis of the device.

The RSX apparatus is composed of several key elements, including plasma guns, a head flange with an integrated window, magnet coils, an external anode, and a stainless steel vacuum vessel. The vacuum vessel, approximately 4 meters in length and 20 cm in radius, is constructed from three sections of stainless steel tubing, each 48 inches long, repurposed from the earlier Field Reversed Configuration experiment (FRX-C). Each section features a nominal outside diameter of 40.6 cm, a wall thickness of 0.48 cm, and is equipped with multiple Conflat flanges to facilitate connections and ensure system integrity. The design of the RSX device, alongside its control and data acquisition systems, provides a comprehensive framework for studying magnetic reconnection and its implications in both astrophysical and laboratory environments.Magnetic reconnection refers to the local breaking of magnetic field lines and subsequent change in the global topology of the magnetic field in the presence of plasmas or conducting fluids. During this process, magnetic field lines of opposite polarity are convected toward each other by fluid flow in the so-called diffusion region.

This region is centered around a neutral magnetic line, across which the reconnecting component of the magnetic field changes sign. In the diffusion region, the "frozen-in" condition of ideal MagnetoHydroDynamics (MHD) equations is broken. The magnetic field can diffuse through the plasma allowing the annihilation of opposite directed magnetic field lines and conversion of magnetic field energy into Ohmic heating and particle acceleration.

During the last four decades, a large effort has been devoted to study magnetic reconnection in plasmas since it is considered to play a crucial role in a variety of different astrophysical and laboratory phenomena. Examples are in the evolution of solar flares, in the dynamics of the earth magnetosphere and in the redistribution of the energy in the universe.

In magnetically confined laboratory plasmas for fusion research, a major role is played by magnetic reconnection in determining the dynamics of relaxation processes, such as sawtooth oscillations and major disruptions in tokamaks or dynamo effects in Reversed Field Pinches. Early 3D laboratory experiments on magnetic reconnection provided detailed measurements of the relaxation to a force-free state produced by the coalescence of two current channels inthe LPD linear device.

Interacting current channels were produced by coating a large cathode source nonuniformly and then biasing it with respect to an external anode. Although 3D features of magnetic reconnection were studied, the Lundquist number of the interacting current channels was limited by the plasma production scheme and ions were not magnetized (EMHD regime).

Over the past few years, developments in plasma gun technology have made plasma guns a reliable laboratory source capable of producing plasmas with large Lundquist number. The Reconnection Scaling Experiment uses this innovative plasma gun technology to study the coalescence of parallel current channels in a 3D linear geometry.

The emphasis will be on using many repetitive plasma discharges to acquire detailed spatial and temporal measurements as the two current channels merge along the axis of the linear device. One major advantage of the plasma gun technology is that it allows a high degree of flexibility in scaling independently the different parameters important in the reconnection process.

A view of the RSX device is shown in Fig. 1 (a), (b) together with a schematic view of the linear geometry of two interacting current channels, Fig. 1 (c). For a picture of the actual status of RSX, click here. In this section, the main elements of the RSX device are described together with the plasma production technique.

An overview is presented of the control and data acquisition system and main diagnostics. Figure 1. Cross section of RSX device: (a) lateral view, (b) head on view; and (c) schematics of two interacting current channels along the axis of the device. RSX main elements are shown: (1) plasma guns, (2) head flange accomodating a large window, (3) magnet coils, (4) external anode, (5) stainless steel vacuum vessel, (6) schematics of the vacuum system, and (7) electro mechanical valve for gas puffing.

The RSX vessel consists of a cylindrical vacuum chamber with approximately 4m length and 20 cm radius, Fig. 1 (a), which is formed by 3 sections 48 inch in length recycled from the Field Reversed Configuration experiment FRX-C.

Each section is fabricated from stainless steel (SS304) tubing with a 40. 6 cm nominal outside diameter, a 0. 48 cm wall thickness and has 16 x 2. 75 inch and 12 x 6 inch Conflat flanges facing radially, al