Types of data produced
Data acquired at the facility include digitized signals from Langmuir probes, magnetic probes, emissive probes, interferometers, spectrometers and other diagnostics as well as fast-framing camera movies of visible light emission. As time goes by and different types of data come into use, the facility will find ways to accommodate them. Data are organized by experimental run, typically centered on obtaining a 1D or 2D spatial profile of plasma parameters by moving a single or multiple probes, from shot-to-shot. Volumetric data can be assembled from multiple two-dimensional data sets.
Standards used for data/metadata format and content
Data from individual experimental runs are stored in HDF5 files. Details on the Hierarchical Data Format, its many benefits, as well as examples programs, tools, and free software are available from the HDF Group (link to http://www.hdfgroup.org/). The choice of HDF5 makes data taken at the BAPSF more accessible to user groups in fields ranging from fusion science, to space physics, to the plasma processing industry, and beyond.
Metadata that describe the basic operational state of the LAPD are stored automatically for each experimental run. These include time series of the plasma source current, voltage, and microwave interferometer traces; axial magnetic field profile; chamber fill pressure; Residual Gas Analysis, etc. Due to the highly dynamic and flexible nature of experiments at the BaPSF, it is the responsibility of individual users to fully document each channel of time series data acquired. Such information may include dimensions of custom-built probes, calibrations, external circuit diagrams, and gain/attenuation settings.
Policies for access and sharing
The leader/PI of an experimental campaign on LAPD receives all data and has exclusive use of the data for analysis and publication.
Policies and provision for re-use
Currently, re-use of data from the BAPSF is at the discretion of the leader/PI of the experimental campaign, and it is their responsibility to maintain compliance with the policies regarding data re-use by their original funding agency or agencies. A PI’s data is not made available to the plasma physics community without their permission.
Copies of HDF5 data files generated by users of the facility are kept for a period of at least three years. These files are stored on RAID arrays with disk-to-disk backup. In the future we will explore other means of data storage such as cloud-based storage and archiving services. Copies of the archived data are available upon request by the user group that originally generated the data.
A second cathode source is insertable from the opposite end of the device. This source is a 20x20cm lanthanum hexaboride (LaB6) cathode-anode system and can be pulsed independently from the larger source. The advantage of the the LaB6-generated plasma is that the emissivity of the cathode is much higher and can produce higher plasma densities (approximately 5x10^13/cm^3).
The LAPD main discharge is controlled by a digital clock and transistor switch capable of 8000 amperes of pulsed current. The discharge may be controlled by the computers in our data acquisition system. The clock circuits include timing pulses which fan out to trigger additional circuits and the analog to digital converters in the data acquisition system. The plasma is pulsed at one Hz to allow for efficient signal averaging and data processing.
Plasma diagnostics include magnetic pickup loops, electric dipole probes, and Langmuir probes for measurement of B(r,t), E(r,t),n(r,t), Te(r,t), laser induced fluorescence for measurements of the ion distribution function f_i(r,v,t) (in Ar) and four 60 GHz interferometers for measurement of chord-averaged plasma density at various axial locations.