Facility overview
The Basic Plasma Science Facility was born in August of 2001. Its mission is to host plasma physicists from all over the world to attack some of the leading and most difficult problems in the field. The facility is housed at UCLA and uses a highly reproducible, magnetized plasma source which was completed in the summer of 2001. The machine, its diagnostics and how to become a user are all described on this website.
The Large Plasma Device (LAPD) is a flexible and low maintenance device for studying a variety of waves and nonlinear effects in fully magnetized plasmas. The plasma column is 60 cm in diameter and 20 meters in length. With 450 6" circular ports, 64 large rectangular ports, and a dozen end ports, the machine has abundant access for probes and antennas. The vacuum chambers are surrounded by 56 electromagnets magnets spaced 32cm apart. Coil construction, consisting of winding, brazing and epoxying the heavy gauge, Oxygen-free Copper, was carried out by our group at UCLA. Each magnet weighs approximately 1/2 ton. The magnets are driven by 11 DC power supplies each rated at 60 Volts, 3000 amps. The magnets are cooled with deionized water from a large (342 GPM) cooling tower, and get their power from a private electrical substation. Both the cooling tower and substation were provided by UCLA in support of this project. The magnetic field can be programmed to be highly uniform along the length of the device or, since the coils are powered by eleven independent supplies, there is an option for magnetic mirrors or a number of field profiles. A link to the 2016 RSI article describing the latest updates and capabilities of the device can be found here: https://aip.scitation.org/doi/10.1063/1.4941079.
The vacuum system is centered around four 1500 liter/sec turbo pumps which produce a base pressure of 5x10^-7 Torr. The pumps are magnetically shielded to allow operation close to the high fringing field of the device magnets. The pumps are controlled by a Vacuum Process controller which automatically performs valve sequencing and other protective functions as the system pressure changes. The controller can also shut down the entire device in the event of vacuum failure. The machine is protected by additional circuitry from loss of coolant to the cathode or power supplies, and power outages. Each turbo pump is backed by a 17.7 cfm mechanical pump. Gas may be fed into the system at several locations along its axis to allow for the production of axial density gradients in the plasma. The vacuum conditions and gas introduced to the system are constantly monitored by a quadrupole mass analyzer.
The plasma is produced by a DC discharge driven by an oxide coated cathode. This type of plasma (H, He, Ne, Ar, Xe, or any mixture) has been proven to be quiescent (core dn/n = 1 %), can be moderately high in density (n < 4x10^12 /cm^3) and, recently, high power discharges have been utilized to produce very highly ionized plasmas of hydrogen or helium. It is important for research plasmas to be stable over long data runs. In wave experiments, one must be able to launch low amplitude waves and map out their dispersion and ray trajectories before moving on to nonlinear or turbulent experiments. Cathode sources are stable for long periods of time (about 4 months ) and produce plasma discharges which are very reproducible from shot to shot.
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.