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UCLA's LArge Plasma Device

The LArge Plasma Device (LAPD) is the main experimental device at UCLA's Basic Plasma Science Facility (BAPSF). LAPD is an 18 m long, 1 m diameter cylindrical vacuum chamber, surrounded by 90 magnetic field coils. Plasmas are generated using a DC discharge. To produce the discharge, a large area (0.75 m diameter) heated barium oxide coated nickel cathode is used along with a molybdenum mesh anode (0.55 m away). A 4 F capacitor bank is connected between the anode and cathode and is used to generate a discharge current of up to 20 kA using a set of high-power IGBT switches. Uniform magnetized plasmas are created in LAPD with a repetition rate of 1 Hz and pulse lengths of 1-10 ms. Magnetic field strengths of 200 G to 4 kG are achievable in LAPD. The available working gases include helium, neon, argon, and hydrogen. While the parameter regime is not directly fusion relevant, incredibly detailed measurements can be made in LAPD. This allows us to significantly challenge the predictive capability of simulation codes and ultimately to advance our theoretical understanding of the basic plasma physics underlying important phenomena in fusion reactors.

The machine has excellent access for probes and optics. There are 450 radial ports; 64 of which are rectangular, allowing a nearly 360 degree view of the plasma in 8 locations along the machine length. There are sixty rotatable "ball valve" flanges, which allow probe placement anywhere in the plasma volume between two axial field magnets. Two portable cryopump vacuum stations allow for evacuation of interlocks attached to these valves so that probes can be moved in and out of the system without breaking vacuum. The machine is outfitted with several computer controlled stepping motors, which can move probes with submillimeter accuracy throughout the plasma volume. Large probes and antennas can be introduced through the rectangular ports at seven locations using custom-built square valves and two additional cryopumps. Data is acquired with 12 channels of 8 bit, 5 GS/s digitizers, and 32 channels of 14-bit, 100 MS/s digitizers which are optically coupled to the data acquisition system. Eight channels of 80 MHz analog optical coupling are available for signal transport. Diagnostics include a 56 GHz microwave interferometer for line-integrated density measurements. Optical diagnostics include laser-induced-fluorescence for measurement of ion temperatures and drifts using a 500 kHz bandwidth low power (1 W) ring laser and a large (1 GHz) bandwidth 15 MW pulsed dye laser. The lab has a 150 MW (7 ns Gaussian pulse) Nd-Yag laser with a 1 Hz repetition rate for production of dense plasmas within the background cathode-produced plasma. For 20 kHz-200 MHz wave launching, the laboratory has two high power (2.5 kW) amplifiers and a handmade 20 kW tuned RF amplifier. A 250 kW pulsed source is available to launch high frequency (8.5-9.5 GHz) waves. The lab also has two arbitrary waveform generators, several high quality digital oscilloscopes, a spectrum analyzer, a network analyzer, a 10 ns image intensified digital camera, and several monitor scopes. The LAPD device is housed in the Science and Technology Research building at UCLA. The building was constructed to support large experiments and has 15 MW of power available to experiments. The building network is connected to the campus by a fiber based ATM network.

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