Probe Group Project

 

Submission to the New Journal of Student Research Abstracts

Building a Probe Drive for a Plasma Device

Roland Hwang, Max Praglin (The Buckley School, Sherman Oaks, CA), Evan Warfel (Palisades High, Pacific Palisades, CA), Bob Baker (University High, Los Angeles, CA), Joe Wise (New Roads School, Santa Monica, CA), Walter Gekelman (UCLA)

 

In an effort to more accurately take measurements with a Langmuir probe, students at the LAPTAG high school plasma physics lab designed and machined a probe drive with a computer monitored control system. The drive is mounted on top of a movable cart with adjustable height having shelves for a computer, control box, and monitor. The probe drive is designed with two movable parts, a rotational axis for turning the probe while inside the plasma device and a horizontal axis for moving the probe in and out of the machine. The horizontal axis consists of a worm gear set upon base blocks at each end with a motor attached in the back. The worm gear moves the cart at 0.5 cm per turn, with the motor turning at increments of 1.8 degrees (.0314 radians), thus giving the possibility of 0.0025 cm steps in and out of the plasma machine. The rotational motor, mounted with the probe atop the cart, provides an accuracy of 0.045 degree turns because of our 40:1 step converter attached from the motor to the probe. Although using a pre-fabricated worm gear and carriage, the students designed and fabricated the system to allow for horizontal and rotational control by machining various gear systems, mounting blocks and plates for the motors and gears, anti-vibration rubber gaskets, and stabilizing wheels for the carriage’s precise movements. To control this drive, students built a control/circuit box consisting of two speed controls that determine how fast or how long each motor runs. Students wired a 68 to 25 pin converter so that wires within the box can be connected to a computer - two sets of wires run from the box, one to each motor and the other to the adjustable limit switches placed to stop the drive to prevent the cart or probe from moving too far in any one direction. (The limit switches are adjustable so that any size or shaped probe can be placed on the drive without having to machine completely new parts.) The control box provides all the power to both the speed controls and the motors - the motors require roughly 0.9 amps of current and 20-25 volts. Students use LabVIEW, a measurement and automation controller software by National Instruments, to change the speeds, velocities, and accelerations of the motors. Using LabVIEW with the oscilloscope, students take data with Langmuir probes at precise intervals inside the machine so that they know, when interpreting data, at what position within the plasma certain phenomena, such as Electron Bernstein waves, occur.

Group members

• Roland Hwang (email)-class of 2009

  

   

• Max  Praglin (email) -class of 2010
•  

• Evan Warfel -class of 2009
•  

Meetings

When should we meet?

Photos

Machining the Probe Drive Track

Probe Shaft Mounted on Rotational Motor                                                                          Top View of Probe

Plasma Machine with Probe Drive in Construction          Measuring the Wormgear

(From the Left): Bob Baker, Prof. Walter Gekelman, Max Praglin

Circuit Box to Control Motors                                                                                         Building the Circuit Box     

(From the Left): Evan Warfel, Roland Hwang, Max Praglin