2. Beam Properties
1. Measured Gas pulse duration:
Gas pulse width depends on the amplitude of the drive current, the mass and the viscosity of the gas being used.
Time is given in microseconds from the valve trigger pulse.
2. Angular beam distribution:
Relative angular beam distribution of Helium expanding from a sonic (pinhole) and a conical (angle 40°) nozzle. The valve was kept at room temperature, stagnation pressure was 100 bar. Notice the forward beam intensity enhancement for our 40 degrees (full angle) conical nozzle. The photo on the right shows the glow from a Neon beam after being electronically excited inside the nozzle (Dielectric Barrier Excitation, explained later).
3. Kinetic energy distribution for various gases:
Measured kinetic energy distribution for several gasses expanding from a conical nozzle.
Ideal gas approximation should result in an almost vertical line. Helium and Neon are good approximation. Departure from ideal gas behavior is for heavier gasses is due to cluster formation. Narrow energy distribution results in a colder beam temperature.
4. Temperature dependence of the Terminal velocity of the beam:
Measured beam velocity for the Noble gases as a function of valve temperature. For the heavier gases the low beam velocity usually is accompanied by heavy cluster formation.
5. Measure beam temperature in the beam:
Speed ratio (Mach number) and translation temperature for various gasses from a room temperature nozzle at 90 bars. While temperatures of 0.1K are achieved for Helium expansions, much higher temperature are achieved for the heavier gasses, as a result of extensive clustering.
6. Cluster formation efficiency at reduced nozzle temperatures:
Lase scattered light was used to monitor the formation of large clusters (nano droplets) in the beam. While Helium required low temperatures (20K), Argon forms clusters already at room temperature.
