6. Excitation Source (DBD)
We developed an excitation discharge source to create very cold plasma at the nozzle itself.
The source creates a discharge through a Dielectric Barrier in the gas. This discharge creates intense population of both positive and negative ions, together with meta-stable carrier gas atoms and excited molecular species. The self limiting discharge prevents the heating of the gas pulse. The following are some measured examples:
1. Intense meta stable source of noble gases:
Side and front views
An excited meta stable Neon beam created inside the nozzle by our discharge source. The beam contains 5*10^9 excited atoms (after the skimmer) moving at almost uniform speed (Mach number of ~100). The plasma translation temperature is less than 0.1K.
Adding a carbon fiber brush (pre-ioizer) reduced the reuired voltage to start the DBD discharge and contributes to the longevity and stabilty of the discharge. The pre-ionizer is biased at a negative DC of 300-800V to emit low current (few na).
DBD source assembled on unmounted Room Temperature Valve.
The front flange containing the DBD is compatible with all our flanges.
A dedicated high voltage RF burst generator is required to operate the discharge. This driver unit is PC software controlled through a USB port.
Performance:
Meta-stable caused current collected on a plate that is placed after the skimmer at 200mm distance from the valve.
The soft excitation (collision with meta stable atoms) is also reflected in intense cluster ions beams. Since the excitation occurs inside the nozzle, there are many collisions to create cold ions and ion clusters, of both positive and negative charges.
Positive and negative ammonia cluster ions. Ion current generated by the DBD discharge collected by a TOF mass spectrometer. Notice the presence of large negative ions.
For more details see our paper:
2. Dielectric Barrier Discharge source for supersonic beams.
The DBD source is driven by a High Voltage RF power supply dedicated to it. It is computer controlled through a USB port. Please see the manuals section on the DBD controller.
Assembly instructions:
1. Please test the valve, outside the vacuum system for proper operation, as explained in the valve operating manuals.
2. Please disassemble the front flange of the valve, according to the standard instructions in the manual.
3. Take one new gasket #2-04-200, supplied with the DBD, and place it in the nozzle side, in the depression provided for it. (7.01 mm in the drawing)
4. Re assemble the DBD flange, in the same way that you assemble the standard front flange & nozzle.
5. Please use the 3 long screws the I supplied with the DBD (Longer then of the standard screws).
6. Gently tighten these 3 screws.
7. Now you should rotate and tighten the rear big 18 mm nut, to the end. No force is require for this tightening.
8. Connect the Teflon coated one wire, going out of the DBD- to your High Voltage (SHV) vacuum feed-through. This wire is rated for 18KV.
9. There are 3 cables supplied to connect the valve to the DBD controller: One cable is a HV coaxial cable with two SHV connectors. This is to supply the DBD electrode with the required pulse train to ignite the discharge. One cable is a simple coax cable with two BNC connectors to connect the valve coil to the valve outlet in the controller. One cable is a double shielded USB cable to connect to the computer controlling the driver functioning.
10. Please refer to the DBD instruction in the manuals section for more details on its operation.