List of GTS Ghost Beam Experiments - 3/11/19

1. Measuring Ions Between the Anode and GS
• Purpose: To determine whether there are trapped ions between the anode and GS - i.e. are there ions present in the accelerator after an electron beam run?
• Theoretical Prediction: Ions can be trapped between the anode and GS while the anode is biased positively and the GS is on. This has been shown in GPT. If the anode is turned off, then the ions will see the large negative potential at the cathode and will accelerate towards it. When the ions hit the cathode, we can measure the ion current, which will give us an idea of how many ions are within the anode-GS trap.
• Experiment Details:
1. Run 100-500uA electron beam for a fixed amount of time with GHV=100kV, GS=150A and anode biased at 1kV...enough to produce a visible ghost beam on viewer 2.
2. Turn off real electron beam
3. With the GHV and GS on, turn anode bias down to zero - if ions are trapped between the anode and GS, they will move towards the cathode.
4. Measure current on cathode via an ammeter. If this is not possible, then we can measure current on the anode via an ammeter.
• Null Hypothesis: No current reading on cathode/anode - no trapped ions between anode and GS
• Duration of Experiment: 1-2 hours (max), several trials to ensure good data if we are able to get a current reading
• Setup/Equipment Needed: Need to be able to measure current on either cathode or anode - perhaps we can connect an ammeter in series with either the cathode or anode?
2. Measuring Ions Within the Solenoid Lenses
• Purpose: Provided the previous experiment is successful, to determine whether there are ions trapped within the solenoid lenses
• Theoretical Prediction: GPT predicts that more ions are trapped within the solenoid lenses (via the magnetic mirror effect) than between the anode and GS. When the GS is turned off, any ions trapped within the solenoid lenses will then be free to move in any direction. Some will travel upstream and then reflect off of the anode bias. Some will hit the beamline and be lost. But some will travel downstream and hit the ion precipitator. Thus, any current reading on the ion precipitator after the electron beam is turned off and the GS is turned off would imply that we are measuring trapped ions from the solenoid lenses.
• Experiment Details:
1. Run 100-500uA electron beam for a fixed amount of time with GHV=100kV, GS=150A and anode biased at 1kV...enough to produce a visible ghost beam on viewer 2.
2. Turn off real electron beam
3. With the GHV and anode bias on, turn GS current down to 0A - if ions are trapped within the GS, some will move downstream towards the ion precipitator.
4. Measure current on the ion precipitator
• Null Hypothesis: No current reading on ion precipitator - no ions trapped within the solenoid lenses.
• Duration of Experiment: 1-2 hours (max), several trials to ensure good data if we are able to get a current reading.
• Setup/Equipment Needed: Need to be able to bias one electrode of ion precipitator negatively (the other electrode will be grounded) and measure any current on it.
3. Measuring Trapped Ion Density as a Function of...
• Purpose Provided the previous two experiments are successful at measuring ions within the predicted traps, to systematically determine how tuning different parameters affects the trapped ion concentrations or "trap density"
• Experiment Details
1. Trap density as a function of electron beam current and duration
1. Run 100uA electron beam for a 5 minutes
2. Turn off real electron beam
3. Confirm that ghost beam is present on viewer 1
4. Keeping the gun HV and GS on, turn off anode bias and measure ion current on cathode via an ammeter
5. Repeat i-iv for 10, 15, and 20 minutes
6. Repeat i-iv for 250uA, 500uA, 750uA and 1mA electron beam current
7. Repeat i-vi, but turn off GS instead of the anode and measure ion current on the ion precipitator