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Laboratory for X-Ray Microimaging and Bioinformatics
 
 
Prometheus Troubleshooting Manual
 
TING MANUAL
 
  1. Low Energy 
  2. Low X-Ray Flux 
  3. No X-Ray Flux
  4. Multiple discharges on thyratron 
  5. Multiple X-Ray pulses per trigger pulse 
  6. Discharge has streamers 
  7. H.V. enable external interlock light is not on 
  8. Filament ready light will turn on
  9. Circuit breaker on M04 keeps tripping 
  10. Only one bank of thyratrons fires 
  11. One rail gap does not fire 
  12. Circuit breakers on thyratron banks keep tripping 
  13. Blowing fuses in MO
 
I. Low Energy
A. Good ASE
Things to check:
  1. There is SF6 gas pressure in the rail gaps
    Make sure the SF6 gas cylinder is not empty and that the tank and the regulator valves are open. The SF6 gas pressure gauge on the control rack should now read ~ 40 psi.

  2. The seed pulse has adequate energy
    Measure the 248nm energy of the seed pulse after the vacuum spatial filter after the excimer. If the energy is less than 100 J then check the seed pulse.

  3. The seed pulse is correctly timed with Prometheus
    Look at the Prometheus photodiode on the digital scope.
    Make sure the setup on the scope is setup 9. See if the seed pulse is riding on top Prometheus ASE.

  4. The seed pulse has good energy when Prometheus fires
    Look at the 248nm energy of the seed pulse coming through the vacuum spatial filter after the excimer. Make sure that there is no consistent drop in this energy when Prometheus fires. This checks to see if there is noise
B. Bad ASE Things to check:
  1. Both thyratron banks are firing
    Look to see that every thyratron in both banks flashes when Prometheus fires.

  2. Railgaps are firing
    Look through the four windows in the HV enclosure doors to see that each one of the railgaps fires.

  3. Gas mix
    Change the gas if it is old.
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II. Low X-ray flux (as measured with the x-ray detector)
Things to check:
  1. X-ray voltage reading on high voltage control unit meter
    The voltage on this meter should be charging to ~ 145 kV.

  2. Relative timing between anode and cathode monitor
    If the relative timing is off, the x-ray flux will suffer. Look at both the anode monitor and the cathode monitor on the scope at the same time. Trigger the scope sweep off of the rising edge of the anode waveform.

  3. Anode monitor waveform

  4. Cathode monitor waveform
Possible causes: Spark gap boards need to be cleaned
Top
III. No X-ray flux
Things to check:
  1. Thyratron in an oil tank is firing
    If the thyratron is getting a trigger signal, you should be able to hear the thyratron click when it fires.

  2. 30 kV power pack in x-ray power supply oil tank
    Check the output with a high voltage probe and a scope. The voltage should be a 30 kV DC source.

  3. Broken connections on thyratron anode
    Drain the oil out of the x-ray high voltagepower supply tank and check all of the connections to make sure that there are not any loose connections.

  4. Broken connections on pulse transformer
    Make sure that the output from the secondary of the transformer to the x-ray gun anode is still connected.
Top
IV. Multiple discharges on thyratron bank
Possible causes:
  1. Loose connections on thyratrons
    Make sure that the screw connections on the thyratron anodes have not come loose.

  2. One or more thyratrons are bad
Top
V. Multiple X-ray pulses per trigger pulse
Possible causes:
  1. Inappropriate heater and reservoir voltages on thyratron.
    This should only affect the jitter of the x-ray emission relative the trigger pulse. One can adjust these voltages in the x-ray anode thyratron heater and reservoir power supply unit.

  2. Bad HY3202 thyratron
    Look at the trigger waveforms to the thyratron.

  3. Bad timing board in the X-ray thyratron power supply.
    Swap this board with a space and see if problem disappears.
Top
VI. Discharge has streamers
Things to check:
  1. There is SF6 gas flow to rail gaps
    Make sure the SF6 supply valve at the rail gaps control rack is open. Make sure the SF6 gas cylinder is not empty and that the tank and the regulator valves are open. The SF gas pressure gauge on the control rack should now read ~40 psi.

  2. X-ray flux
    Check the x-ray flux with the x-ray meter and compare these readings with the ones in the Prometheus notebook.

  3. Rail gaps are working properly
    Make sure that all of the rails fire on every shot.

  4. Timing between anode and cathode is optimum
    If the relative timing is off, the x-ray flux will suffer. Look at both the anode monitor and the cathode monitor on the scope at the same time. Trigger the scope sweep off of the rising edge of the anode waveform.

  5. Timing between anode and modulators is close
    If the relative timing is off, the laser will try to discharge through the gas without the gas being sufficiently ionized. Trigger the scope off the rising edge of the x-ray anode monitor (Amon). The falling edge of the modulator monitor (NDO) should occur near the peak of the anode waveform. One can change the timing by changing the delay on channel D of the Stanford digital delay box. One can optimize this timing by looking at the ASE only from Prometheus and scan channel D on the Stanford digital delay box to maximize the ASE pulse.
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VII. H.V enable ext. interlock light is not on
Possible causes:
  1. Timing module in timing rack is out of sync
    Make sure that the Ti: Sapphire oscillator is modelocked. Press the button on pulse frequency divider #3 box until the lasers are synchronized (the green LED on the sync box turns on).
Top
VIII. H.V enable ext. interlock light is not on
Possible causes:
  1. Filament switch on control unit is not on
    Make sure this toggle switch is on (the up position).

  2. Circuit breaker on M04 has been tripped
    M04 is on the northeastern part of the top of Prometheus. The circuit breaker consists of three circuit breakers tied together (one for each phase of 120VAC). Make sure this circuit breaker is in the up position.

Things to check:
  1. FVoltage meter on M04 front panel
    M04 is on the northeastern part of the top of Prometheus. There is an aluminum box with an ammeter readings match the numbers printed on the aluminum box.
Top
IX. Circuit breaker on M04 keeps tripping
Possible causes:
  1. bad high current diode
    Check each of the six high current diodes to see if one is shorted out or open.
Top
X. Only one bank of thyratrons fires
Possible causes:
  1. No trigger signal
    Check to make sure there is a +15v trigger signal going to the thyratron banks.

  2. Small thyratron is bad (not switching)
    Check to see if the small thyratron banks fires (flashes) when the thyratron bank is triggered.

  3. No switching voltage
    Check the 15kV power pack in each bank with a high voltage probe and scope to make sure that there is 15kv DC.

  4. The resistor from the anode of the small thyratron to the power pack is open
    Check the resistance of the 1M pencil resistor. Also, make sue that the capacitors are not shorted internally or leaking oil.
Top
XI. One rail gap does not fire
Possible causes:
  1. Silicon oil contamination inside rail gap
    There might be silicon oil inside of the rail gap box. You need to empty the oil out of the HV enclosure and lower the doors to be able to check this for sure.

  2. HV cable is not delivering voltage to the rail gap
    For this procedure you need to empty the oil out of the HV enclosure and lower the doors. Then put a grounding stick near (~5mm) the place where the HV cable connects to the gaps. Fire the rail gaps. The idea is that if the trigger pulse arcs from the cable to the grounding stick, the cable is OK.
Top
XII. Circuit breakers on thyratron banks keep tripping
Possible causes:
  1. The HV DC power pack is bad
    Check the 15kV power pack in each bank with a high voltage probe and scope to make sure that there is 15kv DC.

  2. The resistors or capacitors connected to the power pack are bad
    Check the resistance of the 1M pencil resistor. Also, make sure that the capacitors are not shorted internally or leaking oil.
Top
XIII. Blowing fuses in MOO (primarily the middle fuse)
Possible causes:
  1. The charging current to the modulator power supply is too large.
    Check the charging current through the M03 transformer. This should be ~40 Amps, certainly less than 50 Amps. The clamp-on ammeter should show relatively smooth current draw, not one or two large jumps.
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