Wednesday, February 07, 2018, 08:40: A 75 kV Glassman power supply was installed in the rack for use in further HV testing.

-The 75kV power supply is linked into the keyed interlock system. The key & switch labelled BIAS/EZL will unlock it.

-The PS is currently not connected to the epics controls and can only be adjusted manually.

-The old Glassman supply is disconnected and removed from the cage.

The 75kV power supply is now in EPICS under the usual TSG:BIAS controls. The upper limit has been set to 70kV to protect the transformer.

Thursday, February 08, 2018, 16:54

Testing the HV bias I found that the einzel lens was behaving strangely. When I tried to put it higher than 1kV, the current would start spiking from 12uA to > 100uA. The voltage would jump around quite a bit as well (+/- 100V). Everything seems the way it was before, except the EZL power supply is still connected in parallel with the old bias power supply, which is no longer powered. Maybe one of the transorbs connecting line and neutral on the bias side is fried? I will unhook the connection to the old PSU and try again.

Friday, February 09, 2018, 08:25    Disconnected the AC power chain from the old bias supply but now cannot turn on the new bias supply in EPICS because the "TSGBIASSAFETY ok" interlock is tripped. No idea what this means - maybe it checks for AC power?

Friday, February 09, 2018, 08:48    Reconnected power to old bias supply, does not fix problem. Talked to Mike, he thinks it is PLC related, so will call Gelo later.

Friday, February 09, 2018, 11:38 TSGBIASSAFETY ok interlock problem seems to have solved itself, it now appears to be working fine. Will turn off power for now and continue tests on Tuesday. (note: turns out Mike told Dave about the problem and he solved it. No one knows what this interlock is for, but it used to be reset using the Global Reset button and now the RST button for the power supply should also reset it.)

Ramped up to 60kV with the new power supply, same as what we did last time with the standard test stand bias supply (see entry #627 ). Much more instability on the bias current readout (see attached screen shot), develops around 54kV. As well, the old supply read out 37uA at 60kV while the new supply reads out ~85uA. This could just be an EPICS read back issue though.

Sparks at 62kV on the bias.

Turned it down, turned it back up and got a spark at 60kV.

Now up to 63kV, no sparks so far (5 mins). Left EE @ -3100V and EZL @ 28.5kV

There is the sound of a low level continuous discharge, like HV power lines, and a very strong ozone smell coming from the HV duct that sticks into the cage and carries the cables from the HV rack. Also seems to be present near the EE insulating standoff. Can't see anything though. Maybe just moisture in the air? Starts at 55kV on the bias, does not change with EE voltage.

Turned EZL up to 29kV, bias stable at 63kV for 11mins.

Sparks at 63.6kV in the EE spark gap, EE @ -3.1kV.

I vacuumed inside the HV cage, though it has many small areas that are difficult to access so I am not sure how great a job I did.

Turned the bias up and again at 55kV I hear small sparks near the end of the HV duct that brings the cables from the rack. Cannot see anything. If it is really sparking where it sounds like sparking, it must be from the edge of the duct to the faraday cage.

Changing the EZL voltage and the EE voltage has no effect on where it starts sparking.

Found TMSTP6 off, restarted it, seems fine now (drawing 0.8A)

The test stand holds up to 63kV, however at voltages over 54kV there are small discharges, rising to a continuous level around 60kV. The best guess right now is that these are coronal discharges coming from the end of the HV duct to the faraday cage. The only way to fix this would be to round out the edges of the duct, or to move the duct farther away. Since I have heard small discharges in other places, we may need to make a variety of modifications. Things that have had no effect:

1. Changing the EZL/EE voltages - break down is happening only between HV bias and ground

2. Cleaning the faraday cage

3. Locating sparks with a thermal camera

4. Conditioning - break down always happens at the same point

Tuesday, February 20, 2018, 09:01: Sparks at 62.5kV after a couple minutes. Sounds like they were in the EE spark gap but don't appear on the EE read current. Ozone smell around 61kV, so there are still some discharges.

Turned back up to 62.5kV but no sparks. Put it up to 63.5kV and there was a spark, but not in the EE spark gap as expected. Took down TP1B but everything is back up and seems fine.

Friday, February 23, 2018, 08:50

Friday, February 23, 2018, 08:53: BIAS / EZL / EE @ 62.5 / 29 / -1 kV

Friday, February 23, 2018, 08:56: Spark* Turbo pump TMS:TP6 restarted,

Friday, February 23, 2018, 09:13: Bias sitting at 61kV for about 15mins now. Still corona discharges from the area of the EE, but the area of the duct seems fine.

1. Al corona shield installed over end of the HV duct to suppress discharges from the sharp edge of the duct.

2. Some moving and shortening of cables to keep them from running close to different voltages.

3. Changed the angle bracket on the 3M bias-EE resistor chain to a plate, same position.

4. Moved the 164K EE resistor chain to sit flat against feedthrough K.

5. Moved the bias-EE spark gap to sit flat against the back of feedthrough K, required tapping a hole in the back of the copper clamp.

6. Cap and top of rack vacuumed.

7. Piece of shielding removed from top of HV rack

New parts installed. Corona Shield, brackets, and board/spark gap orientation.

Wednesday, February 28, 2018, 11:48: Power on. Ready to test

Wednesday, February 28, 2018, 14:00: BIAS / EZL / EE @ 30 / 13 / 1.5 kV

Wednesday, February 28, 2018, 14:06: BIAS / EZL / EE @ 40 / 17 / 2.0 kV

Wednesday, February 28, 2018, 14:11: BIAS / EZL / EE @ 55 / 24 / 2.8 kV

Wednesday, February 28, 2018, 14:16: BIAS / EZL / EE @ 60 / 28 / 3.1 kV

Wednesday, February 28, 2018, 14:18: BIAS / EZL / EE @ 62 / 30 / 3.2 kV

Wednesday, February 28, 2018, 14:21: BIAS / EZL / EE @ 63 / 31 / 3.2 kV

Wednesday, February 28, 2018, 14:26: BIAS / EZL / EE @ 65 / 32.5 / 3.2 kV

Wednesday, February 28, 2018, 14:32: BIAS / EZL / EE @ 66 / 33 / 3.3 kV

Wednesday, February 28, 2018, 14:35: BIAS / EZL / EE @ 66.5 / 33.5 / 3.3 kV ***2 sparks***

Wednesday, February 28, 2018, 14:37: BIAS / EZL / EE @ 66 / 33 / 3.3 kV

Wednesday, February 28, 2018, 14:41: BIAS / EZL / EE @ 66.5 / 33 / 3.3 kV

Wednesday, February 28, 2018, 14:44: BIAS / EZL / EE @ 67 / 33 / 3.3 kV

Wednesday, February 28, 2018, 14:47: BIAS / EZL / EE @ 68 / 33 / 3.3 kV

Wednesday, February 28, 2018, 14:49: BIAS / EZL / EE @ 68.75 / 33 / 3.3 kV ***Spark***

Wednesday, February 28, 2018, 14:51: BIAS / EZL / EE @ 68 / 33 / 3.3 kV

Wednesday, February 28, 2018, 14:57: *** 2 sparks ***

The BIAS was pushed to 69 kV however the resulting sparks shut down the communications with the test stand computer.

RPM0B was put into a continuous running cycle and had to be shut off manually.

The voltage was brought back down remotely via a separate computer. Turbo pump TMS : TP2 was also restarted.

Turning up bias, no corona discharge at 60kV but a spark at 61.5kV bias, 31kV EZL, -800V EE

Thursday, March 01, 2018, 10:26: BIAS / EZL / EE @ 65 / 32.5 / 3.2 kV

Thursday, March 01, 2018, 10:32: Spark* Knocked out turbo pump TMS : TP6 (Restarted) Communications restarted. RPM0A restarted.

Thursday, March 01, 2018, 10:44: BIAS / EZL / EE @ 61 / 30.5 / 3.1 kV

I have removed the resistor/varistor combinations that go between the poles of the target and tube heaters, and between those two supplies. I tested all the components to make sure they were still working after the sparks - for the record the varistors clamp at 23V, not 33V as implied by the schematic.

Tuesday, March 06, 2018, 10:48  BIAS/EE/EZL = 59.5/-1000/29.5  There was some kind of spark, the current on the bias supply went up to 400uA ( normally at 40 +/- 5 ) and the vacuum jumped a bit ( but still in the 10e-7 range ) but I didn't hear anything. It took out TP6 again. See first attachment.

Tuesday, March 06, 2018, 10:54  BIAS/EE/EZL = 60/-1/30

...

Problems

...

Tuesday, March 06, 2018, 12:00 BIAS/EE/EZL = 60/-1.5/29

Tuesday, March 06, 2018, 12:37 BIAS/EE/EZL = 62/-1.5/30

Tuesday, March 06, 2018, 14:11 BIAS/EE/EZL = 64/-1.5/31 No sparks but occasional ticking sounds from either the EZL or behind where the EE is... see second screenshot

Tuesday, March 06, 2018, 14:40 BIAS/EE/EZL = 65/-1.5/33

Test stand has been sitting at 65kV for about an hour now. Some small increases in bias power supply current but nothing significant (40uA). Some small sparks on the way to this voltage, and I ramped up very slowly. The corona discharges seen before seem to be related to the resistor/varistor combos since there are none now that I have removed them. Will redesign and reinstall.

The resistor/varistor combinations across the target + / -, tube + / - and target- / tube + have been remade and moved to the back of the power supplies to limit the corona discharges at higher voltages. Pictures attached.

First attachment: BIAS/EE/EZL = 63.25/-1.5/31 So far no issues.

Second attachment: BIAS/EE/EZL = 64.25/-1.5/32 Slight spark - bias current jumped from 40uA to 88uA and vacuum jumped from 2e-7 to 2e-6... Steerers went off.

Third attachment: BIAS/EE/EZL = 65/-1.5/32  Some small signs of instability in the bias power supply

Fourth attachment :  BIAS/EE/EZL = 65/-1.5/32  Been running for 20 mins now. More variation on the bias current output than at lower voltages but not too bad

Monday, March 12, 2018, 09:45: Gas lines opened. Leak rate set. Vacuum @ 1.16e-06T

Monday, March 12, 2018, 10:00: RGA on

Monday, March 12, 2018, 10:07: RGA off. Manually shut off power as well

Pressure:

Ramping up:

• Second attachment - bias at 50kV
• Third attachment - bias at 60kV
• Fourth attachment - bias at 65kV

Pressure has been slowly falling since we started this test - now down to 8.7e-7

Spark after 10 mins, see attachment 5. Very slight vacuum jump (8.5e-7 -> 1.2e-6) and bias current jump (36uA -> 113uA). Tripped TP6 and the steerers, as usual. Bias current read back more erratic afterwards (see sixth attachment).

System has been stable for 20mins, though current on bias is still more erratic than before the spark. Increasing He leak rate from 7 to 7.06 to bring vacuum back up to 2e-6 (see attachment 7). No effect from increased pressure.

Tuesday, March 13, 2018, 05:52: Power off.

Tuesday, March 13, 2018, 05:56: Waterlines purged

Tuesday, March 13, 2018, 05:57: Ion gauge, Turbos off.

Tuesday, March 13, 2018, 08:50: Roughing.

Tuesday, March 13, 2018, 09:10: Turbo Pumps started.

Tuesday, March 13, 2018, 09:15: Ion gauge on.

Tuesday, March 13, 2018, 10:17: RGA started.

Tuesday, March 13, 2018, 13:15: Check Vacuum @ 6.56e-07T

Wednesday, March 14, 2018, 07:27: Waterlines opened. No response on RGA. Vacuum ok @ 2.69e-07T

Wednesday, March 14, 2018, 07:30: Power/sources on.

Wednesday, March 14, 2018, 07:35: Auto ramping TGHT to 580 A @ 2A per min.

Wednesday, March 14, 2018, 13:18: Vacuum ok @ 5.48e-07T

 Wednesday, March 14, 2018, 13:29: BIAS/EZL/EE to 30 / 13.5 / 1.5 kV.

BIAS current: 40uA

EZL current: 49uA

EE current: 518uA

Thursday, March 15, 2018, 08:00: Check, Vacuum @ 4.76e-07T

Thursday, March 15, 2018, 13:19: Check, Vacuum @ 4.65e-07T

Thursday, March 15, 2018, 15:13: Started cool down. Vacuum at 4.76e-7 by AM

Friday, March 16, 2018, 06:24: Power/sources off.

Friday, March 16, 2018, 06:27: Waterlines purged

Friday, March 16, 2018, 06:28: RGA, ion gauge, and turbos off.

Friday, March 16, 2018, 07:57: Venting.