PSFC Diborane Discharge Cleaning


Plasma Science and Fusion Center

Office of Environment, Safety, and Health


190 Albany Street, NW21 2nd floor
617-253-8440 (Catherine Fiore)
617-253-8917 (Matt Fulton)
617-253-5982 (Bill Byford)
617-258-5473 (Nancy Masley)
Fax 617-252-1808


Be Safe or Die


Reviewed and Approved By:

PSFC Supervisor--Gary Dekow

PSFC Supervisor--Jim Irby

PSFC Safety Officer--Catherine L. Fiore

Alcator C-Mod

Procedure for Diborane Gas System Discharge Cleaning

Author: Catherine L. Fiore, Chris Reddy, Joe Bosco, Andy Pfeiffer

Version: Version 6.6 Released 6/01/2007 by C. Fiore.

Date: 6/01/2007  Computer filename:  

System: Diborane Gas System

Person responsible: C. Fiore, J.Irby, G. Dekow, A. Pfeiffer

I. Introduction

It has been determined that a possible way to coat the walls of the Alcator C-Mod vacuum vessel with a thin layer of boron is to create a gaseous discharge in diborane gas inside the vacuum vessel. Diborane is highly toxic and flammable, and presents an explosion hazard. The gas delivery system must be of high integrity and leak free. Leak detection and remote control are essential. Procedures for handling, maintenance, process, and emergency response are required, as is training of any personnel directly or peripherally involved with using this material.

II. Required Elements:

A.        Scope/Purpose This document covers the process for running discharge cleaning in Alcator C-Mod using diborane gas and C-Mod Diborane facility.

 

B.        Consequences of procedural failure.

 

Failure to follow this procedure when using the diborane system could result in leakage of diborane gas into the cell or into the diborane housing, which could lead to fire or explosion, or to personnel exposure to toxic gas. Diborane is immediately dangerous to life and health at 40 ppm, and an explosion hazard at 9000 ppm. The exposure which is expected to kill 50% of those exposed is 159 ppm for 15 minutes. Note that the MDA-TLD1 diborane monitors alarm at 0.1ppm but are saturated at 0.3ppm.

 

C.        Definitions

 

MDA-TLD-1-Gas monitor for the diborane system. One is located at the diborane gas cabinet. The other is located near B-port on the igloo, on the first level. A spare unit is normally kept in Catherine Fiore's office, NW21-203.

 

SCBA-Self Contained Breathing Apparatus. Four units are located at the entrance to the C-Mod power room, in the control room.

 

D.       Responsibilities

 

Diborane discharge cleaning should be started and shut down with one of the following people in attendence:

Catherine Fiore,

Andy Pfeiffer,

Gary Dekow,

Sam Pierson

Bill Parkin

Tom Toland

 

Installation and deinstallation of the diborane gas cylinder will be done following the procedure Procedure for Installation/Deinstallation of Diborane Gas. Two persons, trained and approved to wear SCBA, trained in diborane hazards, and trained in all of these procedures will install the diborane gas bottle.

 

These procedures will be reviewed and approved by a committee of no fewer than 3 knowledgeable persons, appointed by the Safety Officer.

 

E.        Required Equipment

 

SCBA must be on hand and in good working order.

 

Welding glove for opening diborane bottle.

 

Three walkie-talkies with good batteries or cell phones.

 

F.        Required Materials

 

 

G.        Assumptions and Prerequisites

 

The PLC system has been installed, completed, and tested.

 

The diborane system has been installed, completed. and tested.

 

All alarms and warning systems have been installed, completed, and tested.

 

A tv camera for remote viewing of the toxic gas cabinet has been installed and is functional.

 

The diborane system test procedure has been completed satisfactorily, and all safety functions are working as designed.

 

The diborane bottle has been installed in the gas cabinet as described in the ``Procedure for Installation/Deinstallationof Diborane Gas.''

 

H. Procedure

Please note: While executing this procedure, please follow the summary check list and have two people initial each step in the check list as they are completed.

NOTE: The next 9 steps can be done at any time prior to the search and lock of the cell. The vacuum system setup (step 9) may be done simultaneously.


1.   Prior to closing the cell, turn off the RGA filament from the RGA PC in the control room.

 

Cell preparations:

The following are in cell preparations which must be done at the upper level:

2.      Turn off the two RGA filament Ametek power supplies.  One is located at H-port horizontal on top of the pumping system and          the other is locaated on top of the Torvac rack.  The Ametek Data logger (located on the middle shelf of the Torvac rac) must              also be turned off.

3.       The gate valves for the machine RGA on H-port right hand and left side must be closed (the handle is kept in the control room) and torqued to 450 inch pounds seal it.

Shutters and gate valves:

At this time, the MSE and two CXRS shutters are under the direct control of Bruce Lipschultz, Bob Granetz and Bill Rowan, and will not be open or shut during setup for boronization.  Make sure that they have closed the shutters.

Go back to step (2) and re-perform steps (2)-(7) for the lower pair of feedthroughs.

4.        OPEN/CLOSE PROCEDURE FOR SHUTTER AT A SIDE This shutter must be OPEN for tokamak discharges, but CLOSED for boronization. It is imperative that it be OPEN during all tokamak discharges. Leaving it closed risks shutting down C-Mod operation and may require manned access into the vessel. Closing the shutter before a boronizaton:

Proceed to the B-port-side of A port. The status of shutter will be given by the red plate velcro'ed to the igloo between A and B ports. The plate says ``A port shutter is... '', with ``OPEN'' or ``CLOSED'' indicated by the appropriate side of the red, velcro'ed plate. It should indicate ``OPEN''.

If the indicator says ``OPEN'', then locate the rotary motion feedthrough located at the bottom left corner of the reentrant A-port-side flange. This feedthrough controls the position of the shutter. It is a Aluminum cylinder about 3.5" long, at the end of which is a knurled knob with a metal-colored locking screw. (Even if the indicator says ``CLOSED'', this position should be verified by executing step 3 and feeling that the knurled head of the rotary motion feedthrough is turned fully clockwise.)

Unscrew the locking screw about one turn to free the feedthrough for rotary motion. It will be difficult to reach your arm into the A side flange area, but do so without damaging the Thomson scattering mirrors or the microwave waveguide. To ``CLOSE'' the shutter, rotate the head of the rotary motion feedthrough approximately 1 full turn CLOCKWISE. If it resists strongly or if you feel that you are using anything more than ``finger strength'', then stop and do not force it. Try to return it to the fully counter-clockwise (OPEN) position. Notify Jim Terry (ext. 3-8637 or at home 323-6597).

Tighten the feedthrough locking screw.

Switch the red plate indicator to show that the A port shutter is ``CLOSED''

 


 

5.       Close the NPA gate valve at F-port top:  The valve is closed manually by rotating fully clockwise. 

 

6.       Start the flow from the vaporizer into the diborane vent work if it is not already flowing.

 

7.       Start the flow from the vaporizer into the vacuum pump outlet by opening ball valve MV5 if it is not already open.  Open the  valve going to the torus roughing pump. The regultor should be set between 5 and 12 PSI.

8.       Verify that MV4(mezzanine level, igloo at AB) is open.


9.       Verify that the lower hybrid wave guide has been pulled back.  This can be done by switching the  encoder from remote to local by flipping the switch up. Check and record that the reading is 1902 (+- 2 counts). Finally return the encoder switch to remote (flip switch down).


10.     Polarimeter:  Verify that the helium tank supplying the polarimeter shutter is above 1000 psi, and that the regulator pressure is at least    15 psi.  Verify that the polarimeter shutter vacuum pump on top of the igloo above k-hor is pumping.  Remove the cover from the          polarimeter mirror housing at k-hor.  Shine in a light and verify that the polarimeter inner wall shutter is closed.


11.     Surface Science Station:  Close the Turbo pump gate valve, then open the manual gatevalve on the beam line for probe insertion.  Set               the N2 purge flow meter on the exhaust of the secondary seal pump to 6-8 SLM to dilute the pump exhaust into the cell exhaust                       system.



 

The following cell preparations are done on the lower level:

12.      Dust injection system:  Close the handvalve at A-port bottom, inner side.   Aaron Bader and Bob Granetz are responsible for this.


13.       Prior to closing the cell, check that the controller unit for the ECDC microwave source has been placed in Analog control mode (center switch on front panel of Lab Power Supply located between D and E port.

 

14.       Prior to closing the cell, check that the camera on the diborane cabinet has a clear view and can be seen on channel 27 in the control room.

 

15.     Verify that manual valves MV1 and MV3 are open. Verify that the diborane regulator (REG1) is set to 30 PSI, the venturi regulator (REG3) is set to 100 PSI, and the helium purge gas regulator (REG2) is set to 30 PSI. PV3 and PV4 and manual valve MV2 will have to be open to set the diborane regulator pressure.

Prepare the Vacuum system and diagnostics

16.         Prepare vacuum system and diagnostics.

 

16.a     Go into the TORVAC PLC. Turn off all filaments specified (IGT, IGP1, IGP2.) Verify that all of the diagnostic gate valves are closed. Close GV3.

 

16.b      Turn off the Ratiomatic (make sure the Ratiomatic has been taken out of Auto mode.)

 

16.c       Close Earl Marmar's K-port shutter from the switch marked Z bolo shutter on Torvac.


16.d      Close the HIREX III gate valve



Prepare the boronization system

17.      Search and lock the cell. Secure and check the access permissive ont he diborane PLC.

 

18.     Activate the purge procedure from the PLC. The AUTO switch on the DIBORANE PLC must be enabled, and the toggle switch for the diborane bottle valve should be in the CLOSED position. Reset PV5. Enable PURGE60. The PLC should open PV valves 1,5,3, and 6.

 

19.     Observe the purge cycle. PV2 will open, causing a drop in the pressure measured by the diborane transducer TR4. PV2 should then close and PV4 should open for 15 seconds, causing an increase the pressure measured by the diborane transducer TR4. PV4 will then close, and PV2 will open for 15 seconds. This sequence will repeat 20 times.

 

20.     At the end of the purge cycle, PV4 will close, and then PV2 will close 15 seconds later. PV1, PV5, PV2, PV3, and PV6 will now close. This is the end of the purge sequence, and the discharge cleaning is ready to commence.

 

21.   Two persons should don the SCBA. Two more SCBA qualified persons should be standing by. The persons wearing SCBA should enter the cell under controlled access, taking 2 wireless phones with them. One should don the welding glove and open the diborane bottle while the other watches the toxic gas detector on the cabinet. After exiting and removing the SCBA, enable the DIBORANE MV OPN bit on the PLC.

 

22.     Return the cell access to secure. Set up for the discharge cleaning cycle. Enable the FILL ENABLE on button on the DIBORANE PLC (top line, upper right hand side). Go into the AFILL screen of TORVAC and clear the fault, even if no fault is indicated.

23.      Go into the ECDC screen of TORVAC and enter the requested scan settings for PEI sweep.

 

24.     Set the pressure by entering 40 mTorr pressure into the DIBORANE PLC and enable the fill request.  PV5, PV3 and PV6 must all open. Activate the diborane discharge cleaning mode from TORVAC. (When the pressure okay permissive is enabled, toggle ECDC ON.)

 

25.     Verify that all systems function as expected. Set the piezo electric valve to 35 mTorr.  If a higher pressure is desired, raise the pressure in increments of 10 mTorr until it reaches 90 mTorr. TC6 should read about 75 mTorr. Initiate the discharge cleaning. Verify that a discharge has formed in the machine. Enable the pulser "on" button on the lower right hand side of the diborane PLC screen. Verify that the discharge is flashing on and of on the TV screen. Maintain discharge cleaning for the desired period.

 

Shutting down the boronization system


26.
      Shut down discharge cleaning. Verify that the Piezo-electric valve has been asked to close.  Toggle the FILL ENABLE off on the              DIBORANE PLC

 

27.     Evacuate the gas line. (This can be done automatically from the DIBORANE PLC by enabling AUTO and enabling PURGE5.) Begin by closing PV5. Open PV3. Open PV1. Open PV2 until the diborane transducer indicates the line is under vacuum. Close PV2. Open PV4. Cycle PV2 and PV4 every 15 seconds a total of 20 times.

 

28.     Don the SCBA and enter the cell under access control. Don the welding glove and close the valve on the diborane bottle. Exit the cell.

29.     Manually set the switch on the PLC which indicates that the diborane bottle valve has been closed.  Secure and check the ACCESS permissive o the DIBORANE PLC. Initiate the PURGE60 cycle.

 

30.     At completion of the purge cycle, shut PV6, PV1, and PV5 and the Piezo-electric valve. PV2, PV3 and PV4 should already be closed. Release the access control system. Close the REG1 regulator and MV1. The discharge cleaning session is now complete.

 

31.     When the vacuum vessel has been pumped out (1 to 1.6 mTorr on TC3), turn on IGT when the pressure drops below 1.10-5. The diagnostic valves which were closed at the beginning of this procedure may be re-opened. DO NOT OPEN GV3. Turn on the remaining filaments.

 

32.      Reopen the shutter and gate valves which were closed earlier:

 

32.a    Opening the shutter after a boronizaton:

 

Proceed to the B-port-side of A port. The status of shutter will be given by the red plate velcro'ed to the igloo between A and B ports. The plate says ``A port shutter is..., with ``OPEN'' or ``CLOSED'' indicated by the appropriate side of the red, velcro'ed plate. It should indicate ``CLOSED''.

 

If the indicator says ``CLOSED'', then locate the rotary motion feedthrough located at the bottom left corner of the reentrant A-port-side flange. (Even if the indicator says ``OPEN'', this position should be verified by executing step 3 and feeling that the black knurled head of the rotary motion feedthrough is turned fully counter-clockwise.)

 

Unscrew the locking screw about one turn to free the the feed through for rotary motion. It will be difficult to reach your arm into the A side flange area, but do so without damaging the Thomson scattering mirrors or the microwave waveguide. To ``OPEN'' the shutter, rotate the head of the rotary motion feedthrough approximately 1 full turn COUNTER-CLOCKWISE. If it resists strongly or if you feel that you are using anything more than ``finger strength'', then stop and do not force it. Try again to rotate it one full turn to the fully counter-clockwise (OPEN) position. If you can move it CLOCKWISE, but not COUNTER-CLOCKWISE, then it is already ``OPEN''. But it it sticks ``CLOSED'', then notify Jim Terry (ext. 3-8637 or at home 323-6597) and Jim Irby and DO NOT PROCEED WITH THE TOKAMAK RUN.

 

Tighten the feedthrough locking screw.

Switch the red plate indicator to show that the A port shutter is ``OPEN''.


32.b   If the surface science station was used, open the S3 gate valve and close the gate valve to the machine.
   


33.
      Pack it in and go home.

 

I.         Training

 

Those responsible should review these procedures in detail, and should receive training in toxic gas hazards, and SCBA usage.

 

J.         Summary Check List

 

PLEASE HAVE TWO PEOPLE INITIAL ITEMS AS THEY ARE PERFORMED

 

NOTE: Steps a-h must be done at any time prior to the search and lock of the cell. The vacuum system setup, item k may be done simultaneously.

 

_____a.

Prior to closing the cell, turn off the RGA filament from the RGA PC in the control room.


Cell preparations:

The following items are done on the upper level of the cell:

_____b. ______Turn off the two RGA filament Ametek power supplies.  One is locate at H-port horizontal on top of the pumping system and the other is located on top of the Torvac rack.

______Turn off the Ametek Data logger located int the Torvac rack, middle shelf

_______At H-port right side and left side close the gate valves for the RGA and torque them.

_____c.

Close the shutters at A, C and F port.


_____MSE Shutter

_____CXRS Shutter (under control of Bruce Lipschultz)

_____CXRS Shutter (under control of Bob Granetz)

At this time, the MSE and CXRS shutters are under the direct control of Bob Granetz and Bill Rowan, and will not be open or shut during setup for boronization.   Check with them to see that they have taken care of the shutter.

 

_____Jim Terry's A port shutter.

Proceed to the B-port-side of A port. The status of shutter will be given by the red plate velcro'ed to the igloo between A and B ports. The plate says ``A port shutter is... '', with ``OPEN'' or ``CLOSED'' indicated by the appropriate side of the red, velcro'ed plate. It should indicate ``OPEN''.

If the indicator says ``OPEN'', then locate the rotary motion feedthrough located at the bottom left corner of the reentrant A-port-side flange. This feedthrough controls the position of the shutter. It is a Aluminum cylinder about 3.5" long, at the end of which is a knurled knob with a metal-colored locking screw. (Even if the indicator says ``CLOSED'', this position should be verified by executing step 3 and feeling that the knurled head of the rotary motion feedthrough is turned fully clockwise.)

Unscrew the locking screw about one turn to free the feedthrough for rotary motion. It will be difficult to reach your arm into the A side flange area, but do so without damaging %the Thomson scattering mirrors or the microwave waveguide. To ``CLOSE'' the shutter, rotate the head of the rotary motion feedthrough approximately 1 full turn CLOCKWISE. If it resists strongly or if you feel that you are using anything more than ``finger strength'', then stop and do not force it. Try to return it to the fully counter-clockwise (OPEN) position. Notify Jim Terry (ext. 3-8637 or at home 323-6597).

Tighten the feedthrough locking screw.

Switch the red plate indicator to show that the A port shutter is ``CLOSED''

_____d

Close the NPA gate valve at F-port top:  The valve is closed manually by rotating fully clockwise. 

_____e.

Start the flow from the vaporizer into the diborane vent work and the vacuum pump outlet by opening ball valve MV5 (mezzanine level, North Wall). The regulator should be opened to at least 5 PSI but no more than 12 PSI.

 

_____f.

Open the valve going to the torus roughing pump. The regulator should be opened to at least 5 PSI but no more than 12 PSI.

 

_____g.

Verify that MV4 (mezzanine level, on igloo at AB) is open.


 

_____h.  Polarimeter shutter:   Verify that the helium tank supplying the polarimeter shutter is above 1000 psi, and that the regulator              pressure is at least 15 psi.  Verify that the polarimeter shutter vacuum pump on top of the igloo above k-hor is pumping.                   Remove the cover from the polarimeter mirror housing at k-hor.  Shine in a light and verify that the polarimeter inner wall               shutter is closed.


_____i. Surface Science Station: Close the Turbo pump gate valve, then open the manual gatevalve on the beam line for probe insertion.     Set the N2 purge flow meter on the exhaust of the secondary seal pump to 6-8 SLM to dilute the pump exhaust into the cell           exhaust system. Verify that the N2 purge is active at the turbo pump exhaust. 

The following items are done on the lower level of the cell:



_____j. Dust Injection System:  Close hand valve on A-port bottom inside.  Aaron Bader and Bob Granetz are responsible.

_____k.

Prior to closing the cell, check that the controller unit for the ECDC microwave source has been placed in Analog control mode (center switch on front panel of Lab Power Supply located between D and E port.

 

_____l.

Prior to closing the cell, check that the camera on the diborane cabinet has a clear view and can be seen on channel 27 in the control room.

 

_____m.

Verify that:

_____Manual valves MV1 and MV3 are open.

_____The diborane regulator (REG1) is set to 30 PSI (this is normally set at the first boroniztion and left set).

_____The venturi regulator (REG3) is set to 100 PSI.

_____The helium purge gas regulator (REG2) is set to 30 PSI (PV3 and PV4 and manual valve MV2 will have to be open to set the diborane regulator pressure.)

 

 

Prepare vacuum system and diagnostics

____n. Verify that the lower hybrid wave guide has been pulled back.  This can be done by switching the  encoder from remote to local by flipping the switch up. Check and record that the reading is 1902 (+- 2 counts). Finally return the encoder switch to remote (flip switch down).

 

_____o.

 _____Go into the TORVAC PLC. Turn off all filaments specified (IGT, IGP1, IGP2)

_____Verify that all of the diagnostic gate valves are closed.

_____Close GV3.

_____Turn off the Ratiomatic (make sure the Ratiomatic has been taken out of Auto mode.)

_____Close the Z Bolo Shutter from Torvac.


_____Close the HIREX III  gate valve.

 

 

Prepare the boronization system

_____p.

Search and lock the cell, power room and diagnostic labs.

______Secure and check the ACCESS permissive on the DIBORANE PLC.

_____q.

Activate the purge procedure from the PLC:

_____Enable the AUTO switch on the DIBORANE PLC.

_____Reset PV5.

_____Enable PURGE60. (This will not work unless the DIBORANE MV CLSD bit is enabled. Do not change this bit without verification of the bottle valve status.)

_____r.

Verify that the PURGE60 cycle is working. Make sure that PV5 is open, and that TR4 is cycling between vacuum and pressure.

_____s.

Open the diborane gas bottle valve:

_____Two persons should don the SCBA. (Two more SCBA qualified persons must be standing by.)

_____The persons wearing SCBA should enter the cell under controlled access, taking 2 walkie-talkies with them.

_____One of the two should don the welding glove and open the diborane bottle while the other watches the toxic gas detector on the cabinet.

_____Exit the cell and remove the SCBA.

_____Enable the DIBORANE MV OPN bit on the PLC.

_____Return the cell access system to a secured state.

_____t.

Set up for the discharge cleaning cycle:

_____Enable the FILL ENABLE on button on the DIBORANE PLC.

_____Go into the AFILL screen of TORVAC and clear the fault, even if no fault is indicated.

_____Go into the ECDC screen of TORVAC and enter requested scan settings for PEI sweep.

_____u.

Set the pressure by entering 35 Mtorr into the DIBORANE PLC and enable the fill request. 

_____v.

if a higher pressure is desiered, raise the pressure in increments of 10 mTorr not to exceed 90 mTorr.

_____w.

Activate the diborane discharge cleaning mode from TORVAC.

_____Verify that a discharge has formed in the machine.

_____Enable the pulser"on" button on the lower right hand side of the diborane PLC screen.

_____Set pulser .3 s off, .7 s on.

_____Verify that the discharge is flashing on and of on the TV screen.

Start up is now complete: Maintain discharge cleaning for the desired period.

_____x.

Shut down discharge cleaning.

_____Verify that the Piezo-electric valve has been asked to close. If it does not close, toggle the Fill request.

_____Toggle the ``FILL ENABLE OFF'' bit.

_____y.

Evacuate the gas line:

_____On the DIBORANE PLC enable AUTO.

_____Enable PURGE5.

_____z.

Don the SCBA and enter the cell under access control. Don the welding glove and close the valve on the diborane bottle. Exit the cell.

_____za.

Enable the DIBORANE MV CLSD switch on the DIBORANE PLC.


_____Secure and check the ACCESS permissive on the DIBORANE PLC.

_____On the DIBORANE PLC enable AUTO and initiate the PURGE60 cycle.

 

____zb.

At completion of the purge cycle verify that all automatic valves are shut.

____zc.

Release the access control system unless setting up for a run later in the day.

____zd.

When the vacuum vessel has been pumped out (1 to 1.6 mTorr on TC3):

_____Turn on IGT.

_____Turn on IGP2.

_____Reopen The diagnostic valves which were closed at the beginning of this procedure

_____DO NOT OPEN GV3.

_____If the surface science station was used, reopen the S3 gate valve and close the gate valve to the machine.

 

 

K.       Cross references

 

Procedure for Installation of Diborane Gas.

 

Test Procedure for Diborane Gas System.

 

Procedure for Diborane Gas System Maintenance.

 

Emergency Procedure for Diborane Gas System.

 

Safety Analysis Report for Diborane Injection in Alcator C-Mod.

 

L.        Distribution

 

E. Marmar, J. Irby, C. Reddy, R. Clifford, J. Bosco, B. Childs, I Hutchinson, F. Silva

 

M.       References

 

Matheson gas catalogue.

 

MDA Scientific `` TLD-1 Toxic Gas Detector Operating Instructions''

This page maintained by Catherine L. Fiore FIORE@PSFC.MIT.EDU