June  7,  2011  

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Plasma  Oven  Controls  System  Specifications  PWFA  Collaboration  

   Overview of the Plasma Oven System The plasma source provides a means to study plasma wakefield acceleration (PWFA). The experimental setup is located on the IP optical table in Sector 20 at FACET. Below is an elevation view of the oven setting on the table. A well-controlled operation of the heat-pipe oven is crucial to the success of this experiment. Experimenters will require correlation of measured beam parameters to the controlled plasma parameters.

Design of the heat-pipe oven from FFTB will be used for the plasma experiment (E-200) at FACET. All of the oven hardware will be kept permanently at SLAC and integrated into the SLAC control system. A dummy oven is used for alignment, controls and interlock testing before putting in the real oven. This dummy oven set up must be configured exactly as it would be for the real lithium oven. All controls, monitors and interlocks must be functioning and tested before installing the lithium oven tube. When ready, the dummy oven tube will be replaced by the lithium oven. The lithium oven consists of a wick, tube, heaters, thermal couples and thermal insulating bricks. The lithium oven tube will replace the dummy oven tube after it is confirmed that there are no leaks, including the two beryllium windows that isolate Helium or Argon gas from the main beamline vacuum, with one on each side of the beam pipe. After repeating the E164 results with lithium, the lithium tube can be replaced by an identical tube containing Cesium.

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Key components of the plasma oven system are shown in the cartoon below.

Here is a preliminary mechanical layout of the plasma oven setup:

US OTR

8" cubessupport oven mover

Bellows

Be Window

Oven moverbellows

Oven gate valves

water jackets

oven heaters

TC feed thruIsolation gate valve

Isolation gate valve

Bypass line

oven pumpline connection

To TurboPumpStation

gate valve

Manifold for 3 vac gaugesIon gauge1000 Torr CM gauge10 Torr CM gauge

Connections forHelium gas inHelium gas out

Beam Direction

Lithium Vapor

DS OTR

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Requirements: The following lists the oven hardware requirements and their controls to be fulfilled by Controls Department. Turbo pump vacuum station: The turbo pump will pump down to 10-6 Torr. We then close the angle valve to turbo pump and backfill He to up to 100 Torr between the Be windows. The turbo pump vacuum station needs to be monitored to assure that it has not failed.

• Operating temperature is 40°C (104°F). • A dry backing pump will be used in conjunction with the turbo pump. • A full range Pirani/IMG gauge will be placed between the turbo pump and the dry

pump and can be interfaced with the Turbo pump Varian V81 AG controller (RS232).

• We are using the Varian V81-M model since Controls have experience with its support at LCLS.

Valves:

• Two oven gate valves pneumatically controlled, interlocked to MPS. • The oven gate valves and beamline gate valves need to be automatically closed

when one of the conditions occurs: o Current too high (TBD); o Voltage too high (TBD) ; o Pressure too high (> 20 Torr) or too low (< 1 Torr).

• Pressure control valves are also needed for controlling He pressure in the oven, with 24VDC solenoids used to activate the pneumatics. Each of these electromechanical solenoid valves is connected to a manual adjustable valve pre-set to allow a proper flow rate. Two independent 24VDC channels are needed to turn on/off the He flow via the Beckoff system: one for filling and the other for removing He.

• An angle valve goes between the turbo pump and the oven. After the region between the Be windows is pumped down, the angle valve is closed and the oven is back filled with He. This should be done either locally or remotely. Both functionalities are needed.

• Control and read back with ‘local control mode’. • Interlock faults close oven gate valves when one of the following occurs:

o Pressure in oven exceeds 20 Torr (oven leak); o Pressure falls below 1 Torr (buffer gas loss); o Leak in FACET beam line.

• Close oven gate valves by removing key to interlock box in trailer. • If anything goes wrong, the default is to close the oven gate valves.

Water Cooling Jacket:

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Water jacket for cooling the Helium gas keeps Lithium confined to a hot zone inside oven. Temperature is set to 25-30°C.

• Water cooling is provided by the magnet LCW water. A Klixon temperature switch in the water return line can be directly interlocked with the beam.

He gas: The heat-pipe oven is filled with Helium buffer gas to constrain Lithium vapor to a specific region. The Helium pressure controls plasma vapor pressure (density).

• Helium pressure needs to be monitored and readout. • Three capacitance diaphragm gauges are planned for: one gauge goes from 0 to

1000 Torr for venting and protecting the Be windows, the other 2 gauges cover the range of experiments for different pressures that the experiment will be running. Two of these 3 gauges will be installed at the 4-way cross in the manifold. They have to be capacitance diaphragm gauges because they are the only one that can measure different pressure correctly and accurately for the different type of gases (He and Ar) planned for the experiment. The accuracy of these gauges should be within 1% of the readings. Heated Baratron absolute capacitance manometers (CM gauges) are chosen and will be interfaced with the MKS 937B gauge controller.

Ion Gauge: A cold cathode ion gauge (Series 422) is used for vacuum leak check at the manifold. The vacuum pump and gauges are teed into the beamline between the downstream Be window and the oven mover. The region between the Be windows cannot have leaks. The MKS 937B gauge controller will interface with the ion gauge as well as the CM gauges mentioned above. Power supply: Sufficient power is supplied to the heater to adjust oven length (the length of the vapor) via a relay. The oven consists of three heater sections each approximately 15 cm long.

• LAN control is required. A switching device will be needed to turn on each heater independently. The relay diagram for switching on the heaters is shown below. In the previous experiment, the relays were activated by 10-volt outputs located on the SRS thermocouple monitor that was controlled by GPIB with LabView. For the current experiment, we would like similar controls via EPICS.

• The heater power supply should be automatically turned off when the oven gate valves are closed.

• The exact current and voltage for the heater set up will be measured at UCLA and provided to the controls department later.

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 Plasma source: Beam-ionized Lithium will be the plasma source for the first experiment. The second experiment (also possible summer 2011) will change to a beam-ionized Cesium plasma. The Cesium oven will function nearly identically to the lithium with the exception of different values for oven temperature and heater power supply current and voltage.

• The oven is heated to 800°C to vaporize solid Lithium (or 250°C for Cesium). • Thermocouples inside plasma measure temperature along oven for a profile of

plasma column. All five thermocouples are type-K with quick disconnect sub mini connectors. The temperature ranges from room temperature to 1000°C.

• The thermocouples need readout in local and remote control system with the Beckhoff system.

• A movable table selects beam path to either plasma or bypass line. Two states: IN, OUT. Require control of valves to switch (if pneumatic) or alternate linear

Kepco 150-16 power supply150 Volts max8 amps max

Relay 1

H1H2H3

Relay 2

Heaters

Relay Control BoxH1 onH1 and H2 onH1, H2 and H3 on

The PS should beturned off beforeswitching heaters toavoid voltage spikesand current surges.

H1-3 are 6.2 ohm each

2/17/2011

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actuator (TBD), read back of state limit switches. The oven mover needs to be interlocked to MPS. No beams should be sent when the mover is moving. It has to be parked at either IN or OUT state. Below is a preliminary sketch of the oven mover.

41.000

9.000

12 foot optical table

Gate Valves

MoverMover plate 1/2"

5.750Oven plate 1/2"

stand

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The standard oven height is 5.75but can be set at 5.00 if needed

Side View

Oven plate 20"x41"area of heaters and bricks

dummy oven tube

bypass line

3.250

Oven plate dimension canbe reduced if needed

Top View

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Plasma Oven Operation The plasma oven operation is summarized in the logic diagram below.

 An operator should be able to either locally or remotely go through the operation procedure to turn on the oven while monitoring the pressure and temperature readings from EPICS. The only automation is in closing the gate valves and shutting off the heater power supply automatically when interlock faults. An interlock bypass key is needed to start up the oven. EPICS Controls The EPICS control panel should display the following for plasma oven monitoring:

• Room/tunnel temperature • Temperature for the water cooling • Temperature for the 5 thermocouples inside the oven • Voltage and current of the heater power supply • State of the heaters (i.e. number of heaters on with each of the 3 heaters being

controlled independently) • Pressures of all gauges (one ion gauge and two CM gauges)

roughing pump on

open angle valve

turbo pump on

open oven gate valves

close angle valve to turbo pump

check outgassing rate or leak rate with

pressure gauges

turn on water

cooling

fill oven with He

activate interlock

system and oven monitor

(EPICS)

turn on heater:1. select # of heaters;2. set relay;3. turn on power supply.

monitor oven status

close oven gate valves

turn off heater power supply

turn off water cooling

pump out He

close oven gate valves

turn off key to interlock

if conditions not ok

Conditions not ok if any one of the following occurs: * water cooling temperature > 50˚C * thermocouple temperature > 920˚C * current too high (TBD) * voltage too high (TBD) * pressure > 20 Torr * pressure < 1 Torr

if desired pressurereached

if not okif ok: < 10 mT

per day

Plasma Oven Operation Logic DiagramInitial conditions:* vacuum sealed and no leaks* plasma oven in beam path* oven at room temperature* atmosphere pressure* all valves closed* all gauges on

check pressure with ion gauge between Be windows

check pressure with ion gauge between Be windows

close oven gate valves

find source of leak and

fix it

perform experiments

close beamline gate valves

for a normal shutdown

if conditions ok

if ok: 10-6 Torr

if ok: 10-6 Torr

oven reaches room

temperature

Any beamline vacuum problem

Controlled by Software

Automatic control

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• Oven mover status (two states: plasma in or out) • Turbo pump status (roughing pump is connected to the turbo pump and can be

turned on remotely) • Status of the oven valve controls (local or remote), indicating if the oven gate

valve is open or close. If any gate valve is closed, beam cannot be sent. The EPICS display shows flashing red warning lights for any of the following:

• Temperature of thermocouple exceeds 920°C; • Current too high (TBD); • Voltage too high (TBD) ; • Pressure too high (> 20 Torr) or too low (< 1 Torr).

Action in any of the above cases: • Close oven gate valves • Shut off heater power

Interlock System There are two types of interlocks:

1. Interlocks that protect equipment from being damaged by the beam. This will be handled by the MPS system.

a. The oven gate valves and oven mover cannot have any direct contact with the beam.

b. The plasma can have contact with the beam but only at a reduced rate of 1 Hz (the rest goes to the positron target, rather than the plasma). There is no need to tie this to the MPS. However, in a subsequent future experiment, a notch collimator is in only if the beam passes through at 1 Hz. In the later case, the notch collimator needs to be tied to the MPS.

c. To prevent damages from radiation via mis-steered beam or scatter from beam obstructions, we already have LION (long ion chamber) in.

d. The oven mover goes into MPS to simply minimize the change of challenging more critical systems such as the Beam Containment System (BCS). Therefore, the oven mover needs to be interfaced to the MPS in order to trip the beam before BCS does.

2. Interlocks that protect equipment from factors other than the beam. This will be handled by Experiment Protection System (EPS). Detailed specifications of the EPS are provided by Keith Jobe in a separate document titled “Plasma Oven – Experiment Protection System Specifications”.

a. Protection for vacuum integrity. It is important to prevent (1). Li escape from the oven, and (2). vacuum leak that causes oven to fail. by closing the oven gate valves.

b. Protection of the Be windows and oven that can be damaged by poor vacuum or high pressure differentials. If the Be windows leak or break, it will contaminate the beamline. The pressure gauge controller is interlocked to the oven gate valves. Hi Low set points close the oven gate valves as a safety measure. The oven gate valves are also interlocked into the beamline vacuum.

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c. Protection of oven that can be damaged from high temperatures due to lack of cooling. If water cooling jackets get too hot which indicates that cooling fails, turn off power supply.

The experimenters need to be able to bypass the interlock system when ramping up or down the system. If an interlock is tripped, the key to interlock should be turned off. After the problem is fixed, an operator will push reset on the interlock box and then turn key on to give EPICS control.