1. Purpose

   1. Goal
      1. The goal of this training module is to provide a detailed procedure on how to safely and efficiently bake an RGA cart. When a RGA cart doesn't meet the clean qualification requirement, baking is the 1st step to requalifying. The procedure will also include how to use a baking controller for ramping up and down in temperature.
   2. Capabilities Include 
      1.  Vacuum skills 
      2.  Designing skills
      3.  Baking skills

2. Subject Matter Experts - May help provide instruction and guidance for this Training Module

   1.  Brady Robertson 
      1. bradyrob@slac.stanford.edu
   2. Ivan Curiel
   3. Ruben Curiel
   4. Cynthia Melendrez
   5. David Amaton

3. Resource List

   1. RGA Cart Maintenance and Operation Document  (List of RGA cart Components)

   2. Amanda's doc: RGA Cart Maintenance and Operation (After baking is complete)

4. Begin Training Content

Step1:

Clear the area for baking preparation and process. Baking temperatures can reach up to 250°C, therefore it is important to have a clear area for minimal supervision during long bakes.

Step 2:

Check that your system is at a pressure of at least 10^-5 torr. The molecules adsorbed onto the chambers inner surfaces and need an exit path after being excited by the ramping increase of heat. Baking without being under vacuum will both absorbs and remove any molecules from the wall of your chamber.

Step 3:

Remove and power off all electronics that cannot withstand baking temperatures. Any components attached or near the chamber should be checked for its bake out temperature.  When deciding what temp to bake a system you must first consider that 150°C is for water and 250°C is for hydrocarbons. Common components to check for are shown bellow.

CCG series 500 is used on most of our RGA carts and its bake out temperature is 250°C (After magnets are removed). The CCG should look like the image bellow after the magnets and electronics are removed.

Link to manual: https://www.mksinst.com/mam/celum/celum_assets/resources/GP-218905-500Gauge-DS.pdf

VAT Gate Valves have bake out temperatures of up to 250°C.

Link: https://www.vatvalve.com/series/ultra-high-vacuum-gate-valve

Most pirani gauges have a low bake out temperature range of about 150°C, therefore making heater tape placement very important when baking.

link: https://www.idealvac.com/files/brochures/GP_275_Gauges_1.pdf

An RGA device has a temperature bake out of about 250°C with and extender or electronics. For more about and RGA go to link:Theory

Link: https://www.mksinst.com/mam/celum/celum_assets/resources/MicroVision2ds.pdf

 Step3:

Prepare all the components needed for the bake.

Step4:

Add thermocouples to your chamber and keep them in place using small aluminum strips spot welded onto the chamber. Where to place the thermal couples is up to you, but placing them where you believe the hottest area will be is sufficient. Type K thermocouples, which are made up of two metals Chromel and Alumel, is what we typical use as temperature sensors.

Link for Info regarding thermocouples: https://www.thermoworks.com/why_use_thermocouples

Step 5: 

Apply a thin layer of aluminum foil to the chamber and on top of thermocouples. Do not cover electronics or handles with aluminum and avoid areas that do not have high bakeout temperatures such as, turbos and roughing pumps. Applying a thin layer of aluminum helps spread the heat provided by the heater tape, since aluminum is a good conductor of heat. If the heater tape is applied directly to a steel chamber you can potentially have hot spots because steel is not a good conductor of heat. 

Step 6:

Start wrapping your chamber with heater tape in a uniform distribution as shown in the picture bellow.  ** Remember not to overlap heater tape** this can cause over heating and damage to the material. Put gloves on when handling the heater tape because most contain fiber glass that can irritate your skin. Furthermore, be sure to leave sufficient space at the end of the tape for connecting to the PID controller. 

Step 7: 

Start wrapping your system with tinfoil try to reach all nooks and crannies for minimal heat escape. For this process using aluminum from the recycle trash bin is okay. Also, adding multiple layers of tinfoil helps the chamber reach high temperatures and keeps the top layer less hot. keeping the top layer cool keeps people safe from touching the system and burning themselves. An example of a good tinfoil wrap is shown bellow.

Step 8: 

Connect your heater tape to the PID controller and start heating. A PID controller helps ramp up/down the heat of your system at a steady pace. If the temperature ramps up/down to fast a leak can develop in your system due to the thermal expansion coefficient of materials. Copper and steel both have different expansion coefficients when heats is applied and removed therefore, it needs to be accounted for when baking.  A PID controller great for ramping is shown in the image bellow and a users guide has been made to simply the learning process of this controller.

User Guide: Setup Guide For CN9300-CN9500.pdf

Manual: CN9300 manual.pdf

Variac controllers can also ramp up/down your temperature, however it has to be done manually. In other words, every other 15 minute, the variac knob has to be slowly roatated to adjust the input voltage until the desired temperature is reached. Variac controller are more simpler to use than PID controllers, but require more work and time.

Step 9:

Lastly cover your chamber with a heat warning sign to aware others of the activity.

Step 10:

When the bake is complete ramp the temperature of your system down to normal temp. When the ramp is complete remove tinfoil/heater tape and start adding electronics back.

bakeout supplies in B758 (B757?)