(Book 13, p 33)
|u-wire 1||G F||1.25|
|u-wire 2||U V||1.20|
|bar 1||P E||0.55|
|bar 2||L T||0.60|
|dimple 1||A B||4.55|
|dimple 2||N D||4.40|
|rf antenna||SMA feed||4.35|
Thermal Properties of Chip / Stack
Chip Heating Characteristics
Here's how the chip heats up, in vacuum, when you run some current through the z-wire:
(24 March 2008)
We spent some time measuring the expansion and contraction of the stack as we run the experiment, 7 July 2009 - 14 July 2009. We measure the position of the chip by looking at the first diffraction chip from the chip's surface using the axial imaging system. By fitting this fringe, we use the centre of the fit as a guide to the position of the chip with respect to the camera (ie, the fixed frame of reference, the table.)
- Warm up time is significant - at least 6 hours before the chip reaches an equilibrium position. It moves about 60 $\mu$m from room temperature to operating temperature.
- When using the optical dipole traps as gravity compensation and balance shifting potentials, the ratio of atoms in the right and left wells strongly depends on the chip position. For a 3.4 $\mu$m (1 pixel) shift of the chip surface, the balance (z = pR - pL) changes by 13%.
- The chip's position is correlated with many things, including:
- the amount of current run through the chip
- the duty cycle of this current
- the temperature of the top flange, to which the stack is connected
- whether there are people in the room
- whether there is nitrogen in the cryopanel
We try to stabilize the system using the following approaches:
- increase the duty cycle of the chip current by passing current through the chip nearly all the time. For now, we use the otherwise unused U wire (labelled "UV"), running current through it during the entire experimental cycle except for the transfer (XFER) segment. We also reprogram the ADwin control and the High Finesse BCS 5/5 such that we can keep current running through the U wire while the experimental cycle is stopped, and overnight. ADwin GUI 13.6.6 created for this purpose.
- tighten some of the screws holding down magnetic coils
- used a chiller for the MOT and XFER coil cooling water to stabilize temperature
- temperature stabilize the top flange of the vacuum system using a small Minco heater (240 $\Omega$)
- enclosing the area around the vacuum system
Flange temperature stabilization
Use a small Minco heater taped with Kapton tape to the feedthrough. Temperature control is done with an Omron ESGN controller. PID control seems very sensitive: choose the following PID settings:
P = 0.1
I = 1
D = 12
CP (control period) = 1
To access P, I, and D control, press grey button, the scroll through to "p", "i", and "d".
To access CP, press and hold grey button, then scroll through to CP.
I also put in a 500 mA fuse in the line to the Minco heater to hopefully prevent any overheating that might happen if the thermocouple came up-taped from the flange.