Segmented Ion Chambers

These ion chambers will consist of four copper pads on a circuit board with a common high voltage plate. These pads will be side-by-side, allowing for four simultaneous, independent measurements. There will be a 1 inch chamber for I₀ and a 2 inch chamber for I_t.

Initial experiment

Use a foil wide enough to be measured by each channel. The goal is to make four simultaneous measurements, each of which is of the same quality as a measure of the foil using a normal set of ion chambers.

We only have 6 v2f channels at X23A2 at this time. This means:

1. We can only test three channels at a time (no feedback, no I_r)

2. We will need to feed back off one of the I₀ channels

Other thoughts:

• Ultimately, we will need a total of 2N+2 signal chains -- one for feedback, one for the reference, N I₀ channels, and N I_t channels. For N=4, that means 10 signal chains. Oh boy! I get to buy stuff for the beamline!

• We probably want vertical knife edges (or at least lead tape) defining the horizontal extent of the beam entering each I₀ channel. Hutch slits will be used to define the vertical extent of the beam.

• We will need a good way of aligning the detectors with the beam coming off the mirror. Perhaps we should start with Pd or some such...

• I will need to write an Athena filter to load these data all at once.

Tests

• Cross talk. Block all but one channel with lead tape and measure all four channels. The goal is to see one good measurement and three null measurements.

• Linearity. Normal linearity test -- attenuate beam before I₀, demonstrate that the ratios of each channel are constant.

• Find an appropriate voltage for linear response

• Map glitch behavior per channel. Do we see a glitch migrating from channel to channel as the energy changes?

• How does the data behave when normalized just by the correct I₀ channel compared to a normalization by the sum of I₀ channels? That is, do we need a segmented I₀ chamber? (I suspect yes, but we need to show this.)

Second experiment

Simon suggests a reactor with space for four samples meeting the geometry of the ion chambers. Experiment 2A will be to fill each sample slot with a materials and run the reactor. All four should measure the same thing. Experiment 2B is to do four independent experiments in the reactor and measure 4 things. Then we publish.

Far future

• Fluorescence experiments are possible by staggering the samples along the beam path and pointing a fluo detector at each sample. Shielding is probably required.
• At NSLS-II, the unfocused beam in the hutch will be 55 mm wide. Once can imagine 10 to 15 side-by-side experiments. Wow!