2023-03-17

Machine Status

Vacuum is 3.8e-7 Pa (yesterday was 3.0e-7).

TORA signal is around (+-) 80 mV at injection.

FAB signal is much larger.

Yesterday's Meeting

Yesterday, there was some uncertainty about the meaning of the "delay" variable that is often quoted, so we wanted to clarify this.

Preliminary Beam Stacking Measurements

In the following section "Beam-1" is the beam that is injected first and has a longer coasting time, and "Beam-2" is the beam injected second.

Initial Measurement

Separation is expected to be around 350 keV. Gap on harmonic 8 is around 62 kHz, corresponding to a difference in revolution frequency of around 340 keV (((35.625-33.573)/(2.600-2.537)) * 2.58120496 * (1.0 - 0.996) * 1e3).

Increasing Beam Energy Separation

Energy separation was increased and is now expected to be 700 keV. We measure around 700 keV.

((35.625-33.573)/(2.600-2.537)) * 2.58120496 * (0.9995 - 0.991) * 1e3 = 714.6

Beam 1 and Beam 2 Difference

Beam 1 coasts for about 33ms more than beam two, so the amplitudes are expected to be different because of the lifetime. The (1/e) beam lifetime is around 400 ms, so we expect an 8% reduction, but we observe a reduction that is larger than this. We are unsure of whether this means the two beams are interacting or whether the RF is affecting the coasting beam. To investigate this, we prepared four different cases as indicated below. 

Comparing Case 1 and Case 3 shows that beam-2 has a slightly larger peak than beam-1. Looking at harmonic-8, beam-1 has an amplitude of around 38, whilst case 3 has an amplitude of around 45. This suggests that the beam with the longer coast (case-1) has an amplitude reduced by around 20%, and that we cannot currently account for around 10% of the amplitude reduction. This could just be shot-to-shot variation, but it could also indicate that the RF performance is not the consistent between the two different RF buckets.

The most significant difference is between case-2 and case-3, since this change in amplitude certainly can't be attributed to the beam lifetime. At the moment, we believe that the second RF bucket must be disturbing the coasting beam. This is a point to optimise, but we will come back to it after we've optimised the peak spacing. 

Variation of Peak Heights with Time

We wanted to see how the peak heights varied through time, so prepared an experiment where the separation between Beams 1 and 2 was 175 keV, then repeated for different delays.

Vary Beam Separation and Recapture

Add flat tops for beam 1 acceleration cycles, beam 2 acceleration cycle and the recapture region. Also move the recapture bucket to the centre of the two coasting beams. This will be done with the beams at 175, 350 and 700 keV separation.

lecroy-utils was updated to allow the vertical scale to be changed. This allowed us to capture bunched-beam data in the flat-top regions for an indication of beam intensity.

Signal acquired at 122 ms, 272 ms and 322 ms to see how the peak heights vary. We then also acquire 25 ms, which gets the flat-top signal for both beams during debunching. We acquire at 365 ms to get the flat-top during recapture.

More beam is recaptured with a smaller gap. 

files 18 and 21 also 175KeV gap but 18 and 21 were taken earlier in the day