November 2023: Testing Magnet Probe Signals at SIS18 Extraction

Table of Contents

TL;DR

Test on 3 November 2023. Seems to work.

Introduction

The b2b system uses timestamping with a White Rabbit timing receiver connected to the capacitive / differential signal of the kicker magnet to measure the time of the rising edge and possibly the length of the kicker flat-top. The main purpose is to provide this information to users in hard realtime: The data is sent via timing messages via the White Rabbit network and delivered (!) within less than 1 millisecond after the kick.

Figure: Comparator hardware.

All software has been merged into the current 'fallout' branch, click.

Measurements

Testing the kicker was done at the following settings

• pattern SIS18_FAST_HHD_MD_BG
• dry beam of element nitrogen 7+ gold @ 500 MeV / u
• at extraction: 1050 kHz revolution frequency, T_rev is 952 ns
• kicker deflection 4.85 mrad
• ParamModi value 'kick offset' 2.0 us

The b2b system uses a dedicated system to tap the magnet probe signal at SIS18 (see here). The main new feature in 2023 is a modification to the comparator module that allows to set the comparator level remotely. The main focus of the measurement reported here is to find a good setting of the comparator level. The comparator is connected to the capacitive (differential) signal of kicker module 1.

Comparator

The procedure has been the following.

1. set comparator level
2. measure delay of probe signal at comparator output relative to CMD_B2B_TRIGGEREXT
3. repeat this for different values of the comparator level

A measurement of the comparator response was done. The total measurement time was about half an hour.

comparator level [%]	delay rising edge [ns]	length output signal
47	n/a	n/a
48	n/a	n/a
49	n/a	n/a
50	3346	3001
51	3352	2982
52	3359	2973
53	3361	1097
54	3366	962
55	3373	562
56	3372	507
57	3378	330
58	3382	233
59	3396	163
60	3405	90
61	n/a	n/a
62	n/a	n/a
62	n/a	n/a

Table: Measured delay of rising edge and length of output signal as a function of comparator level.

Alignment with Digitizer Data

For better comparison with the digitizer data, the delay of the rising edge value of the digitizer signal (at 50%) relative to CMD_B2B_TRIGGEREXT has been determined a couple of times. The average value is a delay of 3307 ns. The calibration of a timestamp measurement with a White Rabbit timing receiver is not known to the nanosecond. However, this internal delay is estimated to about 29 ns.

Data

The data acquired using the comparator and the probe signal acquired by the digitizer connected to module 1 (GS04MK1E: Current_Module1:Triggered@312.5 MHz) are plotted.

Figure: Signal of digitizer (blue) and data of the comparator level (red). Top: Complete signal. Bottom: Zoom at rising edge. The x-axis shows the delay after the trigger signal CMD_B2B_TRIGGEREXT. Left y-axis scale: Signal of digitizer [A]. Right y-axis scale: Comparator level [%]. The signal of comparator at a fixed level is shown in green. See text for details.

The above figures show three sets of data.

• Shown in blue is the signal acquired by the digitizer (left y-axis).
• The red curve shows delays for rising and falling edge of the output signal delivered by the comparator for different levels (right y-axis); as can be seen, good comparator levels for matching the probe signal are within a range of 50..52%.
• The green curve (y-axis: arbitrary units) serves to compare the output signal of the comparator at a level of 51% to the digitizer values.

Both figures show the same data, but the lower figure is zoomed onto the rising edge. The rising edge of the digitizer has a risetime (10% -> 90%) of about 125 ns. The comparator is connected to the capacitive differential signal, which is known to be more precise. In principle, the signal by the comparator is expected to be earlier than shown in the figure above. An exact comparison is difficult; as an example, there are distinct cables from the kicker magnet to the cable room for 'probe signal' (digitizer) and the 'differential signal' (comparator); the exact lengths of both sets of cables is not exactly known.

Conclusion

Today (November 2023) the rise time of the kicker magnet probe signal is measured and delivered to users in the entire facility. In 2023 a new comparator has been installed that allows to detect not only the rising but also the falling edge of the kicker signal. What remains to be done is the delivery of the falling edge timestamp.

-- DietrichBeck - 02 Nov 2023