May 2021: Test Operation and First Real Bunch-to-Bucket SIS18 -> ESR

Table of Contents

Introduction

The bunch-to-bucket transfer system has been used for almost one week in operation. From 11-16 May the focus has been on beam operation to experiments. The planned bunch-to-bucket experiment took place on 17 May.

Setup

See here.

B2B v00.02.40, branch b2b_dietrich_2020-oct-26, commit 4de28554

Log

date Olog time what remark
2021-05-11 08:30 SIS18 and ESR kicker trigger changed from 'Timing Generator' to b2b system  
  09:00 first beam extracted from SIS18 with b2b system  
  15:00 HKR: can't trigger BI equipment properly, see olog see here
the problem is, that B2B triggers extraction ~1ms after EVT_KICK_START, but the integration window of BI ends ~500us after EVT_KICK_START
  16:30 solution: apply correction of -600 us for both extraction (SIS18) and injection (ESR) kickers at the b2b system  
til 2021-05-17 08:00 6 days of routine operation with krypton beam SIS18 -> ESR (bunch to coasting beam), experiment at ESR no issues, users are happy
til 2021-05-18 08:00 7 days of routine operation with xenon beam to HHT (fast extraction) experiment with PHELIX no issues, users are happy
first synchronization of a plasma physics experiment with an extracted bunch to 1 ns  
2021-05-17 14:30 setup ESR with xenon beam; begin injection as coasting beam Sequence ID 1, 124Xe46+ @SIS18, stripper foil, 124Xe54+ @ESR
  16:00 switch to mode buncht-to-bucket; but SIS18 has h=1 and ESR h=2; this does not fit!  
  16:35 no beam in ESR  
  17:00 one of the injection kicker modules at ESR failed, work with remaining two modules at higher energy  
  17:20 SIS18 changed to h=2 and ESR to h=1 (a bit dirty)  
set revolution frequency in SIS18: cavity DDS 1979732.979 Hz (506.118 ns)  
measured revolution frequency in ESR: cavity DDS 1975118.183 Hz (506.3 ns), T_beat 216.7 us  
  17:45 begin bunch-to-bucket test '  
  18:45 end bunch-to-bucket test (experimentalists urgently need to enter ESR)  
Table: Log of beam time. Hours are tentative.

Routine Operation

The bunch-to-bucket transfer system has been used for routine operation serving two different experiment for about 6 days.
  • krypton beam SIS18 -> ESR (as coasting beam)
  • xenon beam with fast extraction to cave HHT (PHELIX)

The main caveat has been triggering of beam instrumentation devices in the transfer lines. Despite all the efforts in retrofitting and modernization, the triggering of a large amount of diagnostic devices along the transfer lines is still based on the MIL event bus.
  • it is not straight forward to trigger on event numbers other than EVT_KICK_START1/2
  • it is not possible to do pre- or post-triggering
As a workaround, an ugly trick has been applied within the bunch-to-bucket transfer system to 'fix' the problem temporarily.

As the bunch-to-bucket system is not yet integrated in to the control-system. While the kicker timing could be set via the ParamModi parameter 'Kicker Offset', the revolution frequency of the ring must be set 'by hand' using a CLI of the b2b system. This was only done while setting up the experiments on 11 May 2021. After that, the b2b transfer system worked without any further intervention until the end of the experiments on 17 May (ESR) and 18 May (HHT).

Measurements with Bunch-to-Bucket Transfer

UTC phase difference [ns] phase difference [degree] cavity gap remark
16:00:23.693 272 193.4 650  
16:00:55.989 147 104.5 650  
16:01:28.280 147 104.5 650  
16:02:00.568 147 104.5 650  
16:02:32.861 397 282.3 650  
16:03:05.150 357 253.8 650  
16:03:37.439 317 225.4 650  
16:04:09.728 437 310.7 650  
16:04:42.030 437 310.7 650  
16:05:14.328 417 296.5 650  
16:05:46.628 417 296.5 650  
16:06:18.319 397 282.3 650  
16:06:50.617 397 282.3 650  
16:07:22.921 387 275.2 650  
16:07:55.233 387 275.2 650  
16:08:27.373 387 275.2 650  
16:08:58.921 387 275.2 650  
16:09:31.075 387 275.2 650  
16:10:03.203 387 275.2 650  
16:10:35.335 640 95.1 650  
16:11:07.464 640 95.1 650  
16:11:39.614 640 95.1 650  
16:12:11.738 630 88.0 650  
16:12:43.872 630 88.0 650  
16:13:15.444 620 80.8 650  
16:13:47.576 650 102.2 650  
16:14:19.704 660 109.3 650 phase max destructive
16:14:51.830 660 109.3 650  
16:15:23.993 660 109.3 650  
16:15:55.572 407 289.4 650 phase optimal (destructive – 180 degree)
16:16:27.752 407 289.4 650  
16:17:00.062 407 289.4 650  
16:17:32.237 407 289.4 650  
16:18:03.945 660 109.3 650  
16:18:36.085 407 289.4 650  
16:19:08.202 407 289.4 650  
16:19:40.350 407 289.4 650  
16:20:12.480 507 0.5 650  
16:20:44.612 507 0.5 650  
16:21:16.745 307 218.3 650  
16:21:48.881 307 218.3 650  
16:22:21.017 407 289.4 650  
16:22:53.175 407 289.4 650  
16:23:25.302 407 289.4 650  
16:23:57.453 407 289.4 650  
16:24:29.592 407 289.4 650  
16:25:01.725 407 289.4 650  
16:25:33.865 154 109.5 650  
16:26:06.008 154 109.5 650  
16:26:38.152 154 109.5 650  
16:27:10.319 154 109.5 650  
16:27:42.470 407 289.4 650  
16:28:14.632 407 289.4 650  
16:28:46.781 407 289.4 650  
16:29:18.931 407 289.4 650  
16:29:51.082 407 289.4 650  
16:30:23.233 407 289.4 650  
16:30:55.372 407 289.4 650  
16:31:27.531 407 289.4 650  
16:31:59.677 407 289.4 650  
16:32:31.844 407 289.4 650 changing gap voltage @optimal phase
16:33:03.408 407 289.4 163  
16:33:35.553 407 289.4 163  
16:34:07.714 407 289.4 163  
16:34:39.855 407 289.4 163  
16:35:11.998 407 289.4 163  
16:35:44.145 407 289.4 163  
16:36:16.310 407 289.4 163  
16:36:48.449 407 289.4 163  
16:37:20.584 407 289.4 163  
16:37:52.719 407 289.4 163  
16:38:24.878 407 289.4 163  
16:38:57.012 407 289.4 1281  
16:39:28.570 407 289.4 1281  
16:40:00.732 407 289.4 1281  
16:40:32.894 407 289.4 1281  
16:41:05.036 407 289.4 1281  
16:41:37.203 407 289.4 320  
16:42:09.351 407 289.4 320  
16:42:41.493 407 289.4 320  
16:43:13.636 154 109.5 320 phase destructive (optimal – 180 degree)
16:43:45.782 154 109.5 320  
16:44:17.928 154 109.5 320  
16:44:50.088 407 289.4 320 phase optimal again
16:45:22.223 407 289.4 320  
16:45:54.382 407 289.4 320  
16:46:26.525 407 289.4 320  
16:46:58.665 407 289.4 320  
16:47:30.798 407 289.4 320  
16:48:02.932 407 289.4 320  
Table Data. Shown are time of measurement as UTC (first column), phase difference of the two h=1 group DDS in nanoseconds (second column, revolution frequency ESR is 506.3 ns), phase difference in degree (third column) and rf-cavity gap voltage (fourth column).

image 160232 phi282-gap650.pngimage 160337 phi225-gap650.pngimage 160409 phi310-gap650.pngimage 160442 phi310-gap650.pngimage 160514 phi297-gap650.pngimage 160618 phi282-gap650.pngimage 160650 phi282-gap650.pngimage 160722 phi275-gap650.pngimage 160827 phi275-gap650.pngimage 161035 phi095-gap650.pngimage 161211 phi088-gap650.pngimage 161315 phi081-gap650.pngimage 161347 phi102-gap650.pngimage 161700 phi289-gap650.pngimage 161803 phi109-gap650.pngimage 161940 phi289-gap650.pngimage 162012 phi001-gap650.pngimage 162116 phi218-gap650.pngimage 162533 phi109-gap650.pngimage 162638 phi109-gap650.pngimage 162742 phi289-gap650.pngimage 162846 phi289-gap650.pngimage 162938 b2b-trapping-efficiency.pngimage 163159 phi289-gap650.pngimage 163407 phi289-gap163.pngimage 163439 phi289-gap163.pngimage 163648 phi289-gap163.pngimage 163857 phi289-gap1281.pngimage 164137 phi289-gap320.pngimage 164241 phi289-gap320.pngimage 164313 phi109-gap320.pngimage 164345 phi109-gap320.pngimage 164632 phi289-gap320.png

Figures: 'Waterfall' images sorted by time. The images have been taken during approximately one hour of measurement time. Numbers in the figure denote time of EVT_KICK_START1 as UTC, phase difference between h=1 Group DDS of SIS18 and ESR in degree and rf-gap-voltage in Volts. Each images shows the signal from FCT GE02DT1FP: Bunch from SIS18 captured in an ESR bucket. x-axis: bunch time [us] relative to h=1 (1.975 MHz), y-axis: time [ms] after acquisition start from bottom to top. Shown are data of ~ 3 ms after acquisition start. Data acquisition, processing and image are done by our colleagues from beam instrumentation.

RF-Phase Difference

Injection as Function of Phase Difference
image_162116_phi218-gap650
Figure: 218 degree phase difference.

image_160337_phi225-gap650
Figure: 225 degree phase difference.

image_160827_phi275-gap650
Figure: 275 degree phase difference.

image_163159_phi289-gap650
Figure: 289 degree phase difference, optimum phase difference (see below).

image_160514_phi297-gap650
Figure: 297 degree phase difference.

image_160442_phi310-gap650
Figure: 310 degree phase difference.

image_162012_phi001-gap650
Figure: 361 degree phase difference.

Determining the Best Phase Difference
Basically, we are novices here. As we tried to determine the best phase, the rf-amplitude was probably to large and it looks like the observation was hampered by quadrupole osciallations. As an alternative we tried to define the best phase, by first finding the worst (= most destructive phase) and then simply add 180 degree. All of the following measurements have been done with identical gap voltage of 650V in the ESR (ferrit cavity).

image_161211_phi088-gap650
Figure: 88 degree phase difference.

image_161035_phi095-gap650
Figure: 95 degree phase difference.

image_161347_phi102-gap650
Figure: 102 degree phase difference.

image_161803_phi109-gap650
Figure: 109 degree phase difference. Looks symmetrically worst!

It was decided that 109 degree looks most symmetrical. Thus, the best phase difference is expected at 109 + 180 = 289 degree.

image_161940_phi289-gap650
Figure: 289 degree phase difference. This is supposed to be the best phase difference for the actual conditions.

Idea: Finding the best conditions involves multiple measurements like the one above but for different rf-gap-voltages.

RF Gap Voltage

It looks like an important parameter is a good value of the RF Gap Voltage. I (db) am not an accelerator physicist, but my naive view is that the 'trapping potential' of the rf-buckets in the injection ring shall match the one of the extraction ring when the bunches are transferred. All of the following measurements have been done with identical rf-phase difference of 289 degree.

image_163407_phi289-gap163
Figure: 163V gap voltage.

image_164241_phi289-gap320
Figure: 320V gap voltage.

image_163159_phi289-gap650
Figure: 650V gap voltage.

image_163857_phi289-gap1281
Figure: 1281V gap voltage.

Reproducibility

reproducability_phi289-gap650.png
Figure: Bunch-to-Bucket transfers at identical conditions. The black horizontal line serves to guide the eye.

The figure above compare transfers that have been done with identical conditions (relative phase 289 degree, gap 650V). Here, data acquisition has been started upon EVT_KICK_START1 + 1ms. However, the time of transfer may vary within a window defined by the beating method. At the three rightmost images, the beam is injected into ESR approximately 0.5ms after start of acquisition, while at the two left images the beam is transferred sooner. A horizontal black line is drawn ~0.5ms after data acquisition. It is interesting to note, that the outer boarders of the 'bunch shapes' almost look identical in all five images, only the 'position of highest intensity' seems to move.

Stability and Precision

b2b-data_2021-may-17JPG.jpg
Figure: On-line data by the b2b system. Stability is demonstrated by the good match of DDS signals (green boxes) and kicker timing (orange boxes). The phase difference of the DDS signals (blue box) is averaged over one hour. Details (see text). Statistical data (average, standard deviation, min, max) represents data of 96 bunch-to-bucket transfers.

The figure above shows the key parameters of the experiment for 96 buncht-to-bucket transfers.
  • beating period ~216 us (~429 rf periods)
  • extraction: h=2; injection h=1

The orange boxes shows the deviation from the measured kicker signals (electronics out) from the ideal value. The standard deviation is only about 1.1 ns for both SIS18 (extraction) and ESR (injection). This is about a factor of three better compared to the 'old' timing generator (see BunchBucketTestMeasurement5).

The blue box shows the phase difference between the two group DDS signals averaged over the full measurement time of about one hour. As the phase difference was the main tuning parameter and changed many times, the shown value is not suitable to estimate the precision.

The green box shows the precise matching of the two group DDS signals at extraction. The standard deviation is only ~ 0.5 ns, while the maximum deviation from the ideal value is only 2 ns.
  • ext(traction): shows the deviation between measured and set-value; the set-value for kicker correction is already subtracted. In the ideal case, this should be 0 ns.
  • inj(ection) : shows the deviation between measrued and set-value; the set-value fors kicker correction as well as the phase difference are already subtracted. A perfect phase match yields a value of 0 ns!
Thus, the difference between set-value and act-value for the relative phase of both h=1 groupDDS signal at transfer is only 0.5 ns @ 1 sigma. This corresponds to a precision of about (0.5 ns / 506 ns) ~ 1e-4 or 0.36 degree. Even the observed worst case deviation was only -2 ns, which corresponds to ~ 4e-3 or 1.4 degree only.

Please keep in mind, that the beating period was only 216 us and extremely short. The trick to achieve such a good precision at short beating times is to calculate the matching of both rf-signals for a couple of beating times in advance and simply pick the best match. This method presently uses a 'brute force' algorithm and limited to 5 beating periods due to available computing power. This method could be improved in the future. However, at long beating times of 10 ms as assumed in the technical concept, such tricks are not required.

Trapping Efficiency with B2B

Unfortunately, we were unable to record long (seconds) signals. Fortunately, one of the analog instruments displayed the signal strength as a function of time for the optimum and worst phase. A screenshot is given in the figure below. First, it can be observed that the bunch remains stored for many seconds in both cases. For the 'worst case', the measured signal (in Volts) is 12 db less than with the 'optimum case'. Thus the signal strength (in Volts) is a factor of four less. This should correspond to the number of stored particles. Thus, when comparing 'worst'/'optimum' phase, the number of particles stored in rf-buckets differs by a factor of four. Remark: There could be more particles in the ring, but these would be outside the RF-potential and lost upon further manipulation such as acceleration or decelaration.

image_162938_b2b-trapping-efficiency.png
Figure: Signal strength of stored beam as a function of time. Shown are two traces. Optimum phase difference of 289 degree (white) and 'most destructive' phase difference of 109 degree (white). When comparing the signal strength for long storage time of about 1s (middle) the signal of the 'worst' phase difference is attenuated by ~ 12db compared to the case, when the bunch-to-bucket transfer is done with correct phase.

Conclusion

The bunch-to-bucket transfer system has been used in standard operation for about one week without issues. To continue using beam instrumentation devices connected to MIL timing, the bunch-to-bucket system should be triggered to an event different than EVT_KICK_START1/2.

Real bunch-to-bucket transfer has been demonstrated from SIS18 into ESR for the first time with the new system. This first attempt was successful. All measurements have been done within one hour only and no quantitative measurements have been performed. The recording time of the bunch signals was only about 3.5ms which should be prolonged for future measurements.

-- DietrichBeck - 9 June 2021
Topic revision: r9 - 04 Nov 2021, DietrichBeck
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