Timing Generator / Kicker Synchronization
Synchronisation of the Rings
For buch-to-bucket transfer, the RF systems in SIS18 and in ESR have to operation inappropriate phase relation. This is achieved by detuning the RF frequencies in SIS18 and ESR and wait until both are in phase. From this point in time, depending on the differences in RF-frequency in both rings, the correct phase relation between both RF-systems is reached after an appropriate waiting time.
Phase relation between RF-systems of both rings is detected by a correlator. It generates a trigger pulse when both systems are in phase.
This trigger pulse is used to synchronously re-start the timing systems of both rings (however, the transfer then is controlled by the delivering ring only). This is, both timng systems wait after preparation for the transfer (when SIS18 can provide the beam and ESR can receive it). The timing sstems continue operation, when both rings are ready, and additionally the RF-systems are in phase. Then for start of beam transfer an event is send.
The timing generators (equipment model description TGX) are used to generate triggers for the extraction / injection kickers of SIS18 and ESR.
Fireing the kickes is initiated by events from the timing system. However, the extraction / injection kickers must be fired in the gap between two bunches (for synchronous injection between two RF-buckets respectively) with a timing precision of at least about 10 ns.
The position of the gap is determined by the accelerating RF. Thus, to precisely hit the gap, the kickers must be synchronised by the RF signal. This results in a staged triggering of the kickers:
- Initiate kick sequence, by event from the timing system
- Synchronize with RF-signal: Next zero-crossing of RF-signal starts trigger generation. Alternatively to the RF signal, a bunch phase signal can be used to determine the gap.
- Delay the trigger output by an adjustable delay, to compensate for all delays in cables, electronics, and the delay between zero-crossing of the RF signal and the gap position (varying with beam velocity only, these delays are constant during an experimental set-up).
- Output start trigger signal to the kickers.
Note, that for beam transfer from SIS to ESR both kickers are triggered by the same signal (both must be fired synchronously). However, the ESR kicker must be delayed respectively to the SIS kicker, to compensate for the beam transfer time - is this adjusted in the kicker delays?
Generating of the trigger signals for the kickers, as described above, is the task by two timing generators S00ZGT (for extraction from SIS) and E00ZGT (for extraction from the ESR, which is seldom done).
The SIS18 can be operated in several harmonic modes, providing 1, 2, 4, (standard operation) or 8 bunches in the synchrotron. For each of theses modes the RF uses independed frequency generators (Group-DDSes). Each of these can be used to operate the two RF accelerating cavities in the SIS18. Sophisticated operation some times requires to operate both accelerating cavities at different harmonic numbers, and even change the harmonic numbers in one accelerating cycle. Therefore, rather than providing a single RF master signal which is relevant (which one would this be?), for all harmonic numbers separate signals are provided. The timing generator then has to select the appropriate signal.
The timing generators have an input for the timing distribution (event bus) system and 8 inputs for RF-signals, from which one is selected by a switch. The event to initiate the trigger generation is decoded internally in the timing generator.
Both timing generators provide two outputs each, one trigger for extraction kicker and one output for the Q-kicker.
The timing generators cannot use the RF signals directly. Discriminators for pulse shaping are needed. For pulse shaping, the input stages of the former timing generator installation is used. The discriminators are located in a multiplexing unit which is seperated from the old timing generator installation. In the SIS, only the discriminator stages are used. In the ESR, the output after the multiplexer is used.
To distribute the trigger signals to the kickers in SIS and ESR, the so called "Ampel Kiste" is used. Seperately for extraction kicker and for Q-kickers, the outputs of the SIS and the ESR timing generators are fed into the "Ampel Kiste". Inputs are combined to outputs for SIS and ESR (?either trigger pulse from SIS or ESR timing generator triggers both kickers, SIS and ESR?).
Both timing generators (S00ZGT and E00ZGT) are mounted into the same crate. This crate is located in the beam diagnostic cave in the so called electronics room. The timing generators are mounted in Rack 10, which is the last row, right end.
Conections for event input, RF trigger signal input, and trigger output is on the back side.
For pulse shaping in the SIS, only the multiplexing unit is installed. It is located in Rack 10, below the timing generators, with access from the rear.
In the ESR, the former timing generator is still installed, connected to the multiplexing unit. Both are installed in rack 23. The multiplexing unit is accessible from the rear only.
The so called "Ampel-Kiste" to distribute the trigger signals to the kickers in SIS and ESR is located in rack 10, below the timing generators. Cabling is from the rear.
Cabling of RF-Signal Inputs
For details on cabling which is provided by the RF department (and which is used partly for input to the timing generators), see Synchrotron HF-Signale für andere GSI Fachgruppen
RF-Signals are provided in the last rack row in the electronics room, in rack 3. The RF provides seperate signals for the possible harmonic numbers. Cables are labeled by the harmonic number ("Gruppen-DDS H=1", "Gruppen-DDS H=2", "Gruppen-DDS H=4", "GRUPPEN DDS H=8"), and by cable nomenclatures ("S--DP-P / DHF PH 2" ... "S--DP-P / DHF PH 5"). Signals are provided by thick cables, with N-type connectro.
The cables from the RF rooms are connected to thinner RG58 cables with BNC connectors, leading to rack 10 (where the timing generator is locatd). Theses connection cables are labelled by "Reserve something" ("Reserve", "Reserve 2", "Reserve 3", "Reserve 4").
In rack 10, the intermediate cables from rack 3 are connected to the discriminator stages of the old timing generator. The output of three of the the discriminator stages are connected by thin Lemo cables to the inputs of the timing generator. The fourth signal from the RF (H=8) is not connected to the timing generator.
The cables as of 16. June 2012:
| Rack 3, from RF Departement
|| Rack 3 to Rack 10
|| Timing Generator
|| Gruppen-DDS H=1 (S--DP-P / DHF PH 2)
|| Reserve 2
|| Gruppen-DDS H=2 (S--DP-P / DHF PH 3)
|| Reserve 3
|| Gruppen-DDS H=4 (S--DP-P / DHF PH 4)
|| Reserve 4
|| GRUPPEN-DDS H=8 (S--DP-P / DHF PH 5)
Input configuration of the timing generator, as of June 9th 2012:
- DDS H=2
- DDS H=4
- DDS H=1
- not connected
- not connected
- not connected
- not connected
- not connected
Here, cables from the RF installations are lead to rack 23 in the electronics room.
It loooks like four cables are provided. The cables are thick as in SIS, with N-connectors. The calbes are labled by yellow marks, showing "E-DP-P /HF PN 1", "E-DP-P /HF PN 2", "E-DP-P /HF PN 3", "E-DP-P /HF PN 4". In addtition, the cables are marked by adhesive tape. Unfortunately, only one of these can be read easily (the others direct to the inside of the rack, and the cables are too stiff to be turned), showing "HF-Master".
The RF cables are connected to the input of the multiplexer of the former timing generator.
The two outputs orf the multiplexer unit (after the multiplexer, not after the discriminator stages as in SIS) are connected to two RG58 cables, labeld "E00ZG-HF-Tank 1" and "E00ZG-HF-Master". These cables seem to led to the timing generator of for the ESR. At least, two of the inputs of the timing genrator (1 and 2) are connected to RG 58 cables showing the same labels. Connection is (as of June 2012):
- E00ZG-HF-Tank 1