Concept B2B-Lite

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Table of Contents

Plan A - Reminder

Figure: Sketch for B2B transfers from SIS18 to SIS100, figure from PhD Bai. Details see text.

A sketch for the B2B between two machines is shown in the above figure. The following tables describes some of the parameters.

what	description	source	comment
virtual cavity	virtual position of RF signals	N/A	reference for RF signals, logic concept
tv_ext	ToF from virtual cavity to kicker	LSA	extraction ring, depends on v/c
tv_inj	ToF from virtual cavity to kicker	LSA	injection ring, depends on v/c

| t_ext | kicker delay | LSA | extraction ring |inis

tinj	kicker delay	LSA	injection ring
tpattern	delay for specific bucket pattern	LSA	same for extraction and injection ring
ToF	Time-of-Flight between rings	LSA	depends on v/c
Th=1,ext	revolution period of ring	LSA	extraction ring
Th=1,inj	revolution period of ring	LSA	injection ring
EKDC	extraction kicker delay compensation	LSA	EKDC = Th=1,inj + tpattern - (ToF + tv_inj + text)
IKDC	injection kicker delay compensation	LSA	IKDC = Th=1,inj + tpattern - (tv_inj + tinj)

Table: B2B parameters

Plan B - B2B-Lite

Definitions

Plan B is B2B without signal reproduction. Instead of reproducing the signal of the injection machine (SIS100) at the extraction machine (SIS18), the idea is to use the bucket label signal '1st' from the extraction machine (SIS18) directly and make use of the known time difference T_diff-sync from the virtual cavity of the extraction machine (SIS18) to the one at the injection machine (SIS100).

• the vaue of T_diff-sync can be calculated from LSA settings
• a FTRN can timestamp digital signals to about 1 ns
• we assume the 1st (#1) at the group DDS of the extraction (injection) machine as digital 'TTL' signals
• we assume the actual frequency values can be read within the respective SCUs via Wishbone
• B2B can predict the synchronization windows sufficiently precise (better 1 us)

Figure: An idea for B2B without the need for SIS100 bucket marker @SIS18 . Top: Sketch of transfer; shown are kicker positions (magenta marker with circle), virtual cavity positions (green marker with square), first bunches in ring (1st, #1). Bottom: Sketch of timing; shown are bunch label markers (1st, #1, vertical black/red lines), (virtual) coincidence of requested bucket pattern at the virtual cavity of the injection machine (green marker with open triangle), trigger signal for kicker electronics (red flashes), 'bunch label marker triggers' (1st, #1, vertical red lines), start time of synchronization windows (red marker with line arrow) and synchronization windows (yellow boxes). Upper cap 'T' marks time differences, whereas lower cap 't' marks timestamps More details see text.

The example depicted in the figure above shows timing scheme for transfer between two rings. Here, the example of a transfer from SIS18 (2nd harmonics) to SIS100 (10th harmonics) is given.

The above table of B2B parameters can be extended:

what	description	source	comment
Tdiff-sync	difference of revolution frequency markers	LSA	tdiff-sync = tv_ext + ToF + tv_inj
Tact, h=1, ext	revolution period of ring	actual value in group DDS1	extraction ring
Tact, h=1, inj	revolution period of ring	actual value in group DDS1	injecting ring
TLSA, h=1, ext	revolution period of ring	LSA	extraction ring
TLSA, h=1, inj	revolution period of ring	LSA	injecting ring
sync-winext	synchronization window	Central B2B Unit	input to 'Trigger Decision' module
sync-wininj	synchronization window	Central B2B Unit	input to 'Trigger Decision' module
1st trigger	bucket label signal, extraction ring	group DDS extraction ring	input to 'Trigger Decision' module (identified by 'sync-winext')
#1 trigger	bucket label signal, injection ring	group DDS injection ring	input to 'Trigger Decision' module (identified by 'sync-wininj')
EKO	extraction kicker offset	LSA	EKO = TLSA, h=1, inj + Tpattern - (ToF + Tv_inj + Text) + Tdiff_sync
			EKO = TLSA, h=1, inj + Tpattern - (ToF + Tv_inj + Text) + Tv_ext + ToF + Tv_inj
			EKO = TLSA, h=1, inj + Tpattern + Tv_ext - Text
IKO	injection kicker offset	LSA	IKO = TLSA, h=1, inj + Tpattern - Tv_inj - Tinj
tsync-ext	start of sync-winext	Central B2B Unit (CBU)
tsync-inj	start of sync-wininj	Central B2B Unit (CBU)
Tsync-ext	length of sync-winext	Central B2B Unit (CBU)
Tsync-inj	length of sync-wininj	Central B2B Unit (CBU)

Table: More B2B parameters for 'plan B'. ¹If control loops are frozen, the actual values of T_{act, h=1} can be directly derived from LSA values (technical note by D. Lens).

Idea

The main idea for 'Plan B' is based on the following assumptions:

1. The values of actual frequencies of the 1st harmonic are exactly determined
   1. by register values in the group DDS of the extraction and injection rings.
   2. by LSA values (beam phase control loops based on phase shift, not on frequency shift)
2. The White Rabbit based timing system and group DDS input clock have a common reference clock.
3. Once the phase difference between 1st harmonic group DDS's of the two rings is known for a specific (White Rabbit) timestamp, the evolution of the phase relationship into the future does
   • not depend on the uncertainty of the frequencies (uncertainty is 0!)
   • only depend on the uncertainty of the phase measurement at the specific (White Rabbit) timestamp
4. As the frequencies are known, the phase difference at a specific time could be derived from the measurement of time difference of '0-crossings' of the two DDS signals.
5. Frequency Beating only, no Phase Shift

As a working hypothesis, the timestamp of a '0-crossing' of the 1st harmonics could be done via the Timestamp Latch Unit (TLU) of a PCIe FTRN with a precision of 1ns. This requires the signal of the 1st harmonics is available as a 50 Ohm TTL output of the group-DDS.

Data Flow and Implementation

Figure: Data Flow. Show is RF equipment (red boxes), B2B equipment (blue boxes), trigger decision module (green boxes) and kicker electronics (brown boxes). Input from LSA is indicated by small yellow boxes. Details see text.

The figure above shows the hardware view of the data flow for B2B. Required hardware components are listed in the following table.

what	HW platform	LSA input	timing event	new HW	new HDL	comment
group DDS's	SCU crates	X	X		?	required: Wishbone access to actual h=1 frequency
				?	?	required: h=1 signal as rectangular TTL 50 Ohm
FTRN TLU	FTRN with ns resolution		X			Pexaria, Exploder or SCU4
FTRN sync-win	FTRN with ns resolution		X			Pexaria, Exploder or SCU4, ns resolution only required for yet unforeseen requirements
CBU	lm32 program	X	X			some lm32 in some FTRN, connection to WR network required
TD	based on DIOB?, SCU crate	X	X	X	X	requires development (HEL?), consider MPS requirements as well
KE	?	X	X	X	X	requires development (HEL?), consider MPS requirements as well

Table: Overview on components for B2B-Lite. Columns LSA input and timing event indicate required input. Columns new HW and new HDL indicate developments that need to be done.

Procedure (Simplified)

The following procedure could be applied

1. ...
2. DM initiates transfer
3. (RF control loops frozen; as control loops use phase-shifting algorithms, the h=1 frequencies are identical to LSA values, if the loops are frozen)
4. (h=1 frequencies known to a Central B2B Unit (CBU), LSA values might be sufficient)
5. ...
6. simultaneous measurement of
   1. phase measurement of '1st harmonics 0-crossing' at extraction machine
   2. phase measurement of '1st harmonics 0-crossing' at injection machine
7. transfer of the phase values to CBU
8. CBU calculates
   1. time when the 1st harmonics of both machines are synchronized
   2. time for '1st trigger' (based on LSA values for T_diff-sync, T_{v_ext}, T_ext), see remark (1)
   3. time for '#1 trigger' (based on LSA values for T_diff-sync, T_{v_inj}, T_inj), see remark (1)
   4. t_sync-ext = t_{1st trigger} - T_{h=1, ext} / 2, will be sent to TDM, see remark (1)
   5. t_sync-inj = t_{#1 trigger} - T_{h=1, inj} / 2, will be sent to TDM, see remark (1)
   6. T_sync-ext = T_{h=1, ext}, for diagnostic purposes
   7. T_sync-inj = T_{h=1, inj}, for diagnostic purposes
9. transfer of t_sync-ext and T_sync-ext to a FTRN_ext close to the 'Trigger Decision Module' at the extraction machine
10. transfer of t_sync-inj and T_sync-inj to a FTRN_inj close to the 'Trigger Decision Module' at the injection machine
11. FTRN_ext generates sync-win_ext (required for Trigger Decision Module)
12. FTRN_inj generates sync-win_inj (required for Trigger Decision Module)
13. Group DDS's at extraction and injection machine generate 1st and #1 signals (required for Trigger Decision Module)
14. 'Trigger Decision Modules' generate the signals 'injection kick trigger' and 'extraction kick trigger' required for kicker electroncis
15. ...

Remark (1)

• it is planned, that the internal logic of the TDM is triggered based on a logical AND of the signals t_sync-inj/ext from the CBU and h=1 sync from the DDS. In that case
  • the values 'time 1st/#1 trigger' serve for diagnostics only
  • the values t_sync-inj/ext will be sent to the TDM
• as an alternative, the CBU could send the value 'time 1st/#1 trigger' directly, but with reduced precision. In this case
  • the values 'time 1st/#1 trigger' will be sent to the TDM (which no longer requires the h=1 input from the DDS)
  • the values t_sync-inj/ext serve for diagnostics only

origin	destination	gid	evtno	param	comment
DM	CBU	EXT_B2B_INJ	CMD_B2B_START	N/A	init transfer
CBU	TR_TLU_EXT	EXT_B2B_INJ	CMD_B2B_PMEXT	Th=1, ext	init phase measurement at extraction machine; has period as parameter
CBU	TR_TLU_INJ	EXT_B2B_INJ	CMD_B2B_PMINJ	Th=1, inj	init phase measurement at injection machine; has period as parameter
TR_TLU_EXT	CBU	EXT_B2B_INJ	CMD_B2B_PREXT	th=1, ext	send result of phase measurement; has timestamp as parameter
TR_TLU_INJ	CBU	EXT_B2B_INJ	CMD_B2B_PRINJ	th=1, inj	send result of phase measurement; has timestamp as parameter
CBU	TR_SYNC_EXT	EXT_B2B_INJ	CMD_B2B_SYNCEXT	N/A	schedule extraction sync trigger, tbd
CBU	TR_SYNC_INJ	EXT_B2B_INJ	CMD_B2B_SYNCINJ	N/A	schedule injection sync trigger, tbd
CBU	diagnostic	EXT_B2B_INJ	CMD_B2B_DIAGMATCH	N/A	diagnostic info, indicates when phases match
CBU	diagnostic	EXT_B2B_INJ	CMD_B2B_DIAGEXT	N/A	diagnostic info, projects measured phase into the future (useful for calibration)
CBU	diagnostic	EXT_B2B_INJ	CMD_B2B_DIAGINJ	N/A	diagnostic info, projects measured phase into the future (useful for calibration)
CBU	KICKER_EXT	EXT_B2B_INJ	CMD_B2B_KICKEXT	N/A	experimental: trigger for kicker
CBU	KICKER_INJ	EXT_B2B_INJ	CMD_B2B_KCIKINJ	N/A	experimental: trigger for kicker
...	...	EXT_B2B_INJ	...	diagnostic data	send diagnostic data (to be discussed)

DEPRECATED Table: Timing messages. As a first idea, a transfer from SIS18 -> SIS100 would use a dedicated timing group SIS18_B2B_SIS100.

Proposal for GID and EvtNo

GID

GID (d)	GID (x)	Name	Description	Source
	0x12c	SIS18_RING	(exists: CMD_B2B_TRIGGER... are sent here)	SIS18 CBU
	0x154	ESR_RING	(exists: CMD_B2B_TRIGGER... are sent here)	ESR CBU
	0x0d2	CRYRING_RING	(exists: CMD_B2B_TRIGGER... are sent here)	CRYRING CBU
	0x136	SIS100_RING	(exists: CMD_B2B_TRIGGER... are sent here)	SIS100 CBU
0d928	0x3a0	SIS18_B2B_EXTRACT	B2B internal: extraction from SIS18	SIS18 CBU
0d929	0x3a1	SIS18_B2B_ESR	B2B internal: transfer SIS18 to ESR	SIS18 CBU
0d930	0x3a2	SIS18_B2B_SIS100	B2B internal: transfer SIS18 to SIS100	SIS18 CBU
0d931	0x3a3	SIS18_B2B_PP	B2B internal: transfer SIS18 to plasma physics (after discussing with S. Goette, I think this is not required)	SIS18 CBU
0d933	0x3a5	ESR_B2B_EXTRACT	B2B internal: extraction from ESR	ESR CBU
0d934	0x3a6	ESR_B2B_CRYRING	B2B internal: transfer ESR to CRYRING	ESR CBU
0d938	0x3aa	CRYRING_B2B_EXTRACT	B2B internal: extraction from CRYRING	CRYRING CBU
0d944	0x3b0	SIS100_B2B_EXTRACT	B2B internal: extraction from SIS100	SIS100 CBU
...	...	...	...

Table: Group numbers used for internal communication by the B2B system.

The table above is not complete and needs to be extended for upcoming machines like CR, HESR using the following scheme:

• < ring A >_B2B_< ring b >: transfer between rings
• < ring A >_B2B_PP: transfer from a ring to PHELIX; (special case, requires synchronizing with laser instead of RF)
• < ring A >_B2B_EXTRACT: extraction from a ring; the target is unspecified and might be an experiment (FRS, PRIOR ...)

EvtNo

!EvtNo (d)	!EvtNo (x)	Name	Description
0d2048	0x800	CMD_B2B_PMEXT	B2B internal: request phase measurement (extraction)
0d2049	0x801	CMD_B2B_PMINJ	B2B internal: request phase measurement (injection)
0d2050	0x802	CMD_B2B_PREXT	B2B internal: send result of phase measurement (extraction)
0d2051	0x803	CMD_B2B_PRINJ	B2B internal: send result of phase measurement (injection)
0d2052	0x804	CMD_B2B_TRIGGEREXT	B2B internal: trigger kicker electronics (extraction) [1]
0d2053	0x805	CMD_B2B_TRIGGERINJ	B2B internal: trigger kicker electronics (injection) [1]
0d2054	0x806	CMD_B2B_DIAGMATCH	B2B internal: optional diagnostic, indicates when phases match
0d2055	0x807	CMD_B2B_DIAGEXT	B2B internal: optional diagnostic (extraction)
0d2056	0x808	CMD_B2B_DIAGINJ	B2B internal: optional diagnostic (injection)
0d2057	0x809	CMD_B2B_DIAGKICKEXT	B2B internal: optional kick diagnostic (extraction)
0d2058	0x80a	CMD_B2B_DIAGKICKINJ	B2B internal: optional kick diagnostic (injection)
...	...	...	...
0d2079	0x81f	CMD_B2B_...	reserved til here

Table: Event numbers used for internal communication of the B2B system. Only 0x800..0x805 are used for operation. Other event numbers serve for optional run-time diagnostics.

[1] CMD_B2B_TRIGGER.... will be sent to the relevant group. Example: CMD_B2B_TRIGGEREXT is sent to SIS18_RING when the extraction kicker shall be triggered.

Phase Matching Algorithm

Due to White Rabbit, timing receivers share a common notion of time. Hence, it is easy to solve phase matching in the time domain. In addition, the lm32 soft-cores don't support floating point calculations and adding numbers is match faster compared to (emulated) divisions. In order to minimize uncertainties due to rounding of numbers, the algorithm described here uses a timescale in atoseconds.

Figure: Shown are markers of h=1 rf-periods for extraction (bottom) and injection (top). The ratio of the rf-periods is 2/3. The h=1 signals match after 2 (3) periods for extraction (injection), markers for a 'match' are shown in red. The lowest combination of harmonic numbers to achieve this situation is h=3 (extraction) and h=2 (injection), see dashed markers.

The figure above shows a situation with two ring machines using (from a operations points of view) a weird rf-ratio of 2/3; there is no beating and the h=1 signals are perfectly matched for the lowest common multiple of frequencies. In this case the periods match when using h=3 for extraction and h=2 for injection. As can be seen in the figure above, the h=1 signals match after 2 * 'h=1 periods' for extraction and 3 * 'h=1 periods' for injection.

Figure: This is the same figure with a slight detuning of frequency to achieve beating. Shown is a situation, where the h=1 frequency of the injection machine is increased slightly. Dashed markers indicate how the red markers of the injection machine evolves compared to the extraction machine. After one iteration, the time difference between red markers is T_diff. Beating can be observed by the time differences (T_D0..D2) between the (almost) matching solid red markers, which becomes smaller witch each iteration.

The figure above shows a situation for frequency beats. From the point of view of the extraction machine, the red marker of the injection machine 'comes closer' with every iteration. One just has to wait until the red marker of the injection machine matches/passes the one of the extraction machine. This is predictable. T_diff is known from LSA values and T_D0 is the time difference between the phase measurements at the two machines, see remark (2). The ratio T_D0 / T_diff is just the number of iterations until phase matching of the h=1 signals will be achieved; the length of one iteration is known too.

Remark (2)

• the algorithm has to distinct between two cases, depending which machine is detuned in which direction
• for practical reasons, the starting conditions of the algorithm has to be chosen such, that T_D0 is smaller than the shortest h=1 period. This can easily be achieved by shifting the measured phase values by their periods
• the algorithm implies
  • rf beam control loops are frozen prior to the start of the phase matching procedure
  • rf beam control loops for stabilization are based on a phase shifting method; in this case the rf frequencies are identical to LSA values

Documents

• B2B-lite_2020-01-30.pdf: short presentation

-- DietrichBeck - 30 Jan 2020