Transcript LHC_Timing_Issues

LHC Fast Timing
Generation & Distribution
P. Baudrenghien AB/RF
Numerology (1)
For each ring:
The 400 MHz RF defines 35640 buckets, spaced by one RF
period, and numbered from 1 to 35640
Bucket 1 is the first bucket after the 3 ms long abort gap
(defined from bucket 34442 to 35640)
For the instrumentation to work, the first (maybe only) bunch
must be in bucket 1
For 25ns operation the bunches will occupy buckets 1, 11,
21 etc. with gaps occurring every PS or SPS kicker gap. For
43 bunch operation the bunches will occupy buckets 1, 811,
1621, etc. (see LHC-OP-ES-0003 rev 1.0 for the different
schemes).
7 May 2007
LEADE meeting
2
Numerology (2)
For 25ns operation the bunches will occupy buckets 1, 11, 21 etc.
with gaps occurring every PS or SPS kicker gap. (see Figure 1
above reproduced from LHC-OP-ES-0003 rev 1.0).
7 May 2007
LEADE meeting
3
Numerology (3)
For 43 bunch operation the bunches will occupy buckets 1, 811,
1621, etc. (see Figure 3 above reproduced from LHC-OP-ES-0003
rev 1.0).
7 May 2007
LEADE meeting
4
Revolution Frequency or Orbit
For each ring:
The revolution frequency (Frev or orbit) is a train of pulses, with one
5 ns long pulse per turn. This pulse points to bucket 1. The
revolution frequency is obtained by dividing the RF by 35640
At a given place in the machine, and at a given beam energy
(that is fixed RF frequency) the delay between the pulse and the
passage of a bunch in bucket 1 will be fixed from run to run
Drift during the ramp: Signals remain in phase with the
corresponding beam in IP4 (RF cavities). During the acceleration,
the revolution frequency increases by 2.2 ppm for protons (868 Hz
@ 400 MHz) and 14 ppm for Pb (5.5 kHz @ 400 MHz). [See LHC
Radio-Frequency Swing, P. Baudrenghien, 14 th Leade meeting,
Dec 15th, 2003]. At a given place, but varying energy (frequency)
the Frev-bunch delay will drift during the acceleration ramp due to
the difference between signal transmission delay and the beam
time of flight. For protons we have 6.5 ps/km, for ions 41.25 ps/km.
Hopefully not a problem.
7 May 2007
LEADE meeting
5
Bunch Clock
For each ring:
The Bunch Clock is a square wave obtained by dividing the
RF by 10. The divider is synchronized on the Revolution
Frequency (see page 8)
At a given place in the machine, and at a given beam
energy (RF frequency) the delay between the edge of the
Bunch Clock and the passage of a bunch will be fixed
from run to run
Drift during the ramp: During the proton ramp the Bunch
Clock frequency increases by 86.8 Hz (protons) and 550 Hz
(Pb). At a given place, but varying energy (frequency) the
edge will drift with respect to the bunch. (Same figures as for
the Revolution Frequency pulses.)
7 May 2007
LEADE meeting
6
Collision Pattern
Ring 1 w.r.t. ring 2:
While for each ring bucket 1 and its revolution frequency are
locked together, the two bunch patterns can be “rotated” with
respect to each other so as to move or set the collision
points
This is usually done before the injection process with
collision (and crossing) points defined before filling. This is
the preferred method as it keeps crossing points fixed from
injection to physics
It can also be done after injection by changing the phase of
one RF system (and thereby the corresponding beam) with
respect to the other (Machine Development)
Convention (proposed): bunches in bucket 1 of the two rings
collide in IP1 (or any other IP. To be agreed before start
commissioning)
7 May 2007
LEADE meeting
7
Clock Generation
Fiber optic links to CCR
(AB/CO+EXP), CMS
Bunch Clock
1 wave)
(square
F rev 1 (orbit)
SR4
Ring 1
400 MHz RF 1
OUT
1/10
Divider
VTU
400 MHz RF 2
RF IN
Sync
F rev 1 (orbit)
Fiber optic links to CCR
(AB/CO+EXP), CMS
Ring 2
F rev 2 (orbit)
RF IN
OUT
1/10
Divider
VTU
Bunch Clock 2
(square wave)
Sync
F rev 2 (orbit)
(pulse train)
400 MHz RF1
(pulse train)
400 MHz RF 1
400 MHz RF 2
(square wave)
400 MHz RF 2
(square wave)
All signals are generated in SR4
They are transmitted to CMS (point 5) directly
And they are transmitted to the other experiments via CCR
(optical splitter 1:4)
7 May 2007
LEADE meeting
8
Reference Clock Generation
Common
(Rephasing)
SR4
7 TeV Synth
400 MHz Ref
400.789658 MHz
Fiber optic links to CCR
(AB/CO+EXP), CMS
400 MHz Ref
(square wave)
Phase shifter
To Beam Control system:
Rephase both rings onto
this reference before
physics
Ref Bunch Clock
1/10
Divider
VTU
Cogging
Cogging of Ref 40 MHz to put it in phase
with the bunch at 7 TeV: phase shift by 0
to 9 full RF periods at 400 MHz
(square wave)
Synchro Bunch
Module Clock 2
TDC
Bunch Clock1
The Ref Bunch Clock is a stable, constant frequency square wave at 40.078966
MHz (7 TeV proton) obtained by asynchronous division (1:10) of a 400 MHz
Reference (400.789658 MHz). This 400 MHz Reference is generated by a
commercial Low Noise Frequency Synthesizer
On the flat top (7 TeV), but before physics starts, the 400 MHz RF1 and RF2
(and the corresponding beams) are rephased onto this 400 MHz Reference. The
Bunch Clocks 1 and 2 follow automatically
But the Ref Bunch Clock can still be off by 1 to 9 periods @ 400 MHz. To fix that
the Ref Bunch Clock will be slowly phase shifted by the proper number of 400
MHz periods to bring it in phase with the bunch
When physics starts, the delay between the edge of the Ref Bunch Clock
and the passage of a bunch will be thus fixed from run to run
7 May 2007
LEADE meeting
9
450 GeV Engineering Run
Reference clock should be at 400.788790 MHz (450 GeV
proton)
Alternatively, the experiments could use the ring 1 or ring 2
clocks as these remain at fixed frequency (no acceleration
ramp). This is much easier for the RF as rephasing and cogging
are not needed in that case. Is it acceptable? To be discussed
after the new LHC commissioning schedule is made public (midMay)
7 May 2007
LEADE meeting
10
Availability of clocks
see also edms 628536 v1, TTC System Upgrade, S. Baron, Sept
29, 2005
1/35640 and 1/10 dividers are resynchronized at each filling, once,
before the first SPS-LHC transfer
During resynchronization the output signal disappears for ~1 ms
Signal presence and validity is then guaranteed, from shortly
before filling until beam dump
After beam dump it is not excluded that the RF manipulate its
equipment (switch a crate off/on) and signal may disappear.
Experiments should make sure that no manual reset is needed in that
case
Presence of signals is not guaranteed outside physics run due to
maintenance needed on the RF equipment, or if basic control facilities
are lacking. That applies in particular to shutdown periods
The AB/RF group is responsible for the transmission up to the Fiber
Optic receivers installed in the experiments (including on-call service).
In return the experiments will make for an easy access to this
equipment and help implement remote acquisition of the status of the
Fiber Optic RX (optical power, presence and frequency of detected RF
signal) so that AB/OP and AB/RF can quickly diagnose the
transmission
7 May 2007
LEADE meeting
11
Installation planning
VME cards Fiber Optic TX/RX eda-1380 and
eda-1382
V1 designed and tested (Angel Monera and S. Baron)
V2 layout finished. (Layout completed at the Design Office
last Friday. Being checked by D. Stellfeld AB/RF)
Proto v2 ready to be tested in June
Series order placed in July. Critical components have
already been ordered (April)
Installation foreseen in September
7 May 2007
LEADE meeting
12