psb injection sequencing in the linac 4 era
DESCRIPTION
PSB Injection Sequencing in the Linac 4 Era. Synthesized information from: M.E. Angoletta, P. Baudrenghien, C. Carli, A. Findlay, T. Fowler, F. Gerigk , A. Lombardi, M. Paoluzzi, F. Pedersen, L. Sermeus, R. Scrivens. - PowerPoint PPT PresentationTRANSCRIPT
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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PSB Injection Sequencing
in the Linac 4 EraSynthesized information from:
M.E. Angoletta, P. Baudrenghien, C. Carli, A. Findlay, T. Fowler, F. Gerigk,A. Lombardi, M. Paoluzzi, F. Pedersen, L. Sermeus, R. Scrivens
07/01/2009
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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The Linac 4 H- beam is injected in the PSB at 160 MeV/c (v=157mm/ns)instead of 50 MeV/c with Linac 2 H+.
Radio-activation of the PSB can be limited by chopping the beam at 3 MeV/c during “dead times” of the multi-turn injection process.
“Dead times” of the multi-turn injection process means:
•Switching time from one ring to the following (distributor rise time 500 ns)
•Out-of-bucket beam injection
Outline
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PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Linac 4 beam from the source
Time
High Voltage
< 1.2 ms0.3 ms
0.15
ms
0.15
ms
Beam segment
RF transient
RF ON segment
HV ON segment
from RF Structures for Linac 4, F. Gerigk, PAC 07
from P. Baudrenghien
07/01/2009
SourcePre-chopper
LEBT
45 keV
Distri
180 m
4*rf
Chopper Amplitude modulatedfor energy modulation (painting)
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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•The beam out of the source is chopped by a pre-chopper until it stabilizes (< 1ms).
•When this is achieved the beam flies through a LEBT which requires 20 μs to let through the full intensity (space charge compensation).
•The beam is then accelerated in the RFQ after which the fast chopper selects the destination: either distributor at the end of the Linac or the 3 MeV dump. This dump position can only be hold for 1 μs.
• Just before the distributor the beam flies through the last two PIMS cells where the voltage can be modulated. This modulates the beam energy and the beam flight time towards the PSB.
•The beam then flies through the distributor which selects its final destination in always the same sequence from Head dump to Tail dump via the 4 PSB rings from ring 4 to ring 1 (top-down). The Linac-to-ring distance varies depending on the selected ring.
Beam generation
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Elements affecting the Chopper timing
1 – The distributor (source T. Fowler, L. Sermeus)
The distributor selects the destination of the Linac beam into the PSB.5 positions selected by 5 magnets that are adding up their fieldRest position = head dump no kick1st position = ring 4 1st magnet fired2nd position = ring 3 1st + 2nd magnets fired3rd position = ring 2 1st + 2nd + 3rd magnets fired4th position = ring 1 1st + 2nd + 3rd +4th magnets fired5th position = Tail dump 1st + 2nd + 3rd + 4th + 5th magnets fired
These 5 magnets should stay active until the end of the Linac pulse (total length 450 μs, see slide 8)
Kicker rise time (10-90%) = 500 nsEstimated value with solid state switches;Could be diminished to 200 ns with thyratronsMore information in June 2009
The beam travel time within the injection channels is different from ring to ring and this affects the beam-to-bucket synchronization
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Elements affecting the Chopper timing
2 – Last 2 PIMS cells (source F. Gerigk)
•The rf amplitude is modulated to modulate the beam output energy (bucket painting) .•From the central 160 MeV/c , an extra ΔE from -1.2 MeV to +1.2 MeV is added.•For each cell, this means a Klystron power ranging from 0.51 MW to 0.84 MW (>1.25 MW available)•The amplitude change rate is limited by the klystron’s power.•For ΔE a single sweep from -1.2 MeV to +1.2 the required time is 8.7 us for 1MW available•For a lower ΔE the sweep time can be decreased proportionnaly (4.35 us from -0.6 to +0.6MeV)
Energy modulation means beam flight time modulation : +/- 3.4 ns difference over the 180 m separating PIMS and PSB injection Foil (source A. Lombardi)This will affect the beam phasing with respect to the debuncher and to the rf buckets.
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The Chopper (source M. Paoluzzi)
•Trise/fall < 3.6 ns
•25 ns < TON < 1000 ns
•TOFF > 40 ns
Values to be checked with the new version of the amplifier to be tested in January 2009The reproducibility of the response time from trigger to kick remains a question mark
Linac bunch length out of the RFQ 280 ps
Chopper IN/OUT
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The (slow) pre-Chopper (source Richard Scrivens)
•Trise < 1ms
•Tfall < 2μs
•Tstable > 1 ms
After Tfall , the beam starts to feed the downstream LEBT (beam transport) which requires 20 us to stabilize (space charge compensation) and deliver the full current
“The pre-chopper is used once per cycle; it doesn’t act at the end of the cycle” “the beam OFF duration is not unlimited”
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Pre-chopperUpstream the RFQ at 45 keV/c
0
10
20
30
40
50
60
70
80
90
-1200 -700 -200 300 800Time (us)
Prechopper
Plasma RF Power / Beam From Source
Beam into RFQ
TstableTrise
0
10
20
30
40
50
60
70
80
90
-80 -60 -40 -20 0 20 40Time (us)
Prechopper
Plasma RF Power / Beam From Source
Beam into RFQ
Tfall
The beam into RFQ rise time is more likely around 20 μs
9
Bucket Painting (source C. Carli)
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
BeamRevolution reference tics
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Consequences of the B field increase during injection
•Injection from the 1st turn into R4 until the last turn into R1 can last 401 μs (4 x 100 turns/ring + 3 x 500 ns distributor rise time)
•Such an injection duration associated with a non-zero Bdot leads to an horizontal injection error if the Linac energy remain constant and if the field in each ring is not compensated for.
•For Bdot = 0.1 T/s, the field increase during 400 μs will be 0.4 Gauss or 4 tics of the 0.1 Gauss B-train.
•With dp=0 => and (dp = 0 frequency law followed by the rf)
( BINJ 160MeV = 2311 G R = 25 m p = 570 MeV/c ΔE [eV] = 0.519. Δp[eV/s] . c)
=> with Bdot = 0.1T/s and the maximum number of turns =>ΔR= -0.26 mm.
This corresponds to a 1 mm error for a presently typical 0.4 T/s at injection with a total ΔB = 1.6 Gauss .
If we can increase the Linac energy by Δp such that dp/p = dB/B in order to have ΔR = 0we would need Δp = 0.11 MeV for ΔB = 1.6 Gauss, and the frequency law should be adapted accordingly.
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B
dB
R
dR
tr
2
1
5.162 tr
B
dB
f
df
tr
2
1
17.1
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Consequences of the B field increase during injection
•If B (0.4 T/s) R (-1mm for 100 turns in each ring) and frequency law =
•If B (0.4 T/s) and p (0.11 MeV) ΔR = 0 and frequency law =
•In both cases with ΔB = 1.6 Gauss, the revolution frequency swing would in the order of 700 Hz
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B
dB
f
df
B
dB
f
df 2
12
Injection scenari (under construction!!)
PSB Injection Sequencing in the Linac 4 era Alfred BLAS07/01/2009
The injection can be made in different ways:One fact is accepted: the field will increase during injection.
If we want the same conditions in each ring, we need to apply a Field compensation with the Bdl magnets. What is the possible amplitude of this correction?Would we like to make the injection at a fixed frequency? Can we make a B-field correction with a slope that compensates the one of the main magnets?
With the B-field compensation, the conditions are identical during the injection but are different from one ring to the other during the catch-up process that follows.
One different approach is to play with the linac energy. The beam energy is increased at a rate that corresponds to the Field increase ΔR=0 and so is the rf. We need to check what the head room is in term of energy increase???
One practical aspect is that having a single rf reference would ease the synchronization of all the linac 4 and PSB elements.
Do we accelerate during injection or do we not?
If we don’t:•If all rings are synchronized to a single reference following a Δp=0 law, the price to pay will be a radial offset (1 mm max for 0.4 T/s)•If we don’t want this radial offset, we can increase the Linac energy at the same rate as B (0.11 MeV max in the most demanding case with 0.4 T/s). The single rf reference will follow this time a different frequency law
•If we don’t want to increase the Linac energy, we can compensate the field in each ring (max 1.6 Gauss with 0.4 T/s) using the Bdl correction. A single rf reference can be applied but it should stay at a fixed value!
If we do:•Each ring has its specific rf following a ΔR=0 law, The proper inter ring rf phasing during ring switching can be pre-established from initial conditions with initial phases and frequencies being set at a specific time, and from then on, the sequence is programmed (we don’t follow the measured Btrain )
B
dB
f
df2
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Information flow-chart
Bucket Shape
VH1
VH2
Stable φ
REV refDistri. Position
Linac Energy offset
Distributor trig
Window generation
+ Gating
ChopperON/OFF
RFFeed-
Forward
•The distributor position impacts the beam flight distance•The energy offset impacts the beam flight time and the bucket boundaries
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Bucket Position
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Bucket Painting
ΔT1 = f(ring selected)ΔT2 = f(ΔE, φS , V1, V2)ΔT3 = f(ΔE, φS , V1, V2)ΔT4 = f(ΔE, φS , V1, V2)ΔT5 = f(ΔE, φS , V1, V2)
Rev. reference
h2 Buckets limits
h1 Bucket limits
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•The chopper ON/OFF control would require revolution tics synchronous with the rf buckets + 5 timing values for each turn in each ring. These values are calculated at an application level and sent to a hardware register for each cycle (ppm).
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Chopping during change of injected ring1. All rings in rf phase
RevolutionReference
Distributor fieldRing X-1
Ring X
Chopping during one period to maintain rf synchronism
T > 1 us -> too long
This approach with all rings synchronized on the same signal is not viableIt requires too long a chopping time for the actual circuit capability
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Ring X reference
Distributor field Ring X-1
Ring X
Force Chopper-ON + changeChopper REV ref
With the REV reference signal delayed by 500 ns or 5/10th of a turn (distributor rise time = 500 ns) for the rings in descending order, the chopping will be limited in time according to the specificationsNB: the diagram is valid for a whole number of turns injected in ringX . If additional 1/10th of a turn are required, the REV reference of the following ring should be delayed accordingly!!!
Ring X-1 reference
Chopping OFF
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Chopping during change of injected ring1. Rf phase different from one ring to another
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Reference signals
PSBInj.REF
Source
Rev
Number of turns& VPROG H1
Rev R4Rev R3RevR2RevR1
SDis R4SDis R3SDisR2SDisR1SDisTail
SDis represented for 1.0 turn injected in Ring 4
1.5 turn in Ring 31.0 turn in Ring 2
0.1 turn in Ring 1
Revolution signal delayed by some 1/10th of a period with respect to the previous ring. The first 5/10th comes for the distr. Delay and the
other 1 to 9/10th for the decimal part of the nb of turns in the previous ring
10*Rev
5/10th of TREV = Distr. Rise time
LLRF
Rev signals follow a Δp = 0 law during injectionNOT ΔR = 0 !!!!
rf R4rf R3rf R2rf R1
To rf synchro= h1 (or h2 if VPROG H1 = 0)
To Distr. and
Chopper Control
NB: All signals in phase with 10*RevOK for counters!!
BIX. SINJ
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ToChopper Control
Chopper ON (high) – OFF (low) {high => no beam to PSB}
Linac rfTo chop in
synchronism with the bunches
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Chopper Control
Chopperand
Energy Modulator
Control
Rev R4Rev R3RevR2RevR1
SDis R4SDis R3SDisR2SDisR1
SDisTail
ΔE R4ΔE R3ΔE R2ΔE R1
To Chopperand RF feed-forward
Chopper ON/OFF
PIMSΔE
Analog modulation
PIMS voltage modulation
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5 timing values for
each injected turn
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Chopper Control
Chopperand
Energy Modulator
Control
To Chopperand RF feed-forward
Chopper ON/OFF
PIMSΔV
Analog modulation
ΔE4 rings
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5 timing values for
each injected turn
PSBInj.REF
Source
Rev
10*RevLLRF
BIX. SINJ
Number of turns& VPROG H1
Rf synchro4 rings
SDIS4 rings
Linac rf
PSB Injection Sequencing in the Linac 4 era Alfred BLAS
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Injection sequencing - Possible setup
Chopper ON/OFF
Voltage modulation
ΔE4 rings
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5 timing values for each injected turn
Rev + 10* REV
BIX. SINJ
Number of turns+ VH1
BIXi.SDIS
SourcePre-chopper
LEBT
45 keV
Distri
180 m
4*rf
Dedicated Injection rf
source in BOR
InjectionSequencing
control
To Linac rf feed-forward
Rf for synchro, 4 rings
Application
Linac rf
Could be a programmable fixed frequency
source at the ISC level