1. PSB Injection scheme in the Linac 4 era
Introduction
The presented scheme will allow injecting the beam either in an accelerating bucket or with a fixed rf frequency.
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

2. Painting h1 Bucket limits h2 Buckets limits
ΔT1 = f(ΔE, φS , V1, V2)
ΔT2 = f(ΔE, φS , V1, V2)
ΔT3 = f(ΔE, φS , V1, V2)
ΔT4 = f(ΔE, φS , V1, V2)
4 timing values should be supplied for each injected turn
Beam Revolution reference tics
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

3. PSB injection scheme with Linac 4
Ring switching
Ring X-1
Distributor field
Ring X
Chopping during one period to maintain rf synchronism
T > 1 us -> too long
Revolution
Reference
All rings cannot be kept in phase at injection due to the chopper BEAM-OFF duration limited to 1μs => different phase in each ring
The dephasing will be chosen as a 1/10th of the revolution multiple to adapt to the present philosophy allowing injecting multiples of a 1/10th revolution.
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

4. Equipment to be synchronized
Pre-chopper
+LEBT
Debuncher
RF Feedforward
Source
Distri
4*rf
180 m
45 keV
Chopper
Amplitude modulated
for energy modulation (painting)
RF feedforward, energy modulator, debuncher, distributor and rf have to be in phase with the Chopper
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

5. Practical considerations - 1
The longest injection will take 100 μs in each ring
The field increase will be 1.2 G/100μs
This means ΔE = 154 keV/100 μs if following the ΔR =0 accelerating law (bucket height = 2.5 MeV). This increase of momentum corresponds to a shift in energy of the accelerating bucket.
This means ΔR = -0.8 mm/100 μs if following the Δp = 0 frequency law. This is the radial steering error that will be obtained if injecting at a fixed energy.
This means ΔE = keV/100 μs and ΔR = mm/100 μs if following the Δf = 0
This decrease of momentum corresponds to a shift in energy of the decelerating bucket.
Δf = 31.6 Hz/0.1Gauss (ΔR = 0 law) = 379 Hz/100μs with 1.2 Gauss/100μs
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

6. Practical considerations - 2
The chopper gates a beam that will arrive in the rf buckets 2μs (flight time) later.
If there is a phase change in the rf buckets, the chopper needs to know 2 μs in advance
At the end of the switching from one ring to the following, the rf signal of the latter needs to be in a pre-determined phase (although not necessarily at the same frequency) with respect to the previous ring rf.
All rings will have the same rf frequency at the very start of the injection in each of them.
After the start of the injection from this initial rf frequency and during the entire injection process, each ring is susceptible to follow an independent frequency law.
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

7. Practical considerations - 3
All rings will be synchronized to a common reference before the start of the injection process with a dephasing determined by the injection conditions in the previous ring(s).
All the process occurring during the injection in each ring needs to be predetermined as the synchronization phase of the following ring cannot be changed instantaneously (>>10 μs response time)
If the chopper receives the common injection reference rf signal, it can calculate the phase advance due to the pre-determined frequency program initiated in each ring during injection.
For the chopper timing to be in phase with the rf change, it must be aware of the frequency change timing (the foreseen beam-control changes its frequency at a rhythm dictated by a so-called “fast-loop-clock”. The frequency step (for the ΔR = 0 law) will be 19 Hz/5μs. (5μs is the foreseen “fast-loop-clock” period).
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

8. Practical considerations - 4
Note that, due to the fact that the rf cannot change in between 2 “fast-loop-clock” tics, below 5 injected turns there will be no frequency change.
For a perfect tracking of the frequency change, the injection process should be in phase with the “fast-loop-clock” .
In case the acceleration is not at all taken into account the integrated phase error over one injection of 100 μs would be : 13.6 degree of the revolution signal
In case the frequency increase is just averaged at the chopper level (the logic estimates an average frequency increase without checking the actual value), the peak phase error would be < 4.3 mo
Averaged
Frequency
Frequency
Updated every 5 μs
379 Hz
100 μs
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

9. Practical considerations - 5
In case we want to update the rf frequency at the B-train rate (1 tic / 8.3 μs) and estimate its average value at the chopper level; the maximum phase error would be equal to 50 mo. (The initial rf would still need to be synchronized to a single reference)
Estimated
Frequency
31.4 Hz
8.3 μs
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

10. PSB injection scheme with Linac 4
Injection in a stationary bucket at a fixed rf frequency
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

11. PSB injection scheme with Linac 4
Injection in an Accelerating Bucket
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

12. PSB injection scheme with Linac 4
Injection with a Δp = 0 rf frequency law
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

13. Hardware layout Injection Sequencing control Application Pre-chopper
+LEBT
Debuncher
Source
Distri
4*rf
180 m
45 keV
To Linac rf
feed-forward
Chopper ON/OFF
Injection
Sequencing control
Voltage modulation
Phase modulation
Number of turns
+ VH1
BIXi.SDIS (One line with 5 pulses possible)
Start injection pulse Ri (One line with 4 pulses possible)
Linac rf
Rev * REV
Rf reference source (h1 or h2)
BIX. SINJ
Fixed Injection reference source
ΔE 4 rings
Application
4 timing values for each injected turn
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

14. Requirements for the rf Low-Level
The beam control of each ring needs to be able to synchronize its rf to a signal that can be either h1 or h2, with a phase offset programmed at an application level and obtained in ppm. This synchronization will occur prior to injection
At the instant of the beginning of the injection, each ring will receive an external start pulse, from which the beam control will start following a frequency law driven either by the B-train or by an internal process. In both case the frequency law will be known to the exterior.
The reference rf could be issued from the R1 LLRF (last ring that will stay at a fixed frequency until it comes to its turn), but there is not much to gain using this approach. The economy of one extra rf source would be obtained at the price of having R1 treated as a special case with no injection synchronization and a specific treatment within the injection sequencing control (ISC) because the injection in ring 1 would become the only case where the reference train could be used without applying the phase advance corresponding to the accelerating law (There would also be a negligible time lag problem due to the fact that the rf will increase but the effect on the beam will be delayed by the rf-ISC-chopper-ring delay)
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

15. Requirements for ISC Injection Sequencing Control
The ISC will receive values indicating the number of turns injected in each ring, so it can provide the required pulses, using the reference rf.
The ISC will receive delay values representing a time lag from a reference tic (see slide 2). These delay values will be available for each single turn. The unit should be able to create the required windows with an absolute precision in the range of 1 ns (1o of the rev = 2.7 ns)
The remaining part of the circuit concerns the elements of the L4 line itself and will thus be treated by the team in charge.
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS

16. Requirements for the application layer
Knowing the number of turns injected in each ring (including decimal values by 1/10th of a turn),
knowing the Bdot at injection,
knowing the injection reference frequency,
calculate the initial phase (inj synchro phase value) of each ring with respect to the reference at injection,
calculate the timing table (with respect to the reference rf) used to trigger the chopper for each single turn of each single ring.
Alfred BLAS /01/2009
PSB injection scheme with Linac 4
Alfred BLAS