1. PSB Injection Sequencing in the Linac 4 Era PSB Injection Sequencing in the Linac 4 era Alfred BLAS 1 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 07/01/2009

2. PSB Injection Sequencing in the Linac 4 era Alfred BLAS 2 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 07/01/2009

3. Linac 4 beam from the source PSB Injection Sequencing in the Linac 4 era Alfred BLAS 3 from RF Structures for Linac 4, F. Gerigk, PAC 07 from P. Baudrenghien 07/01/2009 Source Pre-chopper LEBT 45 keV Distri 180 m 4*rf ChopperAmplitude modulated for energy modulation (painting)

4. PSB Injection Sequencing in the Linac 4 era Alfred BLAS 4 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 07/01/2009

5. Elements affecting the Chopper timing 1 – The distributor (source T. Fowler, L. Sermeus) PSB Injection Sequencing in the Linac 4 era Alfred BLAS 5 The distributor selects the destination of the Linac beam into the PSB. 5 positions selected by 5 magnets that are adding up their field Rest position = head dumpno kick 1 st position = ring 4 1 st magnet fired 2 nd position = ring 31 st + 2 nd magnets fired 3 rd position = ring 21 st + 2 nd + 3 rd magnets fired 4 th position= ring 11 st + 2 nd + 3 rd +4 th magnets fired 5 th position= Tail dump1 st + 2 nd + 3 rd + 4 th + 5 th 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 ns Estimated value with solid state switches; Could be diminished to 200 ns with thyratrons More 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 07/01/2009

6. Elements affecting the Chopper timing 2 – Last 2 PIMS cells (source F. Gerigk) PSB Injection Sequencing in the Linac 4 era Alfred BLAS 6 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. 07/01/2009

7. The Chopper (source M. Paoluzzi) PSB Injection Sequencing in the Linac 4 era Alfred BLAS 7 T rise/fall < 3.6 ns 25 ns < T ON < 1000 ns T OFF > 40 ns Values to be checked with the new version of the amplifier to be tested in January 2009 The 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 07/01/2009

8. The (slow) pre-Chopper (source Richard Scrivens) PSB Injection Sequencing in the Linac 4 era Alfred BLAS 8 T rise < 1ms T fall < 2μs T stable > 1 ms After T fall, 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” 07/01/2009 Pre-chopper Upstream the RFQ at 45 keV/c 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 9 Beam Revolution reference tics 07/01/2009

10. Consequences of the B field increase during injection PSB Injection Sequencing in the Linac 4 era Alfred BLAS 10 Injection from the 1 st 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 B dot leads to an horizontal injection error if the Linac energy remain constant and if the field in each ring is not compensated for. For B dot = 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) ( B INJ 160MeV = 2311 G R = 25 m p = 570 MeV/c ΔE [eV] = 0.519. Δp[eV/s]. c) => with B dot = 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 = 0 we would need Δp = 0.11 MeV for ΔB = 1.6 Gauss, and the frequency law should be adapted accordingly. 07/01/2009

11. Consequences of the B field increase during injection PSB Injection Sequencing in the Linac 4 era Alfred BLAS 11 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 07/01/2009

12. Injection scenari (under construction!!) PSB Injection Sequencing in the Linac 4 era Alfred BLAS 1207/01/2009 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 )

13. Information flow-chart PSB Injection Sequencing in the Linac 4 era Alfred BLAS 13 Bucket Shape V H1 V H2 Stable φ REV ref Distri. Position Linac Energy offset Distributor trig Window generation + Gating Chopper ON/OFF RF Feed- Forward The distributor position impacts the beam flight distance The energy offset impacts the beam flight time and the bucket boundaries 07/01/2009 Bucket Position

14. Bucket Painting PSB Injection Sequencing in the Linac 4 era Alfred BLAS 14 ΔT 1 = f(ring selected) ΔT 2 = f(ΔE, φ S, V1, V2) ΔT 3 = f(ΔE, φ S, V1, V2) ΔT 4 = f(ΔE, φ S, V1, V2) ΔT 5 = f(ΔE, φ S, V1, V2) Rev. reference h2 Buckets limits h1 Bucket limits 07/01/2009 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).

15. Chopping during change of injected ring 1. All rings in rf phase PSB Injection Sequencing in the Linac 4 era Alfred BLAS 15 Revolution Reference 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 viable It requires too long a chopping time for the actual circuit capability 07/01/2009

16. PSB Injection Sequencing in the Linac 4 era Alfred BLAS 16 Ring X reference Distributor field Ring X-1 Ring X Force Chopper-ON + change Chopper REV ref With the REV reference signal delayed by 500 ns or 5/10 th of a turn (distributor rise time = 500 ns) for the rings in descending order, the chopping will be limited in time according to the specifications NB: the diagram is valid for a whole number of turns injected in ring X. If additional 1/10 th of a turn are required, the REV reference of the following ring should be delayed accordingly!!! Ring X-1 reference Chopping OFF 07/01/2009 Chopping during change of injected ring 1. Rf phase different from one ring to another

17. Reference signals PSB Injection Sequencing in the Linac 4 era Alfred BLAS 17 PSB Inj. REF Source Rev Number of turns & V PROG H1 Rev R4 Rev R3 RevR2 RevR1 SDis R4 SDis R3 SDisR2 SDisR1 SDisTail SDis represented for 1.0 turn injected in Ring 4 1.5 turn in Ring 3 1.0 turn in Ring 2 0.1 turn in Ring 1 Revolution signal delayed by some 1/10 th of a period with respect to the previous ring. The first 5/10 th comes for the distr. Delay and the other 1 to 9/10 th for the decimal part of the nb of turns in the previous ring 10*Rev 5/10 th of T REV = Distr. Rise time LL RF Rev signals follow a Δp = 0 law during injection NOT ΔR = 0 !!!! rf R4 rf R3 rf R2 rf R1 To rf synchro = h1 (or h2 if V PROG H1 = 0) To Distr. and Chopper Control NB: All signals in phase with 10*Rev OK for counters!! BIX. SINJ 07/01/2009 To Chopper Control Chopper ON (high) – OFF (low) {high => no beam to PSB} Linac rf To chop in synchronism with the bunches

18. Chopper Control PSB Injection Sequencing in the Linac 4 era Alfred BLAS 18 Chopper and Energy Modulator Control Rev R4 Rev R3 RevR2 RevR1 SDis R4 SDis R3 SDisR2 SDisR1 SDisTail ΔE R4 ΔE R3 ΔE R2 ΔE R1 To Chopper and RF feed-forward Chopper ON/OFF PIMS ΔE Analog modulation PIMS voltage modulation 07/01/2009 5 timing values for each injected turn

19. Chopper Control PSB Injection Sequencing in the Linac 4 era Alfred BLAS 19 Chopper and Energy Modulator Control To Chopper and RF feed-forward Chopper ON/OFF PIMS ΔV Analog modulation ΔE 4 rings 07/01/2009 5 timing values for each injected turn PSB Inj. REF Source Rev 10*Rev LL RF BIX. SINJ Number of turns & V PROG H1 Rf synchro 4 rings SDIS 4 rings Linac rf

20. Injection sequencing - Possible setup PSB Injection Sequencing in the Linac 4 era Alfred BLAS 20 Chopper ON/OFF Voltage modulation ΔE 4 rings 07/01/2009 5 timing values for each injected turn Rev + 10* REV BIX. SINJ Number of turns + V H1 BIXi.SDIS Source Pre-chopper LEBT 45 keV Distri 180 m 4*rf Dedicated Injection rf source in BOR Injection Sequencing 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