1. S2 Discussion Input based on TTF / FLASH and the XFEL Preparation Work Hans Weise / DESY Sept-11, 2006 Thanks to Nobu’s nice summary!!! His summary / remarks / conclusion is in blue, my additions are black (on the following pages)

2. TTF  2 / FLASH (1) Gun –Max 10Hz, 1nC x 7200 bunches. Laser-driven photocathode in 1.6cell L-band NC acc –One 9-cell L-band SC cavity (beam energy: 4MeV  16MeV) Accelerator –Slots for 6 x 8-cavity cryomodules Each cavity is 9-cell. So far, 5 CM slots have been occupied –3 (?) RF  6 CMs  48Cavities (40 so far in OPS) –TTF  2/FLASH is approximately equivalent to 2 ILC units. –Eacc ~ 18MV/m on average  730MeV beam with 5CMs turned on.

3. TTF2 / VUV-FEL (FLASH ) Gun –Max 10Hz, 1nC x 7200 bunches. Laser-driven photocathode in 1.6cell L-band NC acc –One 9-cell L-band SC cavity (beam energy: 4MeV  16MeV) rep.rate 1, 2, 5, 10 Hz NC gun body’s water cooling requires optim.water temperature (typ. 58 deg) regulation, i.e. adopt the rep.rate; since we operate at typ. 3.2 MW RF with long pulses (200-800 µs), initial RF conditioning is an issue; Dark current from the gun/cathode is the main dc source along the whole TTF; when going to long bunch trains, we carefully watch and optimize the linac, i.e. try to collimate this dc. The bunch compression needed for the FEL needs very high LLRF and synchronisation stability; we look for bunch arrival time stability in the order of the bunch length, i.e. 50 fs; this downstream of the dispersive BC sections! The RF Gun and ACC1 (first module) stability is demanding!!! (0.01% and 0.01 deg); if not reached, consequences for photon intensity’s stability

4. Accelerator –Slots for 6 x 8-cavity cryomodules Each cavity is 9-cell. So far, 5 CM slots have been occupied –3 (?) RF  6 CMs  48Cavities (40 so far in OPS) –TTF  2/FLASH is approximately equivalent to 2 ILC units. –Eacc ~ 18MV/m on average  730MeV beam with 5CMs turned on. 5 acc.modules (3 type II, 2 type 3 cryostat) are installed; assembly date -> see TTF overview talks; no warm up since approx. 2 years; 3 klystrons are used, this is due to the BCs, i.e. (ACC1)BC(ACC2+ACC3)BC(ACC4+ACC5) Waveguide system (to some extend) takes care of particular bad cavities, i.e. add.attenuators where required; alread here: no aging of cavities! Gradient for the first 4 cav.in ACC1 is intentionally reduced to approx. 12 MV/m due to long.bunch gymnastics; cav 5 in ACC1 (35 MV/m cav.) is at about 21 MV/m (reduced gradient spread required for LLRF (one klystron!)) TTF2 / VUV-FEL (FLASH )

5. TTF  2 / FLASH (2) Operation Statistics –Injector commissioning since Spring 2004. First lasing in early 2005, user operation since Summer, 2005. –July 2005  Feb 2006: ~3600 hr (150 d). ~50% for users, 16% for FEL studies, the rest for acc studies and maintenance. –Beam delivery ~ 64%, 26% tuning /dev/off time, 16% down time, out of the scheduled user beam time (Weise’s reliability report says 11%. Is this because of different denominator or improvement?) –Downtime beak-down. Klys ~ 30%, cryo (CM and Cryogen?) ~ 30%.Detailed break-downs? Others from laser, MPS, OPS etc. –Issues of schedule pressure from the duty of FEL runs forced the group to launch user operation before establishing full performance validation. Installation Issues –Most of the RF sources, such as klystrons, and electronics are outside the tunnels to meet the FLASH schedule. This makes the layout different from what is envisage at XFEL, yet this allows discussion based on hands-on experience with one layout scenario.

6. Operation Statistics –Injector commissioning since Spring 2004. First lasing in early 2005, user operation since Summer, 2005. Time between Injector commissioning and first lasing is long since… In 2004 we had severe budget problems at DESY. Many components were delayed; we tried to set priorities well matched with milestones; so we interrupted the installation for the inj.comm. and used the time to fabricate the delayed components; we restarted beam operation late fall 2005; This not as an excuse but as an explanation… We were happy to see first lasing an January 14, 2005 at 30 nm… From our point of view this was a quick start… TTF2 / VUV-FEL (FLASH )

7. Operation Statistics –July 2005  Feb 2006: ~3600 hr (150 d). ~50% for users, 16% for FEL studies, the rest for acc studies and maintenance. 25-Jul-2005 to 26-Feb-2006 3,120 h of scheduled user operation which is 52% of the total beam time total beam time (52% for users, 16% FEL studies, 24% accel.studies, 8% maintenance) Statistics for user operation period gives 64% beam delivery 16% downtime (11% for total period) 14% tuning 4% off time (e.g. VIP visits) 1.8% acc.developm. from 27-Feb-2006 to 16-Apr-2006 difficult to draw concl. from statistics since we had a long acc.study period with many diff.experiments incl. test of new LLRF boards etc. TTF2 / VUV-FEL (FLASH )

8. Operation Statistics –July 2005  Feb 2006: ~3600 hr (150 d). ~50% for users, 16% for FEL studies, the rest for acc studies and maintenance. 17-Apr-2006 to 13-Aug-2006 (weeks 16-32) Total scheduled up-time: 2,648 h Scheduled off-time (interlock tests + weekly maintenance): 208 h Users 39% Accelerat or studies 17% FEL studies 37% Off 7% SASE beam for users 32% Developme nts 23% Tuning 25% Down 13% Off 7 % Total time: 2856 h (17 weeks, 7 days/week, 24 h/day) Total up time: 2284.1 h (80%) TTF2 / VUV-FEL (FLASH )

9. Down time weeks 16-32 Total downtime: 370.8 h (13%) 264.7 h (71%) 24.2 h (7%) 20.5 h (6%) 9 h (2%) 17 h (5%) 10 h (3%) 4.2 h (1%) 1.5 h (<1%) 1 h (<1%) 0.8 h (<1%) 10.3 h (3%) 7.6 h (2%) Klystrons / modulators: 71% LLRF: 7% Photonline: 5% Laser: 6% Magnets: 2% Controls: 3% Protection: 2% Other: 3% Water: 1% Klystrons / modulators is the sum of both plus waveguides, pre-amplifier, interlocks…. We urgently have to detail this; about 50% was one single event (bouncer circ. capacitor)

10. Hardware failures – an attempt to analyze the data… no failure Kly/Mod 4, i.e. the MBK (at present every 2nd pulse at 6.5 MW) Kly/Mod 3: all the 129 hours were caused by an oil leakage problem with the HV PS transformer, followed by some trouble with the regulation after replacing the transformer Kly/Mod 2: 56 hours caused by a water leakage problem with a new 5 MW Thales tube (wrong material!) Kly/Mod 5: approx. 25 hours caused by a defect capacitor in the bouncer Kly / Mod. hardware failures weeks 16-32

11. Operation Statistics –July 2005  Feb 2006: ~3600 hr (150 d). ~50% for users, 16% for FEL studies, the rest for acc studies and maintenance. –Beam delivery ~ 64%, 26% tuning /dev/off time, 16% down time, out of the scheduled user beam time (Weise’s reliability report says 11%. Is this because of different denominator or improvement?) –Downtime beak-down. Klys ~ 30%, cryo (CM and Cryogen?) ~ 30%.Detailed break-downs? Others from laser, MPS, OPS etc. Summary operation statistics: From end July 2005 to August 2006 (13 months) we had approx. 10 khours of operation; the typ. downtime was approx. 15%; operation relies on one maintenance day (8 hours) per week TTF2 / VUV-FEL (FLASH )

12. Operation Statistics –Issues of schedule pressure from the duty of FEL runs forced the group to launch user operation before establishing full performance validation. Yes and No…. The FEL user operation was and still is important for our work. Without the user’s request for the XFEL we’ll never build the XFEL… The full performance validation (form the accel.point of view) requires a perfect Machine Protection System; this esp. in view of risking the undulator; here we suffered a lot from the above mentioned gun/cathode dark current; now, the beam transport is much nicer (better power supplies, working BPMs etc. guarantee a stable beam trajectory) and we dared to test the MPS; we recently lased with more than 500 µs!!! TTF2 / VUV-FEL (FLASH )

13. Installation Issues –Most of the RF sources, such as klystrons, and electronics are outside the tunnels to meet the FLASH schedule. This makes the layout different from what is envisage at XFEL, yet this allows discussion based on hands-on experience with one layout scenario. Again Yes and No…. We started with klystrons, electronics etc. outside the tunnel. Nevertheless, a number of power supplies, front end electronics (diagnostics) is inside. We made a lot of measurements… and think, that for the XFEL the installation inside the tunnel is correct; this assumes that the field emission inside the cavities is below the max. accepted level (add.cryo losses); Looking at the ILC this works if the field emission on-set scales nicely with the gradient; By the way, also a MUST w.r.t. the additional cryo load!!! The XFEL layout exists, i.e. we know where to place the electronics incl. shielding. Nevertheless, the time to get access to the front ends is an issue, i.e. an overall philosophy for redundance/spares (hot! (sorry “cold”)) is required. TTF2 / VUV-FEL (FLASH )

14. TTF  2 / FLASH (2) Remarks (Toge) –It would help to see more accounting of RF and cryo problems, if any, from TTF  2 / FLASH, when we attempt to map this experience to what we should be prepared for Test linac facilities for ILC. –Substantial discussions from TTF/FLASH were found on Stability (gun laser, LLRF, orbit and optics) Jitter of longitudinal beam phase space (temperature stabilization is an identified issue) Commissioning and operation of beam diagnostics  while some such issues might not be as stringent as those demanded at XFEL, the system testing of a similar nature for ILC should pay very close attention over a wide range of related subjects. This is probably not something that we extract too easily from SRF experiences from storage rings.

15. Remarks (Toge) –It would help to see more accounting of RF and cryo problems, if any, from TTF  2 / FLASH, when we attempt to map this experience to what we should be prepared for Test linac facilities for ILC. … more accounting of RF problems … I totally agree; we will try to establish a much better statistics; to some extend the actual problem is that the standard operator sees the RF as a kind of turn- key-system, just very few knobs; in principal, this is exactly what we want to have but error analysis becomes more difficult, esp. during nights and weekends; the typical operator treatment… let’s RESET In some cases too high or just wrong set-points for the LLRF cause a ‘klystron problem’, in this case: cavity interlock protects the cav. by switching of the klystron… ok, let’s study details BUT HERE IS AN ADVICE: As long as we have treated TTF as a test facility, there was always an excuse (test of new boards, special conditions…); the only TRUE EXPERIENCE you get if you give the machine to standard operators (techn., eng., ‘even’ physicists) TTF2 / VUV-FEL (FLASH )

16. Remarks (Toge) –Substantial discussions from TTF/FLASH were found on Stability (gun laser, LLRF, orbit and optics) Jitter of longitudinal beam phase space (temperature stabilization is an identified issue) Commissioning and operation of beam diagnostics  while some such issues might not be as stringent as those demanded at XFEL, the system testing of a similar nature for ILC should pay very close attention over a wide range of related subjects. This is probably not something that we extract too easily from SRF experiences from storage rings. … system testing of a similar nature for ILC should pay very close attention over a wide range of related subjects … Thank you, Nobu! I fully agree, 100%!!! From TTF we know: it’s much more than the SRF (look at the downtime statistics); we talk about a new Linac generation which has all the nice features of modern digital (but still new and to some extend untested) control; space projects rely on good old stuff, i.e. the previous and robust generation of electronics (have you ever looked at Space Shuttle technology?); here we try to base projects on new techniques… what a difference!!! TTF2 / VUV-FEL (FLASH )

17. XFEL Availability Considerations (1) System Outline –0.1-0.5GeV: 4 CM = 32Cavs @12.5MV/m; RF station outside tunnel. –0.5-2GeV: 12 CM = 96Cavs @15.1MV/m or 64 Cavs @22.6MV/m; (2+1) RF stations inside tunnel. –2 – 20GeV: 100 CM = 800 Cavs @ 21.7MV/m or 736 Cavs @23.6MV/m; (23+2) RF stations inside tunnel Requirements –20 wks of photon beam user operation per year, including tuning shifts 85% beam delivery 10% tuning 5% downtime (to be compatible with what the SR facility users are used to) Comparison with ILC –XFEL corresponds to approximately 6% of the entire ILC ML, in terms of #CM. About 9%, in terms of #RF stations. NO!!! This was last years TTF/VUV-FEL (FLASH) number; no one would build the XFEL for 20 weeks per year; I guess they want to have 45 to 50 weeks per year

18. XFEL Availability Considerations (2) Solution outline –Injector Dual installation Most infrastructure outside the accelerator tunnels De-rated accelerating gradient (12-15MV/m) Moderate RF power (20% of available max) Early commissioning –ML CM replacement assumed unlikely  hang from the ceiling Pulse cables underneath the floor Prepare for maintenance of klystron and electronics  right next to the transportation area. we start with one injector only; the second one might be a second generation injector In the first module just phase space gymnastics

19. XFEL Availability Considerations (3) Solution outline (continued) –Testing before string-assembly Individual testing of cavities Conditioning of couplers Cold-temperature testing of tuners Magnet excitation (BTW, no cold feed-through’s) –All CMs to be tested cold + RF before installation –Klystrons, 10MW rated, will operate at 5.2MW –WG distribution system to be tested in units of one acc module length prior to tunnel installation –LLRF expected to be reliable, as inferred from TTF/VUV-FEL experience + redundancy being planned. –Cryogenics

20. Remarks It would be nice to see more specific data on component-level failure issues from TTF  1, TTF  2/FLASH, and how they have been or are being addressed, because they represent a large amount of opportunities for new comers (i.e. ILC) to learn. While making the ML components being operational and available, we also need to pay attention to issues related to “stable beam operation” as TTF/XFEL colleagues are emphasizing. We should examine how the XFEL availability improvement solutions would apply to the ILC case. Should we do the same or should we do much better, etc? If we (ILC) sort of “skip” being seriously engaged in Euro-XFEL experiences and declare ourselves ready to go ahead with construction of ILC at around 2010, we need to be clear and confident as to why we can say so. E N D

21. Remarks It would be nice to see more specific data on component-level failure issues from TTF  1, TTF  2/FLASH, and how they have been or are being addressed, because they represent a large amount of opportunities for new comers (i.e. ILC) to learn. Again … again … again … again … If you see any possibility, please do not study the operation and its problems in the daily life from *.doc, *.ppt, *.xls but send well-trained and experienced operators to join the TTF crew; a face-to-face meeting between eng./techn. is probably much more useful than our discussions. The other way would be to ask dedicated questions; again on the techn. level; simulations are nice but we have all seen that the comparison with running accelerators is difficult…

22. Remarks While making the ML components being operational and available, we also need to pay attention to issues related to “stable beam operation” as TTF/XFEL colleagues are emphasizing. What is it we are emphasizing? I guess: operate such systems … (see above)

23. Remarks We should examine how the XFEL availability improvement solutions would apply to the ILC case. Should we do the same or should we do much better, etc? If we (ILC) sort of “skip” being seriously engaged in Euro-XFEL experiences and declare ourselves ready to go ahead with construction of ILC at around 2010, we need to be clear and confident as to why we can say so. ILC probably should do better… but I have to think about it… (see next slides) If ILC wants to “skip” being …. you need more than good arguments. Who in the world would close his eyes and go into a pre-construction phase without trying to understand the 2010 status of the XFEL? Sorry, but the projects were, are, and remain “coupled”. Look at the recent Linac Conference: many small projects refer to the TESLA technology. So all our funding agencies know exactly what we are talking about. Therefore the XFEL and ILC have some common way to go… It is obvious that the success of the XFEL is indispensable, but not sufficient. At present, I do not see that the XFEL work is seen so. Too often I hear that it is not possible to draw conclusions from the XFEL design and preparation work since … (see next slides)

26. Time schedule assumes final project approval & funding at European level in 2006 Site approval (“PFV”) and preparations for placing orders for civil construction will happen before official project start XFEL Time Schedule 2009: LCLS start operation (SLAC) 2006 2012/13 preparationconstructionbeam operation 2014/15 SASE1 SASE2+3, spont. rad project start 2004 2010: Results from major ILC R&D projects and conversion to pre-construction phase input for ILC industrialization of all Linac sub-systems productioncommissioning acceptance test and installation

27. Cavities: Industrial production of 1,000 cavities, couplers, tuners, incl. quality assurance. Final specs. for mass production. Single cavity tests for 1,000 cavities. Coupler conditioning for 1,000 couplers. Cryomodules: Many thermal cycles; starting next spring; at the module test stand. Full specs. for industrial production (fabrication & assembly). Includes all sub-assemblies (cavity, coupler, tuner, quads-package, BPM) and assembly procedures incl. alignment, transport etc. LLRF & front-end: Many test at the module test stand, starting now. Module 6 will be tested up to almost 35 MV/m; this for some months. Radiation measurements inside TTF and at module test stand give input for the design of local shielding. What one can learn from TTF / FLASH and the XFEL (incl. it’s preparation phase)

28. Operation experience (TTF / FLASH): Exercise the daily operation as a user facility. Due to the user facility mode, we allow experts to improve / modify their systems only every xxx weeks; instead of modifications they have to keep it in operation which is a useful exercise. Operation experience is almost independent from the cav.gradient; at least as long as you go to the systems’ performance limit. What one can learn from TTF / FLASH and the XFEL (incl. it’s preparation phase)

29. Cavities: High gradient with increased onset for field emission; As a rule of thumb: XFEL: 23.6 MV/m with f.e. on-set of at least 20 MV/m. We know that we get a factor of 10 in dark current for each 4 MV/m gradient step. At present the typical f.e. on-set is below 20 MV/m. So it’s wise to aim for an f.e. on-set not less than 4 MV/m below the operation gradient. ILC cavities have to be tested… Reproducible cavity quality at the higher gradients. Do we need new recipes for the cavity preparation and treatment? A change in the cavity shape requires o repeat all beam based measurements, i.e. it produces a large effort (TTF size, 100 M$ investment) incl. all the sophisticated beam diagnostics. Cryomodules: If a modified version (type 4) is required, check everything TTC has checked. May be even more due to stronger requirements. BUT industrialization is independent of details in the design, i.e. a company trained to build type 3+ modules can easily fabricate type 4 modules. Here the XFEL pays off, at least in Europe. What one cannot learn from TTF / FLASH and the XFEL (incl. it’s preparation phase)