LC Commissioning, Operations and Availability

Transcription

1 International Technology Recommendation Panel X-Band Linear Collider Path to the Future LC Commissioning, Operations and Availability Tom Himel Stanford Linear Accelerator Center April 26-27, 2004

2 Integrating Luminosity Chris has convinced you that we can attain the energy Tor has convinced you that we can maintain small emittances and get the luminosity My job is to convince you that we can integrate that luminosity It s not quite as simple as: int Lum = L*t International Technology Review Panel April 26-27, 2004 Tom Himel 2

3 Contents: What else is involved? 1. Start commissioning while construction is ongoing (e.g. make positrons and run DRs while linacs are still being constructed.) This allows physics running to start sooner. 2. Include adequate beam diagnostics 3. Sophisticated Machine Protection System 4. Use feedbacks to maintain high luminosity 5. High availability must be designed in Use components with high MTBFs Two tunnels Independent positron source Damping Rings in their own tunnel International Technology Review Panel April 26-27, 2004 Tom Himel 3

4 Phased Commissioning Separate positron source and small damping rings not in the linac tunnel allow their commissioning to start 3 years before construction completion. The DRs are one of the most complex systems and need a lot of commissioning time to find and fix any errors and tune down the coupling. Phased commissioning allows time for the control system hardware, software, modeling, analysis and tuning algorithms to be refined. Phased commissioning allows less check-out to be done after construction completion, reduces the risk of schedule delays, and allows earlier commencement of integrating luminosity. International Technology Review Panel April 26-27, 2004 Tom Himel 4

5 Beam Diagnostics are Crucial Another lesson learned the hard way from the SLC. BPMs needed for beam based alignment and feedbacks Bunch length monitors to check the compression Beam size monitors allow the monitoring of emittance growth Need enough of them to localize the source of a problem. The NLC has 4 diagnostic stations spaced down each linac. This costs money and real estate, but it is more than worth it. Prototypes of all these and more are in various stages of development. International Technology Review Panel April 26-27, 2004 Tom Himel 5

6 Machine Protection System is Vital Warm and Cold: A single bunch drills a hole in anything. Tested at FFTB USLCTOS says high risk Failure is catastrophic (vacuum leak) Not discovered until pre-operations Large system so fix will be expensive and time consuming International Technology Review Panel April 26-27, 2004 Tom Himel 6

7 MPS Concepts from 1996 ZDR w/ 99 update Setup with single bunch high emittance beam at low rep-rate Go to full rate Reduce emittance Add bunches to the train Most devices can t change too much in 1/120 sec Monitor state of others (e.g. kickers) Monitor orbit 20% energy bandpass means some klystrons can be allowed to misfire. (undulator problem) Cold will have to be done differently International Technology Review Panel April 26-27, 2004 Tom Himel 7

8 Feedbacks Work SLC did not work at first. A major reason is that the feedback systems simply weren t done (or even started). Power supplies wander, the ground moves, operators make adjustments, temperatures and phases change. All power supplies and RF systems have feedbacks. Modern synchrotron light sources would not work without them. Your car s cruise control is a feedback. They are used everywhere because they are powerful and they work. We first design to minimize the sources of disturbances and then use feedback to correct what is left. International Technology Review Panel April 26-27, 2004 Tom Himel 8

9 At the end, SLC had feedbacks at about 50 locations. Most controlled 4 parameters. The beam stably went through 8 collimators with 200 micron gaps spaced 100 meters apart. Micron sized beams continuously collided at 120 Hz. We ve learned how to do it even better from full DR to IP simulations with feedbacks and wakefields of both the SLC and NLC. SLC Feedback systems International Technology Review Panel April 26-27, 2004 Tom Himel 9

10 Availability must be designed in Separate e+ source allows independent e+, e- setup, recovery and tuning 2 tunnels allows many repairs to be made with beam and others to be made without cooldown and access recovery. FMEA done on magnets and power supplies gained experience needed for other systems Above decisions were based on instincts honed from years of SLC experience. Now have an availability simulation International Technology Review Panel April 26-27, 2004 Tom Himel 10

11 Availability Simulation Developed as part of the US technology options study. Collected data on MTBFs and MTTRs of components in existing machines to guide our reliability budgeting process Wrote a simulation that given the MTBFs, MTTRs, numbers and redundancies of components, and access requirements for repair calculates average availability and the integrated luminosity per year. Developed a reasonable set of MTBFs that gave a reasonable overall availability. We allowed 25% downtime total. 10% was kept as contingency and MTBFs were tuned so the simulation gave 15% downtime. Iterated as many times as we had time for (one and a half iterations were done) to minimize the overall cost of the LC while maintaining the goal availability International Technology Review Panel April 26-27, 2004 Tom Himel 11

12 Availability: A Conventional e+ Source is Better than an Undulator Source Undulator e+ source has more downtime giving 18% less int lum when fully commissioned and 50% less in the early running. Not due to actual source reliabilities (which weren t modeled in detail and were assumed to be the same.) Completely due to undulator source needing well tuned high energy electrons. Prevents doing scheduled MD in e.g. e- linac and e+ DR simultaneously During downtime recovery cannot tune e+ system until e- linac is tuned. Can t do opportunistic MD in e+ system while e- is down or being tuned. Best to start with a conventional source and later upgrade to a polarized source. International Technology Review Panel April 26-27, 2004 Tom Himel 12

13 Availability: Two tunnels are Better than One The one tunnel option was only simulated for cold, not warm. Give cold results here as warm would be similar. If all components had the same reliability, the cold 1 tunnel design would have a downtime of 25% instead of the 15% of the 2 tunnel design. The required improvements to Mean Time To Failures (MTBFs) of many components and the necessary 6% increase in the energy overhead needed to recover the 15% availability are costly. We don t think it is worth the risk for the minor cost reduction and hence haven t considered a 1 tunnel warm design. International Technology Review Panel April 26-27, 2004 Tom Himel 13

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15 Today in Review: Some Strengths of X-band It has a 30% shorter site because of its higher gradient. This keeps the costs down It has a positron source independent of the high energy electron linac giving a higher availability for the same component MTBFs. It has a working prototype damping ring that has reached the design emittance. It allows for the damping rings to start commissioning 3 years before project completion. It has a linac only twice as long as a running linac based on similar technology. It has short sections which can be removed so new unanticipated devices can be added. It has structure BPMs which allow beam based alignment of the structures It has been designed and simulated from gun to IP by a team of people who made the first and only linear collider work It can reach 1.3 TeV at reduced luminosity It provides a natural transition to higher energy 2 beam accelerators International Technology Review Panel April 26-27, 2004 Tom Himel 15