1. Why we should consider keeping Linac2 as a spare 1 M. Vretenar Linac4 BCC, 29.04.2010

2. Motivations 2 or, I base my calculations on the expectation that luck will be against me (Napoleon) If you want success, plan for disaster (MV)

3. The worst scenario 3 2 nd Murphy’s law: If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong. Let’s assume that:  Linac4 starts operation for PSB as foreseen in 2015, operating reliably.  a “major accident” occurs in 2015-16, requiring months to be repaired. Examples: - a large fire in the equipment building, originating from the explosion of a capacitor in a HV modulator (defective capacitors can develop gas and break in the first year(s) of operation), as in the SPS in May 1997 (3 months of cleaning and repair) or from overheating of a resistor, as at CTF a few months ago. (Probability: 2 events over 6 machines during 20 years = 1.7% /year !) - pollution of an accelerating cavity (from malfunctioning vacuum pumps or else) that leads to internal sparking avoiding to reach the voltage. It happened in 1998, luckily on an RFQ under test. Repair can take >3 months and there is no guarantee that it will work.

4. But over the long term things improve… 4 However, probability for “large-scale” events goes quickly down with time – they are usually related to construction defects in the equipment appearing in the first years of operation. → There is no point in keeping Linac2 operational forever. After a certain time (3-5 years?) we can start dismantling it (or else).

5. What to do in case of a large accident? 5 If: 1.the estimate of the time needed to repair Linac4 is more than X months (with X=time required to put Linac2 back in operation), 2. the pressure from physics is high, or 3. the resources for repairing Linac4 are not available. Then, it could make sense to foresee the option of reverting to Linac2, and reconnecting again Linac4 one (or 2) years later, once Linac4 is completely repaired. This clearly would mean a lot of work, but is a pure catastrophic scenario (very low probability, but we have to consider cases with low probability but high impact!). Any catastrophy requires a lot of work, the point is to identify which scenario requires less work and less time off for physics.

6. Goal of today’s meeting 6 From my point of view, the goals of today’s meeting are: 1.to estimate together a value for the time X. 2.to estimate the additional cost (for the Linac4 project) of keeping Linac2 alive. 3.to estimate the manpower required (for reverting to Linac2 and then connecting back Linac4 a few years later). i.e., give me a quotation for a belt and braces suit…