SNS visit 18-22 November K. Hanke, B. Mikulec, JL Sanchez-Alvarez, JF Comblin, F. Chapuis

1. SNS visit 18-22 November K. Hanke, B. Mikulec, JL Sanchez-Alvarez, JF Comblin, F. Chapuis objective was to see a machine with H- injection in real day-to-day operation, find out what the issues are, frequency and nature of problems, operating model, etc.

2. accelerator complex

3. main machine and beam parameters • rep. rate 60 Hz, one injection every 16.66 ms • number of turns injected into ring: 1000 • the actual cycle within this basic period is only 1 ms • revolution frequency 1.045883 MHz • beam energy nominal 1.0 GeV, presently running slightly below that (932 MeV) due to limited modulator power (capacitor problems + overheating); energy upgrade to come (linac); will go up to 1.3 GeV by installing 9 more cryo-modules, space left in the linac tunnel for more cavities • ring does not accelerate, only bunch compression (presumably required by target)

4. linac • source: 2 RF power supplies (2MHz and 13MHz) • RFQ: old one gives some problems (bad transmission ~60-70%); unclear why; new one had just arrived • chopper: 2 devices: in the LEBT and in the MEBT; they said that they would not even need the second one, only if full beam has to be removed (extinction factor of 1st one ~10-4-10-5) • normal conducting linac gives occasional problems (flashovers, vacuum windows weak point) • super conducting linac perfectly stable

5. ring • only accumulating and bunching, no acceleration • magnets are DC • RF 2 harmonics (H1 = 1.05 MHz; H2=2.10 MHz) • ferrite cavities • 4 cavities (2 running in H1 mode, 1 spare H1, 1 running in H2 mode) • H1 mode gives bunch structure • H2 mode to avoid peak intensity in the bunch • 13 extraction kickers (+1 hot spare) all pulsing together, 200 ns gap provided by the choppers for the extraction kicker rise-time

6. injection process and hardware • horizontal and vertical painting (4 horizontal kickers and 4 vertical kickers) • no longitudinal painting • foil flatters; cause not very well known (mechanical, thermal shock, discharge etc.); under investigation but not conclusive • foil needs conditioning after a foil change; need to start up with reduced intensity for ~hours (but no issue at 1 Hz) • foil: 350 μg/cm2, actual thickness 1 um, size 17 x 54 mm • 3% beam loss (~1-1.5 mA on external dump) • stripping made by 2 foils (1st thin foil strips H-, 2nd thick foil strips remaining H- and H0) • stripping foil damage or failure is diagnosed by the increase of BLM and beam intensity on the dump; results in stop of the MPS • Preventive foil exchange every 4-6 weeks

7. diagnostics and tools • diagnostics do not acquire every pulse, but only 1/10 of them • BEAST = Best Ever Alarm System Tool • unstripped ions measured by a BCT, ~1.5 mA, modulation on the signal visible which is oftendue to foil shaking, also visible on the other BCT; 1.5 mA is the sum of the H- and H0 • laser stripping being developed; issue is to generate short bunch length (~ps);1st result 90% stripping efficiency for 6-7 ns @ 1Hz; needs machine studies; may need dedicated cavity for bunch rotation (currently using 2 last cavity modules); requires 2 MW laser; want to measure the H0; still in MD mode; HW gives lots of prbs. (HV not at required level etc.) • wire scanners: concept of super Gaussian (during the painting the profile becomes non-Gaussian, with steep edges and flat; combination of Gaussians); wire scanners can do simultaneous scans; this causes beam loss and can trigger a beam stop; used during setting up and once per month • BLMs: main tool; they do all the setting up with BLMs (hundreds) • BPMs: there is an equivalent to YASP • SEM grids: HV applied to remove stripped electrons, says that works well but do not see any difference in the profile with and w/o HV • camera on the foil (was broken)

8. BLMs current on injection dump

9. safety and interlocks • PPS (Personnel Protection System): 4 access points equippedwithvideocameras;controlled by two redundant PLC ways; no hardware loop; PPS communicating with MPS (Machine Protection System) • MPS (Machine Protection System) acts on source and choppers.

10. controls • controls of the diagnostics done a lot in LABView (mainly for BI), JAVA, X-Motif • 3 levels of colors: green = system OK, yellow = system drifting (intervention not required), red = system failing (intervention required) • low level: EPICS (equivalent to FESA) • GUI mainly provided by operators; based on synoptic • Java starts to replace the older GUI application

11. issues • anything shorter than 1 min not accounted for • power glitches • power supplies • controls • external faults (storms) • normal conducting linac has prbs.; sparking, vacuum issues • super conducting linac perfectly stable • depending on the breakdown duration need to ramp up slowly to its maximum power • foil flickering, foil temperature high, camera broken • vacuum issues in the DTL

12. operations model • very calm (one user, one beam type) • 12 hours shift periods (06:00 to 18:00, 18:00 to 06:00) • normal operation: 3 people on shift (+ 1 for training; team composed of one shift Leader and two operators • troubleshooting: • - troubleshooting on site not very often • - mainly based on best effort servicevia call-out list • - usually one specialist per equipment family • an Accelerator Physics/Maintenance Period is always followed by a start-up/restore phase of 8 hours • FY2014: operational efficiency for neutron production 92.3%