This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC , the State of Michigan and Michigan State University. Michigan State University designs and establishes FRIB as a DOE Office of Science National User Facility in support of the mission of the Office of Nuclear Physics. Masanori Ikegami Michigan State University Discussion on Linac Commissioning

 Lessens learned from J-PARC linac commissioning (initial commissioning)  Comparison between simulation and experiment in J-PARC linac commissioning (initial commissioning) Outline M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 2

 After MEBT, there is no beam stop until straight dump 300 m downstream  Quadrupole can be adjusted to deliver a low energy beam to the dump (no PMQ)  We could deliver beam from DTL1 to the straight dump without beam steering  We could deliver beam to the straight dump during phase scan tuning without steering Risk of excess radiation or component damage mitigated Good Alignment Helps M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 3

 Average beam power is limited for beam commissioning  RF duty factor as designed from the beginning (except for RFQ) RF was stable through out the commissioning RF Stability Matters M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 4 Peak currentPulse widthRepetition Design30 mA0.5 ms25 Hz Initial commissioning 5 mA0.05 ms1 Hz RF for commissioning -0.6 ms25 Hz

 Experienced sparking problem of RFQ which limited the beam power of entire facility for long  The problem exposed only after starting high duty factor beam operation We should be aware of the risk of single point failure Critical component should be tested early and thoroughly Beware Risk of Single Point Failure M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 5

 Advantage of pre-commissioning IS to DTL1 pre-commissioned at KEK  Smooth initial commissioning All beam diagnostics tested  Feed-back to construction  Some key component was not available Digital LLRF system  Test of RFQ might not be enough Pre-Commissioning of Critical Items M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 6

 Importance of stringent cavity protection Radio Frequency Quadrupole (RFQ) discharging problem limited the beam power and beam availability for more than a year Poor vacuum and cavity damage due to discharging at the first high duty factor operation Extensive Test of Single Point Failure Necessary M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 7 Low power operation due to RFQ discharging problem Careful interlock / Machine Protection System (MPS) design to protect components  Establish a backup plan  Test RFQ early 

 All hardware MPS are connected and off-line tested  No beam loss MPS is activated Beam Loss Monitor was only detector for beam loss MPS Threshold determined after accumulating operating experience  In FRIB, we assume MPS with differential beam current measurement (DBCM) from the beginning to shut off the beam for the next pulse  Fast beam inhibit will be commissioned and experimentally verified before increasing beam power MPS for Commissioning M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 8

 It is difficult to predict beam loss quantitatively Reality is always worse than simulation?  Qualitative behavior is reproduced by PIC simulations Beam loss observed at a location where larger beam size is predicted by simulation (but with no beam loss), and beam loss is mitigated by smoothing the envelope  It is often useful to guide the commissioning  Area with room for improvement? Comparison between Simulation and Experiment M. Ikegami, June 2015 ICFA-CSNS workshop - 05, Slide 9