Minutes of meeting held on 28 Jan 2021 ========================= Link to slides: https://beamdocs.fnal.gov/AD-public/DocDB/ShowDocument?docid=8956 (a) Tan gave an update of work done in Booster (1) Laser notcher cavity has been replaced with a new flange design to facilitate easy install/removal (i) Replacement from letting up and pump down only took about 4 hours. (ii) Problem was coming back up: the laser box was not properly aligned with the RFQ. There is enough slop that the box was installed crooked. (iii) After re-alignment of the laser box to the RFQ another problem arose: a filter was out of place. This caused confusion as to whether high power laser pulses was getting to the beam. The entire re-commissioning took more than 10 hours. (2) Klystron testing continues. The firing circuit was changed out. Pulsing has started. (3) RF phase measurements. Confirmed very odd phase results. Tan thinks he has figured out why. Will discuss at next RF phase meeting. (4) 2nd harmonic. Drafter at TD will work on repair drawings. The outer shell will be removed and cleaned. (5) Mode 2 damper. PIPII review at the end of Feb. Bill will continue looking at mode 2. (b) John Johnstone talked about the effect of H0 stark stripping and irradiation of elements downstream of the foil (1) The underlying concept is that some fraction of the H0 exiting the foil will be in excited states. (2) These excited states can be stripped by the magnetic field of the 3rd orbmp kicker through the Stark effect. (3) The stripped H0's become H+ and will travel on a trajectory different from the closed orbit. (4) Downstream elements will be irradiated if these H+ hit them (5) Goal is to see how much power is deposited and whether it is a concern. (6) For a 600 ug/cm^2 foil, 17 kW of incident H-, about 10W appear as H0. (7) Increasing the thickness of the foil can be used to decrease the number of H0's but this has to be balanced with foil scattering. (i) The simulations are for a uniform foil with no variation in foil thickness. At some point, defects will play a role. However John says the results of the study will show that defects are not that important. (8) The relevant H0 states for the peak B-field inside the orbmp magnet (0.3734T) are the n=4, 5, 6 states at 800 MeV. (i) Each principal quantum number n splits into n(n+1)/2 substates. (9) Dave Johnson made an orbmp field model. For the simulations, the B-field was divided into 50 gauss bin increments. (10) Model 1: Assume a state strips at 1e-11 sec. Then only states 5 and 6 can strip within the end field. n=4 does not contribute. (i) Since MADX doesn't know anything about H0 and stripping, the algorithm starts with H0, goes through B-field and when the value of the lifetime is 1e-11, it immediately strips. Then MADX tracks the H+. (ii) Tracking is done from L11 to L20 with MADX. (iii) For n=5, results show that 9 mW is deposited on the first notcher kicker. (iv) n=6 no losses at all. (v) This result is for a gaussian distribution from the PIPII Linac beam emittance. (11) Model 2: This model was constructed because although for tau=1e-11 s, the n=4 states will not strip in the end field, it is not complete (i) For n=4, some fraction will strip if it is in the magentic field long enough, i.e. stripping within the magnet. (ii) For n= 4 tracking, the individual substates are not tracked like for n=5 &6. (iii) The magnetic field is sliced sufficiently so that the B gives the correct kick angle and that 5% increments in the H+ population can be identified. (iv) Two models for the L11 notch absorber were studied (a) 2-5/8" diameter aperture (b) 3" diameter drift. (v) For aperture model:113 mW deposited in absorber (vi) For drift: 72 mW deposited in absorber (vii) n=5 simulations were revisited. (a) John wasn't comfortable with using tau=1e-11 for immediate conversion. (b) Comparison with previous method and new method, the production peaks look about the same. (c) Result is for 17 kW incident H- beam, the power deposited on 1st notcher is 7 mW. (12) Summary: n=6 all into circulating beam. n=5 will hit nother kicker 7 mW. n=4 all of it into the absorber at L11. (13) Bottomline: RF is safe. (14) More simulations will be done: (i) to see whether the H+ in the circulating beam will be taken care of by the collimators (ii) Compare results with ideal (sharp edged) B-field of orbmp kicker vs B-field shaped for the end-field. How important is the shape of the end field? (iii) L11 region losses to spur disucssion about optimal absorber design. (iv) to show that painting shouldn't really change the results.