ALICE August Summary

AP/FEL/Thz 3 blocks – A)7-11 Aug (7 shifts, # ) – B)16-17 Aug (4 shifts # ) – C)25-29 Aug b. hol. w/end (7 shifts # ) Overall summary – Pursued proper FEL-set-up (BC1 = -12 O ) and THz-for-FEL-set-up (BC1 =-20 O )) with no lasing.. THz-for-FEL set up seems to have too large energy spread (500 keV) – FEL-set-up saw some interesting (not-repeatable later) spectra on one occasion #1980. Largest MCT signal during this period, but no gain – 1 THz 10-h ZF exposure with repeated ‘interesting’ result. – Problems included machine instabilities (long set-up/restore times, MO changes), EMI-1 locked off, FEL mirror misalignments

(A) 7-11 Aug (7 shifts, # ) Pursued FEL proper set up (BC = -12/+25) and THz for FEL (BC = -20/+25). Only one shift with significant spectrometer results, much time spent in troubleshooting or restoring set-ups, fighting unstable machine. Shift #1980 (BC = -12/+25) saw very narrow spectrometer signal but no gain during cavity scan. EMI-1 locked off during this period (due to EMMA ring installation) Thus energy spread after linac not measured. Many phase shifts and significant phase jitter in injector, also instability of beam size in INJ- 2. Master oscillator was replaced with signal generator. FEL cavity mirror alignment went probably after 10th when last decent MCT signal seen (was discovered on 17th) #1980

(B)16-17 Aug (5 shifts # ) Focussed on THz for FEL set-up. Only very small spectrometer signal seen. Problem with FEL cavity mirror alignment discovered THz cells exposure 10 hs run overnight during this period to verify 'interesting' result. Original MO replaced after this period

(C) Aug b. hol. w/end (7 shifts # ) THz 1.1 m from window THz maximum at large off-crest value THz vertical profile characterised RAD surveys: -TCL Lab with standard ER set-up -EMI with beam through Be 20 uS window at 27.5MeV, 10Hz, 40pC, 20us FEL work: THz set-up (BC =-20) spectra too broad, use zero’th order signal. At LC phase set for max THz, EMI-1 energy spread ~ 500 keV Restoring #1980 “FEL set-up” (BC=-12) even poorer signal on MCT Scale? EMI-1 energy spread ~ 500 LC =+17

Other observations THz signal sensitive to quad focussing in ST2 – Can change signal by > 1 V Reducing buncher power 550W  520W improved THz signal. THz signal sensitive to very small changes in linac/booster gradient (0.01 on Grad Set) THz & FEL signals better when ER is poorer Bump on LC2 ER in first ~15  sec caused by beam loss in ST2 manual vale (which is in turn caused by buncher instability over first ~15 usec). Can get rid of bump by focussing in ST2. #2019 Phase jumps are often non-global