APEX HF Schottky Calibration Peter Cameron and Al

APEX HF Schottky Calibration Peter Cameron and Al Dellapenna 17 Mar 2006

Outline • BBQ – parasitic to resonance compensation – “Mission Accomplished”, but…… – 3 D sensitivity to beam loss • Emittance calibration of HF Schottky – Preparation – parasitic behind a store – The experiment – Conclusion – high resolution, significant potential value • Chromaticity Calibration – A caution to Operations • Artus in chrom application did not give meaningful and reliable chrom measurements during this study. • Is this also sometimes the case during normal operations? – HFS chrom measurements are presently useless. This requires further study, algorithm refinement 17 Mar 2006

BBQ • Steve Peggs – “declare Victory” • Peter Cameron – “Mission Accomplished” • One messy little detail – BBQ sensitivity to electrons/beam loss (thank you Mike Brennan) • We are working on it 17 Mar 2006

BBQ during tune scan (x const) Vert I and Q ~. 01 units of tune Horiz I and Q Tunes and beam decay 17 Mar 2006

BBQ – effect of beam loss Vert I and Q Horiz I and Q loss of lock Tunes and beam decay 17 Mar 2006

BBQ • Steve Peggs – “declare Victory” • Peter Cameron – “Mission Accomplished” • Steve Peggs – “tell them what you’re going to tell them, then tell them what you told them” • Peter Cameron – “Mission Accomplished” • Just one messy little detail – Sensitivity to beam loss/electrons • And one more puzzle – Anomalous sensitivity to tune separation (at small and large tune separations, but not at intermediate ie <700 Hz) when fully decoupled 17 Mar 2006

Outline • BBQ – parasitic to resonance compensation • Emittance calibration – Preparation – parasitic behind a store – The experiment • Chromaticity Calibration 17 Mar 2006

e calibration - the principle • Simple • Schottky pickup is moveable controllable beam offset • Schottky signal is macro-particle of charge sqrt(N), where N is number of beam particles • This macro-particle deposits power in the spectrum at both revolution and betatron frequencies • Beam offset at which power in rev line equals power in betatron line is the rms beam sigma (see next slide) • For preliminary exploration we just did this by eye 17 Mar 2006

Spectra at 3 pickup positions Counts = 75 Counts = 675 17 Mar 2006 Counts = 1275

mirrored down for least squares fit Departure from straight line indicates non. Gaussian profile, can be fit to determine profile 17 Mar 2006

Comparison with IPM • Blue IPM and Schottky are both at the Q 4 end of sector 2, a few meters apart • Schottky says s ~ 0. 8 mm • IPM says s ~ 1. 68 mm * sqrt(20/29) = 1. 4 mm • With b difference gives ~factor of 2? Where? 17 Mar 2006

More comparison with IPM flattop • • Resolution > x 10 better No beam kick May be useful on ramp Schottky point every 4 sec 17 Mar 2006

Yet more comparison with IPM Schottky IPM These differences are meaningful – related to shape of transverse profile 17 Mar 2006

The experiment • • • Preliminary data was taken at store This experiment at injection Large distorted revolution line – problem for cal only Distorted betatron lines - from turning Landau off? Abandoned this part of the experiment (can be done parasitically to stores) to concentrate on chromaticity 17 Mar 2006

Schottky emittance measurement • Has excellent resolution – Beam decay monitor more useful than Current monitor for tuning – Might an ‘emittance decay monitor’ (% emittance gain/hr) be more useful than an emittance monitor? – Schottky has sufficient resolution to permit this • • Data is always there, for free – does not perturb the beam Can be given absolute calibration via moveable pickup Profile can be extracted from position scan For the most part agrees well with IPM. When it does not, there is useful information (shape of transverse profile) • Relatively small effort to make this available at store • Slightly larger effort to make it available at injection and on the ramp (LO frequencies need to be tied to frev) 17 Mar 2006

Outline • BBQ – parasitic to resonance compensation • Emittance calibration – Preparation – parasitic behind a store – The experiment • Chromaticity Calibration 17 Mar 2006

x calibration - the principle • Simple • Measure linear and non-linear chrom via standard radial shift method, using Artus and BBQ • Compare with Schottky • Change the chromaticity • Repeat 17 Mar 2006

Blue at the start Artus drawn to other eigenmode? 17 Mar 2006

Blue tunes x +2 both planes x +1 both planes x +2 both planes 17 Mar 2006 x +1 both planes

Blue chromaticity x +2 both planes x +1 both planes x +2 both planes 17 Mar 2006 x +1 both planes

Blue summary • Data pretty confusing, the only one I trust is BBQ in this data set – A caution for operations? • Schottky algorithm needs refinement – Present calculation is ad hoc, complex, many fudge factors – Need to incorporate calculation of non-linear chromaticity 17 Mar 2006

Yellow overall Opposite shift - Artus is wrong sign for +chrom at integer minus tune xh +2 xh +1 xv +1 17 Mar 2006 restore

Yellow Summary • Data dumped to elog was for Blue! • Are chrom measurements archived? – if not, they should be • If we can find chrom data, will go back and analyze yellow Overall summary: Schottky CAN give good chrom data, requires attention 17 Mar 2006