Beam-Prof rofil ile M e Monitor I or Issues ues a at A0PI: The C Case f for r Reduced E Emit mittances Alex Lumpkin for the A0 team Presented at A0 MTG June 19, 2009 Batavia, Illinois
Emittan tance M ce Measurem urement ent I Issues es • Measurements of beam transverse emittances and longitudinal emittance are needed for the incoming and outgoing values in the EEX experiments. • Identify, characterize, and apply needed corrections. • Corrections to the observed projected image profile sizes are warranted. – Camera resolution term of 1.8 to 2.0 pixels can be in play. – YAG:Ce powder screens have a limiting spatial resolution term. • Consider corrections at X5 slit images. • Consider corrections at XS3 energy spread measurement. • Consider corrections at X24 slit images. • The previously reported EEX table results from Feb. 6 and Feb. 11, 2009 should be revised. A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009 2
Iden entif tify C Correc ections tions t to Consid ider er • Camera resolution • Slit finite size • YAG:Ce powder screen spatial resolution • Beta star term in spectrometers • Macropulse blurring effects on energy spread , beam size, and beam divergence in OTR images. • OTR polarization effects. Uncorrected 10 2/6/09 vs X4-Xemit-raw 2/6/09 vs X5-Xemit raw • Camera calibration factor. 2/6/09 vs X4-Yemit-raw Emittance x,y (mm mrad) 8 2/6/09 vs X5-Yemit raw 6 4 2 0 180 190 200 210 220 230 240 250 Solenoid Current (A) 3 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
Observed d vs Actu ctual Sl Slit t Image Si e Size • Uncorrelated terms are treated as a quadrature sum to actual image size as in Lyons’ book a . -- actual (Act) image size, camera resolution (cam), YAG screen effects (YAG), finite slit width (slit). ( In addition there can be macropulse effects and OTR polarization effects.) Obs 2 =Act 2 + YAG 2 +cam 2 + slit 2 Eq. 1 Solving for the actual beam size we have, Act = [Obs 2 - YAG 2 - cam 2 - slit 2 ] ½ Eq. 2 a Louis Lyons: Statistics for Nuclear and Particle Physicists (1986) 4 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
Observed d vs Actu ctual X XS3 S3 Image Si e Size • Uncorrelated terms are treated as a quadrature sum to actual image size as in Lyons’ book a . -- actual (Act) beam size for energy spread, camera resolution (cam), YAG screen effects (YAG), and nondispersed beam size β x ε x / γ . Obs 2 =Act 2 + YAG 2 +cam 2 + β x ε x / γ Eq. 3 Solving for the actual beam size we have, Act = [Obs 2 - YAG 2 - cam 2 - β x ε x / γ ] ½ = η x σ E Eq. 4 a Louis Lyons: Statistics for Nuclear and Particle Physicists (1986) 5 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
YAG:Ce Ce P Powd wder er Sc Scinti tillator S Scr cree eens • The screens have nominally a 5-µm grain size and are coated at 50-µm thickness on various metal substrates. • Usually the A0 substrates are Al or SS and 1 mm thick. • In the A0 geometry the scintillator is on the front surface and oriented at 45 deg to the beam direction. • The response time is about 80 ns FWHM. • There have been reports of saturation of the mechanism for incident electron beam areal charge densities of 10 fC/µm 2 . • This effect can cause a charge dependence of the observed image size in addition to the low charge, screen resolution limit. • Screens provided by Klaus Floettmann at DESY. 6 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
Recent ent C Chrono nolog logy • Tim K. mentions a Chromox screen used in XS3 in Feb. 09 meeting. Initial screen res. concerns raised by AHL. • Detailed description of emittance determinations given by Yin-E on Feb. 11 EEX data. • This talk showed the beam sizes used in pixels at X4, X5, XS3, X24 for the transverse and longitudinal emittances. • Hypothesis on limiting resolution of scintillator screen invoked based on Chromox data. • Question on minimum spatial size term from emittance at XS3 also raised. • Opened XS3 station and found a darkened YAG powder screen and darkened port window. 7 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
Chara racteri cterize T ze Terms • YAG:Ce scintillator screen has a limiting resolution term that must be addressed. • YAG powder screen used in XS3. • YAG powder screens used with slit images at X5 and X24. • Actions: 1) At XS3 install new YAG screen with an OTR thin foil over the top half of the screen. Allows direct comparison of two image sources. March 25. 2) Review data of Feb. 6 and 11, 2009 and find systematic effect of YAG screen vs. OTR. Feb.-March 3) Install X22 two-screen actuator at X5. May 22 4) Evaluate camera resolution and slit term at X4, X24. 8 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
XS3 3 Sp Spectr trometer I Images (0 (04-23-09) 9) • Micropulse charge of 250 pC used; 20 bunches for OTR image. Deduced YAG:Ce res. term of σ =180 µm. YAG:Ce, σ =5.0 pixels=235 µm OTR, σ =3.2 pixels=150 µm 9 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
X24 I Ima mages ( (04-23-09) 09) • Micropulse charge of 250 pC used. Deduced YAG res. term of σ =176 um for this areal charge density. YAG:Ce, σ y =7.0 pixels OTR: σ y =4.3 pixels 10 10 A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009
Ini Initial XS XS3 and nd X2 X24 OTR-YAG YAG r res esults ts (4 (4-23-09 Da Data ta) Table I: Comparison of YAG:Ce and OTR beam images at 250 pC per bunch. Location Screen No. Bunches Fit sigma (pix) Size (µm) XS3 YAG 1 5.0 235 XS3 OTR 10 3.15 150 XS3 OTR 20 3.24 152 X24 YAG-2 1 7.0 224 X24 OTR 20 4.3 138 * The simple quadrature rule gives a YAG screen resolution of 180 um at XS3 and 176 um at X24 for this charge and beam sizes. (The simple quadrature rule at X5 implied 140-180 um for slit image charges before May 22, 2009.) A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009 11 11
XS3 I 3 Images es Exhibit t So Some Ch Char arge De Depen ende dence (4 e (4-27-09) 9) Table II: Comparison of YAG:Ce and OTR beam images at XS3. Location Screen Charge (pC) No. Bunches Fit sigma (pix) Size (µm) XS3 YAG 150 1 4.82 227 YAG 200 1 5.04 237 YAG 250 1 5.26 247 XS3 OTR 150 10 3.20 150 OTR 200 10 3.46 163 OTR 250 10 3.75 176 *The beam sizes are 7-image Gaussian fit averages. The implied XS3 YAG screen resolution terms are 170,172, and 173 µm for the increasing charges, respectively. A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009 12 12
Em Emittan ttance u e using X X3 and X4(O 4(OTR) R)-Sl Slit I t Images es (0 (02-11-09 Da 9 Data ta) ε = γσ σ n ( x 3 ) ( x 4 - Vslits) / 0 . 39 m x x x ⋅ 2.33 pixels 0.0275 mm/pixel = ⋅ ⋅ 28 0 . 73 mm 0.39 m = 3 . 3 mm mrad ε = γσ σ n ( x 3 ) ( x 4 - Hslits) 0 39 m / . y y y ⋅ 2.33 pixels 0.0267 mm/pixel = ⋅ ⋅ 28 0 . 78 mm 0.39 m = 3 . 5 mm mrad 13 13
Em Emittan ttance u e using X X3 and X5 5 (Y (YAG)-slit it Images (2 (2-11-09) 9) ε = γσ σ n ( x 3 ) ( x 5 - Vslits) / 0 . 80 m x x x ⋅ 6.82 pixels 0.0268 mm/pixel = ⋅ ⋅ 28 0 . 73 mm 0.80 m = 4 . 7 mm mrad ε = γσ σ n ( x 3 ) ( x 5 - Hslits) 0 80 m / . y y y ⋅ 6.91 pixels 0.0271mm/p ixel = ⋅ ⋅ 28 0 . 78 mm 0.80 m = 5 . 1 mm mrad A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009 14 14
Energy gy s spre read a d at stra raigh ght lin line σ E =5.5 pixels; Disp.=0.324 m; δp/p= (5.5 pixels *0.0593mm/pixel) /Disp.=0.1% ε n z = γσ z δp/p=28*0.75 mm*0.1% =21 mm mrad A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009 15 15
Tra ransverse e emit mittances a after E r EX ε = γσ σ n ( x2 3 ) ( x2 4 - Vslits) / 0 . 565 m x x x ⋅ 4.5 pixels 0.032 mm/pixel = ⋅ ⋅ 28 2 . 92 mm 0.565m = 21 mm mrad ε = γσ σ n ( x2 3 ) ( x2 4 - Hslits) 0 565 m / . y y y ⋅ 5.4 pixels 0.032 mm/pixel = ⋅ ⋅ 28 0 . 70 mm 0.565 m = 6 . 0 mm mrad A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009 16 16
Dom Dominos Step Steps (outg (outgoing) • For the outgoing transverse emittance we apply the est. 130 µm YAG:Ce screen resolution to the X24 slit image data. This is 4.0 pixels with the reported 32 um per pixel calibration in x and y. • The observed X24 slit image sizes were 5.4 and 4.5 pixels which are corrected to 3.6 and 2.06 pixels for y and x divergences, respectively. • The outgoing emittances are then ε x =9.8 mm mrad and ε y =4 mm mrad, revised downward from 21 and 6 initially. • The outgoing longitudinal emittance was reported as 7.1 mm mrad. The spectrometer beam image size was 11.2 ch X 85 µm per pixel, however the β y ε y term has not been determined or subtracted yet. This is an OTR screen. The bunch length was reported as 0.85 ps. • The emittance term in XS4 needs determination as indicated by the revised EEX table. The bunch length probably needs a redo with new optics. A.H. Lumpkin A A0PI 0PI M Mtg. June e 19, 19, 2009 2009 17 17
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