Accelerator Physics of PEP-I1. Lecture #S. March 20,1998. Dr. John Seeman

Transcription

1 Accelerator Physics of PEP-1 Lecture #S March 2,1998 Dr. John Seeman

2 PEP-1 Accelerator Physics John Seeman March 2 Lecture 2 Magnet system Dynamic aperture Radio-Frequency (RF) Acceleration System Multibunch instabilities Beam impedance and reduction of impedances Vacuum chamber design Beam diagnostics Commissioning results

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8 BZD Baseline DeltaBLeff Distribution e-3 1.Oe-3 O.Oe+O -1.Oe-3-2.Oe-3-3.Oe BZD Magnet with New Chamfer DeltaBLeff Distribution 1.e-3.W -1.Oe $*v -L.m.a -3.e-3-4.Oe-3 1 3,s $4- -5.e

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11 CLL LER V1.45, Latest LER lattice tracked with LEG Local in x, Semi-local in y for chromaticities No Solenoid, Tunes Qx=.57, Qy=.64, beta* = 1.5cm 4 5 Multipole and alignment errors included, dp =1 Updated multipole in quadrupoles and dipoles 15 Seeds Simulated, Yunhai Cai, October, 1997 Dynamic Aperture Plot LEE d( \ n E X nitial amplitude (cm)

12 LER V1.45, Latest LER lattice tracked with LEG Local in x, Semi-local in y for chromaticities No Solenoid, Tunes Qx=.57, Qy=.64, beta" = 1.5cm Multipole and alignment errors included, dp =1 Updated multipole in wigglers, dipoles, and quads 15 Seeds Simulated, Yunhai Cai, February, 1998 Dynamic Aperture Plot 4 1 # /----. c -.- '' \ 8 8 \ 8 t X nitial amplitude (cm)

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14 Typical Cross Section Layout URUTOR at HER STATWN LER LEVEL for arcutaior. - i KLYSTRON sll 12 MW LOADS TUNNEL CABLE TRAY A LER E HERE - --t- --- t.69 m + A m 7

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20 - mpedance (kq) P m 1 _. W sr u1 3 a (D ( R s if; t....,

21 3 ( *, j 3 m N t O C O < H 1. < = ~ l l l l l l l l l ~ 3 N N rl u N m ( + W

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27 5.2 Vacuum System J - 'B t 4 a 5 Us 22 us 11OUs 6OUs h E $ 3 v.- > c v) C a, - z 2 n 5 a, C Fig (a) Radiation power distribution along a half-cell of the HER arc at the design current of.99 A. (b) Radiation power distribution along a half-cell of the LER arc at the design current of 2.14 A. 313

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33 MEASUREMENT OF VERTCAL EMTTANCE AT LEP FROM HARD X-RAYS C. Bovet and E. Rossa European Organization for Nuclear Research (CERN) CH Geneva 23, Switzerland Abstract Two X-ray detectors are installed to measure on line the vertical profiles of both beams in LEP. They consist of 64 elements of CdTe photoconductor deposited with a pitch of 1 pm on a ceramic support. Profiles can be recorded at the rate of bunch passages (44 khz). n this paper calibration curves are established for the evaluation of beam emittance, first experimental results are presented and the planned developments are exposed. 1. ntroduction The aim of the project is to monitor, at a repetition frequency of 44 khz, the vertical distribution of electron and posinon bunches [ 13. Synchrotron radiation, even produced at injection energy in LEP, is energetic enough to get through a thin window (X-rays of 1 kev to 1 kev), and can be directed onto monitors placed outside the machine vacuum. These monitors operating in a fully parasitic mode can be permanently used, provided they can resist very severe inadiation ( 1O2 Sv per anuum). Because there is no imaging of the synchrotron light, only the vertical divergence can be observed... but this is anyhow the most interesting one in a flat beam collider. Furthermore a detector with many parallel channels can measure the beam size at each bunch passage (44 W). Two special recesses have been created in the LEP vacuum chamber near the quadrupoles QD12, on both sides of LSS 1 (one of them is shown in Fig. 1). Then the main dipole synchrotron radiation strikes the detector through a.4 mm Be window covering a surface of about 2 mm height and 2 mm width. vacuum chamber V -3fi Fig. 1. Layout of X-ray monitors in LEP snaight section LSSl

34 1 L e2 c+r o td.- S n Q) el1 W L 4 E t i c, X Qz 1 - c. m -.r,., ; G z c,.- -E E cc Q) 9 3 P 3 e 1 t 11 L d c\1

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36 Synchotron Light Monitor - M Mirror Xray Dump! i 1 =+=

37 Diffraction by Slot in Mirror: Single Electron (HER, h= 4 nm) 1.8 L a, 3.6 a. U a,.- N Normalized Vertical Angle, y /o~~

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39 Streak Camera Slit --h -+ A L?1 Photocathode \ \ m[ / q, o PlHJ Fast sweep high-voltage generator Trigger& J 1 \ Accelerating Microchannel Phosphor grid plate screen TV camera with microcharme!-plate image intensifier Photoelectrons from the photocathode are rapidly deflected in the j- direction (vertically) while travelins across a gap. Pattern of dispersed electrons amplified by a microchannel plate (MCP). Horizontally, the image on the phosphor screen is just the horizontal distribution of the incident light. For a narrow entrance slit, the vertical distribution of the ima, oe shows the time spread of the light-down to.5 ps for the fastest cameras. For a wide slit, vertical distribution of light convolved with time spread. The deflecting signal can be a single-shot trigigered ramp or a repetitive sweep driven by RF ( synchroscan ). Later, ll show an interestins use of synchroscan combined with a slower deflection in the other transverse plane (s).

40 Triggered Dual-Axis Streak-Camera mage of the PEP HER Beam Multibunch fill to 375 ma. 1 ms Full Horizontal Scale The sweep is retriggered every 1 ps (every 14th PEP turn) from the ring clock. Each time, the same bunch is captured and dispersed vertically, but displaced horizontally. Some trigger jitter is visible.

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42 Dual-Axis Synchroscan Streak-Camera mage 7-Bunch Sequential Fill, Every 4.2 ns ( Richter-Dorfan fill), 228 ma Alex Lumpkin and Alan Fisher 3 January ns Full Vertical Scale PO R3/5us/228mA/78/ 1 c ai 5 ps Full Horizontal Scale Time within a bunch is dispersed vertically, while the bunches in the train are displayed horizontally. Because the camera is swept vertically at 119 MHz, half of the bunch-train frequency, even and odd numbered bunches are 18 apart and are swept in opposite directions. They are separated for clarity by a small delay from the precise zero crossing. For this charge per bunch, the train displays these longitudinal instabilities when the length reaches about 5 bunches, but stabilizes again after about 12 bunches. However, with a 5-mA 1658-bunch fill, the middle of the train was unstable.

43 Bunch Currents Current Transformer equiv ma # Filled Buckets 159 Fit Lifetimes based on BC STATE: Quiescent WDT unsec Linear min O Seconds1 Exponsnti al min STOP Calib Status Goal Status MPG Status All old Okay MPG onlbc off niecti on Stopping NJECT^ DCCT Current; 5 second bins; 2 minute full scale 1 Time (m) 2

44 Beam: Currents up to.75 A. Life time A. Stable up to A. Lattice: Rf System: Beta mismatch fixed. Collision configuration standard. 5 statioins commissioned. Direct, comb, dc ripple loops on. Very stable up to 4.5 A. Feedbacks: Transverse f/<b on. Long. f/b wofkilhg, reduced a m pl#ier cs;mpamen t. Diagnostics: BPM working well. SLM wddng up- & downstairs, m,kr& disbiittioli;l limits resolution. DC CT/lEbC waking. BC s6fiwdr-e needs tuning. Tume reado'ut mostly works. Controls: Backgnd: Tune dr'sphy works. Phase medsurem~ent works. Disp. steeiing mcostly works. Lots of data being analysed State of Machine: 2/4/98 1:21

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