HEBT, Ring, and RTBT Pickup Electrode Mechanical and Electrical Design

1. HEBT, Ring, and RTBT Pickup ElectrodeMechanical and Electrical Design Peter Cameron July 23, 2002

2. Outline • Table of BPM Types • Mechanical Construction • Tolerance Stackup • Stripline Impedance • Impedance Implications • Wire Measurements • Conclusions/Action Items BNL Diagnostics Review

3. Table of BPM PUE Types BNL Diagnostics Review

4. Mechanical Construction • Direct descendant of RHIC PUEs – economical, accurate, robust • Stainless steel annealed before machining, copper brazed with integral fixturing to maintain precise mechanical alignment • Contact from stripline to feedthru • Shorted stripline – stripline cantilever is spring • Open striplines – CuNi bellows BNL Diagnostics Review

5. 21cm HEBT PUE BNL Diagnostics Review

6. 21cm Ring PUE BNL Diagnostics Review

7. Ring 21cm PUE Ceramic Supports and Contact BNL Diagnostics Review

8. Ring 21cm PUE Tolerance Stackup Estimated accuracy to the center of quad: • Shoulder screw location .008” • Brazing surface on the outer shell .005” • Rad. Clearance for the brazing .001” • Weld post on the outer shell .005” • Length of ceramic standoff .005” • Groove depth on the stripline .005” • Quad. Surface flatness .020” • Total(rms): .024” < .040 design req. BNL Diagnostics Review

9. PUE on Quad w/o Corrector BNL Diagnostics Review

10. Feedthrus, Cables, and Standoffs • Feedthrus • Lithium silicate glass/ceramic • Thermal expansion matched to stainless steel • Ultra-reliable mechanically • Very good electrically (much better than Kovar-ceramic) • Cables • PUE to tray - flexible coaxial • Tray to service building - 1/4” low loss heliax • Ceramic Standoffs • All ring components to be titanium nitride coated • Results in shielded standoff design to avoid shorting BNL Diagnostics Review

11. Stripline Impedance • Direct scaling from RHIC PUEs • Dual plane, four electrodes • 70 degrees subtended angle, maximum linearity • Sum mode matched to 50 ohms • Simplistically, four relevant impedances • Sum mode = Zs = 50 ohms • Difference mode = Zd = 28 ohms • ‘Matched’ = Z0 = sqrt(Zs * Zd ) = 38 ohms • Termination = Zc = 50 ohms BNL Diagnostics Review

12. Stripline Impedance 2 • Argument is that if you adjust sum and difference mode impedances such that Z0 = sqrt(Zs * Zd ) = 50 ohms (for instance) Then both sum and difference mode will be matched • Not everyone believes this yet, measurements are in progress • S21 and TDR with a wire • BPM into electron beam at ATF BNL Diagnostics Review

13. Stripline Impedance Implications • No implications for narrowband measurements • No implications for HEBT, Ring and RTBT position measurements • No accelerator physics implications (impedance,… • Significant implications for broadband measurements - eg TOF • It may be necessary to modify the six 12cm HEBT TOF PUEs - not yet brazed • Alternatively, it may be necessary to modify the LINAC PUEs? BNL Diagnostics Review

14. 21cm Ring PUE on wire scanner BNL Diagnostics Review

15. WireScanner Measurement • Permits measurement of • Transfer function (and mapping) • Relative mechanical and electrical centers • Presently no plan to do antenna measurement (ala RHIC) to find electrical center of BPM relative to quad fiducials due to vacuum access problems. • Beam-based alignment will accomplish the same thing, only better. BNL Diagnostics Review

16. Conclusions/Action Items • Check current capacity of contacts (especially bellows) • Decision on PUE-to-tray cable, 1/4 vs 3/8 heliax • Pursue Stripline impedance calculations and measurements (including ATF) - motivation is certainty that we have TOF right • Will 30cm Injection Dump PUE (open) work with 402.5MHz electronics? • Wire scanner measurements BNL Diagnostics Review