# Presentation: 407869

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

- Peter Cameron
- July 23, 2002

## Outline

- Table of BPM Types
- Mechanical Construction
- Tolerance Stackup
- Stripline Impedance
- Impedance Implications
- Wire Measurements
- Conclusions/Action Items

- BNL Diagnostics Review

## Table of BPM PUE Types

| location | type | size | qty | comments |
| --- | --- | --- | --- | --- |
| HEBT | shorted | 12cm | 31 | Machining complete |
| HEBT | shorted | 21cm | 5 | Delivered to Vac Group |
| HEBT | open | 30cm | 1 | In front of injection dump |
| Ring | open | 21cm | 28 | Delivered to Vac Group |
| Ring | open | 26cm | 8 | At doublets, mach complete |
| Ring | open | 30cm | 8 | Arc centers, mach complete |
| RTBT | shorted | 21cm | 15 | Machining complete |
| RTBT | shorted | 36cm | 2 | Machining complete |

- BNL Diagnostics Review

## 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

## 21cm HEBT PUE

- BNL Diagnostics Review

## 21cm Ring PUE

*21cm Ring PUE*

- BNL Diagnostics Review

## Ring 21cm PUE Ceramic Supports and Contact

- BNL Diagnostics Review

## 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

## PUE on Quad w/o Corrector

- BNL Diagnostics Review

## 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

## 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

## 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

## 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

## 21cm Ring PUE on wire scanner

- BNL Diagnostics Review

## 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

## 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