# Presentation: 078068

## Beam In Gap Design Review

**Michelle Wilinski**
**March 26, 2003**

## Outline

- Action items from July 2002 Review
- Motivation
- Overview
- AP Analysis – Cousineau, et al
- Process Variables
- Acceptance Criteria
- Summary

- Diagnostics Review  - March 26 & 27, 2003

## July Review Action Items – Critical Findings

- Disconnect between diagnostics & AP regarding magnitude of cleaning kick
- Consensus reached that magnitude should be +/- 7kV
- Number of kicker modules not determined
- Using 3 stripline kickers of 1.5m each in one location

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Rise time of kicker:  beam travels 1m in 3ns, have ~15ns of travel time in stripline

## Action Items – Observations/Recommendations

- Gap cleaning stripline kickers should be designed for 50 ohm impedance in differential mode
- They are designed in this manner
- Pay attention to effective rise time of kicker system as multiple kicker modules are powered electrically in series
- Done
- Measure of beam in gap to 20% accuracy will be difficult
- Working on calibration methods for such
-  Gated phototube system will probably be required
- Design has either gated PMT or MCP (R. Witkover)
- Concern regarding achievable absolute accuracy of BIG calibration using method of kicking out a known quantity of beam not in the gap
- It is a practical method (R. Witkover)

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
R. Witkover has presentation following regarding data acquisition & calibration for BIG
Rise time of kicker:  beam travels 1m per 3ns => have 15ns of stripline kickers

## Motivation

-   Should be no beam in the gap from linac
-   Chopper should be 100% efficient
-   Linac team claims nothing can make it from one end of the Linac to the other, and at the same time find its way from the mini-bunch to the gap
-   However, nuclear scattering, foil losses, RF noise, collimation inefficiency, etc. exist
-   Experience has taught us that in existing machines there is beam in the gap, claimed to sometimes be at the percent level
-   Loss budget is 10-4. Don’t use it up in the gap!

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Some excerpts from paper reference in slide 8

## BIG/Halo Overview

-   Hardware used: pulser, kicker, FBLM (gated PMT or MCP) & associated processing electronics, collimator and/or scraper and associated motion controls
-   Gap/Halo calculations performed in LabVIEW
-   AP range = 0-0.1A
-   AP required accuracy = 20%
-   Operated during last ~100 turns of accumulation cycle

- Diagnostics Review  - March 26 & 27, 2003

## BIG Block Diagram

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Fast A/D still to be selected

## Principle of Operation

-   Kick the gap beam onto collimators/scraper during last 60-100 turns of accumulation; pulser duty cycle limited to ~100 kicks/machine cycle
-   Measure with fast loss monitors (PMT or MCP)
-   Function as both gap monitor and gap cleaner (reduce activation of extraction region)
-   Scraper will be located at wire scanner location immediately adjacent to the IPM
-   Cross calibrate losses
-   Greater sensitivity than collimator

- Diagnostics Review  - March 26 & 27, 2003

## Gap Cleaning Analysis  

- “SNS Beam-In-Gap Cleaning and Collimation”
-  EPAC 2002
- Sarah Cousineau, Indiana
- Daniele Davino, BNL
- Nuria Catalan-Lasheras, BNL/CERN
- John Holmes, ORNL

- Diagnostics Review  - March 26 & 27, 2003

## BIG Holmes 1

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
“borrowed” slide; early simulation, some differences for kicker to be used – only 1 “module” (3 striplines, 1.5m each at one location), kick will be 0.6mrad

## BIG Holmes 2

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
“borrowed” slide, simulation of beam in gap kicker shows good first results

## Gap Cleaning Simulation – S. Cousineau

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Two simulations: left for momentum spread 0.007 & 2 different kicks; 1mrad = 1 by ~35 turns, 0.6mrad = 1 by ~50 turns
Right for momentum spread 0.02; 1mrad = 1 by ~50 turns, 0.6mrad just about 1 by ~80 turns; kicker spec is dp/p=0.01

## Loss Locations

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Fraction of beam absorbed in different sections, add up % of beam lost in locations indicated by blue bars & get just about 90% of beam in gap absorbed by primary & secondary collimators and shielding (all % are approximate: 4% primary, 36% secondary, 7% shielding, 23% secondary, 18% secondary = 88%); remaining losses are distributed amongst beam pipe & quads

## Process Variables – System Inputs

- Kick polarity
- Determines output polarity of kick (+/- or -/+)
- Plane to kick
- Determines plane to kick (horizontal or vertical)
- Kick trigger
- When to trigger the pulser for kick(s)
- Tune
- Feedback for proper BIG cleaning
- Power supply on/off
- Remote control for the power supply
- RTDL
- Event Link

- Diagnostics Review  - March 26 & 27, 2003

## Process Variables - System Outputs

- Kick mode
- Determines mode of pulser operation (Tune or BIG)
- Power supply remote/local
- Readback to determine mode
- Power supply on/off
- Readback to determine if supply is on/off
- Capacitor bank voltage
- Readback to assure power supply is charged as expected
- Gap Current
- Amount of beam measured in the gap
- PMT or MCP voltage

- Diagnostics Review  - March 26 & 27, 2003

## Acceptance Criteria

- List still in development
- Meets applicable FBLM acceptance criteria
- Meets AP specifications
- Range 0-0.1A
- Accuracy 20%
- Pulser meets requirements
- Output +/- 7kV
- Polarity change turn-by-turn
- Select plane to kick
- 1MHz burst of 60-100 pulses
- System integration demonstrated

- Diagnostics Review  - March 26 & 27, 2003

## Summary

- One pulser unit & kicker to be shared between Beam in Gap and Coherent Tune systems
- PC containing standard NI motion control, FDAQ digitizer, LabVIEW (Wim’s template)
- Using gated FBLM for data acquisition – presentation by R. Witkover to follow

- Diagnostics Review  - March 26 & 27, 2003

## ...extras...

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Extra miscellaneous oddities

## Pulser Block Diagram

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Switch configuration changed to half bridge method 3-6-03, cable is 7/8 Heliax to kicker

## Schedule - BIG

- Diagnostics Review  - March 26 & 27, 2003

**Notes:**
Schedule generated for Feb. ORNL visit, vertical line indicates Feb. point