# Presentation: 510292

## Beam-in-Gap Monitor/CleanerPreliminary Design Review

- Peter Cameron
- July 23, 2002

## Outline

- Motivation
- AP Requirements
- Three Methods
- The Kicker and Pulser
- Gap Cleaning Analysis by AP
- Summary and Conclusions

- Diagnostics Review July 2002

## Motivation

- From linac there should be no beam in the gap
- Chopper should be 100% efficient
- Linac guys claim 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
- But nuclear scattering, foil losses, collimation inefficiency, RF noise,...
- 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 July 2002

## AP Requirements for BIG Measurement

- Method
- HEBT - laser neutralization
- Ring - resonant excitation onto the collimator
- Range
- HEBT - 0 - 0.1mA
- Ring - 0 - 0.1A (0.3% of 36A beam)
- Accuracy - HEBT and Ring - 20% (Ring based on HEBT)
- Resolution
- HEBT - 0.5mkA (?)
- Ring - unspecified
- Data Structure
- HEBT - each minipulse
- Ring - each pulse

- Diagnostics Review July 2002

## Three Ring Methods for Ring BIG Measurement

- Use BCM - extensively studied (Witkover, Kesselman), tough
- Use loss monitors to observe losses during normal extraction - As extraction kicker fires, gap beam is swept onto collimator, then progressively upstream into the vacuum chamber, and finally across the Lambertson and into RTBT. Relevant numbers are
- Bunch length 675 ns
- Gap length 275 ns
- Extraction Kicker
- Rise time 200 ns to 95%
- Fires at start of gap
- Resonantly excite beam onto collimator during last 50 turns of accumulation, observe with loss monitors - also cleans gap!

- Diagnostics Review July 2002

## Measure BIG at Extraction

- Most sensitive method by far
- Factor of 15-30 improvement in instantaneous loss over resonant extraction
- Losses are in the open, rather than buried in the collimator, where they are difficult to see by design
- Can attempt calibration of these losses by injecting single 15mA minipulse and extracting on the bunch

- Diagnostics Review July 2002

## Ring Layout

- Diagnostics Review July 2002

## BIG Kicker - similar to RHIC 

- Voltage = +/- 7KV     Aperture = 21cm
- Length = 4.5m - three modules, 1.5m each
- Dual plane, 70 degrees, Zdiff =50 ohms, HVN conn
-  = 0.6mrad   vertical
- But AP wants 1mrad
- 	consider two additional modules immediately downstream of extraction kickers. Might also consider single plane horizontal in this case, even though efficiency onto the collimator may be slightly less

- Diagnostics Review July 2002

## BIG Kicker Pulser - again similar to RHIC  

- Two independent pulsers, each with 7KV power supply, storage cap, 7KV IGBT switch.
- Pulsers will drive two 14KV FET switches into 50 ohm 7/8” heliax
- Rise time 10-20ns for 10-90%
- Burst rate 1 MHz, duty cycle 50 pulses at 60Hz
- Pulse length adjustable 200 - 800 ns (duty cycle tradeoff?)
- Gate Drives accept fiber optic pulse inputs
- Breadboard completed
- First article $125K, additional units $75K
- Delivery 6 mos from Diversified Technologies

- Diagnostics Review July 2002

## BIG Kicker Pulser 

- Diagnostics Review July 2002

## 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 July 2002

## BIG Holmes 1

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## BIG Holmes 2

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## Collimation Fraction vs dp/p

- Diagnostics Review July 2002

## Loss Locations

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## Summary and Conclusions

- Some confidence based on RHIC experience with similar system
- Questions about switching for dual plane, quadrupole mode
- Momentum/tune spread in gap makes larger/longer kick desirable - effort will be devoted to this
- Questions about calibration - discussed in more detail in next presentation

- Diagnostics Review July 2002