Beam-in-Gap Monitor/Cleaner Preliminary Design Review

1. Beam-in-Gap Monitor/CleanerPreliminary Design Review Peter Cameron July 23, 2002

2. Outline • Motivation • AP Requirements • Three Methods • The Kicker and Pulser • Gap Cleaning Analysis by AP • Summary and Conclusions Diagnostics Review July 2002

3. 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

4. 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

5. 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

6. 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

7. Ring Layout Diagnostics Review July 2002

8. 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 q = 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

9. 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

10. BIG Kicker Pulser Diagnostics Review July 2002

11. 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

12. BIG Holmes 1 Diagnostics Review July 2002

13. BIG Holmes 2 Diagnostics Review July 2002

14. Collimation Fraction vs dp/p Diagnostics Review July 2002

15. Loss Locations Diagnostics Review July 2002

16. 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