Barrier RF Stacking

Weiren Chou and Dave WildmanFermilab, U.S.A.

October 20, 2004

Presentation at the Proton Driver SessionICFA-HB2004, Bensheim, Germany, Oct 18-22, 2004

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Barrier RF Study Group

Fermilab-KEK-Caltech collaboration:

• Fermilab - D. Wildman, J. Griffin, K.Y. Ng, J. MacLachlan, C. Bhat, W. Chou• KEK - A. Takagi, Y. Mori• Caltech - H. Zhang, D. Michael

Acknowledgement: Helpful discussions with Takayama’s group

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Outline

Motivation Goals and methods Simulations Barrier rf system Beam experiments Summary

http://www-bd.fnal.gov/pdriver/barrier/

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Collider Experiment Run2

Pbar target

CDF

D0

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Neutrino Experiment NuMI

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Booster – the Bottleneck

The new Main Injector can accept 25e12 protons per Booster cycle.

However, the old Booster can only deliver 5e12 particles per cycle.

Beam Energy Lost During Acceleration10/9/2000 Data (Notch off & excluding extraction)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4 5 6

Protons/Pulse (E12) at 8GeV

Kil

ojo

ule

s/P

uls

e L

os

t in

Rin

g

Beam Loss vs Intensity

0

0.05

0.1

0.15

0.2

0.25

0 1 2 3 4 5

Intensity (e12 protons/pulse)

Ener

gy L

ost

(KJo

ules

/pul

se)

Webber’s data in October 2000

Prebys/Lackey’s data in January 2004

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Solution - Stacking

A solution is to stack two Booster bunches into one Main Injector RF bucket

This is possible because the Main Injector longitudinal acceptance (0.72 eV-s) is larger than the Booster beam emittance (0.13 eV-s)

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Goals

Run2 – To increase protons per second (pps) on the pbar target by 100%

• Present: 5e12 every 2 sec

• Goal: 2 x 5e12 every 2 sec

NuMI – To increase pps on the NuMI target by 70%

• Baseline: 3e13 every 2 sec

• Goal: 2 x 3e13 every 2.333 sec

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Two Methods

Adiabatic stacking: Beam injected on-axis

Adiabatically compress the beam by moving rf barrier

Fast stacking: Beam injected off-axis

Using two barriers, one stationary, another moving

Continuous injection and stacking

First proposed by J. Griffin

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Two Types of Barrier

Stationary barrier

Moving barrier

+V

-V

+V

-V

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Adiabatic Stacking

Simulation (K-Y. Ng)

Measurement

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Fast Stacking Simulation: 2-Batch

(courtesy K.Y. Ng)

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2-Batch Stacking (cont…)

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Fast Stacking Simulation: 12-Batch

(courtesy K.Y. Ng)

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12-Batch Stacking (cont…)

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12-Batch Stacking (cont…)

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12-Batch Stacking (cont…)

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12-Batch Stacking (cont…)

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12-Batch Stacking (cont…)

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12-Batch Stacking (cont…)

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Barrier RF System

Design goal: 6 kV wideband RF system

Two main components: Cavity: made of Finemet cores (Hitachi, Japan)

Modulator: made of high voltage fast switches (Behlke, Germany)

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Specifications

Fast Switch (Behlke)

HTS 161-06-GSM Peak voltage 2

16kV Peak current 60 A Pulse width 300 ns Pulse spacing 0.4-11s Repetition rate 100

kHz Burst length 400 ms Burst rep rate 0.5 Hz

Finemet Core (Hitachi)

FT3M OD 500 mm ID 139.8 mm thickness 25 mm Inductance 56 H (per

core) Resistance 190 (per

core)

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Barrier RF System (cont…)

Finemet core High voltage fast switch

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Finemet vs. Ferrite (4M2)

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Barrier RF System (cont…)

Modulator Cavity

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Full-Bridge Push-Pull Bipolar Circuit

in the tunnel

upstairs

9:1 1:9

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Bench Test

triggercurrent

primary voltage

gap voltage

Before tuning After tuning

6 kV

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Beam Experiment in the Main Injector

capture

debunchsqueez

e

rebunch

acceleration

Beam intensity

RF voltage

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Beam Experiment (cont…)

Squeezing Squeezed

Moving barrier

Beam squeezing

6 kV

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Mountain View

Stacking off Stacking on

t

1.6 s

3.2 s

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More Mountain Views

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8.3e12

@120 GeV

squeezing

High Beam Intensity after Stacking

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53 MHz RF voltage

Beam intensity (10e12)

Try Even Higher Beam Intensity

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Emittance Simulation ESME (2 x 5e12, final bunch after recapture, courtesy J.

MacLachlan)

Bucket size = 0.30 eV-s

Bucket size = 0.35 eV-s

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Stationary bucket, beam intensity = 5.23e12, emittance = 0.13 eV-s

Emittance Measurement – Injected Bunch

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Low intensity

Emittance Measurement – Stacked Bunch

High intensity

Medium intensity

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Bunch width = 10 ns moving area factor = 0.45

Stationary bucket area = 1.6 eV-s bunch emittance = 0.72 eV-s

Emittance Measurement – Accelerated Bunch

Width of Constant H Contours

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Synchronous phase (degrees)

Co

nto

ur

wid

th (x

pi)

phi(N=1)

phi(N=0.9)

phi(N=0.8)

phi(N=0.7)

phi(N=0.6)

Area Factor of Contant H Contours

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Synchronous phase (degrees)

Are

a fa

ctor

alpha(N=1)

alpha(N=0.9)

apha(N=0.8)

alpha(N=0.7)

alpha(N=0.6)

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Summary

A barrier RF system has been built and installed in the Main Injector

It has successfully stacked two Booster batches into one and reached 8.3e12 at 120 GeV, ~ 60% increase in beam intensity

There is large emittance dilution during stacking Causing losses at the beginning of acceleration

Making bunch too long for pbar production

But not a problem for NuMI

A second system is under construction and will be used for fast stacking experiment

Questions?