ERL

Differential Current Measaurementin the BNL Energy Recovery Linac

Proof-of-Principle Experiment

Peter Cameron

ERLThe Collaboration

ERLThe Evolution/Recipe• Start with RHIC

• 500 GeV center of mass polarized protons collisions• 200 GeV/nucleon center of mass heavy ion collisions

(~ 40 TeV/collision)

• Get some electrons 'in the kitchen'• ERL PoP Experiment - this talk

• Get some electrons 'in the stew' - eCooling• Make electrons a main ingredient - eRHIC

ERLRHIC II - electron Cooling

Linac

EBIS Booster

AGS

RHIC II

Electro

n

cooling

http://www.agsrhichome.bnl.gov/eCool/

electrons

ions Gun

Linac 1Linac 2

Linac 3

Linac 4Stretcher

Compressor

electrons

ions

ions Beam dump

x30 increase in Au-Au luminosity

x10 increase inin p-p luminosity

stretcher!

ERLGoals of PoP Experiment• Test key components of the High Current Energy Recovery Linac

based solely on SRF technology• Test 500 mA 703.75 MHz SRF gun• Test high current 5-cell SRF linac with HOM absorbers

• Single turn - 500 mA• Two turns - 1 A…..

• Test beam stability criteria for CW beam currents ~ 1 A

• Test attainable ranges of electron beam parameters in SRF ERL

• Test key components for future linac-ring e-p and e-ion collidereRHIC with luminosity of 1034 cm-2sec-1 per nucleon• 10-25 GeV SRF ERL for eRHIC• SRF ERL based FEL-driver for high current polarized electron gun

ERLMachine ParametersTable 1 Machine Parameters

Parameter [units] high chg low emit

inj energy [MeV] 3-5 3-5

beam energy [MeV] 15-20 15-20

rms bunch length [ps] ~20 ~20

RF frequency [MHz] 703.75 703.75

revolution freq [MHz] 9.383 9.383

bunching freq [MHz] 9.383/28.15 703.75

charges/bunch ~1e11 4e9

beam current [mA] ~150/450 500

rms energy spread 10e-3 10e-4

εx, εy [mm-mrad] 30 1-3

beampipe dia [cm] 6 6

energy recovery [%] 99.95 99.95

current recovery [%] 99.9995 99.9995

requires measurement resolution of ~10-6

ERLERL Diagnostics Layout

BPMBPM

BTF Kicker

BTF PickupSL

SL

DCCT

cross(ws, flag,...)

ERL Diagnostics Layout

ERLSchedule

Task Name Start Finish2004H1

2004H2

2005H1

2005H2

2006H1

2006H2

2007H1

e-CX/ERL Project 3-Feb-03 15-Mar-07

Develop the 5-cell RF cavity shape 3-Feb-03 30-Nov-05

Assemble SRF Cavity & Associated Components 3-Oct-05 4-Dec-05

Electron Gun Procurement 3-Feb-03 6-Jan-06

Photocathode System Procurement 3-Feb-03 23-Mar-06

Assemble & Test of RF Gun & Associated Systems 2-Feb-04 4-Apr-06

Design & Procurement of ERL Vacuum System 10-Jan-05 8-Mar-06

Beam Dump Procurement 1-Oct-03 25-Aug-05

Assemble Photocathode, RF Gun, Cavity & Beam D24-Aug-05 25-Sep-06

Design & Procurement of ERL Magnetic System 8-Jan-04 2-Nov-06

ERL installation 26-Sep-06 15-Mar-07

Building 912 Facility modifications for ERL 3-Feb-03 15-Feb-06

ERL commissioning 1-Mar-07

ERL

ERLAP Requirement on current recovery

• AP wants to accomplish 99.9995% current recovery. How will they know?• loss monitors? calibration? • Diagnostics then has to measure differential current

with resolution of ~10-6

• for now, let's assume resolution of 10-5 on 100mA beam, see what this entails

• Two toroids available (gun, dump)

ERLMachine Protection?• Assume current threshold ~independent of beam energy• Operational criterion (courtesy Micheal Tiefenback)

• JLab uses ~2.5x104 µA-µsec (or 0.025 µA-sec) with resonantcavity pickups - remarkable accomplishment

• This sits on top of ~1µA known loss• not calibrated, but rather determined by operational experience

• Damage threshold (courtesy Geoff Krafft) • 100mA for 100µsec will burn a hole• less than 107 µA-µsec (or 10 µA-sec)

• With 100mA beam in BNL ERL and 10-5 resolution wecan resolve at the level of ~1µA (level of known loss atJLab)

ERLNPCT Specs (Bergoz)

output accuracy +/- .005• output noise (magnetic core noise) ~0.3µA/rootHz• magnetic field sensitivity ~100µA/gauss• temperature coefficient ~5µA/K• gain and linearity ~1ppm/mA• bandwidth 10KHz

ERL« Electronic » noise

Klaus Unser NPCT paperhttp://desyntwww.desy.de/mdi/CARE/Lyon/ABI-Lyon.htm

It is conceivable magnetic cores noise could bereduced below 1 ppm by processing: integration, filters...

Mains frequency noise must be rejected

ERLCore noise - 0 to 3Hz

NPCT noise measurements (FFT)

Range 20 mA (10V output)0 to 3 Hz

2µA

0.2µA

rms Hz

ERLCore noise - 0 to 12.5KHz

Range 20 mA (10V output)0 to 390 Hz

0.2µA

0.02µA

NPCT noise measurements (FFT)

Range 20 mA (10V output)0 to 12.5 kHz

0.002 µA

rms Hz

ERLRelative noise strengths

current 1mA 10mA 100mA 500mA comments

assume 0.01Gauss

assume 0.2K

gain10ppm/mA

.01uA 0.1uA 1uA 5uA

field100uA/Gauss

1uA 1uA 1uA 1uA

temp5uA/K

1uA 1uA 1uA 1uA

core noise0.3uA/rtHz

0.3uA 0.3uA 0.3uA 0.3uA

ERLERL Diagnostics Layout

BPMBPM

BTF Kicker

BTF PickupSL

SL

DCCT

cross(ws, flag,...)

ERL Diagnostics Layout

null

ERLEffect of nulling• output noise (magnetic core noise) ~0.3uA/rootHz

• no effect• magnetic field sensitivity ~100µA/gauss, shielded to 0.01

Gauss• removes 'global' variations

• temperature coefficient ~5µA/K, stabilized to 0.2K• removes 'global' variations

• gain and linearity 1ppm/mA• effectively removes this problem (but only an issue at highest

currents)• A caution - don't introduce additional noise with nulling

• flux (Barkhausen) noise is considerably (~50dB?) above thermal

ERLConclusions• Main issues will be field and temperature dependence• Maximum practical effort must be devoted to

minimizing these variations - space limitations?• 'Nulling' may diminish these problems

• requires knowledge of timescale for re-zeroing with no beam• interrupting operations for calibration is always problematic

• 'Measure and Correct' can also offer some relief• It does appear possible to offer some machine

protection by this method• Real need to gain practical experience with this

approach - early purchase of NPCTs