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MPS Experience at BNL-RHIC

BNL Collider Complex Overview

MPS at the collider acceleratordepartment (C-AD)

RHIC Accelerator Protection Elements

Operational Experience

Summary


MPS at C-AD



Summary

MPS at C-AD

The Machine Protection Systems at BNL are very mature. Conception and implementation for the pre-injectors was established long ago, before the RHIC-era. The RHIC MPS was designed in the 1990’s and leveraged strongly off the experiences from FNAL.

This talk will present the machine protections systems of the presently operating accelerator facilities at C-AD.

The Machine Protection System at BNL consists of three parts:

1) input measurements (and subsystem interlock systems) 2) beam interlock system (“permit system”)3) consequences: mechanisms for preventing beam into regions of

interest (injectors) or dumping the beams (in RHIC)

Presently there are 5 permit links (which are not interdependent) and a stand-alone MPS for the linac.

RHIC

NSRLLINAC

Booster AGS

EBIS

#1 Booster prevent beam in the NSRL line / acceleration in Booster

Permit Link Function

#2 AGS prevent accelerating beam in the AGS

#3 AtR (U/V/W) prevent beam from entering the AtR line

#4 Arc prevent beam from entering RHIC

#5 RHIC eliminate circulating beam in RHIC

AGS-to-RHIC transport (AtR)

These protect the accelerators from damage due to the beam. At RHIC, the superconducting magnets are also protected from the release of stored energy by quench protection links.

Booster MPS

20

0 M

eV

LIN

AC

H-50 mA

(polarized) protons1 nA

NSRL (NASA Space Radiation laboratory)

EBISHe to Au~ 2 mA

BOOSTERAGS

12 M

V L

IN

AC

~ 1 GeV/A Au~ 2.3 GeV pol protons

prevents beam in the NSRL line and acceleration in the Booster

R-Line

vacuum valves (R-line)vacuum valves* (Booster)

power supply status (R-line)

The Booster permit link system also allows for inhibiting beam to R-Line while allowing beam in Booster for other Booster-users (e.g. AGS and/or other Booster beam development)

input measurements

consequences booster RF drive signal set to zero R-Line extraction bumps inhibitedmain magnet power supply ramped up to spiral beam

into dump

condition for beam inhibit

valves closedvalves closed

on/off status fault

dose on NSRL target sample(measured using ion chambers)

desired dose achieved

Booster MPS

PLCs

* (reachback to chopper in linac fast-beam inhibit system)

Booster Permit Link configuration and status

inputs status of inputs input enable/disable

link monitoringstatus

example operator level readbacks

AGS MPS

BOOSTER AGS~ 1 GeV/A Au~ 2.3 GeV pol

protons

~ 10 GeV/A Au~ 24 GeV pol

protons

prevents accelerating beam in the AGS

vacuum valvesloss monitor managerloss monitors at sensitive locations magnet (“snake”) quench detectordump bump power supply status

input measurements

consequences AGS RF drive signal set to zero extraction bumps inhibitedif operating with polarized protons, source is inhibited


valve closedbeam loss exceeds thresholdbeam loss exceeds thresholdquench eventon/off status fault

beam current transformer (2 units)

transformer keep-alive statuses

beam current exceeds threshold (and AtR dipoles on)

status fault

BtA

U/V/W (Accelerator to RHIC) MPS

AGS~ 10 GeV/A Au~ 24 GeV pol

protons

prevents beam from entering the AtR line

ARC MPS prevents beam from entering RHIC

RHIC~ 100 GeV/A Au~ 250 GeV pol

protons

input measurements

consequences extraction kicker triggers from AGS disabled


vacuum valves valve closed

PASS (aka PPS) status, division APASS status, division B

access control state not in “no access”

input measurements

consequences switching magnet turned off


vacuum valves valve closed

RHIC permits to the arc

Blue magnet quench detectorYellow magnet quench detector

quench eventquench event

fault

RHIC MPS eliminates circulating beam in RHIC

RHIC

~ 100 GeV/A Au~ 250 GeV pol

protons

input measurements

consequences RHIC abort kickers triggered


loss monitorsvacuum valves

power supply status

beam loss exceeds thresholdvalve closed

on/off status fault

roman pot positions (both rings)beam loss at roman pots

position errorbeam loss exceeds threshold

RF cavity voltage voltage status fault

PASS (aka PPS) status, division APASS status, division BPASS Beam Stop status (A and B)

access controls state not in “no access”

Blue magnet quench detector Yellow magnet quench detector

quench detector (snakes and rotators)

quench eventquench event

quench event

PLCs


MPS at C-AD



Summary


Equipment monitoring systemsBeam monitoring systemsBeam interlock system (“permit system”) Beam dumping system

(collimation and “gap cleaning” primarily for detector backgrounds)

Equipment monitoring systems

Conventional: vacuum valves, vacuum pump status, power supply outputs,…

RHIC specific: superconducting magnet quench protection system

RHIC superconducting magnet quench protection system

one QD in every arc’s center alcovemonitoring voltage taps in the arcs

two QDs in service buildings monitoringmagnet and lead voltage taps in theinsertion regions

voltage readout at 720 Hz

consists ofquench detectorsquench protection assembly

(and interface chasses)quench protection switchesquench link (one link per ring)

Beam monitoring systems: beam loss monitors (BLM)

~ 430 gas ionization chambers (RHIC)~ 100 in AGS to RHIC transfer line

based on Tevatron design (R. Shafer)

For MPS:

Other beam loss diagnostics:pin diodes (Bergoz) photomultiplier tubes (JLAB-CEBAF design)

BLM data handling, two paths:

(1) to MADCs (1 Hz averaged data for logging, 720 Hz for post mortem analyses) (2) to pair of threshold detectors (comparators) for detection of

slow losses (time constant ~ 20 ms)fast losses (time constant ~ 100 ms)

which produce an inhibit if threshold is exceeded

Beam monitoring systems: beam current monitors

Pair (for redundancy) of back-to-back Bergoz NPCTs with internal keep-alive circuit (constant 15 mA rms / 65 mV rms, 31.25 kHz signal). Fault produced if current exceeds threshold or if keep-alive current not measured.

Plan for ERL: pair of Bergoz New Parametric Current Transformers (NPCT) for differential beam loss measurement

assembly in shop as installed in the AGS

Beam interlock system

consists of 10 MHz carrier(s)3 permit links (2 for QDs, 1 for all else)32 beam interlock controllers (BIC)up to 192 distributed “user system” inputs 1 dedicated “master” to initiate establishment of a permit

Full system tests on demand (typically during startup)Max response time (permit failure to abort) ~ 40 microseconds or ~ 3.2 turns

BIC, conceptual view BIC FEClist QD link inputs

Beam dumping system

consists of kicker magnetspulse forming networks (PFNs) dump absorber

design assumptions: Emax = 200 kJ at 100 GeV/A with Nb=60, Nppb=1E9 (Au)

concern: secondary particle emission from dump absorber could heat and quench downstream superconducting magnets

response time: charging supply for PFN disconnect ~ 10 ms (~ 1 turn) trigger synchronization (~ 1 turn)(plus transit time from permit link ~ 3 turns 5 turns total or 60 ms)

RHIC blue dump kicker assemblies RHIC blue beam dump


MPS at C-AD



Summary


The well-established C-AD MPS system generally works as expected.

There may be more permit pulls than necessary, but not excessively so.

“Failures” of the MPS concern dynamics either not considered in the MPS design or result from operation with beam intensities higher than envisioned in the MPS design.

These lessons learned will be reviewed next.

AGS beam-induced vacuum failures (2008)

Issue operation with 4 Au bunches, 5E9 ppb resulted in 3 vacuum leaks

Remediesdump moved closer to beamplunging stripping foil implemented

motivation: force Au ions to lose 2 remaining electrons in 1 mil Tungsten foil resulting in beam rigidity decrease and hencelarger deflection due to dump bump

Recent issue (2014): MPS designed to inhibit beam to downstream systems but not to protect the accelerator from itself (plethora of spurious BLM readings causing beam inward spiral during acceleration due to rf turn-off strategy)

dump bump amplitude increased

AGS beam dump AGS plunging stripping foil

RHIC quenches due to beam aborts (2010)

Issue beam aborts at high energy caused quenching of magnets downstreamof dump

Remedies

simulations: no quenches for up to 2.5E11 ppb (250 GeV protons)

additional BLMs installed (subsequently determined desire for lesssensitive BLMs avoiding saturation during an abort as potentiallyuseful in understanding beam abort dynamics)

additional absorbers (20 5-inch sleeves) installed in the RHIC beam pipe adjacent to the dump to increase wall thickness

no abort-induced quenches in following year of operations

dump shielding sleeve

RHIC quenches due to beam aborts (2013)

Remedies actively being investigated

Issue quenches caused by beam abort

Observations

measured abort kicker currents does not track with new fast-sampled beam position measurements

measured abort kicker currents different (during operations and maintenance days)

plan for major abort kicker upgrades in summer, 2014

inductance of ferrites changes with beam-induced temperature rise

Diagnosis

RHIC abort kicker pre-fires (up to and including 2013)

Remedy – run 14

Issue damage to experiment’s detectors (STAR in particular)

move beam towards aperture so that prefire deposits beam upstream

Remedy > run 14 installation of dedicated collimator(s)

Summary

• The RHIC physics program entails a very wide variety of particle species and energies

• The MPS design for the C-AD preinjectors is mature, maybe rudimentary by today’s standards, but robust

• Ever-increasing beam intensities required by the evolving requirements of the physics programs have motivated and continue to motivate MPS sub-system upgrades

• A new era of MPS systems is under development at C-ADfor (electron-based) new projects including electron lenses, “conventional” electron cooling, coherent electron cooling (new), and the energy recovery linac project

Acknowledgements (for this presentation)

For MPS as seen by Operations throughout the accelerator complex: Travis Shrey

For user-distributed inputs: general: Travis Shrey and Greg Marr (Operations)

+ Loralie Smart (Vacuum)+ John Butler (RF)+ Don Bruno (Power Supplies, Quench Detection)+ David Gassner, Peter Oddo, Michelle Wilinski (Beam Instrumentation)

For photographs: Don Bruno, Dave Gassner, Paul Sampson, Joe Tuozzolo

For beam permit system: Kevin Brown, Peter Ingrassia, Travis Shrey, Charles Theisen

For RHIC beam dump: RHIC Configuration Manual (2006)

For operational experience: AGS vacuum issues – Leif AhrensRHIC quenches due to beam aborts, 2010 – Christoph MontagRHIC quenches due to beam aborts, 2013 –Rob Hulsart, Rob Michnoff,

Peter ThiebergerRHIC abort kicker prefires, 2013 – Angelika Drees, Christoph Montag,

Rob Hulsart, Aljosa Marusic, Rob Michnoff, Peter Thieberger, Simon White

Current and Future Developments in Controls

A stand-along MPS system for the Electron Beam Ion Source (EBIS), called EGIS, was developed by Omar Gould

Also under development is a stand-alone quench detection system for the ERL superconducting solenoids (using NI PXIe platform)

MPS designs for future projects Energy Recovery Linac (ERL)electron lensnew 56 MHz SC cavity for RHICCoherent Electron Cooling

are being developed using NI CompactRIO platforms

The Controls portion of the MPS for these systems is being developed by:

Zeynep Altinbas, Mike Costanzo, Chung Ho and Charles Theisen (systems design and permit link boards)

Jim Jamilkowski, and Prerana Kankiya (ADO manager interfaces)Peggy Harvey (MPS interfaces to rf systems) Prachi Chitnis (student, reliability analysis)

spare slides

Quench protection in RHIC

Preparation for higher beam intensities: beam position monitors

Issue The “cold” BPM cables (those located in the insulating vacuum) consist of a stainless steel outer conductor with a “tefzel” dielectric. If the beam-induced power is too large, this dielectric will melt.

BPM excursion monitor developed based on absolute BPM measurements (striplines)

achieved bunch length

limitation by cryogenic system

nominal intensity intensity after upgrades

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