Double Drift in DUNE: Discussion on HV Implications including - - PowerPoint PPT Presentation

Double Drift in DUNE: Discussion on HV Implications including trade-offs between ACA and CAC configurations

CERN, 20/6/2019

• F. Pietropaolo

Double drift configurations for DUNE

• Two possible configurations of the DUNE far detector with a doubled

drift distance have been considered:

• One central cathode plane and two APA array on the sides (ACA

configuration)

• Two cathode planes on the external sides and one APA array at the

center (CAC configuration)

• Both configurations require a partial redesign of some of the

subsystems of the far detector.

• The amount of modification needed in both cases are discussed in the

document.

• The most affected subsystems are the high voltage (HV) and photon

detection system (PDS) and the cryostat/DSS design

• It has been assumed that no modification will be done to the

design of the APA and to Cold Electronics

DUNE SP Far Detector HV System

4 June 2019 HVS-SP PDR Meeting 3

12m ~ 5 8 m

APA CPA APA CPA APA CPA

3.5 m 7.0 m

• Present TPC configuration:
• APACACA: Chosen mainly to avoid HV

facing too close to cryostat membrane

• Double drift configurations:

Common aspects to ACA and CAC

• High Voltage on the CPA increased by factor of ~two, while maintaining

the current CPA/Field cage concept (including ground planes):

• Larger distance required from CPA outer edges to closest ground reference, to

prevent discharges

• Requirements for both configurations:
• the absolute value of the electric field should be kept below the maximum

acceptable value of 30 kV/cm - in any region of the cryostat;


• the energy stored between the field cage and the cryostat must be minimized as

much as possible, to avoid damage to the cryostat and detector in case of fast discharges.

• Doubling the distance from the CPA to the Top/Bottom Ground Planes

from 30 cm to 60 cm is a reasonable approach to accomplish the above requirements.

• CPA height need to be shortened by at least 60 cm (30 cm from upper and

lower edges) with respect to the present configuration.

• Inevitable redesign of CPA & field cage modules:
• amount of redesign differs in the two configurations (ACA and CAC).

Proposed HV configurations

ACA configuration

• Design more similar to current one (less R&D required):
• Outer APA’s in the same position, CPA moved in the middle
• Drift distance can be doubled (and include 1 APA thickness).
• CPA plane structure and its construction / assembly operations can be

maintained approximately as in the present design.

• The field cage modules could rely on maintain the present design concept,

however thicker I-beams would probably be required and the hanging/deploying operation should be revised due to the double length.

• Ground planes as in present design
• HV feed-through / cable and PS similar to NP02
• The requirement of unmodified APA structure and size implies:
• "tilted" top/bottom field cage modules with a slight slope of ~30cm over 7 m

drift length

HVS-SP design (evolution from TRD)

4 June 2019 HVS-SP PDR Meeting 7

Changes from the baseline design:

Top ground plane directly supported by DSS

• beams. No standoffs between FC and GP.

FC profile support I- beams / box beams are inside the field cage. No external insulators in high field region. EW profiles have bent corners to close the large gap in ProtoDUNE SP FC Top ground plane installed as a separate but quick step to the DSS support beams.

Long FC modules

• Typical FRP beams comes in 20’ length, some vendor seems to have 25’

length.

• With hypothetical 7m long 6” FRP I-beam, the module has a deflection of

about 4 cm warm, less than 2cm in LAr.

6” I-beam 6.4-7.0 m 4” I-beam 3.5 m

ACA configuration

• Reduction of active volume: ~ 2.5%.
• due to shorter CPA ad tilted FC modules
• 1 APA volume gained
• However:
• Fiducial volume could be less affected due to reduced amount of

passive material in LAr bulk

• Interfaces with the cryostat and DSS structures;
• displacement of the HV feedthrough ports
• Two intermediate hanging beams removed.
• Remaining beams in the same place as for the 3.5 m drift case; outer ones

support APA; the central one for the CPA.

• Current CPA DSS ports above the endwalls may be useful for the EWFC

installation and support

CAC configuration

• CPA layout modification :
• the distance of the CPA from the long walls of the cryostat need to be

increased with respect to the present 40 cm (distance of the APA to the cryostat walls in the 3.5 drift in current configuration).

• mainly to avoid sparks from CPA to ground that could release the large

energy stored in the CPA to membrane gap in the CAC configuration.

• A detailed and careful study should be performed in order to address

quantitatively this effect.

• Further optimization of the cathode resistivity necessary to slow-down

any potential discharges in order to minimise the instantaneous dissipated power.

• Safe preliminary estimate: ~100 cm
• similar to what is presently assumed in DUNE DP as cathode-to-

cryostat distance.

• As a consequence, the drift distance is reduced to at most 6.4 m.

CAC configuration

• @ ~350 kV on CPA, energy stored in detector to membrane volume is ~

1.5 kJ (3x ACA case) mainly at the CPA faces (with 1 m separation)

• Electric field well below 30 kV/cm

CPA design: to be revised for CAC

• Sharp edges of FFS
• Surrounding profiles
• Aluminum Hinges
• the lifting bar under higher

voltage

CAC configuration

• Reduction of active volume: ~ 11%.
• due shorter drift distance (6.4 m)
• In addition to shorter CPA and tilted FC modules
• Interfaces with the cryostat and DSS structures;
• major redesign of cryostat penetrations/rail suspensions due to
• displacement of HV feedthrough ports
• displacement the DSS outer beams to account for the 6.4 m drift distance

(instead of 3.5+3.5m).

Construction/Assembly/Installation: CAC & ACA

• The CPA assembly procedure will not chance with respect to the

presently sequence:

• Construction of base units (Panels+Frame+HVbus) at remote factories
• Assembly in 11.4 m high columns in the clean room underground
• Top and Bottom FC modules:
• I-beams are industrially available up to ~ 6 m: being extruded bars, it

should be possible to have them extended to 6.4 / 7 m (to be verified).

• Sagging calculation could indicate that thicker beams are required:

sagging itself is not an issue “electrically” provided that it is known.

• Given the length of the beams, the modules should be preferentially

assembled in the Clean room underground (but remote factory option not limited by size)

• Deploying of T/B modules, End-walls:
• It should be possible to adopt similar procedure to the one presently

developed

Construction/Assembly/Installation: CAC & ACA

• Similar installation sequence

for CPA + Top FC as in the present design should be possible for both CAC and ACA

• A manual 7+m gantry crane

may be problematic for the lower FC installation.

• It should be possible to take

advantage of the larger CPA- floor clearance to install the Bottom FC directly above the floor.

Present Bottom FC installation (under evaluation) CPA + Top FC installation/deploying

Risk and mitigation

• ProtoDUNE NP04 running stably at 180 kV.
• If confirmed during the remaining of the long stability run, the minimal goal of 250 V/cm

could be considered at reach.

• this minimal goal acceptable only if the LAr purity in the far detector similar to that reached

in ProtoDUNE NP04

• there is a tighter link between electric field and purity with a longer drift, similar to DUNE-DP
• A higher risk is associated to the CAC configuration, since the surface area at maximum

HV facing ground is larger.

• Mitigation requires HV simulations and dedicated test (to be defined)
• Running at 320-350 kV on the CPA is an unexplored field.
• ProtoDUNE NP02 would help clarifying how high this risk will be.
• The design of the NP02 HV feedthrough require small modification

to run at 350 kV.

• Need some R&D for PS and cable (could be performed as

intermediate step toward the 600 kV for DUNE-DP).

Impact on costs (rough estimate)

• In the ACA configuration, overall CPA core cost is halved (only one

CPA row instead of two):

• potential core cost saving up to ~ 1.5 M$
• The total cost of the field cage modules should not vary considerably:

the material budget is the same and the assembly operations could be very similar to present design.

• Hanging and deploying procedures would deserve dedicated tests in

Ash River. Higher costs would derive by the additional vertical ground planes, the higher resistivity Kapton layer, and the redesign of the cryostat facing CPAs for the CAC configuration.

• The re-design and the related testing campaign of the two

configurations described above imply a possible cost increase with respect to the present baseline layout.

• A reliable estimate of these (probably non-negligible) costs requires a

more in-depth revision of the HVS design.

Testing in ProtoDUNE

• Given the inner size of the ProtoDUNE cryostat, just a ONE

double-drift volume can be tested. Hence:

• CPA has to face the membrane for both the CAC and ACA

configurations.

• With 7 or even 6.4 m drift, CPA will be too close to the membrane

(beam right) or to cryogenic piping (beam left).

• Probably a max drift of not-more-than-6m can be implemented.
• In case of the ACA configuration, a dummy short drift field cage has

to be foreseen to “protect” the CPA from high field exposure (to be carefully designed).

• Field cage module deployment procedure could be maybe

tested for the TOP-FC modules, if drift is shorter that 6m.

Testing in ProtoDUNE

• Narrow space:
• Top module can be hang to

the CPA and deployed if length < 6m

• Bottom FC module to be

inserted and positioned independently (sequence to be verified at Ash River)

6.0 m

Impact on HV Schedule

• HVS consortium has tight program and milestones

toward first SP far detector with present baseline.

• Next two years:
• Optimization of HVS-SP design
• Mechanical tests @ Ash River
• Module 0: ProtoDUNE-II construction/installation
• Then:
• ProtoDUNE-II commissioning / operation
• Start Procurement & Production for first SP module
• In case of double drift option, additional activities

need to be accommodated in parallel to demonstrate feasibility and reliability:

• New HVS design development
• R&D
• ProtoDUNE tests?
• Which Module #?