The CLEAR test facilityCERN Linear Electron Accelerator for Research

Erik Adli

Department of Physics, University of Oslo, Norway and CERN

With the CLEAR team: W. Farabolini, D. Gamba, R. Corsini, S. Curt, S. Doebert

K. N. Sjøbæk, G. McMonagle, P. Skowronski, F, Tecker …

Special thanks to CLEAR technical support people, groups and services involved in the modification/re-commissioning of CTF3 (RF, BI, CO, EN, TE/VSC, …)

CERN A&T seminar, November 30, 2017

https://clear.web.cern.ch

CLIC Test Facility and CLEAR

30 A, 140 ns

120 MeV

30 A, 140 ns60 MeV

3

CLEAR consists of the experimental hall, CLEX, housing the 200 MeV S-band electron CALIFES linac.

The test facility shut down at the end of 2017, after completing main targets.

CLIC Test Facility and CLEAR

History• Interest from external users, outside and within the CLIC,

project to keep an electron test beam facility at CERN• Should be open to all users, not only CLIC or linear

collider related activities• Workshop to poll interest from outside community held

in September 2016; more than 90 participants from different laboratories and different research fields

• Approved by CERN management for 2+2 years operation• Modification and some upgrades first half of 2017• First beam: August 18, 2017

From DG's New Year address January 2017 :

CLEAR parameters

Energy

Bunch-length(rms)

Present and planned European electron test beams(not complete)

10 MeV

1 fs

1 ps

100 MeV 1 GeV

10 ps

Open user facilityOpen through collaborationNot open for users (yet)

CLEAR (CERN) 2017

SINBAD (DESY H.) 2018

PRAE (Orsay) 2020

SPARC LAB (INFN Frascati) online

Flash Forward(DESY H.) 2017

CLARA (Daresbury)Online@50 MeV

MaxIV injector(MaxIV) ?

PITZ (DESY Z.) online

More details can be found at https://goo.gl/sn4dqP

FLUTE (KIT) 201?

CLEAR parameters

CTF3 Two Beam Module area (as it was)

CLIC Two

Beam Module

CALIFES(about 23 m long)

Spectrometer and

diagnostic

The idea: add some more space for new experiments

Exhange of RF StationsSignificant RF replacement and upgrades for the preparation of CLEAR

• The Modulator/Klystron MKS30 is being transferred to AWAKE.

• The RF network of MKS11 and MKS15 (compatible with requirements from TE/EPC andBE/CO), was reconfigured to feed the CLEAR linac.

G. McMonagle

CLEAR: “making of”Montage by D. Gamba

CLEAR completed due to heroic effort by Wilfrid Farabolini and Davide Gamba.

CLEAR experimental beam-line(s) (as it is)

Plasma Lens

former

CLIC Module

Available test space

Spectrometer and in-air test stand

CALIFES

injector

VESPER

Highlight from the 2017 run

M. Talis, R. Garcia Alia,

W. Farabolini et al.

Operation resumed in September:• Using dark current only• 10 pC total charge• 5 Hz repetition rate• Energy from 60 to 180 MeV

Successful measurements with

ESA and TRAD in week 46!

Overnight and over weekendoperation possible.

VESPER

First tests at VESPER: European Space Agency (ESA)

Beam homogenity - 175 MeV, 8 pC/pulse

Radionsensitive film ESA SEU monitor

First tests have been performed with ESA SEU monitor, results compatible with previous years :

50, 115, 175 MeVESA SEU monitor + AlRadiosensitive films

From Maris Tali

A.Lyapin (R. Holloway), J. Nadenau (Juelich), M. Wendt(CERN), R. Lillestøl (Oslo), E. Adli (Oslo), K.N.Sjøbæk (Oslo) et al.

Experiments resumed last week!

Former CLIC module: cavity BPM and wake field monitor tests

New installations for CLIC Wakefield monitors in CLEAR: • Combined cavity BPM and WFM measurements• variable phase shifter measurements on WFMs

Data from last week (to be analysed in detail)

A. E. Dyson, C. Thornton, and S. M. Hooker, Rev. Sci. Instrum. 87, 093302 (2016)

Active plasma lens studies

Oxford Compact Marx Bank: Inexpensive and precise source of ~20 kV, ~500 A discharges

Capillary and holder design by DESY, based on experience from DESY and Oxford

Overall experiment design, and assembly, integration and test, by Oslo.

Goal: strong, linear radial focusing from driving current a gas discharge.

Novelty for CTF3:- Gas in beamline- HV in beamline- New materials- Thin-foil vacuum

barriers

Plasma lens:Integrations and tests in the lab completed(August 2017)

C.A. LindstrømJ.H. RøckemannA. Dyson

Huge amount of work (integration of gas, HV, vacuum, beam windows),but, CLEAR vacuum integration now completed.

First electron beam sent cleanly through capillary end September. Marx bank outside

vacuum, but close to capillary.

Clean beam observed on downstream OTR

OTRIntegrated incapillary holder

Plasma lens:Latest commissioning results, from last night (30/11, 23h30)

Possible first focusing effect observed!(no analysis done, very preliminary!)

However, we still have a problem with sparks to ground.-Currently working on increasing gas path length to ground- Also changing from He to Ar

(No Champagne yet :( )

Reference shot: no discharge

”Late night crew”

BI Activities

T. Lefevre, et al.

Many activities planned (most ongoing).

Two main goals:

1) Consolidate and improve beam

instrumentation for CLEAR

2) Diagnostics R&D

OTRI setup

BI Activities

T. Lefevre, et al.

Several beam diagnostics recovered from CTF3, and adapted to CLEAR needs.

Will assess performances, modify if needed, eventually extend numbers.

WCM

Inductive

BPM

Beam Phase

monitor,

WG monitor

(bunch length)

OTR, ChR, ChDR

setup

Successfully seen first signals on

modified instrumentation.

To be continued!

AWAKE spectrometer, BPMsTest and calibration of AWAKE electron spectrometer, for electron commissioning Dec 2017. AWAKE BPMs also tested in CLEAR/CTF.

o Rapid advances in compact high-gradient (> 𝟏𝟎𝟎MV/m) accelerator technology in recent years CLIC (> 100 MV/m) NLC (~70MV/m), W-band (> 200MV/m)*

• Superior dose deposition properties compared to MV photons

• High dose-reach in tissue

• High dose rate (compared to photons)

• More reliable beam delivery around inhomogeneous media

• Better sparing of surrounding healthy tissue

• Particle steering

VHEE

𝟓𝟎𝐌𝐞𝐕 𝐕𝐇𝐄𝐄

𝟐𝟓𝟎𝐌𝐞𝐕 𝐕𝐇𝐄𝐄

Dose maps of wide (𝝈 = 𝟐𝟎𝐦𝐦) VHEE beams in water

50 MeV

150 MeV

Dose maps of narrow (𝝈 = 𝟓𝐦𝐦) VHEE beams in water

250 MeV

M. Bazalova-Carter et al, «Treatment planning for radiotherapy with very high-energy electron beams and comparison of VHEE and VMAT plans», Medical Physics, vol. 42(5), 2015.

VHE

E

VMA

T

Absorbed dose histograms for surrounding organs-at-risk.

• Clinical studies by M. Bazalova-Carter et al.

(2015) have compared 100 MeV VHEE with conventional (𝟔 and 𝟏𝟓MV) VMAT (Volumetric Modulated Arc Therapy) photon radiotherapy plans

• Pediatric brain tumour, lung and prostate cases

• VHEE therapy plan showed a decrease of dose up to 70% in surrounding organs-at-risk (OARs)

• VHEE plan was found to be more conformal than VMAT plan

*V. Dolgashev, HG2016

Brain tumour dose maps for 100 MeV VHEE and 6 MV volumetric modulated arc photon therapy (VMAT) .

24

VHEE: Very High Energy Electron Radiotherapy

Manchester University: A. Lagzda, R. Jones and other- Project to characterize VHEE irradation on radiosensitive films

VHEE experiments at CLEAR

Beam parameter (end of linac)

Value range

Energy 197 MeVEnergy spread < 0.5 MeV FWHMBunch charge 0.5 nCTrain length 50 bunchesBeam spot size 1 mmCharge Jitter ≈ 20 %Relative energy spread 1 %

• Beam dosimetry experiments in water tank with radiosensitive films.

• Preliminary studies was done December 2016.• Planned for CLEAR/VESPER week 49, 2017.

BeamToroid

Beam alignmnent

screensMoving stage

Water tank with films

30 cm

46 cm

• 100 bunches of 50 pC/shot spaced by ~1 sec. at 8 cm distance corresponds to 100 Gy.

25

A. Lagzda et al., IPAC’19

Injector optimisation

• Collaboration with LAL colleagues.

• Aim to:– Verify the theoretical best

performance achievable (0.1 ps bunch length, 5 mm-mrad possible?)

– Crosscheck of ASTRA simulations.– Guide the optimisation of our injector.

26 Oct 2017

CLEAR operation 2017

Week

33First beam!August 18

34Cont’dcommissioning

35Cont’dcommissioning

36First beam to usersVESPER

37Installation ofplasma lens

38Beam throughplasma lens

39VESPER

40Beam tuning,plasma lens

41BCM improvementWFM

42WFMFirst sparkplasma lens

43Inductive BPMsLAL: injector optimisation

44Cavity BPMs

45Laser spot studyVESPER

46ESA at VESPERTHz studies

47CombinedWFM and Cavity BPMs

48AWAKE screen

49: VHEE50-51: Plasma lens, instrumentation, THz….

Upcoming activities

In vacuum test space• About 1.5 m available space.• Possibility to install equipment on remotely controllable transverse mover (>10 mm range)

Transverse mover

End-of-line in-air test space

Ready to be exploited!

Novel accelerator techniques: THz

Steve Jamison, CLIC Workshop, CERN, March 2017 :

Study of THz generation (2017+) : THz acceleration (2018+ ?) :

Collaboration CLEAR – STFC/U. Rome being discussed. If moving forward: significant amount of resources (manpower, hardware, diagnostics ) to CLEAR starting from ~ 2018.

This effort would also profit other CLEAR experiments.

M. Petrarca, CLIC Workshop, CERN, March 2017 :

(from the 2016 workshop)

• Reviewing possibilities for generating coherent

THz pulses using short electron bunches

1. Coherent Transition and Diffraction

Radiation from metallic foils or slits (nJ to uJ)

• Discussing Simulation tools:• i.e. CST, Magic, Vsim

• Defining a plan for having first tests on CLEAR of Coherent radiation

by the end of 2017 up to frequencies of 0.1GHz

• Defining a roadmap for having short electron bunches available on

CLEAR in 2018

2. Higher power using Coherent Smith-Purcell Radiation in grating or Coherent

Cherenkov Radiation in dielectrics and meta-material

Coherent Cherenkov radiation in prismastic target with Magic

First topical CLEAR user workshop: THz (40 people, 13 talks)

https://indico.cern.ch/event/672235/

From T. Lefevre, CERN

• THz for beam diagnostics measuring short bunches,

e.g. in AWAKE measuring coherent radiation up to

320GHz

• A THz platform on CLEAR for developing THz sources and THz

detectors : i.e. in contact with PSI and universite of Chambery

• THz for acceleration using beam-based and laser-based THz

generation techniques

Example with the in-air testing area at

the end of the CLEAR

Identifying THz Applications and Synergies

New CERN fast Wire scanners for PSB, PS, SPS and LHC

From T. Lefevre, CERN

2018: test of wire scanners with beam.Measure fields on antenna in tank.

X-band and high-gradient R&D

35

CLEAR: may get access to 12 GHz 50 MW RF power supply (X-box 1). Could be connected to CLEAR in 2018. Would increase energy to 250-300 MeV

Could be used for generic high-gradient studies, beneficial for CLIC, FEL, medical etc :1. The effect of a beam on the high-gradient behavior of a structure : Example: beam

loading effect on gradient (17% less output field with beam). A CLEAR program allows new studies such as effect of controlled beam loss on gradient, as well as continuation of tests of beam loading.

2. The effect of high-gradient acceleration on the beam. Example: further understand effect of break down and dark current on beam quality and luminosity.

3. Further Wake-fields and structure-based beam measurements. Example: resolution measurements with X-band acceleration mode

Possible upgrades:Towards a unique test-facility

To fit all proposed experiments, both space and downstream compability may be very challenging to handle with a single beam line. Space and hardware exists for a second beam line. Probable push to prepare the second line sometime in 2018 (but pending review of all requests).

Several users also ask for shorter bunches (fraction of a ps). Bunch compressions could be built into dogleg (studies have started).

AWAKE, CLEAR synergy:short pulse electron injector

• Interesting option for AWAKE 2nd run and CLEAR upgrade, using x-band technology for acompact injector

• Much of the X-band hardware might be available, X-band expertise exists in the CLIC project• The possibility of ultra short bunches could be a big asset for the future test facility

AWAKE Run 2 requirements:E. Adli et al., WEPMY008, IPAC’16

Design is taking shape,S. Doebert, CERN and M. Kelisani, IPM

S. Doebert, EAAC 2017 :Ultra-short bunch injector for AWAKE RUN2

How to become a CLEAR user

CLEAR Scientific Board

2017: most users contributed with ideas/proposal at ”CALIFES workshop 2016”

From 2018 proposals for experiments or test beam will pass by the CLEAR Scientific board.

The CLEAR Scientific Board will meet about meet 2-3 times per year to review the progress of the experimental program, and to referee the new proposals of the experimental teams on the basis of their physics interest and of the availability of the facility.

First meeting will be around the CLIC workshop 2018.

A Technical board will also meet at the same frequency, in order to review the technical, safety and radio-protection issues on the experiments recommended by the Scientific Committee, and fit them in the facility schedule.

Similar structure to HiRadMat.

CLEAR Experimental Requests

https://clear.web.cern.ch/sites/clear.web.cern.ch/files/documents/CLEAR_Experiment_Request_Form.docx

The experimental teams should also provide manpower to integrate experiments into the beam line and control system, and to help operate them during beam time.

Questions: CLEAR-Info@cern.ch

Conclusions• CLEAR: 200 MeV electron beam test facility at CERN

• Started operation August 18, 2017

• A mix of existing users - including CLIC, AWAKE [- and new users are already using CLEAR

• Instrumentation, linear collider technology, novel acceleration technology, irradiation…

• Interested users are encouraged to take contact with the CLEAR team, fill out experimental requests

• With added short bunch injector and two beam lines, CLEAR would have unique test-facility characteristics in Europe

Thanks a lot to Davide Gamba, Wilfrid Farabolini, Robert Corsini, Thibaut Lefevreand many others, for providing material for this presentation.

Extra

CERN ABP Impedance studies. first candidate: study of SPS wire scanner heating. Complexity of problem makes numerical studies and bench measurements. possibilities for CLEAR tests in 2017-2018.

Other interests in CLEAR

Impedance studies Electron irradiation studies

CLEAR: open facility, all user/communities welcome to propose experiments.

R2E: Tests for ESA space missions (Juice)(ESA, Jyvaskyla and others)

Tests for VHEE radiation therapy(Cockcroft)