High gradient tests with beam loaded accelerating structure

High gradient tests with beam loaded accelerating structure. I. Syratchev CLIC Workshop 2013, CERN

Introduction Loaded (CLIC) Gradient along the structure Increasing current Unloaded CLIC nominal Unloaded Testing of accelerating structure with nominal beam loading was a missing block in our testing program. Such a test will be done using CTF 3 (1. 2 A) drive beam and RF power delivered from X-box 1 (90 MW) via modified 30 GHz low loss transfer line (60 MW). The main target of this experiment is to compare loaded and unloaded accelerating structure breakdown trip rate. CLIC Workshop 2013, CERN

Accelerating gradients achieved in tests. Status: 4 -9 -2012 loaded CLIC Workshop 2013, CERN

Location of the Dog-leg experiment structure Beam dog-leg Former 30 GHz RF transfer line CLIC Workshop 2013, CERN X-box 1

Structure under test: CERN’s T 24 (12 WNDSvg 1. 8 KEK N 1) No damping CLIC Workshop 2013, CERN

Dog-leg experiment phase #1 (beam only) Drive beam, 1 -3 A, 100 -50 Me. V Main objective of this phase: Ø To establish routine beam transportation through the structure without losses. Ø To integrate RF signal acquisition and the beam control systems. CLIC Workshop 2013, CERN

Dog-leg experiment phase #1. Current status. T 24 is installed in dog-leg… Port 4, -49. 1 d. B Port 3, -49. 1 d. B OUT IN Port 1, -48. 6 d. B Port 2, -48. 7 d. B Beam direction CLIC Workshop 2013, CERN

…and calibrated -49. 32 -52. 04 Insertion losses of the input/output waveguide network (splitter and bends) is -0. 15 d. B ( =0. 967) CLIC Workshop 2013, CERN

XBOX#1 Breakdown (fast) RF channels acquisition Ip#1 Wave forms (slow) Vacuum interlocks (slow) Ip#2 Load#2 CTF 3 Load#2 #4 Dir. coupler#2 #3 #1 #2 BPM/I #2 Accelerating structure beam losses Dir. coupler#1 BPM/I #1 Beam optic Beam Gun control This test will be fully operated from CTF 3 CR and run in parallel with XBOx#1 test stand. The RF breakdown will be defected by comparing 3 sequent signals in channel #3, reflected signal in channel #2 and vacuum measurements (no Faraday cups or similar). CLIC Workshop 2013, CERN

Beam Optics Design (F. Tecker) Beam current 1 A (CLIC main beam) => energy ~100 Me. V (no change of the RF pulse compression) Line re-matched for higher beam energy with waist in the accelerating structure – done by Mohsen Dayyani Kelisani collimator position optimized wrt. beam size sufficient clearance in the accelerating structure Vertical beam size Dispersion function Vertical beta function Horizontal beta function CLIC Workshop 2013, CERN dogleg bends Horizontal beam size dogleg bends 10

Beam Commissioning (F. Tecker) Rescale linac quadrupole currents for higher energy Measure final energy and Twiss parameters on girder 10 Rematch linac and dogleg optics to design Setup at 1 Hz (need new pulse compression setup if >10 Hz later) Initial structure conditioning by beam pulse length structure Beam dog-leg energy measurement Twiss measurement Former 30 GHz RF transfer line X-box 1 CLIC Workshop 2013, CERN

Dog-leg experiment phase #1. Experimental program. RF peak power generated by beam at the structure output RF power profiles along the structure (100 MV/m unloaded) Processing (RF breakdowns expected) >30 MV/m last cells Klystron driven 100 MV/m last cell Power at 100 MV/m unloaded Power at 100 MV/m loaded Beam driven (2. 7 A) Nominal current When compared with klystron driven tests, accelerating structure testing with beam opens unique opportunity to process only downstream part of the structure. To get meaningful results from this test, few hundred hours (>300) should be allocated. CLIC Workshop 2013, CERN

Dog-leg experiment phase #2 RF power from XBOX#1 CTF 2 XBOX#1 test stand CLIC Workshop 2013, CERN XBOX#1 power source connected to accelerating structure in CTF 3 linac tunnel via 18 meters of low loss waveguide network.

Complete Dog-leg test RF network layout (calculated RF transfer efficiency ~0. 75) Mode converter type#2 RF 50 mm circular waveguide Beam The number of 12 GHz new RF components were fabricated by CERN and CEA to re-adjust ‘old’ 30 GHz low losses transfer line to the new frequency. CLIC Workshop 2013, CERN

New RF components (closer view) H 10 -> H 01 mode converters and tapers #1 (CEA) RF/vacuum gate valve and pumping port Compact RF pumping port with high vacuum conductivity. H 10 -> H 01 Jog mode converters #2 (CEA) CLIC Workshop 2013, CERN

Tentative Planning Phase 1: Ø Accelerating structure installation in CTF 3 dog-leg area (done). Ø Available for testing with drive beam. Weeks 6 -20. Phase 2: Ø RF transfer line modification. Weeks 21 -22. Ø Structure processing with klystron. Week 29 onwards. Ø Operation in beam loaded mode can be started at week 35. CLIC Workshop 2013, CERN